Discussion:
Atmospheric Flight to Orbit
(too old to reply)
Craig Fink
2007-02-26 02:28:16 UTC
Permalink
Anybody want to talk about Atmospheric Flight to Orbit and what it takes to
get to Orbit?

Personally, I think Atmospheric Flight is the way to get to Orbit.
--
Craig Fink
Courtesy E-Mail Welcome @ ***@GMail.Com
kT
2007-02-26 02:47:12 UTC
Permalink
Post by Craig Fink
Anybody want to talk about Atmospheric Flight to Orbit and what it takes to
get to Orbit?
Personally, I think Atmospheric Flight is the way to get to Orbit.
Then simulate it for us, with Orbiter.

If you can't simulate it for me, I can't take you seriously.

And furthermore, don't ever ever ever followup to sci.space.tech. The
moderator quit, and the group is, for all practical purposes - dead.
--
Get A Free Orbiter Space Flight Simulator :
http://orbit.medphys.ucl.ac.uk/orbit.html
Quadibloc
2007-02-28 12:07:26 UTC
Permalink
Post by Craig Fink
Anybody want to talk about Atmospheric Flight to Orbit and what it takes to
get to Orbit?
Personally, I think Atmospheric Flight is the way to get to Orbit.
The automatic response is that this is a silly idea. After all, orbit
requires that there not be an atmosphere, otherwise the orbit will
decay really quickly. So you have to have *left* the think part of the
atmosphere usable for flight for some time before reaching orbit.

But it is true that plane tickets are way cheaper than rocket
launches.

And the *first* stage of a rocket doesn't go very far.

So why not get rid of the first stage, fly a plane as high and fast as
we can, and then have the rocket start its journey from the moving
plane? That way, we build a much smaller rocket for the same payload,
and the big expensive first stage is replaced by an airplane trip.

The X-15 rocket plane was launched from under the wing of another
airplane. So this isn't a completely new, untried idea.

It seems much more achievable, as a way to radically decrease launch
costs, than a "space elevator", or even such relatively modest
proposals, not requiring advanced materials, as a 25-mile-high
artificial mountain with an evacuated railgun tube going gradually up
its side, or even a railgun held aloft by giant helium balloons.

Perhaps the problem is that the first stage of a rocket makes the
rocket go really fast, and an airplane burning atmospheric oxygen
doesn't go nearly that fact, so you can't really eliminate a whole
stage that way, making the benefits not worth the bother.

John Savard
Joe Strout
2007-02-28 15:09:27 UTC
Permalink
Post by Quadibloc
So why not get rid of the first stage, fly a plane as high and fast as
we can, and then have the rocket start its journey from the moving
plane? That way, we build a much smaller rocket for the same payload,
and the big expensive first stage is replaced by an airplane trip.
The X-15 rocket plane was launched from under the wing of another
airplane. So this isn't a completely new, untried idea.
You might mention SpaceShip1 as well, though of course that doesn't go
to orbit (but then, neither does the X-15). For an orbital example,
look at Pegasus.
Post by Quadibloc
It seems much more achievable, as a way to radically decrease launch
costs, than a "space elevator", or even such relatively modest
proposals, not requiring advanced materials, as a 25-mile-high
artificial mountain with an evacuated railgun tube going gradually up
its side, or even a railgun held aloft by giant helium balloons.
More achievable yes; radically decrease launch costs, no.
Post by Quadibloc
Perhaps the problem is that the first stage of a rocket makes the
rocket go really fast, and an airplane burning atmospheric oxygen
doesn't go nearly that fact, so you can't really eliminate a whole
stage that way, making the benefits not worth the bother.
That's pretty much it. You do gain some advantages from launching at
altitude. These advantages are quite large for a small or suborbital
rocket, which otherwise spend a lot of their fuel plowing through the
lower atmosphere. For a larger rocket, they're not so great, since they
spend a very small portion of their fuel in the lower atmosphere, and
most of it getting up to orbital speed (including that in the first
stage). However, you do get some extra benefits in that you can tune
your engines to vacuum conditions -- especially significant if you're
trying to do SSTO. If what you're launching is also a plane, then there
are safety advantages in releasing at altitude too.

I suspect that SpaceShipThree, or whichever version goes all the way to
orbit, will still launch from altitude, from what will have to be a
truly titanic carrier plane. It's a help, but it's not a breakthrough
like what a space elevator or railgun would be.

Best,
- Joe
john hare
2007-03-01 02:03:38 UTC
Permalink
Post by Joe Strout
I suspect that SpaceShipThree, or whichever version goes all the way to
orbit, will still launch from altitude, from what will have to be a
truly titanic carrier plane. It's a help, but it's not a breakthrough
like what a space elevator or railgun would be.
I believe that similar air launch results in the large scale would be
cheaper by a custom design ship compared to an existing aircraft.
Designing a carrier vehicle for the express purpose of providing
airlaunch could have a very different set of trade offs. You can
trade efficient wings and aero surfaces for robust ones that are
lighter and stronger. Aerodynamic efficiency is much less important
to a few vehicles that fly an hour a day at the most, than it is to
large quantities of aircraft that must compete on multiple flights daily.

I believe the carrier plane should be closer to a fly back booster
than a modified airliner.
Post by Joe Strout
Best,
- Joe
Henry Spencer
2007-03-02 01:26:17 UTC
Permalink
Post by john hare
I believe the carrier plane should be closer to a fly back booster
than a modified airliner.
Trouble is, the more you start designing for robustness and simplicity
rather than aerodynamic efficiency, the more interested you get in engines
that are far lighter and much less fussy and much more powerful than jet
engines, if somewhat less fuel-efficient -- that is, rocket engines. What
lies at the end of that evolutionary path *is* a recoverable rocket stage,
not an airplane.

An awful lot of design concepts that start out with an airbreathing lower
stage and a rocket upper stage quietly drop that idea when the designer,
just for completeness, does a comparison to an all-rocket system... and
discovers that the all-rocket system performs better and would be easier
to develop and cheaper to operate.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | ***@spsystems.net
john hare
2007-03-02 10:11:13 UTC
Permalink
Post by Henry Spencer
Post by john hare
I believe the carrier plane should be closer to a fly back booster
than a modified airliner.
Trouble is, the more you start designing for robustness and simplicity
rather than aerodynamic efficiency, the more interested you get in engines
that are far lighter and much less fussy and much more powerful than jet
engines, if somewhat less fuel-efficient -- that is, rocket engines. What
lies at the end of that evolutionary path *is* a recoverable rocket stage,
not an airplane.
My thinking is use enough airbreathing engine to safely fly the stage
back from serious down/cross range distances. Any advantage in
airbreathing engines will not be in performance. It will be in operational
flexibility. If the trades do not give serious advantages in that aspect,
then the airbreathing engines should be dropped.
Post by Henry Spencer
An awful lot of design concepts that start out with an airbreathing lower
stage and a rocket upper stage quietly drop that idea when the designer,
just for completeness, does a comparison to an all-rocket system... and
discovers that the all-rocket system performs better and would be easier
to develop and cheaper to operate.
--
I think the best lower stage will have some mix of the two engine types.
When you require high flight rates to a variety of orbits, it may be
worthwhile to develop a vehicle that can get the near SSTO vehicle to
a launch location clear of the thunderstorm that cropped up an hour
before the limited launch window of the fixed pads.

The lower stage/flyback booster should replace the launch pads
and reduce third party risks and paperwork, like Sealaunch, not
the Tristar.
Post by Henry Spencer
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |
Craig Fink
2007-03-02 14:51:11 UTC
Permalink
I would think that the advantages of airbreathing engines are tremendous. A
payload increase in the 100% to 1000% range. There is a huge performance
gap (ISP to SPF Specific Fuel Consumption) between rocket engines and
airbreathing engines. From 600 for the best chemical rockets to the
1000-4000 for airbreathing engines. Doubling the ISP of the best rocket
engine will more than double the payload.

In my opinion, not much has been done or studied to bridge this gap. If your
trades don't give a serious advantage then something is wrong with your
trades. Like, maybe they had the wrong engine.
--
Craig Fink
Courtesy E-Mail Welcome @ ***@GMail.Com
--
Post by john hare
My thinking is use enough airbreathing engine to safely fly the stage
back from serious down/cross range distances. Any advantage in
airbreathing engines will not be in performance. It will be in operational
flexibility. If the trades do not give serious advantages in that aspect,
then the airbreathing engines should be dropped.
Rand Simberg
2007-03-02 15:15:57 UTC
Permalink
On Fri, 02 Mar 2007 14:51:11 GMT, in a place far, far away, Craig Fink
Post by Craig Fink
I would think that the advantages of airbreathing engines are tremendous.
You'd be wrong.
Post by Craig Fink
A payload increase in the 100% to 1000% range. There is a huge performance
gap (ISP to SPF Specific Fuel Consumption) between rocket engines and
airbreathing engines. From 600 for the best chemical rockets to the
1000-4000 for airbreathing engines. Doubling the ISP of the best rocket
engine will more than double the payload.
In my opinion, not much has been done or studied to bridge this gap. If your
trades don't give a serious advantage then something is wrong with your
trades. Like, maybe they had the wrong engine.
No, it's been studied extensively, by many competent people. The cost
of staying in the atmosphere long enough to take advanage of
airbreathing always tends to outweigh (often by a lot) any benefit
gained thereby.
Fred J. McCall
2007-03-02 22:07:07 UTC
Permalink
Craig Fink <***@GMail.Com> wrote:

:I would think that the advantages of airbreathing engines are tremendous. A
:payload increase in the 100% to 1000% range. There is a huge performance
:gap (ISP to SPF Specific Fuel Consumption) between rocket engines and
:airbreathing engines. From 600 for the best chemical rockets to the
:1000-4000 for airbreathing engines. Doubling the ISP of the best rocket
:engine will more than double the payload.
:
:In my opinion, not much has been done or studied to bridge this gap. If your
:trades don't give a serious advantage then something is wrong with your
:trades. Like, maybe they had the wrong engine.

Perhaps you'd care to actually make your case with a hypothetical
vehicle?

Remember, the goal is to get stuff to orbit (or beyond).
--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw
john hare
2007-03-03 04:32:50 UTC
Permalink
Post by Craig Fink
I would think that the advantages of airbreathing engines are tremendous. A
payload increase in the 100% to 1000% range. There is a huge performance
gap (ISP to SPF Specific Fuel Consumption) between rocket engines and
airbreathing engines. From 600 for the best chemical rockets to the
1000-4000 for airbreathing engines. Doubling the ISP of the best rocket
engine will more than double the payload.
In my opinion, not much has been done or studied to bridge this gap. If your
trades don't give a serious advantage then something is wrong with your
trades. Like, maybe they had the wrong engine.
The regulars here have excersized diplomacy in not pointing out that
I have a vested interest in finding a use for air breathing engines for
spaceflight. I did a short talk on an air breathing engine I invented
at Space Access 04. On paper it should have a very high T/W ratio
with fair fuel consumption. Better than any jet flying today. I did
the trades. On pure performance, pure rocket wins every time. I
have to find other reasons to justify use of my concept.

The ABE Isp is only good for narrow bands of speed and altitude. The
very high weight of most air breathing engines is dead mass for the
rockets to carry from their cut off velocity to the vehicle final velocity.
That dead mass eats up far more fuel than is saved in the early climb.
My concept engine, a variation on the air-turborocket, should get
25+ to 1 thrust to weight, with an Isp well over 1,000. The trades still
don't close for it on performance alone.
Post by Craig Fink
--
Craig Fink
--
Post by john hare
My thinking is use enough airbreathing engine to safely fly the stage
back from serious down/cross range distances. Any advantage in
airbreathing engines will not be in performance. It will be in operational
flexibility. If the trades do not give serious advantages in that aspect,
then the airbreathing engines should be dropped.
Craig Fink
2007-03-03 14:44:59 UTC
Permalink
Cool, so your engine is an attempt to bridge the ISP gap between jets and
rockets. Sounds like it does.

A child must learn to crawl before it can walk, then walk before it can run.
Sounds like your engine is in the crawling stage of Atmospheric Flight to
Orbit. Does your engine take you from 0 to 5k-6k fps with an ISP of 1000+?

It also sounds like your study was attempting to run all the way to Orbit.
An SSTO? If you turned the engine off, you should have dropped it. What was
your performance gain when you turned the engine off? Could I have a copy
of your paper? Sounds like interesting reading.
--
Craig Fink
Courtesy E-Mail Welcome @ ***@GMail.Com
--
Post by john hare
Post by Craig Fink
I would think that the advantages of airbreathing engines are tremendous. A
payload increase in the 100% to 1000% range. There is a huge performance
gap (ISP to SPF Specific Fuel Consumption) between rocket engines and
airbreathing engines. From 600 for the best chemical rockets to the
1000-4000 for airbreathing engines. Doubling the ISP of the best rocket
engine will more than double the payload.
In my opinion, not much has been done or studied to bridge this gap. If your
trades don't give a serious advantage then something is wrong with your
trades. Like, maybe they had the wrong engine.
The regulars here have excersized diplomacy in not pointing out that
I have a vested interest in finding a use for air breathing engines for
spaceflight. I did a short talk on an air breathing engine I invented
at Space Access 04. On paper it should have a very high T/W ratio
with fair fuel consumption. Better than any jet flying today. I did
the trades. On pure performance, pure rocket wins every time. I
have to find other reasons to justify use of my concept.
The ABE Isp is only good for narrow bands of speed and altitude. The
very high weight of most air breathing engines is dead mass for the
rockets to carry from their cut off velocity to the vehicle final
velocity. That dead mass eats up far more fuel than is saved in the early
climb. My concept engine, a variation on the air-turborocket, should get
25+ to 1 thrust to weight, with an Isp well over 1,000. The trades still
don't close for it on performance alone.
john hare
2007-03-04 12:18:21 UTC
Permalink
Post by Craig Fink
Cool, so your engine is an attempt to bridge the ISP gap between jets and
rockets. Sounds like it does.
A child must learn to crawl before it can walk, then walk before it can run.
Sounds like your engine is in the crawling stage of Atmospheric Flight to
Orbit. Does your engine take you from 0 to 5k-6k fps with an ISP of 1000+?
It is an engine concept with a reasonable chance of working, not hardware.
It would be usefull to about that speed if very active measures were taken
to handle intakes and thermal problems. The variable intakes to handle that
mach variety mass more than the engine itself. The heat loads on the
vehicle
and engine through that range add considerable mass, complexity and design
problems.
Post by Craig Fink
It also sounds like your study was attempting to run all the way to Orbit.
An SSTO? If you turned the engine off, you should have dropped it. What was
your performance gain when you turned the engine off? Could I have a copy
of your paper? Sounds like interesting reading.
I didn't do a formal paper. To get an idea of the concept, look up
air-turborockets.
Then check out centrifugal compressors and radial inflow turbines. My
concept
recognizes the similarity between a squirrel cage fan and those two
turbomachines
to give a regen cooled engine.

My point is that I have a vested interest in air breathing engines for this
purpose,
and they fail.
Post by Craig Fink
--
Craig Fink
--
Post by john hare
Post by Craig Fink
I would think that the advantages of airbreathing engines are tremendous. A
payload increase in the 100% to 1000% range. There is a huge performance
gap (ISP to SPF Specific Fuel Consumption) between rocket engines and
airbreathing engines. From 600 for the best chemical rockets to the
1000-4000 for airbreathing engines. Doubling the ISP of the best rocket
engine will more than double the payload.
In my opinion, not much has been done or studied to bridge this gap. If your
trades don't give a serious advantage then something is wrong with your
trades. Like, maybe they had the wrong engine.
The regulars here have excersized diplomacy in not pointing out that
I have a vested interest in finding a use for air breathing engines for
spaceflight. I did a short talk on an air breathing engine I invented
at Space Access 04. On paper it should have a very high T/W ratio
with fair fuel consumption. Better than any jet flying today. I did
the trades. On pure performance, pure rocket wins every time. I
have to find other reasons to justify use of my concept.
The ABE Isp is only good for narrow bands of speed and altitude. The
very high weight of most air breathing engines is dead mass for the
rockets to carry from their cut off velocity to the vehicle final
velocity. That dead mass eats up far more fuel than is saved in the early
climb. My concept engine, a variation on the air-turborocket, should get
25+ to 1 thrust to weight, with an Isp well over 1,000. The trades still
don't close for it on performance alone.
Craig Fink
2007-03-06 01:08:15 UTC
Permalink
It is an acceleration profile, not a range/endurance which most engines have
been optimized for. I've always felt the best variable intake would be a
fluid (or gas) variable intake for an acceleration type mission, even
though it's not very useful for a range/endurance type mission profile.

It helps in a lot of ways with the crawl stage. The inlet's variable
structure can be optimized for only a few Mach numbers (maybe even just
one) instead of having to be continously variable. Precools the air,
enriches the air with Oxygen, extends the useful Mach range, keeps heat
loads down, increases acceleration...it simplifies a lot. Of course, the
extra Oxygen onboard does weigh something, but this can be minimized with
the right Mission profile.

I'm missing something about why you think they fail. Getting to a Mach 6 or
7 with an ISP over 1000 is a pretty good. Are you saying zero (or negative)
performance gain to Mach 6? Could you give me a reference to the trade
study you are referring too?

This is about the velocity at which most rockets stage. For rockets, a large
percentage of their energy is consumed just getting to this point.
--
Craig Fink
Courtesy E-Mail Welcome @ ***@GMail.Com
--
Post by john hare
Post by Craig Fink
Cool, so your engine is an attempt to bridge the ISP gap between jets and
rockets. Sounds like it does.
A child must learn to crawl before it can walk, then walk before it can run.
Sounds like your engine is in the crawling stage of Atmospheric Flight to
Orbit. Does your engine take you from 0 to 5k-6k fps with an ISP of 1000+?
It is an engine concept with a reasonable chance of working, not hardware.
It would be usefull to about that speed if very active measures were
taken to handle intakes and thermal problems. The variable intakes to
handle that
mach variety mass more than the engine itself. The heat loads on the
vehicle
and engine through that range add considerable mass, complexity and design
problems.
Post by Craig Fink
It also sounds like your study was attempting to run all the way to
Orbit. An SSTO? If you turned the engine off, you should have dropped it.
What was
your performance gain when you turned the engine off? Could I have a copy
of your paper? Sounds like interesting reading.
I didn't do a formal paper. To get an idea of the concept, look up
air-turborockets.
Then check out centrifugal compressors and radial inflow turbines. My
concept
recognizes the similarity between a squirrel cage fan and those two
turbomachines
to give a regen cooled engine.
My point is that I have a vested interest in air breathing engines for
this purpose,
and they fail.
Post by Craig Fink
--
Craig Fink
--
Post by john hare
Post by Craig Fink
I would think that the advantages of airbreathing engines are tremendous. A
payload increase in the 100% to 1000% range. There is a huge
performance gap (ISP to SPF Specific Fuel Consumption) between rocket
engines and airbreathing engines. From 600 for the best chemical
rockets to the 1000-4000 for airbreathing engines. Doubling the ISP of
the best rocket engine will more than double the payload.
In my opinion, not much has been done or studied to bridge this gap. If your
trades don't give a serious advantage then something is wrong with your
trades. Like, maybe they had the wrong engine.
The regulars here have excersized diplomacy in not pointing out that
I have a vested interest in finding a use for air breathing engines for
spaceflight. I did a short talk on an air breathing engine I invented
at Space Access 04. On paper it should have a very high T/W ratio
with fair fuel consumption. Better than any jet flying today. I did
the trades. On pure performance, pure rocket wins every time. I
have to find other reasons to justify use of my concept.
The ABE Isp is only good for narrow bands of speed and altitude. The
very high weight of most air breathing engines is dead mass for the
rockets to carry from their cut off velocity to the vehicle final
velocity. That dead mass eats up far more fuel than is saved in the
early climb. My concept engine, a variation on the air-turborocket,
should get 25+ to 1 thrust to weight, with an Isp well over 1,000. The
trades still don't close for it on performance alone.
john hare
2007-03-06 10:28:11 UTC
Permalink
Post by Craig Fink
I'm missing something about why you think they fail. Getting to a Mach 6 or
7 with an ISP over 1000 is a pretty good. Are you saying zero (or negative)
performance gain to Mach 6? Could you give me a reference to the trade
study you are referring too?
This is about the velocity at which most rockets stage. For rockets, a large
percentage of their energy is consumed just getting to this point.
--
Craig Fink
I will try to do a serious post in a few days when the work slows down.
For now I will say that until any of the rest of us ran the numbers
personally,
it didn't make sense to us either. Few of the serious posters here are good
at taking somebodys word for it without checking.
Craig Fink
2007-03-07 01:36:59 UTC
Permalink
Post by john hare
Post by Craig Fink
I'm missing something about why you think they fail. Getting to a Mach 6 or
7 with an ISP over 1000 is a pretty good. Are you saying zero (or negative)
performance gain to Mach 6? Could you give me a reference to the trade
study you are referring too?
This is about the velocity at which most rockets stage. For rockets, a large
percentage of their energy is consumed just getting to this point.
--
Craig Fink
I will try to do a serious post in a few days when the work slows down.
For now I will say that until any of the rest of us ran the numbers
personally,
it didn't make sense to us either. Few of the serious posters here are
good at taking somebodys word for it without checking.
OK, later then...
john hare
2007-03-08 12:13:57 UTC
Permalink
Post by Craig Fink
It is an acceleration profile, not a range/endurance which most engines have
been optimized for. I've always felt the best variable intake would be a
fluid (or gas) variable intake for an acceleration type mission, even
though it's not very useful for a range/endurance type mission profile.
I've read a couple of intake textbooks and a few papers on the subject
without seeing any mention of the variable fluid intake. I have a thought
or two on the matter, but would be interested in your approach.
Post by Craig Fink
It helps in a lot of ways with the crawl stage. The inlet's variable
structure can be optimized for only a few Mach numbers (maybe even just
one) instead of having to be continously variable. Precools the air,
enriches the air with Oxygen, extends the useful Mach range, keeps heat
loads down, increases acceleration...it simplifies a lot. Of course, the
extra Oxygen onboard does weigh something, but this can be minimized with
the right Mission profile.
Precoolers are usefull if one is determined to use airbreathing across a
wide mach range.
Post by Craig Fink
I'm missing something about why you think they fail. Getting to a Mach 6 or
7 with an ISP over 1000 is a pretty good. Are you saying zero (or negative)
performance gain to Mach 6? Could you give me a reference to the trade
study you are referring too?
The best explanation is to set up a simple scenerio to work the numbers
around. This lets you do your own trade studies with various assumptions
Start with a design condition that an upper stage of one metric
ton must be boosted to mach 6. Anyone that disagrees with the one ton
can multiply to get their favorite size.

First, know your enemy. The rocket stage to mach 6 will need a bit over
3,000 meters per second of impulse including drag and gravity losses.
This is about the exhaust velocity of a rocket in this mode which makes
the mass ratio 2.72 or so of GLOW. A take off, this vehicle will have
about 63% propellant and 37% first stage hardware and upper stage.

The rocket engine will mass about 1.25% of GLOW if it has a
thrust/weight of 100 and an acceleration of 0.25 gee plus a gee of
gravity losses. Tanks for Lox/Kero will mass <2% of propellant
for a weight of 1.26% of GLOW. WAG is that shrouds, attachments,
control systems and whatnot will mass about 3% of GLOW.

Total first stage mass is about 69% of GLOW in an all rocket system.
Total GLOW is about 3.25 tons. Rocket engines and tanks will
mass about 41 kilograms each.

Second, is know yourself. The jet first stage to mach 6 will need well
over 3,000 meters per second of impulse due to the much higher drag
of the required flight profile for airbreathing. Mass ratio will be at
least 1.35 with an Isp of 1,000. Total hardware for the rocket stage
was about 195 kilograms. To match performance you have 1,195
kilograms of hardware and upper stage, plus 418 kilograms of fuel.
Total Glow is down to 1,613 kilograms.

Cutting GLOW in half seems like a clear win, which causes almost
everybody to check it out at least once. The 195 kilograms of hardware
is the critical factor. Does the airbreathing system save expensive
hardware? If shrouds and stuff still mass 3% of GLOW, you have 48
kilograms of that plus 9 kilograms of tankage, leaving 138 kilograms
for the jet engines and intakes. You need 2 tons of thrust to leave the
pad. This would require a 200 kilogram normal jet engine, or an 80
kilogram turborocket if I could get it to work.

Three problems are apparent already. An intake weighing as much
as the engine blows the mass budget in even the best case. At even
5 kilometers altitude air density is halved which drops thrust by
half, which means the vehicle won't accelerate without even more
engine. And most important, engine mass costs more than tank
or shroud mass. Jet derivitives are more expensive to get right
than rockets. The rocket stage needed only 41 kilograms of engine.
The jet derivitive will cost more per kilogram of mass, and
require more mass in the first place.

Designers frequently resort to wings or other lifting surfaces to
salvage a concept. From a pure performance standpoint, this
kludges things up even worse.
Post by Craig Fink
This is about the velocity at which most rockets stage. For rockets, a large
percentage of their energy is consumed just getting to this point.
Energy is far cheaper than hardware. If you do a rocket with 1% of
GLOW as final payload, you will be behind most other launch vehicles.
However, 99 kilograms of propellant to launch 1 kilogram of payload
would cost less that $50.00. Anything over $50.00 a kilogram to
orbit goes to hardware and overhead. Cut overhead to really see
savings.

You have to run numbers yourself rather than take someones word
for it. That is the best way to move yourself forward.
It is not always obvious which posters here know what they are
talking about. I am an inventor with an interest in this field. That
does not make me an expert, or even competant on the subject.

Several of the people that answered you in this thread are
professionals that know their stuff, as well as at least one netloon.
Post by Craig Fink
--
Craig Fink
--
Post by john hare
Post by Craig Fink
Cool, so your engine is an attempt to bridge the ISP gap between jets and
rockets. Sounds like it does.
A child must learn to crawl before it can walk, then walk before it can run.
Sounds like your engine is in the crawling stage of Atmospheric Flight to
Orbit. Does your engine take you from 0 to 5k-6k fps with an ISP of 1000+?
It is an engine concept with a reasonable chance of working, not hardware.
It would be usefull to about that speed if very active measures were
taken to handle intakes and thermal problems. The variable intakes to
handle that
mach variety mass more than the engine itself. The heat loads on the
vehicle
and engine through that range add considerable mass, complexity and design
problems.
Post by Craig Fink
It also sounds like your study was attempting to run all the way to
Orbit. An SSTO? If you turned the engine off, you should have dropped it.
What was
your performance gain when you turned the engine off? Could I have a copy
of your paper? Sounds like interesting reading.
I didn't do a formal paper. To get an idea of the concept, look up
air-turborockets.
Then check out centrifugal compressors and radial inflow turbines. My
concept
recognizes the similarity between a squirrel cage fan and those two
turbomachines
to give a regen cooled engine.
My point is that I have a vested interest in air breathing engines for
this purpose,
and they fail.
Post by Craig Fink
--
Craig Fink
--
Post by john hare
Post by Craig Fink
I would think that the advantages of airbreathing engines are tremendous. A
payload increase in the 100% to 1000% range. There is a huge
performance gap (ISP to SPF Specific Fuel Consumption) between rocket
engines and airbreathing engines. From 600 for the best chemical
rockets to the 1000-4000 for airbreathing engines. Doubling the ISP of
the best rocket engine will more than double the payload.
In my opinion, not much has been done or studied to bridge this gap.
If
your
trades don't give a serious advantage then something is wrong with your
trades. Like, maybe they had the wrong engine.
The regulars here have excersized diplomacy in not pointing out that
I have a vested interest in finding a use for air breathing engines for
spaceflight. I did a short talk on an air breathing engine I invented
at Space Access 04. On paper it should have a very high T/W ratio
with fair fuel consumption. Better than any jet flying today. I did
the trades. On pure performance, pure rocket wins every time. I
have to find other reasons to justify use of my concept.
The ABE Isp is only good for narrow bands of speed and altitude. The
very high weight of most air breathing engines is dead mass for the
rockets to carry from their cut off velocity to the vehicle final
velocity. That dead mass eats up far more fuel than is saved in the
early climb. My concept engine, a variation on the air-turborocket,
should get 25+ to 1 thrust to weight, with an Isp well over 1,000. The
trades still don't close for it on performance alone.
Craig Fink
2007-03-09 17:04:46 UTC
Permalink
Hi John,

Thanks for the nice comparison post, I'm going to have to think about it a
for a bit.

If you had a couple of thoughts about variable fluid intakes yesterday, you
must have at least four by now.

Most Precoolers are physical heat exchangers. A variable fluid intake is
not. The fluid (liquid/gas) is added in the intake, supersonic region.

Example, if an intake were designed for Mach 3, there is an optimal area
ratio that between the area of the front of the intake and the throat. It's
fixed. To go faster, the size of the intake area must be increased, or the
throat decreased to keep the throat at Mach 1. Instead of moving something,
open a valve and add a fluid like LOX. The additional fluid decreases the
apparent throat area as far a the incoming air is concerned. All kinds of
good things happen, LOX cools the flow, becomes a gas constricting the
throat area to the proper size, enriching the air with Oxygen, reduces
intake heating, reduces intake structure and complexity.

Also, there are other interesting things that can be done. Preheat the LOX
(in a precooler or just use the stators), turning it into a high pressure
warm gas. A little Oxygen thruster, to dynamically close the area of the
throat. This would reduce the LOX usage.

At the same time it's probably a good idea to increase the fuel flow, even
go from a lean fuel mixture to the other side of the temperature curve, a
super rich fuel mixture. Spin that turbine and compressor up, while
maintaining a good turbine inlet temperature.

Then dump that fuel rich turbine exhaust into the bi-pass air. Really giving
it a final boost of acceleration before separation of the Crawl Stage.

There are at least a dozen other interesting things to do with with a
variable fluid intake, especially when taking about ramjet, scramjets, and
turboscramjetrockets. And it's not limited to just the intake. Manipulating
one fluid with another.

What were your thoughts? I'm interested.
--
Craig Fink
Courtesy E-Mail Welcome @ ***@GMail.Com
--
Post by john hare
Post by Craig Fink
It is an acceleration profile, not a range/endurance which most engines have
been optimized for. I've always felt the best variable intake would be a
fluid (or gas) variable intake for an acceleration type mission, even
though it's not very useful for a range/endurance type mission profile.
I've read a couple of intake textbooks and a few papers on the subject
without seeing any mention of the variable fluid intake. I have a thought
or two on the matter, but would be interested in your approach.
Post by Craig Fink
It helps in a lot of ways with the crawl stage. The inlet's variable
structure can be optimized for only a few Mach numbers (maybe even just
one) instead of having to be continously variable. Precools the air,
enriches the air with Oxygen, extends the useful Mach range, keeps heat
loads down, increases acceleration...it simplifies a lot. Of course, the
extra Oxygen onboard does weigh something, but this can be minimized with
the right Mission profile.
Precoolers are usefull if one is determined to use airbreathing across a
wide mach range.
Post by Craig Fink
I'm missing something about why you think they fail. Getting to a Mach 6 or
7 with an ISP over 1000 is a pretty good. Are you saying zero (or negative)
performance gain to Mach 6? Could you give me a reference to the trade
study you are referring too?
The best explanation is to set up a simple scenerio to work the numbers
around. This lets you do your own trade studies with various assumptions
Start with a design condition that an upper stage of one metric
ton must be boosted to mach 6. Anyone that disagrees with the one ton
can multiply to get their favorite size.
First, know your enemy. The rocket stage to mach 6 will need a bit over
3,000 meters per second of impulse including drag and gravity losses.
This is about the exhaust velocity of a rocket in this mode which makes
the mass ratio 2.72 or so of GLOW. A take off, this vehicle will have
about 63% propellant and 37% first stage hardware and upper stage.
The rocket engine will mass about 1.25% of GLOW if it has a
thrust/weight of 100 and an acceleration of 0.25 gee plus a gee of
gravity losses. Tanks for Lox/Kero will mass <2% of propellant
for a weight of 1.26% of GLOW. WAG is that shrouds, attachments,
control systems and whatnot will mass about 3% of GLOW.
Total first stage mass is about 69% of GLOW in an all rocket system.
Total GLOW is about 3.25 tons. Rocket engines and tanks will
mass about 41 kilograms each.
Second, is know yourself. The jet first stage to mach 6 will need well
over 3,000 meters per second of impulse due to the much higher drag
of the required flight profile for airbreathing. Mass ratio will be at
least 1.35 with an Isp of 1,000. Total hardware for the rocket stage
was about 195 kilograms. To match performance you have 1,195
kilograms of hardware and upper stage, plus 418 kilograms of fuel.
Total Glow is down to 1,613 kilograms.
Cutting GLOW in half seems like a clear win, which causes almost
everybody to check it out at least once. The 195 kilograms of hardware
is the critical factor. Does the airbreathing system save expensive
hardware? If shrouds and stuff still mass 3% of GLOW, you have 48
kilograms of that plus 9 kilograms of tankage, leaving 138 kilograms
for the jet engines and intakes. You need 2 tons of thrust to leave the
pad. This would require a 200 kilogram normal jet engine, or an 80
kilogram turborocket if I could get it to work.
Three problems are apparent already. An intake weighing as much
as the engine blows the mass budget in even the best case. At even
5 kilometers altitude air density is halved which drops thrust by
half, which means the vehicle won't accelerate without even more
engine. And most important, engine mass costs more than tank
or shroud mass. Jet derivitives are more expensive to get right
than rockets. The rocket stage needed only 41 kilograms of engine.
The jet derivitive will cost more per kilogram of mass, and
require more mass in the first place.
Designers frequently resort to wings or other lifting surfaces to
salvage a concept. From a pure performance standpoint, this
kludges things up even worse.
Post by Craig Fink
This is about the velocity at which most rockets stage. For rockets, a large
percentage of their energy is consumed just getting to this point.
Energy is far cheaper than hardware. If you do a rocket with 1% of
GLOW as final payload, you will be behind most other launch vehicles.
However, 99 kilograms of propellant to launch 1 kilogram of payload
would cost less that $50.00. Anything over $50.00 a kilogram to
orbit goes to hardware and overhead. Cut overhead to really see
savings.
You have to run numbers yourself rather than take someones word
for it. That is the best way to move yourself forward.
It is not always obvious which posters here know what they are
talking about. I am an inventor with an interest in this field. That
does not make me an expert, or even competant on the subject.
Several of the people that answered you in this thread are
professionals that know their stuff, as well as at least one netloon.
Post by Craig Fink
--
Craig Fink
--
Post by john hare
Post by Craig Fink
Cool, so your engine is an attempt to bridge the ISP gap between jets and
rockets. Sounds like it does.
A child must learn to crawl before it can walk, then walk before it can run.
Sounds like your engine is in the crawling stage of Atmospheric Flight to
Orbit. Does your engine take you from 0 to 5k-6k fps with an ISP of 1000+?
It is an engine concept with a reasonable chance of working, not hardware.
It would be usefull to about that speed if very active measures were
taken to handle intakes and thermal problems. The variable intakes to
handle that
mach variety mass more than the engine itself. The heat loads on the
vehicle
and engine through that range add considerable mass, complexity and design
problems.
Post by Craig Fink
It also sounds like your study was attempting to run all the way to
Orbit. An SSTO? If you turned the engine off, you should have dropped it.
What was
your performance gain when you turned the engine off? Could I have a copy
of your paper? Sounds like interesting reading.
I didn't do a formal paper. To get an idea of the concept, look up
air-turborockets.
Then check out centrifugal compressors and radial inflow turbines. My
concept
recognizes the similarity between a squirrel cage fan and those two
turbomachines
to give a regen cooled engine.
My point is that I have a vested interest in air breathing engines for
this purpose,
and they fail.
Post by Craig Fink
--
Craig Fink
--
Post by john hare
Post by Craig Fink
I would think that the advantages of airbreathing engines are tremendous. A
payload increase in the 100% to 1000% range. There is a huge
performance gap (ISP to SPF Specific Fuel Consumption) between rocket
engines and airbreathing engines. From 600 for the best chemical
rockets to the 1000-4000 for airbreathing engines. Doubling the ISP
of the best rocket engine will more than double the payload.
In my opinion, not much has been done or studied to bridge this gap.
If
your
trades don't give a serious advantage then something is wrong with your
trades. Like, maybe they had the wrong engine.
The regulars here have excersized diplomacy in not pointing out that
I have a vested interest in finding a use for air breathing engines
for spaceflight. I did a short talk on an air breathing engine I
invented at Space Access 04. On paper it should have a very high T/W
ratio
with fair fuel consumption. Better than any jet flying today. I did
the trades. On pure performance, pure rocket wins every time. I
have to find other reasons to justify use of my concept.
The ABE Isp is only good for narrow bands of speed and altitude. The
very high weight of most air breathing engines is dead mass for the
rockets to carry from their cut off velocity to the vehicle final
velocity. That dead mass eats up far more fuel than is saved in the
early climb. My concept engine, a variation on the air-turborocket,
should get 25+ to 1 thrust to weight, with an Isp well over 1,000. The
trades still don't close for it on performance alone.
Craig Fink
2007-03-13 14:58:09 UTC
Permalink
--->>>Here

So, what did you find on variable fluid intakes, that turned your jet into a
rocket ever so slowly as it accelerates?

Thanks for the Milan and Murthy references. I think a trip to the library
might be in order.

I'm still interested in what your thoughts were and are?
--
Craig Fink
Courtesy E-Mail Welcome @ ***@GMail.Com
--
Post by john hare
One of my books is Combustion and Propulsion--Fourth Agard
Colloquium. High Mach Number Air-Breathing Engines.
It is a collection of papers on the subject from a meeting in Milan
Italy. Meeting date-April 4-8, 1960. And others more recent
like High-Speed Flight Propulsion Systems edited by Murthy
and Curran. Scads of papers in The Journal of Propulsion and
Power. We are bored with this repeatedly discredited field.
Hi John,
Thanks for the nice comparison post, I'm going to have to think about it a
for a bit.
If you had a couple of thoughts about variable fluid intakes yesterday,
you must have at least four by now.
Most Precoolers are physical heat exchangers. A variable fluid intake is
not. The fluid (liquid/gas) is added in the intake, supersonic region.
Example, if an intake were designed for Mach 3, there is an optimal area
ratio that between the area of the front of the intake and the throat.
It's fixed. To go faster, the size of the intake area must be increased,
or the throat decreased to keep the throat at Mach 1. Instead of moving
something, open a valve and add a fluid like LOX. The additional fluid
decreases the apparent throat area as far a the incoming air is concerned.
All kinds of good things happen, LOX cools the flow, becomes a gas
constricting the throat area to the proper size, enriching the air with
Oxygen, reduces intake heating, reduces intake structure and complexity.
Also, there are other interesting things that can be done. Preheat the LOX
(in a precooler or just use the stators), turning it into a high pressure
warm gas. A little Oxygen thruster, to dynamically close the area of the
throat. This would reduce the LOX usage.
At the same time it's probably a good idea to increase the fuel flow, even
go from a lean fuel mixture to the other side of the temperature curve, a
super rich fuel mixture. Spin that turbine and compressor up, while
maintaining a good turbine inlet temperature.
Then dump that fuel rich turbine exhaust into the bi-pass air. Really
giving it a final boost of acceleration before separation of the Crawl
Stage.
There are at least a dozen other interesting things to do with with a
variable fluid intake, especially when taking about ramjet, scramjets, and
turboscramjetrockets. And it's not limited to just the intake.
Manipulating one fluid with another.
What were your thoughts? I'm interested.
john hare
2007-03-14 03:30:43 UTC
Permalink
Post by Craig Fink
--->>>Here
So, what did you find on variable fluid intakes, that turned your jet into a
rocket ever so slowly as it accelerates?
The intake concepts of interest to me do not turn a rocket into
a jet or vice versa. The intake is simply a way of getting more
mach range from a standard jet derived engine. One oddball
thing is the possibility of using a spike of air instead of a physical
moving one at the very leading edge of the intake system.
Connecting the intake compressed air to the leading edge pipe
such that the relative compression of various machs creates
a near contious shock on lip. Not researched, have no idea
if it will really work. No moving parts.

The other is a series of backflow tubes inside the physical
ramps such that the higher pressure air behind each series
of shocks is routed forward to reenergize the boundery
layers to keep them from detaching under the adverse
pressure gradient. There is some background on this
somewhere in my references.

The trades put mach three plus airbreathing as very bad.
The thermal and trajectory problems created in addition
to the intake recovery situation make it a losing proposition
without seriously improved systems beyond reasonable
economy.

My interest in the air breathing engines is driven by the local
investment environment and flight test requirements by the
investors. We need the ability to cruise a few miles offshore
before doing rude noisy things. That is if we ever get going again.

One report we got for an airframe concept came back as a poor
idea, but included a superior alternative. It is dated 10 September
2001. Bad timing.
Post by Craig Fink
Thanks for the Milan and Murthy references. I think a trip to the library
might be in order.
There are three Murthy and Curran books on various aspects of high
and higher speed flight. You might also take a look at ISABE,
International Society for Air Breathing Engines. The symposium
papers on disk are quite reasonable for purchase through AIAA.
Post by Craig Fink
I'm still interested in what your thoughts were and are?
Air breathing engines can be usefull if properly applied. It must
not be confused as superior to rockets in areas that they are
not. The more effectively self delusion can be avoided, the more
focus is available for things that do work. It can't be avoided,
just mitigated somewhat.

It is crucial to put the numbers to the competing concepts.
It is cheaper to ride a bicycle than drive a car except that
your time and safety have value, not to mention passenger
seating and a place for the groceries.

Precooling the air seems to do nice things like double the T/W
of an engine and such. The problem with most of the concepts
I have seen is that they put a patch on a box on the side of a
kludge to barely achieve things a rocket can do without effort.
Most papers on the subject call for advances in their field
but none by the competition. Abundant wishtonium.
Post by Craig Fink
--
Craig Fink
--
Craig Fink
2007-03-10 21:14:02 UTC
Permalink
Running the numbers for two scenarios is fine, I've run many a trade study
or optimization study myself and I understand that sometimes intuition can
be wrong. I've always thought of these as opportunities, to learn something
new about the subject and gain a better understanding.

Rockets are at a highly developed and optimized stage. While an Atmospheric
Flight to Orbit vehicle has yet to be built, and yet to be optimized.

From the Preface "Mechanics and Thermodynamics of Propulsion" Second Edition
by Philip Hill and Carl Peterson,

"The basic premise of this book is that a few fundamental physical
principles, rightly applied, can...<good first paragraph>

It would not do, of course to stress fundamental principles exclusively;
only in application do the basic ideas really come alive to stimulate both
analysis and invention..."

There has been little or no "application" of these principles, only the
study of the principles through simulation and analysis of the Atmospheric
Flight to Orbit. It's missing, unlike rockets, where "application" has
occurred many times and has come alive and has stimulated a much better
understanding of them.

To compare the two will also lead to false conclusions. Like trying to
compare the pictures of two puzzles. One fully completed, the other only a
third of the way done. An unsolved puzzle, that when solved and then
optimized will IMO outperform ascent to Orbit with Rockets.

As far as I know there has been only a few unsuccessful and one successful
experiment in the Walking stage of this problem. That being NASA Hyper-X.
What I found most interesting from it was that 10% of the thrust came from
the Rocket motor that boosted it up to speed. I'd don't know if that was
planned or optimized into it, or if it was just that they need to keep
things from melting in the engine, which I suspect. A couple of pieces come
together, atmospheric flight provides an avenue to get greater energy than
the fuel alone can provide. It still needs to be optimized to go further
and faster.

I still think it's the "Golden Age of Chemical Rockets", and it will come to
an end with a Sonic Boom.
--
Craig Fink
Courtesy E-Mail Welcome @ ***@GMail.Com
--
Post by john hare
The best explanation is to set up a simple scenerio to work the numbers
around. This lets you do your own trade studies with various assumptions
Start with a design condition that an upper stage of one metric
ton must be boosted to mach 6. Anyone that disagrees with the one ton
can multiply  to get their favorite size.
First, know your enemy. The rocket stage to mach 6 will need a bit over
3,000 meters per second of impulse including drag and gravity losses.
This is about the exhaust velocity of a rocket in this mode which makes
the mass ratio 2.72 or so of GLOW. A take off, this vehicle will have
about 63% propellant and 37% first stage hardware and upper stage.
The rocket engine will mass about 1.25% of GLOW if it has a
thrust/weight of 100 and an acceleration of 0.25 gee plus a gee of
gravity losses. Tanks for Lox/Kero will mass <2% of propellant
for a weight of 1.26% of GLOW. WAG is that shrouds, attachments,
control systems and whatnot will mass about 3% of GLOW.
Total first stage mass is about 69% of GLOW in an all rocket system.
Total GLOW is about 3.25 tons. Rocket engines and tanks will
mass about 41 kilograms each.
Second, is know yourself. The jet first stage to mach 6 will need well
over 3,000 meters per second of impulse due to the much higher drag
of the required flight profile for airbreathing. Mass ratio will be at
least 1.35 with an Isp of 1,000. Total hardware for the rocket stage
was about 195 kilograms. To match performance you have 1,195
kilograms of hardware and upper stage, plus 418 kilograms of fuel.
Total Glow is down to 1,613 kilograms.
Cutting GLOW in half seems like a clear win, which causes almost
everybody to check it out at least once. The 195 kilograms of hardware
is the critical factor. Does the airbreathing system save expensive
hardware? If shrouds and stuff still mass 3% of GLOW, you have 48
kilograms of that plus 9 kilograms of tankage, leaving 138 kilograms
for the jet engines and intakes. You need 2 tons of thrust to leave the
pad. This would require a 200 kilogram normal jet engine, or an 80
kilogram turborocket if I could get it to work.
Three problems are apparent already. An intake weighing as much
as the engine blows the mass budget in even the best case. At even
5 kilometers altitude air density is halved which drops thrust by
half, which means the vehicle won't accelerate without even more
engine. And most important, engine mass costs more than tank
or shroud mass. Jet derivitives are more expensive to get right
than rockets. The rocket stage needed only 41 kilograms of engine.
The jet derivitive will cost more per kilogram of mass, and
require more mass in the first place.
Designers frequently resort to wings or other lifting surfaces to
salvage a concept. From a pure performance standpoint, this
kludges things up even worse.
Post by Craig Fink
This is about the velocity at which most rockets stage. For rockets, a large
percentage of their energy is consumed just getting to this point.
Energy is far cheaper than hardware. If you do a rocket with 1% of
GLOW as final payload, you will be behind most other launch vehicles.
However, 99 kilograms of propellant to launch 1 kilogram of payload
would cost less that $50.00. Anything over $50.00 a kilogram to
orbit goes to hardware and overhead. Cut overhead to really see
savings.
You have to run numbers yourself rather than take someones word
for it. That is the best way to move yourself forward.
It is not always obvious which posters here know what they are
talking about. I am an inventor with an interest in this field. That
does not make me an expert, or even competant on the subject.
Several of the people that answered you in this thread are
professionals that know their stuff, as well as at least one netloon.
Rand Simberg
2007-03-10 21:35:11 UTC
Permalink
On Sat, 10 Mar 2007 21:14:02 GMT, in a place far, far away, Craig Fink
Post by Craig Fink
Running the numbers for two scenarios is fine, I've run many a trade study
or optimization study myself and I understand that sometimes intuition can
be wrong. I've always thought of these as opportunities, to learn something
new about the subject and gain a better understanding.
Rockets are at a highly developed and optimized stage.
For performace, perhaps. They're a long way from it for cost or
operability.
Fred J. McCall
2007-03-10 23:38:06 UTC
Permalink
Craig Fink <***@GMail.Com> wrote:

:Running the numbers for two scenarios is fine, I've run many a trade study
:or optimization study myself and I understand that sometimes intuition can
:be wrong. I've always thought of these as opportunities, to learn something
:new about the subject and gain a better understanding.

You should run the numbers. See what 'assumptions' you have to make
to get the air-breathing case to win.

:Rockets are at a highly developed and optimized stage. While an Atmospheric
:Flight to Orbit vehicle has yet to be built, and yet to be optimized.

And there is a REALLY good reason for that, apparently.

:... IMO ...

:I still think ...

All very nice, but hardly reason for any of the folks who have spent a
lot of time looking at the problem to change their opinions.
--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw
john hare
2007-03-11 12:12:00 UTC
Permalink
Post by Craig Fink
Running the numbers for two scenarios is fine, I've run many a trade study
or optimization study myself and I understand that sometimes intuition can
be wrong. I've always thought of these as opportunities, to learn something
new about the subject and gain a better understanding.
Rockets are at a highly developed and optimized stage. While an Atmospheric
Flight to Orbit vehicle has yet to be built, and yet to be optimized.
Rockets are not highly developed at this time. They are in a similar
position as gunpowder weapons in 1850 with half a millenium of
development.
Post by Craig Fink
From the Preface "Mechanics and Thermodynamics of Propulsion" Second Edition
by Philip Hill and Carl Peterson,
"The basic premise of this book is that a few fundamental physical
principles, rightly applied, can...<good first paragraph>
Right under rightly applied are the words -deep understanding.
Post by Craig Fink
It would not do, of course to stress fundamental principles exclusively;
only in application do the basic ideas really come alive to stimulate both
analysis and invention..."
There has been little or no "application" of these principles, only the
study of the principles through simulation and analysis of the Atmospheric
Flight to Orbit. It's missing, unlike rockets, where "application" has
occurred many times and has come alive and has stimulated a much better
understanding of them.
To compare the two will also lead to false conclusions. Like trying to
compare the pictures of two puzzles. One fully completed, the other only a
third of the way done. An unsolved puzzle, that when solved and then
optimized will IMO outperform ascent to Orbit with Rockets.
Airbreathing systems are close to completion, not fully completed,
and rockets are probably far less than a third of the way.
It is necessary to compare systems that have the same application.
And as you point out yourself, rockets at less than a third done,
win against airbreathing systems that are near completion.
Investment should go to systems that have profit potential.
Post by Craig Fink
As far as I know there has been only a few unsuccessful and one successful
experiment in the Walking stage of this problem. That being NASA Hyper-X.
What I found most interesting from it was that 10% of the thrust came from
the Rocket motor that boosted it up to speed. I'd don't know if that was
planned or optimized into it, or if it was just that they need to keep
things from melting in the engine, which I suspect. A couple of pieces come
together, atmospheric flight provides an avenue to get greater energy than
the fuel alone can provide. It still needs to be optimized to go further
and faster.
Scramjets are not feasable for space applications. Anyone capable of
proper study on them that solicits funds on the spaceflight side should
be investigated for fraud. There are people doing multiple life sentences
in prison for stealing a tiny fraction of what the scrammers have.
Post by Craig Fink
I still think it's the "Golden Age of Chemical Rockets", and it will come to
an end with a Sonic Boom.
The Golden age ended with a sonic boom as you say in June 2004, and
has been moving forward since.

The people on this group are travelers with destinations in the same general
direction. We are not a team, but we do help each other from time to time
in the journey. There are a few things that are good ideas for walking here
even if they are not actual rules.

Your medium length top posting without direct connection to others points
comes across as a short lecture. Many of us will read lectures if they are
from someone we respect on a subject of interest. You have not gained
the respect from most here. We are not interested in yet more lectures
on things that have been studied and discussed to death. That is part of
the resistance you see. This subject comes up about once or twice a year.

One of my books is Combustion and Propulsion--Fourth Agard
Colloquium. High Mach Number Air-Breathing Engines.
It is a collection of papers on the subject from a meeting in Milan
Italy. Meeting date-April 4-8, 1960. And others more recent
like High-Speed Flight Propulsion Systems edited by Murthy
and Curran. Scads of papers in The Journal of Propulsion and
Power. We are bored with this repeatedly discredited field.

Don't bore us or lecture us and we will be more inclined to discuss
things of mutual interest. A good third of my posts have been wrong.
That is not a problem with people that forgive and guide me. If I
didn't listen, I would have been killfiled long ago. You appear to
not listen well, and strike out at people that disagree, like Len and
Henry.

I think you have some good ideas and ability to reason. This is not
one of those ideas.
Craig Fink
2007-03-13 14:57:52 UTC
Permalink
Post by john hare
Post by Craig Fink
Running the numbers for two scenarios is fine, I've run many a trade
study or optimization study myself and I understand that sometimes
intuition can be wrong. I've always thought of these as opportunities, to
learn something
new about the subject and gain a better understanding.
Rockets are at a highly developed and optimized stage. While an Atmospheric
Flight to Orbit vehicle has yet to be built, and yet to be optimized.
Rockets are not highly developed at this time. They are in a similar
position as gunpowder weapons in 1850 with half a millenium of
development.
Post by Craig Fink
From the Preface "Mechanics and Thermodynamics of Propulsion" Second Edition
by Philip Hill and Carl Peterson,
"The basic premise of this book is that a few fundamental physical
principles, rightly applied, can...<good first paragraph>
Right under rightly applied are the words -deep understanding.
Post by Craig Fink
It would not do, of course to stress fundamental principles exclusively;
only in application do the basic ideas really come alive to stimulate
both analysis and invention..."
There has been little or no "application" of these principles, only the
study of the principles through simulation and analysis of the
Atmospheric Flight to Orbit. It's missing, unlike rockets, where
"application" has occurred many times and has come alive and has
stimulated a much better understanding of them.
To compare the two will also lead to false conclusions. Like trying to
compare the pictures of two puzzles. One fully completed, the other only
a third of the way done. An unsolved puzzle, that when solved and then
optimized will IMO outperform ascent to Orbit with Rockets.
Airbreathing systems are close to completion, not fully completed,
and rockets are probably far less than a third of the way.
It is necessary to compare systems that have the same application.
And as you point out yourself, rockets at less than a third done,
win against airbreathing systems that are near completion.
Investment should go to systems that have profit potential.
Post by Craig Fink
As far as I know there has been only a few unsuccessful and one
successful experiment in the Walking stage of this problem. That being
NASA Hyper-X. What I found most interesting from it was that 10% of the
thrust came from the Rocket motor that boosted it up to speed. I'd don't
know if that was planned or optimized into it, or if it was just that
they need to keep things from melting in the engine, which I suspect. A
couple of pieces come
together, atmospheric flight provides an avenue to get greater energy
than the fuel alone can provide. It still needs to be optimized to go
further and faster.
Scramjets are not feasable for space applications. Anyone capable of
proper study on them that solicits funds on the spaceflight side should
be investigated for fraud. There are people doing multiple life sentences
in prison for stealing a tiny fraction of what the scrammers have.
Post by Craig Fink
I still think it's the "Golden Age of Chemical Rockets", and it will come to
an end with a Sonic Boom.
The Golden age ended with a sonic boom as you say in June 2004, and
has been moving forward since.
The people on this group are travelers with destinations in the same
general direction. We are not a team, but we do help each other from time
to time in the journey. There are a few things that are good ideas for
walking here even if they are not actual rules.
Your medium length top posting without direct connection to others points
comes across as a short lecture. Many of us will read lectures if they are
from someone we respect on a subject of interest. You have not gained
the respect from most here. We are not interested in yet more lectures
on things that have been studied and discussed to death. That is part of
the resistance you see. This subject comes up about once or twice a year.
One of my books is Combustion and Propulsion--Fourth Agard
Colloquium. High Mach Number Air-Breathing Engines.
It is a collection of papers on the subject from a meeting in Milan
Italy. Meeting date-April 4-8, 1960. And others more recent
like High-Speed Flight Propulsion Systems edited by Murthy
and Curran. Scads of papers in The Journal of Propulsion and
Power. We are bored with this repeatedly discredited field.
Don't bore us or lecture us and we will be more inclined to discuss
things of mutual interest.
lol, if it looks like a lecture, smell like a lecture, tastes like a
lecture, must be a lecture. Even if it comes at the top, bottom, intermixed
or in the margins. Quit yaking during the lecture, or I'll throw you out of
the room. And if your bored the lecture, your in the wrong room. ;-)
Post by john hare
A good third of my posts have been wrong.
That is not a problem with people that forgive and guide me. If I
didn't listen, I would have been killfiled long ago. You appear to
not listen well, and strike out at people that disagree, like Len and
Henry.
I think you have some good ideas and ability to reason. This is not
one of those ideas.
Although I have never met Henry, I would not have spent several days and
several revisions of the post to Henry if I did not like the guy. I just
would not have bothered. I am a slow reader, and can't write very well. I
don't expect you to understand my reasons, logic, ... nor wish to explain
it to you at this time. Nor, my posting style, which changes often and is
still evolving. Nor my spelling...

What I see in you is a creative person who had an idea, a good idea, who was
led down some path that concluded with you... But, still confident that if
you keep looking you can find purpose... Your need to fit in seems to be
overwhelming your creativity, if you continue it ... If you want to read
some highly creative postings go read some of Brad Guth's. Hi Brad. I
particularly like the Life on Venus one, it really does fit with Cosmology
when the Sun was much cooler, when it was in the Habitable Zone, which will
be centered about Mars some day. Fun to think about anyway. What to look
for? Probably some refined metal?

Each and every day as we encounter many different people and interact with
them. In each interaction there is an exchange... Ah, what the heck <looks
around, gees, I'm lecturing in the wrong room today> ... I read your post
and do take it into consideration, you seemed to be more concerned with
Henry and Len than a technical discussion on your idea. Otherwise, you
would have posted to a different subthread.

Now that you must be total pissed, I'll take part of this quickly diverging
subthread over here--->>>
--
Craig Fink
Courtesy E-Mail Welcome @ ***@GMail.Com
b***@gmail.com
2007-03-14 08:42:03 UTC
Permalink
Post by Craig Fink
What I see in you is a creative person who had an idea, a good idea, who was
led down some path that concluded with you... But, still confident that if
you keep looking you can find purpose... Your need to fit in seems to be
overwhelming your creativity, if you continue it ... If you want to read
some highly creative postings go read some ofBradGuth's. HiBrad. I
particularly like the Life on Venus one, it really does fit with Cosmology
when the Sun was much cooler, when it was in the Habitable Zone, which will
be centered about Mars some day. Fun to think about anyway. What to look
for? Probably some refined metal?
Venus is technically doable as is, where is. It's merely geothermally
cooking from the inside out, and that's only because it's much less
old than Earth, whereas our icy to the core Mars is simply much older
than Earth, as well as having been much less salty.

ETs or possibly as evolved local Venusians are within a degree of
biological spec, of what we should expect to discover, that is
whenever we're not so deep into the process of summarily pillaging,
raping and polluting mother Earth for all she's worth, and then some.

A far better question is; What's not to be found on Venus?
-
Brad Guth
Craig Fink
2007-03-15 13:44:02 UTC
Permalink
Yes Brad, it may be doable, but it's in the wrong direction. It would only
be to expand an intelligent being's presence, another planet for growing
room. It would require a constant high level of diligence and maintenance
to keep it livable. Lacking that at any point, it would most likely revert.

Intelligent Venusians would have realized this too and prepared the next
logical planet in the sequence for a self sustaining system in the moving
Habitable Zone. That would have been Earth, which may have required a few
things like Mars currently does.

They might have taken their Moon, and slammed it into Earth, then fine tuned
it with a bombardment from the Kuiper belt and/or Oort cloud to get the
mechanics and mixture ratios right for a self sustaining system.

We should really consider taking this particular thread back to your Life on
Venus one, but not really sure which one or where it would belong as many
of your threads have been bombarded with... My vote for something
like, "The Venusian handbook, How to make Earth Habitable"

Just some food for thought.
--
Craig Fink
Courtesy E-Mail Welcome @ ***@GMail.Com
--
Post by b***@gmail.com
Post by Craig Fink
What I see in you is a creative person who had an idea, a good idea, who
was led down some path that concluded with you... But, still confident
that if you keep looking you can find purpose... Your need to fit in
seems to be overwhelming your creativity, if you continue it ... If you
want to read some highly creative postings go read some ofBradGuth's.
HiBrad. I particularly like the Life on Venus one, it really does fit
with Cosmology when the Sun was much cooler, when it was in the Habitable
Zone, which will be centered about Mars some day. Fun to think about
anyway. What to look for? Probably some refined metal?
Venus is technically doable as is, where is. It's merely geothermally
cooking from the inside out, and that's only because it's much less
old than Earth, whereas our icy to the core Mars is simply much older
than Earth, as well as having been much less salty.
ETs or possibly as evolved local Venusians are within a degree of
biological spec, of what we should expect to discover, that is
whenever we're not so deep into the process of summarily pillaging,
raping and polluting mother Earth for all she's worth, and then some.
A far better question is; What's not to be found on Venus?
Jeff Findley
2007-03-12 17:27:44 UTC
Permalink
Post by Craig Fink
Running the numbers for two scenarios is fine, I've run many a trade study
or optimization study myself and I understand that sometimes intuition can
be wrong. I've always thought of these as opportunities, to learn something
new about the subject and gain a better understanding.
Rockets are at a highly developed and optimized stage. While an Atmospheric
Flight to Orbit vehicle has yet to be built, and yet to be optimized.
<snip>
Post by Craig Fink
I still think it's the "Golden Age of Chemical Rockets", and it will come to
an end with a Sonic Boom.
Wishful thinking and hand waving arguments are no substitute for sound
engineering analysis. If you're not going to do the engineering analysis,
you might as well wish for warp drive.

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)
Henry Spencer
2007-03-03 20:36:27 UTC
Permalink
Post by Craig Fink
I would think that the advantages of airbreathing engines are tremendous.
Yes, many people keep thinking that, and it accounts for the continuing
obsession with the subject. As John noted, when you look more carefully
at the issues, the rocket engines actually win on performance every time.
Post by Craig Fink
...There is a huge performance
gap (ISP to SPF Specific Fuel Consumption) between rocket engines and
airbreathing engines. From 600 for the best chemical rockets to the
1000-4000 for airbreathing engines.
Only at low speeds. An orbital vehicle does much of its accelerating at
very high speeds, where the Isp advantage is much smaller and the
technical problems of airbreathing are daunting.

And even at low speeds, that price for that high-sounding Isp is very
heavy engines.
Post by Craig Fink
Doubling the ISP of the best rocket
engine will more than double the payload.
Uh, no, it's not that simple. Other things being equal, such a gain in
Isp would indeed have fairly impressive effects on payload... but other
things are *not* equal. Isp is not the only important number in *vehicle*
performance.

To take a simpler case, I believe the highest Isp ever actually measured
for a chemical rocket is still the 542s of the Li/F2/H2 engine tested in
the early 1960s. Yet if you sketch out a *vehicle* using that
combination, you find that for Earth-to-orbit, it never performs better
than LOX/LH2, despite an Isp advantage of nearly 100s. Its density is so
low that the vehicle hardware ends up quite heavy, and that completely
wipes out the Isp advantage.

(And similarly, LOX/LH2 has an Isp advantage of over 100s over the older
combinations like LOX/kerosene... yet achieving high *stage* performance
is actually easier with LOX/kerosene. The handling complications and low
density of LH2 more than cancel the Isp advantage.)

Air is the same way, only worse, much worse. Even at sea level it's three
orders of magnitude less dense than LOX, and the impact of that on engine
mass is tremendous. A jet engine with thrust/weight of 10 is impressive,
while a rocket engine with T/W of 100 is nothing very special. And those
are the numbers at sea level: as the air thins out, the jet's T/W
deteriorates rapidly, while the rocket's *increases*.
Post by Craig Fink
In my opinion, not much has been done or studied to bridge this gap. If your
trades don't give a serious advantage then something is wrong with your
trades. Like, maybe they had the wrong engine.
It's been studied incessantly, and the answer keeps coming out the same:
for getting into space, rockets are better. The airbreathing-engine
enthusiasts keep insisting that this result *cannot possibly* be right --
that the Emperor just *couldn't* be standing there without any clothes on,
so therefore he somehow isn't. Need more studies, with yet more newer and
better assumptions -- they *know* what the answer is supposed to be, by
God, and they won't give up until they get it!

The most ingenious of the airbreathing folks in recent times, the HOTOL
designers, have recently shamefacedly admitted that when they compared
HOTOL to an all-rocket solution, to their horror they found that the
rockets looked better...
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | ***@spsystems.net
Monte Davis
2007-03-04 18:03:55 UTC
Permalink
Post by Henry Spencer
The airbreathing-engine
enthusiasts keep insisting that this result *cannot possibly* be right --
that the Emperor just *couldn't* be standing there without any clothes on,
so therefore he somehow isn't. Need more studies, with yet more newer and
better assumptions -- they *know* what the answer is supposed to be, by
God, and they won't give up until they get it!
That's why I keep suggesting that they leave it to military and
commercial aviation -- which have much bigger markets, development
budgets, and constituencies than space.

When air forces and/or airlines demonstrate sustained flight with
worthwhile loads at Mach 5 or 10, then -- not before -- I'll be happy,
nay eager, to think about replacing those loads with a cheap and
cheerful rocket stage to orbit.

Monte Davis
http://montedavis.livejournal.com
Len
2007-03-05 23:56:25 UTC
Permalink
Post by Henry Spencer
Post by Craig Fink
I would think that the advantages of airbreathing engines are tremendous.
Yes, many people keep thinking that, and it accounts for the continuing
obsession with the subject. As John noted, when you look more carefully
at the issues, the rocket engines actually win on performance every time.
Post by Craig Fink
...There is a huge performance
gap (ISP to SPF Specific Fuel Consumption) between rocket engines and
airbreathing engines. From 600 for the best chemical rockets to the
1000-4000 for airbreathing engines.
Only at low speeds. An orbital vehicle does much of its accelerating at
very high speeds, where the Isp advantage is much smaller and the
technical problems of airbreathing are daunting.
And even at low speeds, that price for that high-sounding Isp is very
heavy engines.
Post by Craig Fink
Doubling the ISP of the best rocket
engine will more than double the payload.
Uh, no, it's not that simple. Other things being equal, such a gain in
Isp would indeed have fairly impressive effects on payload... but other
things are *not* equal. Isp is not the only important number in *vehicle*
performance.
To take a simpler case, I believe the highest Isp ever actually measured
for a chemical rocket is still the 542s of the Li/F2/H2 engine tested in
the early 1960s. Yet if you sketch out a *vehicle* using that
combination, you find that for Earth-to-orbit, it never performs better
than LOX/LH2, despite an Isp advantage of nearly 100s. Its density is so
low that the vehicle hardware ends up quite heavy, and that completely
wipes out the Isp advantage.
(And similarly, LOX/LH2 has an Isp advantage of over 100s over the older
combinations like LOX/kerosene... yet achieving high *stage* performance
is actually easier with LOX/kerosene. The handling complications and low
density of LH2 more than cancel the Isp advantage.)
Air is the same way, only worse, much worse. Even at sea level it's three
orders of magnitude less dense than LOX, and the impact of that on engine
mass is tremendous. A jet engine with thrust/weight of 10 is impressive,
while a rocket engine with T/W of 100 is nothing very special. And those
are the numbers at sea level: as the air thins out, the jet's T/W
deteriorates rapidly, while the rocket's *increases*.
Post by Craig Fink
In my opinion, not much has been done or studied to bridge this gap. If your
trades don't give a serious advantage then something is wrong with your
trades. Like, maybe they had the wrong engine.
for getting into space, rockets are better. The airbreathing-engine
enthusiasts keep insisting that this result *cannot possibly* be right --
that the Emperor just *couldn't* be standing there without any clothes on,
so therefore he somehow isn't. Need more studies, with yet more newer and
better assumptions -- they *know* what the answer is supposed to be, by
God, and they won't give up until they get it!
The most ingenious of the airbreathing folks in recent times, the HOTOL
designers, have recently shamefacedly admitted that when they compared
HOTOL to an all-rocket solution, to their horror they found that the
rockets looked better...
Thanks Henry. A good statement of the real facts.

I guess I have tired of trying to enlighten various
generations of airbreathing mafias after more than
forty years of doing so. I think the most damage
was done by Bob Williams of DARPA when he
almost single-handedly derailed Boeing's proposal
to build the RASV on a fixed-price contract. The
end result, of course, was a very worthwhile program
called NASP :-)

Len
Post by Henry Spencer
--
spsystems.net is temporarily off the air; | Henry Spencer
Craig Fink
2007-03-08 14:21:10 UTC
Permalink
Your arguments are fallacious.

To me, Chemical Rocket Engines are to Orbital Flight as Balloons were to
Human Atmospheric Flight. Yes, you can fly in a balloon, but you don't see
very many people doing it these days. All through history there have been
the nay sayers, who have eventually been proven wrong. If man were meant to
fly, he'd have wings, as he watches the bird fly over his head.

You focus on the negative, throw your hands up in the air and quit. And
worst, you try to convince everyone else to quit with you. Pointing to all
the studies of things than don't work, is not proof than everything can't
work. Many of the studies done by large government institutions that are
more interested in using them for military purposes, or at the very best
some sort of dual use (military purposes again). And you can't even talk
about them because they don't publish their results, like the HOTOL
project.

Lets go ahead a take a look at the HOTOL.
http://en.wikipedia.org/wiki/HOTOL
...unique air-breathing engine, the RB545...
http://en.wikipedia.org/wiki/RB545
The exact details of this engine are covered by the UK's Official Secrets
Act... Kind of futile to talk about what they did wrong and how it can be
improved, isn't it. Pointing to studies you can't read, as proof you can't
do it.

Then you bring up the Emperor, who in the story *is* naked. To that I
respond:

Ahh, the pyramid builders. Yes, each generation is blessed, or cursed, with
those who will take from others with grand schemes to build the pyramids of
there time. The age old problem of getting the attention of those ignorant
few in power. Internal life can be yours, just fund my project with the
fruits of society and it is yours.

How do you get funding for your pyramid? The brass ring. Go for the brass
ring. Round and round we go, up and down, reaching each time the ring comes
around. Fund mine, I'll get it this time, I'll give you the brass ring.

SSTO being the brass ring. Without staging, we would still be standing on
the ground with Chemical Rockets. Staging vastly simplifies the problem and
brings a better understanding of it. What is the performance gain during
the Crawl Stage of Atmospheric Flight to Orbit?

You talk about big and bulky hardware, pointing to a low density/high isp
rocket, because it can beat another low density/high isp rocket. Yes, LH2
is a wonderful rocket fuel, isn't it. It's also a great fuel to burn with
air. Only uses one Oxygen atom to burn two Hydrogen, unlike Carbon.

Even in Orbit, Chemical Rockets will be replaced, with big and bulky
hardware. Enjoy the Golden Age of Chemical Rockets, because it's days are
numbered before it is replaced with something better.

And then you put the cart before the horse wanting to talk about all the
high speed acceleration in the final Run Stage to Orbit. Which by the way,
for Rockets the least amount of energy is consumed. Even here, the physics
of the problem are not nearly so bleak as the picture you paint.

Before we start running, don't you think we should learn to walk, and before
that crawl? What is the performance difference between a rocket and
Atmospheric Flight to Orbit vehicle in the Crawl Stage?

The physics and time are on my side of this argument...
--
Craig Fink
Courtesy E-Mail Welcome @ ***@GMail.Com
--
Post by Henry Spencer
Post by Craig Fink
I would think that the advantages of airbreathing engines are tremendous.
Yes, many people keep thinking that, and it accounts for the continuing
obsession with the subject. As John noted, when you look more carefully
at the issues, the rocket engines actually win on performance every time.
Post by Craig Fink
...There is a huge performance
gap (ISP to SPF Specific Fuel Consumption) between rocket engines and
airbreathing engines. From 600 for the best chemical rockets to the
1000-4000 for airbreathing engines.
Only at low speeds. An orbital vehicle does much of its accelerating at
very high speeds, where the Isp advantage is much smaller and the
technical problems of airbreathing are daunting.
And even at low speeds, that price for that high-sounding Isp is very
heavy engines.
Post by Craig Fink
Doubling the ISP of the best rocket
engine will more than double the payload.
Uh, no, it's not that simple. Other things being equal, such a gain in
Isp would indeed have fairly impressive effects on payload... but other
things are *not* equal. Isp is not the only important number in *vehicle*
performance.
To take a simpler case, I believe the highest Isp ever actually measured
for a chemical rocket is still the 542s of the Li/F2/H2 engine tested in
the early 1960s. Yet if you sketch out a *vehicle* using that
combination, you find that for Earth-to-orbit, it never performs better
than LOX/LH2, despite an Isp advantage of nearly 100s. Its density is so
low that the vehicle hardware ends up quite heavy, and that completely
wipes out the Isp advantage.
(And similarly, LOX/LH2 has an Isp advantage of over 100s over the older
combinations like LOX/kerosene... yet achieving high *stage* performance
is actually easier with LOX/kerosene. The handling complications and low
density of LH2 more than cancel the Isp advantage.)
Air is the same way, only worse, much worse. Even at sea level it's three
orders of magnitude less dense than LOX, and the impact of that on engine
mass is tremendous. A jet engine with thrust/weight of 10 is impressive,
while a rocket engine with T/W of 100 is nothing very special. And those
are the numbers at sea level: as the air thins out, the jet's T/W
deteriorates rapidly, while the rocket's *increases*.
Post by Craig Fink
In my opinion, not much has been done or studied to bridge this gap. If
your trades don't give a serious advantage then something is wrong with
your trades. Like, maybe they had the wrong engine.
for getting into space, rockets are better. The airbreathing-engine
enthusiasts keep insisting that this result *cannot possibly* be right --
that the Emperor just *couldn't* be standing there without any clothes on,
so therefore he somehow isn't. Need more studies, with yet more newer and
better assumptions -- they *know* what the answer is supposed to be, by
God, and they won't give up until they get it!
The most ingenious of the airbreathing folks in recent times, the HOTOL
designers, have recently shamefacedly admitted that when they compared
HOTOL to an all-rocket solution, to their horror they found that the
rockets looked better...
Paul F. Dietz
2007-03-08 14:50:01 UTC
Permalink
Post by Craig Fink
Your arguments are fallacious.
And yet, you don't actually point out any fallacies. Arguments from
analogy don't cut it, Craig.

There are fact-based reasons why air breathing launch appears
unpromising. Proponents have to do more than huff and puff
in indignation to get around these unfortunate facts.
Post by Craig Fink
All through history there have been
the nay sayers, who have eventually been proven wrong.
Naysayers are usually right, Craig. Most ideas don't work or aren't
competitive. We remember the cases where they were wrong, but
focusing on those cases is selection bias.

Paul
Len
2007-03-08 15:54:56 UTC
Permalink
Post by Craig Fink
Your arguments are fallacious.
If you are looking for fallacious arguments,
run the numbers. If you want to take
oxygen from the air, you have to take in
five times as much air--which generally
increases the delta-vee requirements by
about 50 percent. This is a real killer when
you are dealing with a logarithmic equation.
Run the simulation, and you will start to
discover the real facts. And then there
are other devils in the detail: 1) the
disastrous impact on structures; 2) the
much higher costs and masses of
airbreathing engines and, even more
importantly, inlets; and 3) many etc.s.
Post by Craig Fink
To me, Chemical Rocket Engines are to Orbital Flight as Balloons were to
Human Atmospheric Flight. Yes, you can fly in a balloon, but you don't see
very many people doing it these days. All through history there have been
the nay sayers, who have eventually been proven wrong. If man were meant to
fly, he'd have wings, as he watches the bird fly over his head.
You focus on the negative, throw your hands up in the air and quit. And
worst, you try to convince everyone else to quit with you. Pointing to all
the studies of things than don't work, is not proof than everything can't
work. Many of the studies done by large government institutions that are
more interested in using them for military purposes, or at the very best
some sort of dual use (military purposes again). And you can't even talk
about them because they don't publish their results, like the HOTOL
project.
Lets go ahead a take a look at the HOTOL.http://en.wikipedia.org/wiki/HOTOL
...unique air-breathing engine, the RB545...http://en.wikipedia.org/wiki/RB545
The exact details of this engine are covered by the UK's Official Secrets
Act... Kind of futile to talk about what they did wrong and how it can be
improved, isn't it. Pointing to studies you can't read, as proof you can't
do it.
Then you bring up the Emperor, who in the story *is* naked. To that I
Ahh, the pyramid builders. Yes, each generation is blessed, or cursed, with
those who will take from others with grand schemes to build the pyramids of
there time. The age old problem of getting the attention of those ignorant
few in power. Internal life can be yours, just fund my project with the
fruits of society and it is yours.
How do you get funding for your pyramid? The brass ring. Go for the brass
ring. Round and round we go, up and down, reaching each time the ring comes
around. Fund mine, I'll get it this time, I'll give you the brass ring.
SSTO being the brass ring. Without staging, we would still be standing on
the ground with Chemical Rockets. Staging vastly simplifies the problem and
brings a better understanding of it. What is the performance gain during
the Crawl Stage of Atmospheric Flight to Orbit?
Not necessarily so. I have spent 50 years
looking at all types of concepts, including
a number of airbreathing concepts. A
chemically powered SSTO space transport
appears possible if it is large enough.
However, large SSTOs do not make as much
economic sense as smaller TSTOs while we
are still fighting the traffic-level problem. Once
high traffic levels are established, many types
and sizes of space transports may make sense
--just as many types of sizes of aircraft now
make sense.

With a large dose of optimism, a smaller SSTO
seems possible. However, the airbreather
is even more sensitive to assumptions; any
possibility of actually working tends to
evaporate on a realistic day.
Post by Craig Fink
You talk about big and bulky hardware, pointing to a low density/high isp
rocket, because it can beat another low density/high isp rocket. Yes, LH2
is a wonderful rocket fuel, isn't it. It's also a great fuel to burn with
air. Only uses one Oxygen atom to burn two Hydrogen, unlike Carbon.
Even in Orbit, Chemical Rockets will be replaced, with big and bulky
hardware. Enjoy the Golden Age of Chemical Rockets, because it's days are
numbered before it is replaced with something better.
And then you put the cart before the horse wanting to talk about all the
high speed acceleration in the final Run Stage to Orbit. Which by the way,
for Rockets the least amount of energy is consumed. Even here, the physics
of the problem are not nearly so bleak as the picture you paint.
Before we start running, don't you think we should learn to walk, and before
that crawl? What is the performance difference between a rocket and
Atmospheric Flight to Orbit vehicle in the Crawl Stage?
The physics and time are on my side of this argument...
If you want to cite physics, you had better
run the numbers in realistic simulations.

Henry's arguments are not fallacious.

Len
Post by Craig Fink
--
Craig Fink
--
Post by Henry Spencer
Post by Craig Fink
I would think that the advantages of airbreathing engines are tremendous.
Yes, many people keep thinking that, and it accounts for the continuing
obsession with the subject. As John noted, when you look more carefully
at the issues, the rocket engines actually win on performance every time.
Post by Craig Fink
...There is a huge performance
gap (ISP to SPF Specific Fuel Consumption) between rocket engines and
airbreathing engines. From 600 for the best chemical rockets to the
1000-4000 for airbreathing engines.
Only at low speeds. An orbital vehicle does much of its accelerating at
very high speeds, where the Isp advantage is much smaller and the
technical problems of airbreathing are daunting.
And even at low speeds, that price for that high-sounding Isp is very
heavy engines.
Post by Craig Fink
Doubling the ISP of the best rocket
engine will more than double the payload.
Uh, no, it's not that simple. Other things being equal, such a gain in
Isp would indeed have fairly impressive effects on payload... but other
things are *not* equal. Isp is not the only important number in *vehicle*
performance.
To take a simpler case, I believe the highest Isp ever actually measured
for a chemical rocket is still the 542s of the Li/F2/H2 engine tested in
the early 1960s. Yet if you sketch out a *vehicle* using that
combination, you find that for Earth-to-orbit, it never performs better
than LOX/LH2, despite an Isp advantage of nearly 100s. Its density is so
low that the vehicle hardware ends up quite heavy, and that completely
wipes out the Isp advantage.
(And similarly, LOX/LH2 has an Isp advantage of over 100s over the older
combinations like LOX/kerosene... yet achieving high *stage* performance
is actually easier with LOX/kerosene. The handling complications and low
density of LH2 more than cancel the Isp advantage.)
Air is the same way, only worse, much worse. Even at sea level it's three
orders of magnitude less dense than LOX, and the impact of that on engine
mass is tremendous. A jet engine with thrust/weight of 10 is impressive,
while a rocket engine with T/W of 100 is nothing very special. And those
are the numbers at sea level: as the air thins out, the jet's T/W
deteriorates rapidly, while the rocket's *increases*.
Post by Craig Fink
In my opinion, not much has been done or studied to bridge this gap. If
your trades don't give a serious advantage then something is wrong with
your trades. Like, maybe they had the wrong engine.
for getting into space, rockets are better. The airbreathing-engine
enthusiasts keep insisting that this result *cannot possibly* be right --
that the Emperor just *couldn't* be standing there without any clothes on,
so therefore he somehow isn't. Need more studies, with yet more newer and
better assumptions -- they *know* what the answer is supposed to be, by
God, and they won't give up until they get it!
The most ingenious of the airbreathing folks in recent times, the HOTOL
designers, have recently shamefacedly admitted that when they compared
HOTOL to an all-rocket solution, to their horror they found that the
rockets looked better...
Craig Fink
2007-03-08 20:20:21 UTC
Permalink
Hi Len,

Well were not in agreement here.

To say that we've studied many concepts and none of them worked, therefore
no concept will work, is fallacious.

As far as I know, in a Newtonian world, the physics of propulsion will
always favor pushing on some other reaction mass (something else). If I
have a cart full of rocks, I'm going to get a lot further pulling or
pushing it than I am if I start throwing the rocks out. If I have a boat
full of rocks, I going to get a lot further paddling than throwing rocks
out. If the cart has wing and I'm in the air, I'm still going to get
further pushing on the air than throwing rocks out. If I'm in Space in a
vacuum with a cart full of rocks, well I guess I'm going to have to throw
rocks then.

I'm going to take a break for a while this particular part of the tread,
till all the rock throwing settles down a bit. Last time I brought up this
vary basic concept, there was a bunch of rock throwing too.

Don't forget all that "great" Nitrogen in the air, as long as it's leaving
the vehicle faster than it arrived it's helping.
--
Craig Fink
Courtesy E-Mail Welcome @ ***@GMail.Com
--
Post by Len
Post by Craig Fink
Your arguments are fallacious.
If you are looking for fallacious arguments,
run the numbers. If you want to take
oxygen from the air, you have to take in
five times as much air--which generally
increases the delta-vee requirements by
about 50 percent. This is a real killer when
you are dealing with a logarithmic equation.
Run the simulation, and you will start to
discover the real facts. And then there
are other devils in the detail: 1) the
disastrous impact on structures; 2) the
much higher costs and masses of
airbreathing engines and, even more
importantly, inlets; and 3) many etc.s.
Post by Craig Fink
To me, Chemical Rocket Engines are to Orbital Flight as Balloons were to
Human Atmospheric Flight. Yes, you can fly in a balloon, but you don't
see very many people doing it these days. All through history there have
been the nay sayers, who have eventually been proven wrong. If man were
meant to fly, he'd have wings, as he watches the bird fly over his head.
You focus on the negative, throw your hands up in the air and quit. And
worst, you try to convince everyone else to quit with you. Pointing to
all the studies of things than don't work, is not proof than everything
can't work. Many of the studies done by large government institutions
that are more interested in using them for military purposes, or at the
very best some sort of dual use (military purposes again). And you can't
even talk about them because they don't publish their results, like the
HOTOL project.
Lets go ahead a take a look at the
HOTOL.http://en.wikipedia.org/wiki/HOTOL ...unique air-breathing engine,
the RB545...http://en.wikipedia.org/wiki/RB545 The exact details of this
engine are covered by the UK's Official Secrets Act... Kind of futile to
talk about what they did wrong and how it can be improved, isn't it.
Pointing to studies you can't read, as proof you can't do it.
Then you bring up the Emperor, who in the story *is* naked. To that I
Ahh, the pyramid builders. Yes, each generation is blessed, or cursed,
with those who will take from others with grand schemes to build the
pyramids of there time. The age old problem of getting the attention of
those ignorant few in power. Internal life can be yours, just fund my
project with the fruits of society and it is yours.
How do you get funding for your pyramid? The brass ring. Go for the brass
ring. Round and round we go, up and down, reaching each time the ring
comes around. Fund mine, I'll get it this time, I'll give you the brass
ring.
SSTO being the brass ring. Without staging, we would still be standing on
the ground with Chemical Rockets. Staging vastly simplifies the problem
and brings a better understanding of it. What is the performance gain
during the Crawl Stage of Atmospheric Flight to Orbit?
Not necessarily so. I have spent 50 years
looking at all types of concepts, including
a number of airbreathing concepts. A
chemically powered SSTO space transport
appears possible if it is large enough.
However, large SSTOs do not make as much
economic sense as smaller TSTOs while we
are still fighting the traffic-level problem. Once
high traffic levels are established, many types
and sizes of space transports may make sense
--just as many types of sizes of aircraft now
make sense.
With a large dose of optimism, a smaller SSTO
seems possible. However, the airbreather
is even more sensitive to assumptions; any
possibility of actually working tends to
evaporate on a realistic day.
Post by Craig Fink
You talk about big and bulky hardware, pointing to a low density/high isp
rocket, because it can beat another low density/high isp rocket. Yes, LH2
is a wonderful rocket fuel, isn't it. It's also a great fuel to burn with
air. Only uses one Oxygen atom to burn two Hydrogen, unlike Carbon.
Even in Orbit, Chemical Rockets will be replaced, with big and bulky
hardware. Enjoy the Golden Age of Chemical Rockets, because it's days are
numbered before it is replaced with something better.
And then you put the cart before the horse wanting to talk about all the
high speed acceleration in the final Run Stage to Orbit. Which by the
way, for Rockets the least amount of energy is consumed. Even here, the
physics of the problem are not nearly so bleak as the picture you paint.
Before we start running, don't you think we should learn to walk, and
before that crawl? What is the performance difference between a rocket
and Atmospheric Flight to Orbit vehicle in the Crawl Stage?
The physics and time are on my side of this argument...
If you want to cite physics, you had better
run the numbers in realistic simulations.
Henry's arguments are not fallacious.
Len
Post by Craig Fink
--
Craig Fink
--
Post by Henry Spencer
Post by Craig Fink
I would think that the advantages of airbreathing engines are tremendous.
Yes, many people keep thinking that, and it accounts for the continuing
obsession with the subject. As John noted, when you look more
carefully at the issues, the rocket engines actually win on performance
every time.
Post by Craig Fink
...There is a huge performance
gap (ISP to SPF Specific Fuel Consumption) between rocket engines and
airbreathing engines. From 600 for the best chemical rockets to the
1000-4000 for airbreathing engines.
Only at low speeds. An orbital vehicle does much of its accelerating
at very high speeds, where the Isp advantage is much smaller and the
technical problems of airbreathing are daunting.
And even at low speeds, that price for that high-sounding Isp is very
heavy engines.
Post by Craig Fink
Doubling the ISP of the best rocket
engine will more than double the payload.
Uh, no, it's not that simple. Other things being equal, such a gain in
Isp would indeed have fairly impressive effects on payload... but other
things are *not* equal. Isp is not the only important number in
*vehicle* performance.
To take a simpler case, I believe the highest Isp ever actually
measured for a chemical rocket is still the 542s of the Li/F2/H2 engine
tested in
the early 1960s. Yet if you sketch out a *vehicle* using that
combination, you find that for Earth-to-orbit, it never performs better
than LOX/LH2, despite an Isp advantage of nearly 100s. Its density is
so low that the vehicle hardware ends up quite heavy, and that
completely wipes out the Isp advantage.
(And similarly, LOX/LH2 has an Isp advantage of over 100s over the
older combinations like LOX/kerosene... yet achieving high *stage*
performance
is actually easier with LOX/kerosene. The handling complications and
low density of LH2 more than cancel the Isp advantage.)
Air is the same way, only worse, much worse. Even at sea level it's
three orders of magnitude less dense than LOX, and the impact of that
on engine
mass is tremendous. A jet engine with thrust/weight of 10 is impressive,
while a rocket engine with T/W of 100 is nothing very special. And those
are the numbers at sea level: as the air thins out, the jet's T/W
deteriorates rapidly, while the rocket's *increases*.
Post by Craig Fink
In my opinion, not much has been done or studied to bridge this gap. If
your trades don't give a serious advantage then something is wrong with
your trades. Like, maybe they had the wrong engine.
for getting into space, rockets are better. The airbreathing-engine
enthusiasts keep insisting that this result *cannot possibly* be right
-- that the Emperor just *couldn't* be standing there without any
clothes on,
so therefore he somehow isn't. Need more studies, with yet more newer
and better assumptions -- they *know* what the answer is supposed to
be, by God, and they won't give up until they get it!
The most ingenious of the airbreathing folks in recent times, the HOTOL
designers, have recently shamefacedly admitted that when they compared
HOTOL to an all-rocket solution, to their horror they found that the
rockets looked better...
--
Craig Fink
Courtesy E-Mail Welcome @ ***@GMail.Com
Len
2007-03-08 21:06:18 UTC
Permalink
Post by Craig Fink
Hi Len,
Well were not in agreement here.
To say that we've studied many concepts and none of them worked, therefore
no concept will work, is fallacious.
I generally never say never. However, studying
a lot of concepts does shed light on what appear
to be basic principles. In light of these prinicples,
I have to downgrade heavily the possibility of
airbreathing approaches being beneficial for
acceleration missions.
Post by Craig Fink
As far as I know, in a Newtonian world, the physics of propulsion will
always favor pushing on some other reaction mass (something else). If I
have a cart full of rocks, I'm going to get a lot further pulling or
pushing it than I am if I start throwing the rocks out. If I have a boat
full of rocks, I going to get a lot further paddling than throwing rocks
out. If the cart has wing and I'm in the air, I'm still going to get
further pushing on the air than throwing rocks out. If I'm in Space in a
vacuum with a cart full of rocks, well I guess I'm going to have to throw
rocks then.
When you are playing a mass-ratio game,
then throwing the rocks out can be surprisingly
effective. This is perhaps the most important
benefit of the rocket approach--the attractivenes
of which I admit is initially counter-intuitive.
Post by Craig Fink
I'm going to take a break for a while this particular part of the tread,
till all the rock throwing settles down a bit. Last time I brought up this
vary basic concept, there was a bunch of rock throwing too.
You can reply later if you wish, when you
get back from your break. In either case,
I don't expect any new, persuasive arguments
on the subject.
Post by Craig Fink
Don't forget all that "great" Nitrogen in the air, as long as it's leaving
the vehicle faster than it arrived it's helping.
Ah. And there's the rub. It takes more
energy to get it to move faster than you
get out of the extra mass flow.

As I noted above, the attractiveness of the
rocket approach is counter-intuitive. The
airbreather starts out attractive, but deteriorates
rapidly with the reality of detailed analysis.
Meanwhile, the rocket appproach just gets
better with detailed analysis--especially when
accompanied with clever design tricks that
can yield a high payoff in the mass-ratio
game.

Len
Post by Craig Fink
--
Craig Fink
--
Post by Len
Post by Craig Fink
Your arguments are fallacious.
If you are looking for fallacious arguments,
run the numbers. If you want to take
oxygen from the air, you have to take in
five times as much air--which generally
increases the delta-vee requirements by
about 50 percent. This is a real killer when
you are dealing with a logarithmic equation.
Run the simulation, and you will start to
discover the real facts. And then there
are other devils in the detail: 1) the
disastrous impact on structures; 2) the
much higher costs and masses of
airbreathing engines and, even more
importantly, inlets; and 3) many etc.s.
Post by Craig Fink
To me, Chemical Rocket Engines are to Orbital Flight as Balloons were to
Human Atmospheric Flight. Yes, you can fly in a balloon, but you don't
see very many people doing it these days. All through history there have
been the nay sayers, who have eventually been proven wrong. If man were
meant to fly, he'd have wings, as he watches the bird fly over his head.
You focus on the negative, throw your hands up in the air and quit. And
worst, you try to convince everyone else to quit with you. Pointing to
all the studies of things than don't work, is not proof than everything
can't work. Many of the studies done by large government institutions
that are more interested in using them for military purposes, or at the
very best some sort of dual use (military purposes again). And you can't
even talk about them because they don't publish their results, like the
HOTOL project.
Lets go ahead a take a look at the
HOTOL.http://en.wikipedia.org/wiki/HOTOL...unique air-breathing engine,
the RB545...http://en.wikipedia.org/wiki/RB545The exact details of this
engine are covered by the UK's Official Secrets Act... Kind of futile to
talk about what they did wrong and how it can be improved, isn't it.
Pointing to studies you can't read, as proof you can't do it.
Then you bring up the Emperor, who in the story *is* naked. To that I
Ahh, the pyramid builders. Yes, each generation is blessed, or cursed,
with those who will take from others with grand schemes to build the
pyramids of there time. The age old problem of getting the attention of
those ignorant few in power. Internal life can be yours, just fund my
project with the fruits of society and it is yours.
How do you get funding for your pyramid? The brass ring. Go for the brass
ring. Round and round we go, up and down, reaching each time the ring
comes around. Fund mine, I'll get it this time, I'll give you the brass
ring.
SSTO being the brass ring. Without staging, we would still be standing on
the ground with Chemical Rockets. Staging vastly simplifies the problem
and brings a better understanding of it. What is the performance gain
during the Crawl Stage of Atmospheric Flight to Orbit?
Not necessarily so. I have spent 50 years
looking at all types of concepts, including
a number of airbreathing concepts. A
chemically powered SSTO space transport
appears possible if it is large enough.
However, large SSTOs do not make as much
economic sense as smaller TSTOs while we
are still fighting the traffic-level problem. Once
high traffic levels are established, many types
and sizes of space transports may make sense
--just as many types of sizes of aircraft now
make sense.
With a large dose of optimism, a smaller SSTO
seems possible. However, the airbreather
is even more sensitive to assumptions; any
possibility of actually working tends to
evaporate on a realistic day.
Post by Craig Fink
You talk about big and bulky hardware, pointing to a low density/high isp
rocket, because it can beat another low density/high isp rocket. Yes, LH2
is a wonderful rocket fuel, isn't it. It's also a great fuel to burn with
air. Only uses one Oxygen atom to burn two Hydrogen, unlike Carbon.
Even in Orbit, Chemical Rockets will be replaced, with big and bulky
hardware. Enjoy the Golden Age of Chemical Rockets, because it's days are
numbered before it is replaced with something better.
And then you put the cart before the horse wanting to talk about all the
high speed acceleration in the final Run Stage to Orbit. Which by the
way, for Rockets the least amount of energy is consumed. Even here, the
physics of the problem are not nearly so bleak as the picture you paint.
Before we start running, don't you think we should learn to walk, and
before that crawl? What is the performance difference between a rocket
and Atmospheric Flight to Orbit vehicle in the Crawl Stage?
The physics and time are on my side of this argument...
If you want to cite physics, you had better
run the numbers in realistic simulations.
Henry's arguments are not fallacious.
Len
Post by Craig Fink
--
Craig Fink
--
Post by Henry Spencer
Post by Craig Fink
I would think that the advantages of airbreathing engines are tremendous.
Yes, many people keep thinking that, and it accounts for the continuing
obsession with the subject. As John noted, when you look more
carefully at the issues, the rocket engines actually win on performance
every time.
Post by Craig Fink
...There is a huge performance
gap (ISP to SPF Specific Fuel Consumption) between rocket engines and
airbreathing engines. From 600 for the best chemical rockets to the
1000-4000 for airbreathing engines.
Only at low speeds. An orbital vehicle does much of its accelerating
at very high speeds, where the Isp advantage is much smaller and the
technical problems of airbreathing are daunting.
And even at low speeds, that price for that high-sounding Isp is very
heavy engines.
Post by Craig Fink
Doubling the ISP of the best rocket
engine will more than double the payload.
Uh, no, it's not that simple. Other things being equal, such a gain in
Isp would indeed have fairly impressive effects on payload... but other
things are *not* equal. Isp is not the only important number in
*vehicle* performance.
To take a simpler case, I believe the highest Isp ever actually
measured for a chemical rocket is still the 542s of the Li/F2/H2 engine
tested in
the early 1960s. Yet if you sketch out a *vehicle* using that
combination, you find that for Earth-to-orbit, it never performs better
than LOX/LH2, despite an Isp advantage of nearly 100s. Its density is
so low that the vehicle hardware ends up quite heavy, and that
completely wipes out the Isp advantage.
(And similarly, LOX/LH2 has an Isp advantage of over 100s over the
older combinations like LOX/kerosene... yet achieving high *stage*
performance
is actually easier with LOX/kerosene. The handling complications and
low density of LH2 more than cancel the Isp advantage.)
Air is the same way, only worse, much worse. Even at sea level it's
three orders of magnitude less dense than LOX, and the impact of that
on engine
mass is tremendous. A jet engine with thrust/weight of 10 is impressive,
while a rocket engine with T/W of 100 is nothing very special. And those
are the numbers at sea level: as the air thins out, the jet's T/W
deteriorates rapidly, while the rocket's *increases*.
Post by Craig Fink
In my opinion, not much has been done or studied to bridge this gap. If
your trades don't give a serious advantage then something is wrong with
your trades. Like, maybe they had the wrong engine.
for getting into space, rockets are better. The airbreathing-engine
enthusiasts keep insisting that this result *cannot possibly* be right
-- that the Emperor just *couldn't* be standing there without any
clothes on,
so therefore he somehow isn't. Need more studies, with yet more newer
and better assumptions -- they *know* what the answer is supposed to
be, by God, and they won't give up until they get it!
The most ingenious of the airbreathing folks in recent times, the HOTOL
designers, have recently shamefacedly admitted that when they compared
HOTOL to an all-rocket solution, to their horror they found that the
rockets looked better...
--
Craig Fink
Craig Fink
2007-03-10 17:02:03 UTC
Permalink
I'm not looking for an argument, really just wanting to talk about
Atmospheric Flight to Orbit, even if it does turn out worst that a Rocket.
You, 50 years. Me, I've only been Eating, Sleeping, Dreaming, Working,
Studying about rockets for 40 years. Also, Atmospheric Flight to Orbit is
much more interesting to me right now. Rockets are nothing new, really a
little boring right now.

Continuing on the Atmospheric Flight to Orbit theme with a positive
attitude. :-)

Here is my understanding of the problem so far,

The three Stages of Atmospheric Flight to Orbit, even if you don't actually
stage:

The Crawl Stage:

Thick atmosphere, great energy to motion conversion. A range of zero to Mach
7 or 8. The Nitrogen cannot and should not be ignored in the realm. As you
point out there is diminishing returns the fast the vehicle goes. I looked
it up, page 15 of Mechanics and Thermodynamics of Propulsion by Philip Hill
and Carl Peterson. The breakeven point for propellers and rockets is
3000fps (Mach 3). This region is relatively benign wrt heating, the air
flowing past the window is cool. It's also the best understood region.

The Walk Stage:

Mach 7-8 to Mach 15-16, the air is getting warm outside. This is the
transition realm, much less understood. The crossover point for scramjets
and rockets is most likely within this range. Even, here as long as the
Nitrogen is leaving the vehicle faster than it arrives there is thrust, but
energy consumption continues to climb. This region is the hump to get over,
much the same as the Sound Barrier was a hump to cross to get to supersonic
flight. Or, the transonic region, whichever. The area where your between
Crawling and Running. Crawling, inlet ram pressure recovery is all
important and heating is a hindrance a problem. Running, where inlet ram
pressure in unimportant and heating is all important. The Nitrogen still
plays an important part here.

The Run Stage:

Mach 15-16 to Mach 25+, the air is finally hot. This is the least understood
realm. Many things change here and should be considered. First and foremost
is that the energy consumed in the Crawl and Walk stages has not been lost.
It is still there in terms of Kinetic (velocity**2) and Potential
(altitude) Energy. The Kinetic energy can be thought of as stored in the
Vehicle's Velocity, or conversely thought of as energy from the past stored
in the Nitrogen. This realm, is above the exhaust velocity of the best
LH2/LOX rocket engine. The energy stored in the atmosphere is above the
energy contained in LH2 and LOX. We have crossed over, huge amounts on
energy are required to accelerate the Nitrogen further, but, conversely,
huge amounts of stored energy can be acquired from it with little drag.

T = f(Drag,Mdot) is important in this realm to use the stored energy.

Essentially, the Equations of Propulsion of the Crawl Stage have to be used,
or thought of, in reverse during the Run Stage. They have crossed over,
very similar to what happens between Subsonic and Supersonic
converging/diverging nozzles.

Heat and Drag just became my friend.

I agree this would most likely be catastrophic for a propulsion concept, but
there is another important consideration. The Run Stage is also the
trans-Orbital region. Lift requirements are diminishing quickly because the
effective gravity is going to zero.

L = -EffectiveGravity = -(G - CentrifugalAcceleration)
or approximately;
L = -G(1 - (M/25)**2)

Thrust also supplies lift making aerodynamic lift requirements even smaller.

Time is no longer of the essence as EffectiveGravity goes to zero, allowing
for large variations along the Thrust/ISP tradeoff line for the right
engine. Energy a constraint while going from High Thrust/Low ISP to Low
Thrust/High ISP.

So, to me the successful Atmospheric Flight to Orbit vehicle will have the
following characteristics....
--
Craig Fink
Courtesy E-Mail Welcome @ ***@GMail.Com
--
Post by Len
Post by Craig Fink
Hi Len,
Well were not in agreement here.
To say that we've studied many concepts and none of them worked,
therefore no concept will work, is fallacious.
I generally never say never. However, studying
a lot of concepts does shed light on what appear
to be basic principles. In light of these prinicples,
I have to downgrade heavily the possibility of
airbreathing approaches being beneficial for
acceleration missions.
Post by Craig Fink
As far as I know, in a Newtonian world, the physics of propulsion will
always favor pushing on some other reaction mass (something else). If I
have a cart full of rocks, I'm going to get a lot further pulling or
pushing it than I am if I start throwing the rocks out. If I have a boat
full of rocks, I going to get a lot further paddling than throwing rocks
out. If the cart has wing and I'm in the air, I'm still going to get
further pushing on the air than throwing rocks out. If I'm in Space in a
vacuum with a cart full of rocks, well I guess I'm going to have to throw
rocks then.
When you are playing a mass-ratio game,
then throwing the rocks out can be surprisingly
effective. This is perhaps the most important
benefit of the rocket approach--the attractivenes
of which I admit is initially counter-intuitive.
Post by Craig Fink
I'm going to take a break for a while this particular part of the tread,
till all the rock throwing settles down a bit. Last time I brought up
this vary basic concept, there was a bunch of rock throwing too.
You can reply later if you wish, when you
get back from your break. In either case,
I don't expect any new, persuasive arguments
on the subject.
Post by Craig Fink
Don't forget all that "great" Nitrogen in the air, as long as it's
leaving the vehicle faster than it arrived it's helping.
Ah. And there's the rub. It takes more
energy to get it to move faster than you
get out of the extra mass flow.
As I noted above, the attractiveness of the
rocket approach is counter-intuitive. The
airbreather starts out attractive, but deteriorates
rapidly with the reality of detailed analysis.
Meanwhile, the rocket appproach just gets
better with detailed analysis--especially when
accompanied with clever design tricks that
can yield a high payoff in the mass-ratio
game.
Len
Post by Craig Fink
--
Craig Fink
--
Post by Len
Post by Craig Fink
Your arguments are fallacious.
If you are looking for fallacious arguments,
run the numbers. If you want to take
oxygen from the air, you have to take in
five times as much air--which generally
increases the delta-vee requirements by
about 50 percent. This is a real killer when
you are dealing with a logarithmic equation.
Run the simulation, and you will start to
discover the real facts. And then there
are other devils in the detail: 1) the
disastrous impact on structures; 2) the
much higher costs and masses of
airbreathing engines and, even more
importantly, inlets; and 3) many etc.s.
Post by Craig Fink
To me, Chemical Rocket Engines are to Orbital Flight as Balloons were
to Human Atmospheric Flight. Yes, you can fly in a balloon, but you
don't see very many people doing it these days. All through history
there have been the nay sayers, who have eventually been proven wrong.
If man were meant to fly, he'd have wings, as he watches the bird fly
over his head.
You focus on the negative, throw your hands up in the air and quit.
And worst, you try to convince everyone else to quit with you.
Pointing to all the studies of things than don't work, is not proof
than everything can't work. Many of the studies done by large
government institutions that are more interested in using them for
military purposes, or at the very best some sort of dual use (military
purposes again). And you can't even talk about them because they don't
publish their results, like the HOTOL project.
Lets go ahead a take a look at the
HOTOL.http://en.wikipedia.org/wiki/HOTOL...unique air-breathing
engine, the RB545...http://en.wikipedia.org/wiki/RB545The exact
details of this engine are covered by the UK's Official Secrets Act...
Kind of futile to talk about what they did wrong and how it can be
improved, isn't it. Pointing to studies you can't read, as proof you
can't do it.
Then you bring up the Emperor, who in the story *is* naked. To that I
Ahh, the pyramid builders. Yes, each generation is blessed, or cursed,
with those who will take from others with grand schemes to build the
pyramids of there time. The age old problem of getting the attention
of those ignorant few in power. Internal life can be yours, just fund
my project with the fruits of society and it is yours.
How do you get funding for your pyramid? The brass ring. Go for the
brass ring. Round and round we go, up and down, reaching each time the
ring comes around. Fund mine, I'll get it this time, I'll give you the
brass ring.
SSTO being the brass ring. Without staging, we would still be standing
on the ground with Chemical Rockets. Staging vastly simplifies the
problem and brings a better understanding of it. What is the
performance gain during the Crawl Stage of Atmospheric Flight to
Orbit?
Not necessarily so. I have spent 50 years
looking at all types of concepts, including
a number of airbreathing concepts. A
chemically powered SSTO space transport
appears possible if it is large enough.
However, large SSTOs do not make as much
economic sense as smaller TSTOs while we
are still fighting the traffic-level problem. Once
high traffic levels are established, many types
and sizes of space transports may make sense
--just as many types of sizes of aircraft now
make sense.
With a large dose of optimism, a smaller SSTO
seems possible. However, the airbreather
is even more sensitive to assumptions; any
possibility of actually working tends to
evaporate on a realistic day.
Post by Craig Fink
You talk about big and bulky hardware, pointing to a low density/high
isp rocket, because it can beat another low density/high isp rocket.
Yes, LH2 is a wonderful rocket fuel, isn't it. It's also a great fuel
to burn with air. Only uses one Oxygen atom to burn two Hydrogen,
unlike Carbon.
Even in Orbit, Chemical Rockets will be replaced, with big and bulky
hardware. Enjoy the Golden Age of Chemical Rockets, because it's days
are numbered before it is replaced with something better.
And then you put the cart before the horse wanting to talk about all
the high speed acceleration in the final Run Stage to Orbit. Which by
the way, for Rockets the least amount of energy is consumed. Even
here, the physics of the problem are not nearly so bleak as the
picture you paint.
Before we start running, don't you think we should learn to walk, and
before that crawl? What is the performance difference between a rocket
and Atmospheric Flight to Orbit vehicle in the Crawl Stage?
The physics and time are on my side of this argument...
If you want to cite physics, you had better
run the numbers in realistic simulations.
Henry's arguments are not fallacious.
Len
Post by Craig Fink
--
Craig Fink
--
Post by Henry Spencer
Post by Craig Fink
I would think that the advantages of airbreathing engines are tremendous.
Yes, many people keep thinking that, and it accounts for the continuing
obsession with the subject. As John noted, when you look more
carefully at the issues, the rocket engines actually win on
performance every time.
Post by Craig Fink
...There is a huge performance
gap (ISP to SPF Specific Fuel Consumption) between rocket engines
and airbreathing engines. From 600 for the best chemical rockets to
the 1000-4000 for airbreathing engines.
Only at low speeds. An orbital vehicle does much of its
accelerating at very high speeds, where the Isp advantage is much
smaller and the technical problems of airbreathing are daunting.
And even at low speeds, that price for that high-sounding Isp is
very heavy engines.
Post by Craig Fink
Doubling the ISP of the best rocket
engine will more than double the payload.
Uh, no, it's not that simple. Other things being equal, such a gain
in Isp would indeed have fairly impressive effects on payload... but
other
things are *not* equal. Isp is not the only important number in
*vehicle* performance.
To take a simpler case, I believe the highest Isp ever actually
measured for a chemical rocket is still the 542s of the Li/F2/H2
engine tested in
the early 1960s. Yet if you sketch out a *vehicle* using that
combination, you find that for Earth-to-orbit, it never performs better
than LOX/LH2, despite an Isp advantage of nearly 100s. Its density
is so low that the vehicle hardware ends up quite heavy, and that
completely wipes out the Isp advantage.
(And similarly, LOX/LH2 has an Isp advantage of over 100s over the
older combinations like LOX/kerosene... yet achieving high *stage*
performance
is actually easier with LOX/kerosene. The handling complications
and low density of LH2 more than cancel the Isp advantage.)
Air is the same way, only worse, much worse. Even at sea level it's
three orders of magnitude less dense than LOX, and the impact of
that on engine
mass is tremendous. A jet engine with thrust/weight of 10 is impressive,
while a rocket engine with T/W of 100 is nothing very special. And those
are the numbers at sea level: as the air thins out, the jet's T/W
deteriorates rapidly, while the rocket's *increases*.
Post by Craig Fink
In my opinion, not much has been done or studied to bridge this gap.
If your trades don't give a serious advantage then something is
wrong with your trades. Like, maybe they had the wrong engine.
for getting into space, rockets are better. The airbreathing-engine
enthusiasts keep insisting that this result *cannot possibly* be
right -- that the Emperor just *couldn't* be standing there without
any clothes on,
so therefore he somehow isn't. Need more studies, with yet more
newer and better assumptions -- they *know* what the answer is
supposed to be, by God, and they won't give up until they get it!
The most ingenious of the airbreathing folks in recent times, the
HOTOL designers, have recently shamefacedly admitted that when they
compared HOTOL to an all-rocket solution, to their horror they found
that the rockets looked better...
Rand Simberg
2007-03-10 17:08:39 UTC
Permalink
On Sat, 10 Mar 2007 17:02:03 GMT, in a place far, far away, Craig Fink
Post by Craig Fink
I'm not looking for an argument, really just wanting to talk about
Atmospheric Flight to Orbit, even if it does turn out worst that a Rocket.
The rest of us would like to talk about things worth talking about.
Len
2007-03-10 21:16:58 UTC
Permalink
Post by Craig Fink
I'm not looking for an argument, really just wanting to talk about
Atmospheric Flight to Orbit, even if it does turn out worst that a Rocket.
You, 50 years. Me, I've only been Eating, Sleeping, Dreaming, Working,
Studying about rockets for 40 years. Also, Atmospheric Flight to Orbit is
much more interesting to me right now. Rockets are nothing new, really a
little boring right now.
Continuing on the Atmospheric Flight to Orbit theme with a positive
attitude. :-)
Here is my understanding of the problem so far,
...snip....

Well, I'll have to say that you have given Atmospheric
Flight to Orbit a lot of thought :-)

The result of my thinking on the subject is
that I personally really don't want to waste any
more time on unpromising approaches. If other
do, that's fine--except for one problem. The
superficial attractiveness of airbreathing
acceleration to orbit has probably resulted
in far more, scarce research dollars being
spent on this approach than on straightforward
rocket approaches that could actually work---
even in the near future. I normally like to live
and let live. However, when the "let-live"
aspect tends to derail--as it has done in the
past--much simpler, straightforward approaches,
then it becomes annoying and detrimental.
Part of the problem is that airbreathing
acceleration is so complex, that it is very
time consuming and expensive even to study.
Moreover, by the time each expensive
excursion collapses--notably the 1960s
Aerospace Plane effort, and the more
recent NASP effort, not to mention HOTOL
--then a new, naive bureaucracy becomes
ready to fund another fiasco.

Len
Fred J. McCall
2007-03-09 02:59:00 UTC
Permalink
Craig Fink <***@GMail.Com> wrote:

:Hi Len,
:
:Well were not in agreement here.
:
:To say that we've studied many concepts and none of them worked, therefore
:no concept will work, is fallacious.
:
:As far as I know, in a Newtonian world, the physics of propulsion will
:always favor pushing on some other reaction mass (something else).

Jesus Christ, take a basic physics course!
--
"Ignorance is preferable to error, and he is less remote from the
truth who believes nothing than he who believes what is wrong."
-- Thomas Jefferson
Fred J. McCall
2007-03-09 02:42:05 UTC
Permalink
Craig Fink <***@GMail.Com> wrote:

:Your arguments are fallacious.

And you then precede to show you are unable to disprove them

[Big snip of pretty words signifying nothing.]

Hint: I used to think that an air-breathing first stage that behaved
like an airplane was the way to go. However, I've seen several people
now present convincing arguments for why it's generally a losing
proposition and I've seen NOBODY put forward any convincing case to
contend that it's a winner.
--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw
Henry Spencer
2007-03-02 01:12:03 UTC
Permalink
Post by Quadibloc
So why not get rid of the first stage, fly a plane as high and fast as
we can, and then have the rocket start its journey from the moving
plane? That way, we build a much smaller rocket for the same payload,
and the big expensive first stage is replaced by an airplane trip.
The idea is not ridiculous, but whether you can get big cost reductions
that way is unproven, at best. A rocket first stage is not particularly
costly, especially if you can recover and reuse it; it is the upper stage
that's expensive to build and maintain. And big airplanes are expensive,
and *custom-built* big airplanes are very expensive.

My feeling is that it's potentially a sensible idea, if you can fit on an
existing aircraft. Building your own aircraft, it's much more difficult
to see a net gain.

Even with an existing aircraft, it's by no means clear that you save
money. The example of Pegasus and Taurus is not encouraging. Pegasus is
air-launched from under a slightly-modified ex-airliner TriStar. Taurus
is essentially a wingless Pegasus on top of a big existing solid rocket
motor, for ground launch. Taurus's price is about 50% more than Pegasus's,
but it has about 3x the payload. (Of course, cost and price are different
things, but cost is harder to assess...)
Post by Quadibloc
Perhaps the problem is that the first stage of a rocket makes the
rocket go really fast, and an airplane burning atmospheric oxygen
doesn't go nearly that fact, so you can't really eliminate a whole
stage that way, making the benefits not worth the bother.
An aircraft, especially an off-the-shelf airliner, indeed doesn't give you
as much boost as a good rocket first stage. However, it probably is
*enough* to eliminate a stage -- even people who don't think SSTO is
possible will reluctantly concede that a really good upper stage doesn't
need a *lot* of initial boost to reach orbit with a modest payload.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | ***@spsystems.net
Michael Turner
2007-03-02 15:48:05 UTC
Permalink
Post by Henry Spencer
Post by Quadibloc
So why not get rid of the first stage, fly a plane as high and fast as
we can, and then have the rocket start its journey from the moving
plane? That way, we build a much smaller rocket for the same payload,
and the big expensive first stage is replaced by an airplane trip.
The idea is not ridiculous, but whether you can get big cost reductions
that way is unproven, at best. A rocket first stage is not particularly
costly, especially if you can recover and reuse it; it is the upper stage
that's expensive to build and maintain. And big airplanes are expensive,
and *custom-built* big airplanes are very expensive.
My feeling is that it's potentially a sensible idea, if you can fit on an
existing aircraft. Building your own aircraft, it's much more difficult
to see a net gain.
Even with an existing aircraft, it's by no means clear that you save
money. The example of Pegasus and Taurus is not encouraging. Pegasus is
air-launched from under a slightly-modified ex-airliner TriStar. Taurus
is essentially a wingless Pegasus on top of a big existing solid rocket
motor, for ground launch. Taurus's price is about 50% more than Pegasus's,
but it has about 3x the payload. (Of course, cost and price are different
things, but cost is harder to assess...)
Post by Quadibloc
Perhaps the problem is that the first stage of a rocket makes the
rocket go really fast, and an airplane burning atmospheric oxygen
doesn't go nearly that fact, so you can't really eliminate a whole
stage that way, making the benefits not worth the bother.
An aircraft, especially an off-the-shelf airliner, indeed doesn't give you
as much boost as a good rocket first stage. However, it probably is
*enough* to eliminate a stage -- even people who don't think SSTO is
possible will reluctantly concede that a really good upper stage doesn't
need a *lot* of initial boost to reach orbit with a modest payload.
--
spsystems.net is temporarily off the air; | Henry Spencer
".... big airplanes are expensive, and *custom-built* big airplanes
are very expensive."

For that matter, custom-built *small* airplanes are pricey. I believe
the cost overruns for the DARPA RASCAL's launcher plane were the main
reason for its eventual cancellation.

IIRC, in RASCAL they wanted to use a trick employed by Soviet
interceptor jets as far back as the late 50s: carry along LOX and
inject it into the (otherwise air-breathing) engines late in the
climb, when air starts to get thin. To make this approach work
optimally, you undoubtedly need to design a whole new aircraft with
the technique in mind. But that takes you down relatively unexplored
evolutionary paths, and that kind of thing almost always gets
expensive in aerospace engineering. Given the mission rationale of
Soviet interceptor jets -- taking down strategic bombers -- they could
rationalize this innovative use of existing flight hardware pushed to
its upward screaming limits, and accept the risk of possible loss of
craft and crew. Milions of lives would be at stake, after all. But
if you're pioneering new space access ideas, on a modest budget, it's
a different game, with different rules.

-michael turner
Len
2007-03-06 00:05:36 UTC
Permalink
Post by Michael Turner
For that matter, custom-built *small* airplanes are pricey. I believe
the cost overruns for the DARPA RASCAL's launcher plane were the main
reason for its eventual cancellation.
No, IMO from personal involvement, the
program eventually got cancelled because
the ground rules violated the laws of physics
--something that was obvious to some of us
in Phase I, but became painfully evident to all
with the detailed design efforts in Phase II.

Len
Post by Michael Turner
-michael turner
Craig Fink
2007-03-06 01:25:20 UTC
Permalink
Post by Len
Post by Michael Turner
For that matter, custom-built *small* airplanes are pricey. I believe
the cost overruns for the DARPA RASCAL's launcher plane were the main
reason for its eventual cancellation.
No, IMO from personal involvement, the
program eventually got cancelled because
the ground rules violated the laws of physics
--something that was obvious to some of us
in Phase I, but became painfully evident to all
with the detailed design efforts in Phase II.
Could you be more specific as to which law of physics it violated?
Len
2007-03-06 01:37:13 UTC
Permalink
Post by Craig Fink
Post by Len
Post by Michael Turner
For that matter, custom-built *small* airplanes are pricey. I believe
the cost overruns for the DARPA RASCAL's launcher plane were the main
reason for its eventual cancellation.
No, IMO from personal involvement, the
program eventually got cancelled because
the ground rules violated the laws of physics
--something that was obvious to some of us
in Phase I, but became painfully evident to all
with the detailed design efforts in Phase II.
Could you be more specific as to which law of physics it violated?
Yes. Zoom climb and high-speed airbreathing
are not compatible.

Len
Pat Flannery
2007-03-06 02:17:46 UTC
Permalink
Post by Len
Yes. Zoom climb and high-speed airbreathing
are not compatible.
Yeah, that would make sense, wouldn't it? Thrust would drop off as the
air density dropped, and eventually everything would just grind to a
halt due to diminishing returns.
It's funny they went with zoom climb; you'd assume one would use a
shallower angle and slowly build up speed.

Pat
Len
2007-03-06 03:31:15 UTC
Permalink
Post by Pat Flannery
Post by Len
Yes. Zoom climb and high-speed airbreathing
are not compatible.
Yeah, that would make sense, wouldn't it? Thrust would drop off as the
air density dropped, and eventually everything would just grind to a
halt due to diminishing returns.
It's funny they went with zoom climb; you'd assume one would use a
shallower angle and slowly build up speed.
Pat
Well, the object was staging at very low dynamic
pressure--which is basically a reasonable idea. The
problem is that the atmosphere is just not thick
enough to supply enough air to the engines while
supporting a large vertical turn radius at
high speed.

Rocket power can solve the problem, but that
was not was wanted--at least early enough in
the game.

You might want to look at our post-RASCAL concept:

http://www.tour2space.com/archives/f-14lv/f-14st.htm

Len
Len
2007-03-06 03:33:39 UTC
Permalink
Post by Len
Post by Pat Flannery
Post by Len
Yes. Zoom climb and high-speed airbreathing
are not compatible.
Yeah, that would make sense, wouldn't it? Thrust would drop off as the
air density dropped, and eventually everything would just grind to a
halt due to diminishing returns.
It's funny they went with zoom climb; you'd assume one would use a
shallower angle and slowly build up speed.
Pat
Well, the object was staging at very low dynamic
pressure--which is basically a reasonable idea. The
problem is that the atmosphere is just not thick
enough to supply enough air to the engines while
supporting a large vertical turn radius at
high speed.
Rocket power can solve the problem, but that
was not was wanted--at least early enough in
the game.
http://www.tour2space.com/archives/f-14lv/f-14st.htm
Len
Ooops. Try

http://www.tour2space.com/archives/f-14lv/f-14-st.htm

Len
Pat Flannery
2007-03-06 14:31:25 UTC
Permalink
Post by Len
Ooops. Try
http://www.tour2space.com/archives/f-14lv/f-14-st.htm
Isn't your CG way too far forward with that?

Pat
Len
2007-03-06 19:46:39 UTC
Permalink
Post by Pat Flannery
Post by Len
Ooops. Try
http://www.tour2space.com/archives/f-14lv/f-14-st.htm
Isn't your CG way too far forward with that?
Pat
You're right in that the it's rather difficult to
get weight aft with the F-14. However, even
in concept 1, most of the store mass is in
the LOx, which is close to the c.g. of the F-14.
The forward kerosene tank presents a problem
and needs to be balanced with extra JP tanks
aft and a need not to use this JP until after
separation. Concept 2 is a little easier to
balance since the store mass is futher
aft. In either case, separation is at rather
low dynamic pressure, as far as problems
with the store c.g. are concerned.

I didn't spend much time wringing these
concepts out, since I decided the Space Van
was a lot more promising. Moreover, I haven't
looked at the older concepts in some time.

If I were actively pursuing any of these
concepts, I would probably have to work out
some of the bugs, and that might require some
reconfiguring.

Len
Pat Flannery
2007-03-06 14:26:39 UTC
Permalink
Post by Len
http://www.tour2space.com/archives/f-14lv/f-14st.htm
That page isn't there anymore, but I've seen drawings of the F-14
version before.
The Su-27 would also work in that capacity due to its layout.

Pat
Craig Fink
2007-03-06 14:36:17 UTC
Permalink
Post by Len
Well, the object was staging at very low dynamic
pressure--which is basically a reasonable idea. The
problem is that the atmosphere is just not thick
enough to supply enough air to the engines while
supporting a large vertical turn radius at
high speed.
Rocket power can solve the problem, but that
was not was wanted--at least early enough in
the game.
http://www.tour2space.com/archives/f-14lv/f-14st.htm
A very low dynamic pressure isn't necessary for a clean separation. For a
rocket second stage, a higher flight path angle is good. For Atmospheric
Flight to Orbit, it isn't. Wings, the right engine, and a low flight path
angle is probably better to walk up to the final run to Orbit.

Your F-14 has a large wing and can probably handle the gees to turn the
velocity vector better than those Rascally tiny wings.
Jeff Findley
2007-03-06 18:22:48 UTC
Permalink
Post by Craig Fink
A very low dynamic pressure isn't necessary for a clean separation.
It may not be necessary, but it certainly does make things easier. And it's
easier to sell due to spectacular failures like the D-21.

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)
Ed Ruf (REPLY to E-MAIL IN SIG!)
2007-03-07 01:38:38 UTC
Permalink
On Tue, 6 Mar 2007 13:22:48 -0500, in sci.space.policy "Jeff Findley"
Post by Jeff Findley
Post by Craig Fink
A very low dynamic pressure isn't necessary for a clean separation.
It may not be necessary, but it certainly does make things easier. And it's
easier to sell due to spectacular failures like the D-21.
But can anyone address the details of the incident. The NASA Hyper-X
successful flights demonstrated successful Mach 7 and 10 separations at
1000 psf. It's easy to say with one failure data point it can't be done.
We now have three with two successes. What's the difference?
--
Ed Ruf (***@EdwardGRuf.com)
Henry Spencer
2007-03-07 05:50:50 UTC
Permalink
Post by Ed Ruf (REPLY to E-MAIL IN SIG!)
Post by Jeff Findley
It may not be necessary, but it certainly does make things easier. And it's
easier to sell due to spectacular failures like the D-21.
But can anyone address the details of the incident. The NASA Hyper-X
successful flights demonstrated successful Mach 7 and 10 separations at
1000 psf. It's easy to say with one failure data point it can't be done.
We now have three with two successes. What's the difference?
There were successful D-21 separations too. What mattered was the
demonstration of a previously-unsuspected failure mechanism, proving
that the situation was more complicated than anybody thought. Two
successful X-43 separations are too small a sample to show much.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | ***@spsystems.net
Pat Flannery
2007-03-08 04:49:00 UTC
Permalink
Post by Henry Spencer
There were successful D-21 separations too. What mattered was the
demonstration of a previously-unsuspected failure mechanism, proving
that the situation was more complicated than anybody thought. Two
successful X-43 separations are too small a sample to show much.
On the X-43, the test vehicle was at the front of the stack, so it
didn't need to be concerned about shockwaves from its carrier vehicle.
In the case of the D-21, the separating drone had to penetrate the
M-12's shockwave as it climbed away from the aircraft's back.
They ran into the same problem with having to pierce the shockwave under
the YF-12 when its missiles were fired.

Pat
Craig Fink
2007-03-07 13:47:15 UTC
Permalink
Here is some good reading on the subject
http://en.wikipedia.org/wiki/Lockheed_D-21/M-21
first test flight showed major problems, last test flight showed they didn't
fix it properly.

Think of the flow field around a supersonic aircraft. Now, a drone called
arrow. Arrow is going to try to separate at, well zero angle of attack. Not
to realistic, but it's just a thought experiment.

First, arrow is going to separate perpendicular to the velocity vector at
the tail. Aligned with the flow field, arrow would have a positive
separation angle relative to the aircraft. That's because the air that
flowed around the aircraft has been compressed and turned at the front of
the aircraft to create a hole in the air (the aircraft), and expanded by
the expansion fan to fill in the hole in the air at the tail.

As the arrow moves out towards the bow shock, it rotates with the airflow.
First pointed away from the velocity vector, then parallel to the velocity
vector, and finally towards the velocity vector and the aircraft.

Now think about what happens as the arrow crosses the bow shockwave. The
nose of the arrow is going to cross the shockwave first, into the clean
air. Yes, the bow shockwave is a compression wave, but also important is
that it also changes the direction the airflow. An instantaneous change in
angle of attack across the shockwave.

As the tip of the arrow crosses the shockwave, it has a different angle of
attack than the tail of the arrow. A large angle of attack difference,
creating lift on the tip of the arrow, creating a moment, and rotation of
the arrow back towards the aircraft.

So, to separate the arrow properly, it must have a large enough angle of
attack difference between the arrow and aircraft to fly through a large
angle of attack (and flow field) transient caused by the bow shockwave. If
it doesn't it going to stop and pause at the shockwave, or worst come right
back to the aircraft.

There are a lot of good and easy ways to fly through this angle of attack
transient.

The Hyper-X doesn't have this problem because it is flying at the nose of
the rocket in clean air. It is creating the bow shock, and when the rocket
burns out it has a huge amount of drag. The problem of separating the
Hyper-X is all behind it so to speek.
--
<post and posted>
Craig Fink
Courtesy E-Mail Welcome @ ***@GMail.Com
--
Post by Ed Ruf (REPLY to E-MAIL IN SIG!)
On Tue, 6 Mar 2007 13:22:48 -0500, in sci.space.policy "Jeff Findley"
Post by Jeff Findley
Post by Craig Fink
A very low dynamic pressure isn't necessary for a clean separation.
It may not be necessary, but it certainly does make things easier. And
it's easier to sell due to spectacular failures like the D-21.
But can anyone address the details of the incident. The NASA Hyper-X
successful flights demonstrated successful Mach 7 and 10 separations at
1000 psf. It's easy to say with one failure data point it can't be done.
We now have three with two successes. What's the difference?
Len
2007-03-07 01:38:15 UTC
Permalink
Post by Craig Fink
Post by Len
Well, the object was staging at very low dynamic
pressure--which is basically a reasonable idea. The
problem is that the atmosphere is just not thick
enough to supply enough air to the engines while
supporting a large vertical turn radius at
high speed.
Rocket power can solve the problem, but that
was not was wanted--at least early enough in
the game.
http://www.tour2space.com/archives/f-14lv/f-14st.htm
A very low dynamic pressure isn't necessary for a clean separation. For a
rocket second stage, a higher flight path angle is good. For Atmospheric
Flight to Orbit, it isn't. Wings, the right engine, and a low flight path
angle is probably better to walk up to the final run to Orbit.
True, very low dynamic pressure isn't necessary.
However, 1 psf staging was one of the RASCAL
ground rules. IMO, some dynamic pressure at
staging can be helpful for staging for some
concepts; our Space Van 2011 stages at mach 2
at 40 km, which corresponds to about 750 Pa (~16 psf).
Post by Craig Fink
Your F-14 has a large wing and can probably handle the gees to turn the
velocity vector better than those Rascally tiny wings.
The basic problem is that airbreathing engines
want high dynamic pressure and/or huge inlets,
which runs counter to a low-wing loading design
for a pullup. Moreover, RASCAL pullup was
limited by g constraints on the overall trajectory.
It just doesn't compute, literally.

Len
Jeff Findley
2007-03-06 18:17:56 UTC
Permalink
Post by Len
Yes. Zoom climb and high-speed airbreathing
are not compatible.
Yeah, that would make sense, wouldn't it? Thrust would drop off as the air
density dropped, and eventually everything would just grind to a halt due
to diminishing returns.
It's funny they went with zoom climb; you'd assume one would use a
shallower angle and slowly build up speed.
But that leads to higher drag and higher heating, both of which you have to
pay for in the design.

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)
Craig Fink
2007-03-06 11:50:18 UTC
Permalink
Post by Len
Post by Craig Fink
Post by Len
Post by Michael Turner
For that matter, custom-built *small* airplanes are pricey. I believe
the cost overruns for the DARPA RASCAL's launcher plane were the main
reason for its eventual cancellation.
No, IMO from personal involvement, the
program eventually got cancelled because
the ground rules violated the laws of physics
--something that was obvious to some of us
in Phase I, but became painfully evident to all
with the detailed design efforts in Phase II.
Could you be more specific as to which law of physics it violated?
Yes. Zoom climb and high-speed airbreathing
are not compatible.
I'm sorry dude, but everyone in the Military already knows it takes a
minimum of 3 states for the SR-71 to turn around. I hope you aren't a
peaceful person and that working on a weapons system isn't going to do you
any harm.

It doesn't violate the laws of physics, it's just the mission profile that
does. It's a fine weapons system and I'm sorry to say, Phase III doesn't
require the same group of people. Sorry for the subterfuge.
Len
2007-03-07 01:51:11 UTC
Permalink
Post by Craig Fink
Post by Len
Post by Craig Fink
Post by Len
Post by Michael Turner
For that matter, custom-built *small* airplanes are pricey. I believe
the cost overruns for the DARPA RASCAL's launcher plane were the main
reason for its eventual cancellation.
No, IMO from personal involvement, the
program eventually got cancelled because
the ground rules violated the laws of physics
--something that was obvious to some of us
in Phase I, but became painfully evident to all
with the detailed design efforts in Phase II.
Could you be more specific as to which law of physics it violated?
Yes. Zoom climb and high-speed airbreathing
are not compatible.
I'm sorry dude, but everyone in the Military already knows it takes a
minimum of 3 states for the SR-71 to turn around. I hope you aren't a
peaceful person and that working on a weapons system isn't going to do you
any harm.
Zoom climb involves a vertical turn, not a
horizontal turn. The atmosphere is simply
not three states thick.
Post by Craig Fink
It doesn't violate the laws of physics, it's just the mission profile that
does. It's a fine weapons system and I'm sorry to say, Phase III doesn't
require the same group of people. Sorry for the subterfuge.
The mission profile was an inflexible ground
rule. I stated that the ground rules--which also
demanded airbreathing acceleration and pullup
--violated the laws of physics.

The 1973 Procurement Commission and the
resulting OMB A-109 state that procurements
should be based upon mission element needs,
not preconceived solutions. Unfortunately,
OMB A-109 is generally ignored in RFPs--
and so the waste continues.

Len
Craig Fink
2007-03-06 23:19:37 UTC
Permalink
Seriously though, DARPA is a military institution, what their intent was
with the RASCAL program only those who need to know, know. They aren't in
the business of developing new technology for the advancement of humankind.
They are in the business of developing technology to destroy things better,
faster, bigger, small, more accurate... It could have actually been a
satellite launching program, or a technology development program, they may
have canceled it, they may not have, or it could be a weapons delivery
vehicle. Who knows? Only those with a need to, and those may not (or,
probably don't) include those who working on it.

On the Shuttle program I worked on several DOD missions, it wasn't fun, they
were particularly safe (one in particular), and I have no idea what it was
I was participating in. Kind of make one wonder?

At 10 gees, it could pull up to 30 degrees in about 11 seconds and only gain
20,000 ft in altitude. That's a reasonable zoom climb attitude.
--
Craig Fink
Courtesy E-Mail Welcome @ ***@GMail.Com
--
Post by Len
Post by Craig Fink
Post by Len
Post by Michael Turner
For that matter, custom-built *small* airplanes are pricey. I believe
the cost overruns for the DARPA RASCAL's launcher plane were the main
reason for its eventual cancellation.
No, IMO from personal involvement, the
program eventually got cancelled because
the ground rules violated the laws of physics
--something that was obvious to some of us
in Phase I, but became painfully evident to all
with the detailed design efforts in Phase II.
Could you be more specific as to which law of physics it violated?
Yes. Zoom climb and high-speed airbreathing
are not compatible.
I'm sorry dude, but everyone in the Military already knows it takes a
minimum of 3 states for the SR-71 to turn around. I hope you aren't a
peaceful person and that working on a weapons system isn't going to do you
any harm.

It doesn't violate the laws of physics, it's just the mission profile that
does. It's a fine weapons system and I'm sorry to say, Phase III doesn't
require the same group of people. Sorry for the subterfuge.
Rand Simberg
2007-03-07 00:48:44 UTC
Permalink
On Tue, 06 Mar 2007 23:19:37 GMT, in a place far, far away, Craig Fink
Post by Craig Fink
Seriously though, DARPA is a military institution, what their intent was
with the RASCAL program only those who need to know, know. They aren't in
the business of developing new technology for the advancement of humankind.
They are in the business of developing technology to destroy things better,
faster, bigger, small, more accurate...
No. They are in the business of doing both.
Post by Craig Fink
On the Shuttle program I worked on several DOD missions, it wasn't fun, they
were particularly safe (one in particular), and I have no idea what it was
I was participating in. Kind of make one wonder?
Given that it's you, no, not at all. In fact, it's exactly what I'd
expect.

I am a little concerned that you were working on the Shuttle program,
though. It explains a lot about it.
steve
2007-03-07 01:38:45 UTC
Permalink
One interesting idea that has been suggested is to build a large
airship powered by electrostatic thrusters (solar powered ?).
It flies to its maximum altitude under normal propulsion and using its
buoyancy. Then it can slowly accelerate up to orbital velocity using
its electric thrusters.
Whether this is really possible needs to be discussed.
Sylvia Else
2007-03-07 01:57:18 UTC
Permalink
Post by steve
One interesting idea that has been suggested is to build a large
airship powered by electrostatic thrusters (solar powered ?).
It flies to its maximum altitude under normal propulsion and using its
buoyancy. Then it can slowly accelerate up to orbital velocity using
its electric thrusters.
Whether this is really possible needs to be discussed.
Seems improbable to me. When it reaches its maximum height available
through buoyancy, there must still be a fair amount of air around.
Accelerating it is going to involve pushing a large object through that air.

Sylvia.
Len
2007-03-07 01:58:04 UTC
Permalink
Post by steve
One interesting idea that has been suggested is to build a large
airship powered by electrostatic thrusters (solar powered ?).
It flies to its maximum altitude under normal propulsion and using its
buoyancy. Then it can slowly accelerate up to orbital velocity using
its electric thrusters.
Whether this is really possible needs to be discussed.
If you have buoancy, you have air. if you
have air, you have drag. If you have drag
at supersonic and hypersonic velocities,
electric thrusters are going to fall far short
of hacking it.

Possible. I dunno; however, I sure as hell
don't know how to make it work.

Len
Henry Spencer
2007-03-07 05:45:20 UTC
Permalink
Post by steve
One interesting idea that has been suggested is to build a large
airship powered by electrostatic thrusters (solar powered ?).
It flies to its maximum altitude under normal propulsion and using its
buoyancy. Then it can slowly accelerate up to orbital velocity using
its electric thrusters.
Whether this is really possible needs to be discussed.
That's JP Aerospace's concept. Nobody else can make the math add up, and
JPA is not talking. They need an utterly fantastic hypersonic L/D
(lift/drag ratio) in the molecular-flow realm, and there is no indication
of how they might get it. (Normally, "hypersonic" means really lousy L/D
and "molecular flow" makes it even worse.)

The betting is that they have goofed, perhaps with an aerodynamic analysis
using subtly-incorrect assumptions. Notably, one of the standard simple
approximations for hypersonic aerodynamics could easily lead you to
believe that a very long, slim vehicle could achieve a very high
hypersonic L/D... but that approximation is valid only for short blunt
vehicles. More careful analysis of a long, slim design shows the same old
lousy hypersonic L/Ds.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | ***@spsystems.net
Jeff Findley
2007-03-07 21:02:55 UTC
Permalink
Post by steve
One interesting idea that has been suggested is to build a large
airship powered by electrostatic thrusters (solar powered ?).
It flies to its maximum altitude under normal propulsion and using its
buoyancy. Then it can slowly accelerate up to orbital velocity using
its electric thrusters.
Whether this is really possible needs to be discussed.
It's not.

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)
Craig Fink
2007-03-06 01:37:18 UTC
Permalink
Post by Len
Post by Michael Turner
For that matter, custom-built *small* airplanes are pricey. I believe
the cost overruns for the DARPA RASCAL's launcher plane were the main
reason for its eventual cancellation.
No, IMO from personal involvement, the
program eventually got cancelled because
the ground rules violated the laws of physics
--something that was obvious to some of us
in Phase I, but became painfully evident to all
with the detailed design efforts in Phase II.
Could you be more specific as to which law of physics it violated?

Or, should I have asked which ground rule (requirements)?
Alex Terrell
2007-03-04 14:27:26 UTC
Permalink
Post by Henry Spencer
Post by Quadibloc
So why not get rid of the first stage, fly a plane as high and fast as
we can, and then have the rocket start its journey from the moving
plane? That way, we build a much smaller rocket for the same payload,
and the big expensive first stage is replaced by an airplane trip.
The idea is not ridiculous, but whether you can get big cost reductions
that way is unproven, at best. A rocket first stage is not particularly
costly, especially if you can recover and reuse it; it is the upper stage
that's expensive to build and maintain. And big airplanes are expensive,
and *custom-built* big airplanes are very expensive.
T-Space have argued otherwise. I suspect they would argue that custom
built big planes were very expensive, when prototypes were needed and
then aluminium moldings. However, carbon fibre can be formed quite
cheaply in one-offs, and the simulations can be done on computer. All
this could be true as long as the plane doesn't need good performance
or good economy.

And with the T-Space approach, the launch speed is trivial. The
benefit comes from a higher launch altitude and more escape options if
something goes wrong.
Henry Spencer
2007-03-04 18:35:25 UTC
Permalink
Post by Alex Terrell
Post by Henry Spencer
The idea is not ridiculous, but whether you can get big cost reductions
that way is unproven, at best. A rocket first stage is not particularly
costly, especially if you can recover and reuse it; it is the upper stage
that's expensive to build and maintain. And big airplanes are expensive,
and *custom-built* big airplanes are very expensive.
T-Space have argued otherwise.
T/Space, so far, is using existing aircraft... and existing aircraft paid
for by other people, at that. Unless things have changed recently, the
farthest they've suggested going toward a custom aircraft is putting
longer landing gear on a 747. (And note that even a stock 747 is a $200M
aircraft, unless you can get a good deal on an old used one.)
Post by Alex Terrell
I suspect they would argue that custom
built big planes were very expensive, when prototypes were needed and
then aluminium moldings. However, carbon fibre can be formed quite
cheaply in one-offs, and the simulations can be done on computer.
Yes, if all you want is an *experimental* aircraft, it might not be all
that costly any more. Something that can be certified -- so it can carry
cargo for paying customers -- is a very different kettle of fish. Getting
a new aircraft certified costs 10-100x the cost of the prototype. (And a
big all-new design by a new company is going to be at the high end.)

It's easy to grossly underestimate just how difficult and expensive it is
to build, test, and certify a new aircraft. Even Burt Rutan has been
tripped up by this.

By the way, simulations are not the same thing as flight tests. To
quote Brig. Gen. Duane W. Deal, USAF, one of the members of the Columbia
accident-investigation board:

"To ensure it employs technology over technique, an organization must,
if possible, certify all critical hardware through testing -- not just
analysis. However, if analysis must be used, it should be verified by
testing. For example, even today's computerized aircraft-design process
does not eliminate the necessity for flight-testing..."
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | ***@spsystems.net
Rand Simberg
2007-03-04 20:54:10 UTC
Permalink
On Sun, 4 Mar 2007 18:35:25 GMT, in a place far, far away,
Post by Henry Spencer
Post by Alex Terrell
Post by Henry Spencer
The idea is not ridiculous, but whether you can get big cost reductions
that way is unproven, at best. A rocket first stage is not particularly
costly, especially if you can recover and reuse it; it is the upper stage
that's expensive to build and maintain. And big airplanes are expensive,
and *custom-built* big airplanes are very expensive.
T-Space have argued otherwise.
T/Space, so far, is using existing aircraft... and existing aircraft paid
for by other people, at that.
As long as they continue to get support from the Air Force. If the
blue suiters pull out, but DARPA wants to continue the program, it
would be interesting to see what they do. Go to Canada, perhaps? :-)
Post by Henry Spencer
Unless things have changed recently, the
farthest they've suggested going toward a custom aircraft is putting
longer landing gear on a 747. (And note that even a stock 747 is a $200M
aircraft, unless you can get a good deal on an old used one.)
You actually can get a good deal on a used one, but they don't have
tail doors, do they? All of the 747Fs that I'm aware of are side
loaders.
Post by Henry Spencer
Post by Alex Terrell
I suspect they would argue that custom
built big planes were very expensive, when prototypes were needed and
then aluminium moldings. However, carbon fibre can be formed quite
cheaply in one-offs, and the simulations can be done on computer.
Yes, if all you want is an *experimental* aircraft, it might not be all
that costly any more. Something that can be certified -- so it can carry
cargo for paying customers -- is a very different kettle of fish. Getting
a new aircraft certified costs 10-100x the cost of the prototype. (And a
big all-new design by a new company is going to be at the high end.)
That's an interesting legal question. It seems to me that if that's
its only purpose, you simply declare it a flyback first stage, and get
a launch license for it with the rest of the vehicle. No
certification required. ;-)

In fact, I wonder if OSC got a special type certification for
Stargazer, when they modded the Tri-Star to carry Pegasus? If not,
they're flying "uncertified" as well. With paying customers.
Henry Spencer
2007-03-05 03:15:16 UTC
Permalink
Post by Henry Spencer
farthest they've suggested going toward a custom aircraft is putting
longer landing gear on a 747...
...they don't have tail doors, do they? All of the 747Fs that I'm
aware of are side loaders.
There's no tail-door version of the 747 that I know of... but the reason
for the extended landing gear was external carry of the rocket, under
either wing or belly. (That was their NASA-COTS bid, now somewhat
academic because they didn't win.)

To get a tail door, or even a high wing, in a big freighter you pretty
much have to go military. And unless you stretch the landing gear, an
airliner's low wing severely limits rocket diameter, because even the big
freighters have limited ground clearance. (If memory serves, if OSC's
TriStar makes a worst-case bottom-the-shocks hard landing with a Pegasus
XL underneath, there's only an inch or so of clearance between the Pegasus
and the runway. And Pegasus isn't very big.)
Post by Henry Spencer
Yes, if all you want is an *experimental* aircraft, it might not be all
that costly any more. Something that can be certified -- so it can carry
cargo for paying customers -- is a very different kettle of fish...
That's an interesting legal question. It seems to me that if that's
its only purpose, you simply declare it a flyback first stage, and get
a launch license for it with the rest of the vehicle. No
certification required. ;-)
Alas :-), I suspect that won't work unless there is, at minimum, a major
rocket phase in the first stage's flight. The exact boundary between AST
and the aviation people remains to be defined for such things -- the
"suborbital rocket" definition doesn't literally apply to an orbital
vehicle -- but the suborbital-rocket precedent is a reasonable one and
it's likely that they'd extend it somehow rather than going back to the
drawing board entirely. So if you don't have a rocket-powered phase with
thrust exceeding wing lift for more than 50% of the phase duration, it's
pretty definitely an aircraft and certification applies.
In fact, I wonder if OSC got a special type certification for
Stargazer, when they modded the Tri-Star to carry Pegasus?
I believe they did, yes. Not a huge problem, with an already-certified
aircraft modified by an experienced aircraft maintainer/rebuilder
(Marshall Aerospace in the UK).
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | ***@spsystems.net
john hare
2007-03-05 11:20:12 UTC
Permalink
Post by Henry Spencer
Post by Henry Spencer
farthest they've suggested going toward a custom aircraft is putting
longer landing gear on a 747...
...they don't have tail doors, do they? All of the 747Fs that I'm
aware of are side loaders.
Post by Henry Spencer
Yes, if all you want is an *experimental* aircraft, it might not be all
that costly any more. Something that can be certified -- so it can carry
cargo for paying customers -- is a very different kettle of fish...
That's an interesting legal question. It seems to me that if that's
its only purpose, you simply declare it a flyback first stage, and get
a launch license for it with the rest of the vehicle. No
certification required. ;-)
Alas :-), I suspect that won't work unless there is, at minimum, a major
rocket phase in the first stage's flight. The exact boundary between AST
and the aviation people remains to be defined for such things -- the
"suborbital rocket" definition doesn't literally apply to an orbital
vehicle -- but the suborbital-rocket precedent is a reasonable one and
it's likely that they'd extend it somehow rather than going back to the
drawing board entirely. So if you don't have a rocket-powered phase with
thrust exceeding wing lift for more than 50% of the phase duration, it's
pretty definitely an aircraft and certification applies.
How much trouble will Virgin have with the White Knight 2 carrier
for Space Ship 2? It almost certainly won't be a certified aircraft.
It also will not be likely to use rockets.
Post by Henry Spencer
In fact, I wonder if OSC got a special type certification for
Stargazer, when they modded the Tri-Star to carry Pegasus?
I believe they did, yes. Not a huge problem, with an already-certified
aircraft modified by an experienced aircraft maintainer/rebuilder
(Marshall Aerospace in the UK).
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |
Rand Simberg
2007-03-05 12:29:59 UTC
Permalink
On Mon, 5 Mar 2007 03:20:12 -0800, in a place far, far away, "john
Post by john hare
Post by Henry Spencer
Alas :-), I suspect that won't work unless there is, at minimum, a major
rocket phase in the first stage's flight. The exact boundary between AST
and the aviation people remains to be defined for such things -- the
"suborbital rocket" definition doesn't literally apply to an orbital
vehicle -- but the suborbital-rocket precedent is a reasonable one and
it's likely that they'd extend it somehow rather than going back to the
drawing board entirely. So if you don't have a rocket-powered phase with
thrust exceeding wing lift for more than 50% of the phase duration, it's
pretty definitely an aircraft and certification applies.
How much trouble will Virgin have with the White Knight 2 carrier
for Space Ship 2? It almost certainly won't be a certified aircraft.
It also will not be likely to use rockets.
Yup. This issue may rear its head quite soon. Of course, Rutan
claims to *want* to be certified...
Rand Simberg
2007-03-05 12:28:53 UTC
Permalink
On Mon, 5 Mar 2007 03:15:16 GMT, in a place far, far away,
Post by Henry Spencer
Post by Rand Simberg
Post by Henry Spencer
Yes, if all you want is an *experimental* aircraft, it might not be all
that costly any more. Something that can be certified -- so it can carry
cargo for paying customers -- is a very different kettle of fish...
That's an interesting legal question. It seems to me that if that's
its only purpose, you simply declare it a flyback first stage, and get
a launch license for it with the rest of the vehicle. No
certification required. ;-)
Alas :-), I suspect that won't work unless there is, at minimum, a major
rocket phase in the first stage's flight. The exact boundary between AST
and the aviation people remains to be defined for such things -- the
"suborbital rocket" definition doesn't literally apply to an orbital
vehicle -- but the suborbital-rocket precedent is a reasonable one and
it's likely that they'd extend it somehow rather than going back to the
drawing board entirely. So if you don't have a rocket-powered phase with
thrust exceeding wing lift for more than 50% of the phase duration, it's
pretty definitely an aircraft and certification applies.
Well, with a new design you might be able to do that (though it would
take pretty big engine). I think, though, at some point, the FAA
would have to see the absurdity of arbitrarily requiring a different
regulatory regime for the first and second stages of an all-new
vehicle, regardless of thrust level or whether or not it was an
airbreather. If not, perhaps some further amendments to the CSLA are
required (though that would open up the door to troublemaking from
Oberstar).
Len
2007-03-06 02:06:36 UTC
Permalink
Post by Henry Spencer
Post by Henry Spencer
farthest they've suggested going toward a custom aircraft is putting
longer landing gear on a 747...
...they don't have tail doors, do they? All of the 747Fs that I'm
aware of are side loaders.
There's no tail-door version of the 747 that I know of... but the reason
for the extended landing gear was external carry of the rocket, under
either wing or belly. (That was their NASA-COTS bid, now somewhat
academic because they didn't win.)
To get a tail door, or even a high wing, in a big freighter you pretty
much have to go military. And unless you stretch the landing gear, an
airliner's low wing severely limits rocket diameter, because even the big
freighters have limited ground clearance. (If memory serves, if OSC's
TriStar makes a worst-case bottom-the-shocks hard landing with a Pegasus
XL underneath, there's only an inch or so of clearance between the Pegasus
and the runway. And Pegasus isn't very big.)
This is why--for a while--I was so interested in
Tupolov aircraft, which tend to be rather "tall
dogs." The Bear has a lot of ground clearance
for the Kitchen and also to clear the large
propellers with the 15,000 HP Kuznetzov's
turboprops. But we've moved on quite a ways
from trying to use existing subsonic aircraft
--a potentially good idea, but not nearly as good,
IMO, as our current concept.
Post by Henry Spencer
Post by Henry Spencer
Yes, if all you want is an *experimental* aircraft, it might not be all
that costly any more. Something that can be certified -- so it can carry
cargo for paying customers -- is a very different kettle of fish...
That's an interesting legal question. It seems to me that if that's
its only purpose, you simply declare it a flyback first stage, and get
a launch license for it with the rest of the vehicle. No
certification required. ;-)
Alas :-), I suspect that won't work unless there is, at minimum, a major
rocket phase in the first stage's flight. The exact boundary between AST
and the aviation people remains to be defined for such things -- the
"suborbital rocket" definition doesn't literally apply to an orbital
vehicle -- but the suborbital-rocket precedent is a reasonable one and
it's likely that they'd extend it somehow rather than going back to the
drawing board entirely. So if you don't have a rocket-powered phase with
thrust exceeding wing lift for more than 50% of the phase duration, it's
pretty definitely an aircraft and certification applies.
I'm quite sure we will fit the "unless" category for
our mach 2 carrier for the Space Van 2011, Henry,
We do carry a couple of JT8Ds, but these are
rather incidental for takeoff and climb; they are
there mainly for operational safety and convenience
(they do seem to pay their own way on exit,
however). Main propulsion is LOx/kero for both
stages.
Post by Henry Spencer
In fact, I wonder if OSC got a special type certification for
Stargazer, when they modded the Tri-Star to carry Pegasus?
I believe they did, yes. Not a huge problem, with an already-certified
aircraft modified by an experienced aircraft maintainer/rebuilder
(Marshall Aerospace in the UK).
Perhaps this is what actually happened, although I
had heard indirectly, that Orbital was rather
sorry at one point they were dealing with a certified
aircraft.

Len
Post by Henry Spencer
--
spsystems.net is temporarily off the air; | Henry Spencer
Pat Flannery
2007-03-06 02:42:13 UTC
Permalink
Post by Len
This is why--for a while--I was so interested in
Tupolov aircraft, which tend to be rather "tall
dogs." The Bear has a lot of ground clearance
for the Kitchen and also to clear the large
propellers with the 15,000 HP Kuznetzov's
turboprops. But we've moved on quite a ways
from trying to use existing subsonic aircraft
--a potentially good idea, but not nearly as good,
IMO, as our current concept.
You want to see some odd Russian rocket carriers?:
Loading Image...
Loading Image...
Loading Image...
Loading Image...
Loading Image...
Loading Image...
Loading Image...
Loading Image...
Loading Image...
Those are all from here: http://tinyurl.com/3a4z6v

Pat
Len
2007-03-06 01:49:29 UTC
Permalink
Post by Rand Simberg
On Sun, 4 Mar 2007 18:35:25 GMT, in a place far, far away,
Post by Henry Spencer
Post by Alex Terrell
Post by Henry Spencer
The idea is not ridiculous, but whether you can get big cost reductions
that way is unproven, at best. A rocket first stage is not particularly
costly, especially if you can recover and reuse it; it is the upper stage
that's expensive to build and maintain. And big airplanes are expensive,
and *custom-built* big airplanes are very expensive.
T-Space have argued otherwise.
T/Space, so far, is using existing aircraft... and existing aircraft paid
for by other people, at that.
As long as they continue to get support from the Air Force. If the
blue suiters pull out, but DARPA wants to continue the program, it
would be interesting to see what they do. Go to Canada, perhaps? :-)
Post by Henry Spencer
Unless things have changed recently, the
farthest they've suggested going toward a custom aircraft is putting
longer landing gear on a 747. (And note that even a stock 747 is a $200M
aircraft, unless you can get a good deal on an old used one.)
You actually can get a good deal on a used one, but they don't have
tail doors, do they? All of the 747Fs that I'm aware of are side
loaders.
Post by Henry Spencer
Post by Alex Terrell
I suspect they would argue that custom
built big planes were very expensive, when prototypes were needed and
then aluminium moldings. However, carbon fibre can be formed quite
cheaply in one-offs, and the simulations can be done on computer.
Yes, if all you want is an *experimental* aircraft, it might not be all
that costly any more. Something that can be certified -- so it can carry
cargo for paying customers -- is a very different kettle of fish. Getting
a new aircraft certified costs 10-100x the cost of the prototype. (And a
big all-new design by a new company is going to be at the high end.)
That's an interesting legal question. It seems to me that if that's
its only purpose, you simply declare it a flyback first stage, and get
a launch license for it with the rest of the vehicle. No
certification required. ;-)
Yes, as involved as a launch license may be,
it is far removed from the cost of certification
--assuming of course, a reasonable concept
for the launch vehicle.

And for some launch vehicle concepts lifting first
stages with a relatively low thrust-to-weight at
takeoff such as our own, it may be possible to do
a lot of of initial testing under experimental
aircraft rules. Moreover, much of our carrier
stage is now carbon fiber, which, as Henry
(I think) points out can be relatively cheap in
one-off prototypes.
Post by Rand Simberg
In fact, I wonder if OSC got a special type certification for
Stargazer, when they modded the Tri-Star to carry Pegasus? If not,
they're flying "uncertified" as well. With paying customers.
As I understand it, Orbital was rather sorry they
picked a certified aircraft to modify. Messing
around with a certified aircraft can be costly.

Len
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