Scrapping Scram

I was reading that NASA will be scrapping its Scramjet research
program after the next X43 test:

http://www.e4engineering.com/story.a...d-a7bd9b6a4258

Is scram considered to be the weakest of the available technologies to
get into orbit?

I'd thought that this particular technology was supposed to be the
most promising for usage by the commercial mainstream for rapid
intercontinental transit, as well as high-speed intercontinental
bombers and cruise missiles.

Maybe NASA should sell its technology to Richard Branson, if nobody
else will pursue it. It seems a shame to waste it. Or will the
military take up the mantle?

On 28 Oct 2004 16:12:50 -0700, in a place far, far away,
(sanman) made the phosphor on my monitor glow in
such a way as to indicate that:

I was reading that NASA will be scrapping its Scramjet research
program after the next X43 test:

http://www.e4engineering.com/story.a...d-a7bd9b6a4258

Is scram considered to be the weakest of the available technologies to
get into orbit?

Depends on who you ask. I'm sure that I could come up with weaker
ones (e.g., anti-gravity, etc.) but I don't think it holds much
promise for launch vehicles. That's not to say that it's not useful,
just that it's not particularly relevant to getting into space.

h (Rand Simberg) wrote in message . ..

Depends on who you ask. I'm sure that I could come up with weaker
ones (e.g., anti-gravity, etc.) but I don't think it holds much
promise for launch vehicles. That's not to say that it's not useful,
just that it's not particularly relevant to getting into space.

Well, I'd heard that adding on some rocket boosters would allow you to
leap from the uppermost atmosphere into orbit.
And doesn't the intercontinental rapid transit aspect mean a greater
commercial viability? In today's global marketplace, I would think
that this would fill a growing need (ie. live in Bora Bora, commute to
work in New York, visit the relatives in Tokyo)
At least you'd have a basic transportation market to leap off of.

Is the atmosphere more of a hindrance or help in getting into space?
Some people want to use the buoyancy, some people want the free
oxidizer on the way up,

I presume there's a consensus that atmosphere is at least a help in
coming back down, for braking purposes. Or would it nicer to avoid the
heatshield weight, and just fire braking rockets at the end?

sanman wrote:
h (Rand Simberg) wrote in message . ..
snip
Is the atmosphere more of a hindrance or help in getting into space?
Some people want to use the buoyancy, some people want the free
oxidizer on the way up,

In most cases, it's almost an irrelevance.
Its general effects are to mean that you need slightly beefier structures,
to handle aerodynamic loads, and a little bit of thermal protection.
And a fair amount more delta-vee.

The people that want to use bouyancy tend to attract strange looks in
gatherings of people in the industry, as their numbers simply don't work,
by several orders of magnitude.

Yes, there is oxygen in the atmosphere, but to use it means you've got
to stay in the atmosphere.
This means extreme heating and drag.
And even if you can get to Mach 10 this way, you've still got to put on
about 85% of the remaining energy in order to get into orbit.
And you've got to carry the heavy thermal protection systems and scramjet
dead-weight into orbit.




I presume there's a consensus that atmosphere is at least a help in
coming back down, for braking purposes. Or would it nicer to avoid the
heatshield weight, and just fire braking rockets at the end?

Braking rockets are barking mad, unless you are using something with
better than conventional ISP (say 10000 rather than the 500 or so
of conventional systems)

Heatshields can be very very light.

For example, there were proposals (that nobodies really come up with reasons
they wouldn't work, and are only just being tested in some forms) in the
60s/70s for taking a suited astronaught, and getting them safely to the
surface of the earth using significantly less than their own weight in
reentry capsules.

Doing the same with rockets would take many tons.

"Ian Stirling" wrote in message
...
Yes, there is oxygen in the atmosphere, but to use it means you've got
to stay in the atmosphere.
This means extreme heating and drag.
And even if you can get to Mach 10 this way, you've still got to put on
about 85% of the remaining energy in order to get into orbit.
And you've got to carry the heavy thermal protection systems and scramjet
dead-weight into orbit.

Air-breathing lower stage (White Knight, AN-225 [Russian 'mini-shuttle' from
a couple of years ago - already at prototype construction stage with engine
tested]) and a rocket upper stage (SS1+ and other vehicles).

The reason these vehicles work (would work, in the case of the Russian
system) is due to their very combination of different concepts.

--
Alan Erskine
We can get people to the Moon in five years,
not the fifteen GWB proposes.
Give NASA a real challenge

October 29, 2004

sanman wrote:


Well, I'd heard that adding on some rocket boosters would allow you to
leap from the uppermost atmosphere into orbit.


Then why bother with the scramjet?

It's never wise to burn the air you breathe.

Thomas Lee Elifritz
http://elifritz.members.atlantic.net

"sanman" wrote in message
om...

Is the atmosphere more of a hindrance or help in getting into space?
Some people want to use the buoyancy, some people want the free
oxidizer on the way up,

The atmosphere is a hinderance on the way up. Oxygen used in air breathing
engines is not free. The hardware needed to capture and use that oxygen is
heavy. Try comparing the weight of the merely subsonic GE-90 engine to a
similar thrust rocket engine (i.e. the thrust to weight ratio).

Also remember that LOX is one of the cheapest fluids on the planet since
it's literally made from air. Anyone who thinks that the cost of LOX is a
big issue for launch vehicles is seriously deluding themselves. Have you
priced LOX lately?

In a 1996 posting, Henry said it costs $0.01 per pound if you use so much of
it you build your own LOX plant. Let's say it costs $0.02 per pound today.
It has a density of about 70 lb/cubic foot and the shuttle ET holds nearly
20,000 cubic feet of it. That means that the LOX used for a shuttle launch
costs maybe $28,000 dollars. Clearly the cost of LOX isn't what drives
shuttle launch costs so high. Please note that a shuttle launch costs
hundreds of millions to over a billion dollars, depending on your
assumptions when you calculate the cost.

I presume there's a consensus that atmosphere is at least a help in
coming back down, for braking purposes. Or would it nicer to avoid the
heatshield weight, and just fire braking rockets at the end?

Your "braking rocket" would need to be almost as big as your launch vehicle,
because of the incredible velocity you need to shed. A "normal" reentry
which uses a heat shield to shed velocity is definitely the way to go (when
compared to chemical rocket engines).

Jeff
--
Remove icky phrase from email address to get a valid address.

So there is a general consensus on how to get upto orbit -- use
rockets.

But then what is considered the best way to get back down?

Parachutes? Wings? Ballute?

The SpaceshipOne uncontrolled rolling on ascent was partly caused by
the wings or canards which gave it susceptibility to wind shear in the
upper atmosphere.
Wings are also typically heavier than other solutions.

The ballistic plummeting of a space capsule or even the feathered
Spaceship one gives desired stability on descent through the upper
atmosphere, but it's the final approach through the lower atmosphere
that's at issue.

At least SpaceshipOne's wings can be deployed reliably, but a
parachute poses the danger of tangling, as well as reduced control on
final approach. A ballute seems to pose slightly less danger of
tangling, but still reduced control on final approach. Both are still
lighter than wings.

Hmm, spaceship design still seems like more of an art than a science.
Otherwise, you should just rigidly plug all the design elements into
an optimization matrix, and it will spit out the best combination of
design elements or systems to use.

Gee, I guess 2-stage does make sense, then. You have a first stage
that gets you to the edge of the atmosphere, and then a real rocket
that travels to orbit. What is the consensus on what's the best
2-stage combination? Does Da Vinci's balloon count as a flyback
booster, or is the balloon disposable? How much does a balloon like
that cost, anyway?

October 30, 2004

sanman wrote:

So there is a general consensus on how to get upto orbit -- use
rockets.

Very large cryogenic rockets, with very large aluminum tanks that can be
converted to habitats.

But then what is considered the best way to get back down?

Very carefully.

Thomas Lee Elifritz
http://elifritz.members.atlantic.net

"sanman" wrote in message
om...
So there is a general consensus on how to get upto orbit -- use
rockets.

But then what is considered the best way to get back down?

Parachutes? Wings? Ballute?

There is a third alternative: Rocket Braking.

The SpaceshipOne uncontrolled rolling on ascent was partly caused by
the wings or canards which gave it susceptibility to wind shear in the
upper atmosphere.
Wings are also typically heavier than other solutions.

The ballistic plummeting of a space capsule or even the feathered
Spaceship one gives desired stability on descent through the upper
atmosphere, but it's the final approach through the lower atmosphere
that's at issue.

At least SpaceshipOne's wings can be deployed reliably, but a
parachute poses the danger of tangling, as well as reduced control on
final approach. A ballute seems to pose slightly less danger of
tangling, but still reduced control on final approach. Both are still
lighter than wings.

Hmm, spaceship design still seems like more of an art than a science.
Otherwise, you should just rigidly plug all the design elements into
an optimization matrix, and it will spit out the best combination of
design elements or systems to use.

Gee, I guess 2-stage does make sense, then. You have a first stage
that gets you to the edge of the atmosphere, and then a real rocket
that travels to orbit. What is the consensus on what's the best
2-stage combination? Does Da Vinci's balloon count as a flyback
booster, or is the balloon disposable? How much does a balloon like
that cost, anyway?

There doesn't seem to be a consensus. My preference is for 2-stage VTOL.
The weight of propellants required to land a rocket stage vertically would
almost certainly be less than the weight of wings, wheels, brakes, control
surfaces, etc. - plus the weight of the associated TPS - required to land it
horizontally. An essentially axially-symetric design would also be much
cheaper to design and manufacture than a complex lifting design.