National Aerospace Plane (X-30) announced 20 years ago

Reducing newsgroup list to just sci.space.shuttle and sci.space.history.

"Alistair Gunn" wrote in message
. ..
In rec.aviation.military Joe D. twisted the electrons to say:
Each separate propulsion system would require its own fuel,
structure, systems and thermal insulation. Each adds weight,
complexity and development cost.

Wasn't HOTOL meant to use the same engine for both jet and rocket
propulsion? IIRC, to switch to rocket propulsion the idea was that
they'd start injecting oxidiser as well as fuel into the engine?

Yes, it envisioned a Liquid Air Cycle Engine (LACE). In theory that would
reduce the number of discrete propulsion systems to two, although
the LACE also introduces additional complexity, so not sure it's
a net gain: http://en.wikipedia.org/wiki/Liquid_air_cycle_engine


The thermal problem alone is daunting. Unlike conventional
launchers that quickly get above the atmosphere and spend most
of their ascent thrusting mostly horizontally in a vacuum, an orbital
airbreather must fly a depressed trajectory and stay within the
atmosphere
for most of the ascent.

Though it hardly meets the description of SSTO, maybe the way forwards
would be something like Pegasus or Spaceship One (or the X15 for that
matter) - where an airbreathing craft is used to lift the exo-atmospheric
craft up into the atmosphere?

Air launch is interesting, but for a man-carrying vehicle of meaningful
size, it requires a gigantic mother ship. SpaceShipOne is misleading,
as it only had about 1/65th the energy required for orbital flight.
An orbit-capable man carrying upgrade would be vastly different
from White Knight and SpaceShipOne.

E.g, the January 2006 issue of Air & Space magazine mentions t/Space
is considering having Rutan to build a sufficiently large White Knight-
type mothership to air launch a useful sized orbiter. The mothership
would weight one million pounds, have a payload of 150 tons,
and a wingspan of 320 feet. It would make the B-52 which launched
the X-15 look like a Piper Cub.

Even given the large investment for a sufficiently large mothership
air launcher, plus the investment of the orbiter itself, the actual
performance benefit of air launch may be less than you'd think.
Maybe insufficient to justify the expense and complexity.

Note this quote from an AIAA paper:

"Surprisingly, a typical straight and level subsonic horizontal air launch
such as used by the X-15 research rocketplane does not result in any
significant changes in the delta V requirement as compared to a baseline
vertical surface launch."

http://mae.ucdavis.edu/faculty/sarig...a2001-4619.pdf

-- Joe D.

In article ,
"Joe D." wrote:

Reducing newsgroup list to just sci.space.shuttle and sci.space.history.

"Alistair Gunn" wrote in message
. ..
In rec.aviation.military Joe D. twisted the electrons to say:
Each separate propulsion system would require its own fuel,
structure, systems and thermal insulation. Each adds weight,
complexity and development cost.

Wasn't HOTOL meant to use the same engine for both jet and rocket
propulsion? IIRC, to switch to rocket propulsion the idea was that
they'd start injecting oxidiser as well as fuel into the engine?

Yes, it envisioned a Liquid Air Cycle Engine (LACE). In theory that would
reduce the number of discrete propulsion systems to two, although
the LACE also introduces additional complexity, so not sure it's
a net gain: http://en.wikipedia.org/wiki/Liquid_air_cycle_engine

That concept goes back at least to 1962, when it was proposed for the
Aerospaceplane that I worked on. Nobody seemed to know, however, how we
could get all that air liquefied, how we could haul all of the
liquefication hardware around, or where we could put the payload (if
there were any).

--
Remve "_" from email to reply to me personally.

"Joe D." wrote:

Though it hardly meets the description of SSTO, maybe the way forwards
would be something like Pegasus or Spaceship One (or the X15 for that
matter) - where an airbreathing craft is used to lift the exo-atmospheric
craft up into the atmosphere?

Air launch is interesting, but for a man-carrying vehicle of meaningful
size, it requires a gigantic mother ship. SpaceShipOne is misleading,
as it only had about 1/65th the energy required for orbital flight.
An orbit-capable man carrying upgrade would be vastly different
from White Knight and SpaceShipOne.

Consider the C-5 needed to haul a Minuteman into the air.. Consider
the orbital payload of the Minuteman is probably on the order of a ton
or so...

Sober up and head back to the drawing board.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

In article ,
Joe D. wrote:
Wasn't HOTOL meant to use the same engine for both jet and rocket
propulsion? IIRC, to switch to rocket propulsion the idea was that
they'd start injecting oxidiser as well as fuel into the engine?

Yes, it envisioned a Liquid Air Cycle Engine (LACE).

HOTOL's engine wasn't exactly a LACE system, because it didn't liquefy the
air, just cooled it drastically and compressed it before injecting it into
the rocket chamber. (This was a significant innovation, reducing the
amount of extra LH2 that had to be carried for cooling the air.)

In theory that would
reduce the number of discrete propulsion systems to two...

To one, actually, for the HOTOL scheme. HOTOL's engine *wasn't* a
scramjet; it switched to pure rocket at around Mach 5. And since it used
a turbocompressor, it could run at zero airspeed. The key idea was a
different approach, as Alan Bond commented:

"Any hybrid engine must end up being a very efficient rocket for most
of the flight. I began with a good rocket engine and made it a bad
air-breather. Everybody previously had done the reverse."

He also had some unkind things to say about scamjets, er excuse me I
meant scramjets:

"Scramjets do not have an intrinsic performance benefit and even if they
did the cost of engineering the hardware required would be much greater
than the other options. The demise of the X-30 NASP may be a belated
realisation of this fact."

(Both quotes are from an article/interview in the May 1993 Spaceflight.)
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

In article ,
Joe D. wrote:
"Surprisingly, a typical straight and level subsonic horizontal air launch
such as used by the X-15 research rocketplane does not result in any
significant changes in the delta V requirement as compared to a baseline
vertical surface launch."

Note, though, that that's only half the story. True, the launch velocity
is insignificant, and reduced air drag doesn't matter much because drag is
not a major loss for sizable vehicles. What you do get from air launch is
reduced back pressure on the engine, which permits higher expansion ratios
for higher Isp.

There are also some useful secondary issues, like getting out from under a
lot of launch-site hassles (e.g., the problems SpaceX had at Vandenberg),
and being able to move the launch point to improve launch windows for
rendezvous missions.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

"Henry Spencer" wrote in message
...

HOTOL's engine wasn't exactly a LACE system, because it didn't liquefy the
air, just cooled it drastically and compressed it before injecting it into
the rocket chamber.

Henry thanks for the corrections and all the other info.

-- Joe D.

Gentlemen:

With today's technoogy there is no reason to create a multistage,
multiengined NASP. The SSME works fine at ALL altitudes. Using 'air'
as an oxidizer has disadvantages anyway. It is not exactly the right
mix of oxygen and includes other gases which dampen the reaction. With
slush tanks hydrogen can be compressed yielding greatly increased fuel
per volume. This was not available when NASP was first designed.

Ceramics are much better understood today, as well as their problems.
Ceramic can be 'fused' to metals using lasers. Back when NASP was
designed this was impossible. That is why 'cement' was used on the
Shuttle tiles.

Today, titanium can be easily worked, not so 20 years ago. Titanium
can take 2500 deg. F. to melt. Far, far better than aluminum. Also,
composite is established technology and has properties that allow for
greatly strengthening an airframe as well as insultating it.

NASA should be building a waverider SSTO replacement for the Shuttle.
Today, it is very feasible.


tomcat

the idea of air as a oxidiser is to save taking it with you from
launch.
akk that extra mass costs as it takes up valuable margin.

the 2 stage to orbit spaceplane is better, since all the fuel and
oxidiser, right to the edge of space are ground supplied.

Bob Haller wrote:
the idea of air as a oxidiser is to save taking it with you from
launch.
akk that extra mass costs as it takes up valuable margin.

the 2 stage to orbit spaceplane is better, since all the fuel and
oxidiser, right to the edge of space are ground supplied.


The air vs. liquid oxygen issue is a tradeoff. Yes, air breathing
equipment saves on the LOX, but it adds its own weight to the
spaceplane. And, yes, the "margin" you speak of is valuable where the
extra pounds really count.

But complexity is a 'real' factor too. Add a stage, add engines, add
separation of stages, and all for what? So that Murphys Law can run
wild? So that it takes longer to design and build? Not to mention
what to do with the jettisoned first stage. Should parachutes be used
and then have ships do a pick up, return the stage to a rehab facility?
Or just throw it away and let it burn up in the atmosphere.

Reaching the edge of space in a spaceplane using SSMEs will take about
3 1/2 minutes. That extra complexity for a couple of minutes of less
LOX use is a tradeoff I don't want to make. And, as I said earlier,
air isn't the best mix of oxygen. Hydrogen burns with a certain ideal
oxygen mix. So to optimize performance the inlet air has to be
enriched. So, there goes some of the advantage on top of the
additional complexity.

The main thing you accomplish with 2 stages is the jettison of the
'weight' of the first stage. But that leads to the problems of
recovery or waste of the first stage. In short you will end up with
the Shuttle's expenses when the vehicle is supposed to be cheaper.

Slush hydrogen tanks hold a lot more fuel. I wish I knew the exact
amounts, but I am guessing at least double the fuel per volume. The
SSME is 'old reliable' and can be used for 50 ignitions without
replacement.

I maintain that the next Orbiter/SSTO should be cleaner, simpler than
the Shuttle with greatly increased payload and altitude capability. No
external tank, no SRB's (though they may be necessary for a direct
Moon/planet mission), no jets, rams, or scrams.

I am dreaming of a nice shiny triangle with SSME's on the back capable
of hauling a quarter of a million poujnds into space and returning,
with a 3 day turn around. Each would cost 8 billion dollars to build
and have all the comforts of home for the 2 man crew, even on extended
voyages to the Moon or beyond where SRBs will probably have to be used.


tomcat

Again a TWO STAGE vehicle, stage one a big overgrown airliner using
regular air breathing engines to get the spaceplane to release
altitude, like 40,000 feet.

Stage 2 a small manned mini spaceplane, with its own rocket engine to
get the spaceplane to orbit.

please note thats the way private industry is going