GTX, the now-cancelled air-breathing SSTO...

[Lee]

Hi,
This is my first post, so I'm trying out the software...

I haven't seen anything in this forum concerning the proposed NASA H2/O2 powered GTX launch vehicle.
Here's the link from a U.S. Gov't web site:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050214850_2005217631.pdf

I think using H2 for a propellant makes for a much bigger vehicle. Several studies I have at home indicate hydrocarbon fuels have competitive density impulse values. What do you think?

I also have additional research papers that I would have to look up the titles to at home, but I can post those links later as long as the 'Web links aren't broken.

 

[robunos]

i had a look on NTRS and found these:-

Structural Sizing of a 25,000-lb Payload, Air-Breathing Launch Vehicle for Single-Stage-to-Orbit

http://ntrs.nasa.gov/search.jsp?R=252372&id=3&qs=No%3D30%26Ntt%3DGTX%26Ntk%3Dall%26Ntx%3Dmode%2520matchall%26N%3D0%26Ns%3DHarvestDate%257c1

SRM-Assisted Trajectory for the GTX Reference Vehicle

http://ntrs.nasa.gov/search.jsp?R=390726&id=10&qs=No%3D20%26Ntt%3DGTX%26Ntk%3Dall%26Ntx%3Dmode%2520matchall%26N%3D0%26Ns%3DHarvestDate%257c1

Affordable Flight Demonstration of the GTX Air-Breathing SSTO Vehicle Concept

http://ntrs.nasa.gov/search.jsp?R=868035&id=5&qs=No%3D20%26Ntt%3DGTX%26Ntk%3Dall%26Ntx%3Dmode%2520matchall%26N%3D0%26Ns%3DHarvestDate%257c1


cheers,
Robin.

 

[Lee]

Excellent, Robin...!

Those were some of the papers I was referring to.

I have a ream or more of stuff on the same subject at home.

However, I never did think highly of the scramjet engines. The test unit launched on the American Pegasus launcher was described or considered complex and difficult to ignite. (Like lighting a match in a F5 tornado.)

Marquardt invented an injector fan/ramjet system that would go Mach 8 on paper calculations burning hydrogen, at least.

Then there's the likes of cooling air intake streams to the fan/engine by cold hydrogen fuel, but a leak in the H2 heat exchanger could cause a fire.

I'm not at home and I'm on a borrowed computer, but I'll try to look for the Marquardt paper when I get home tonight and at least get the title, if not the link.

 

[Lee]

Partial answer to 'Web search...

rubunos and others,

The name of the Marquardt system is the Supercharged Ejector Ramjet(SERJ) . There is another reference to this subject in the Aviation of forum of secretprojects, but a 'Web search indicates the paper I thought of appears to be published now by the AIAA as a paper presented at a particular meeting somewhere.

That means they took out the link(s) to the Gov't sites, probably at the request of the AIAA. One needs a personal copy already printed beforehand or pay AIAA for a copy.

The Internet will be no help.

 

[robunos]

Orionblamblam has some stuff on the SERJ, as adapted for the X-15 here:-

http://www.up-ship.com/apr/extras/serjx15.htm

cheers,
Robin.

 

[Lee]

The drawing of the SERJ in Orionblamblam's or the posting above is also of the SERJ in the paper I have at home.
However, whatever software Marquardt used to calculate performance of the SERJ accounted for a WAY larger unit than can fit on an X-15. Takeoff thrust at sea level for most computer simulations was 750,000-1,000,000 lbs. or more. Fan intake diameter was usually 10-12 ft., depending on the fuel being burned. The total length of engine and intake nacelle was about 115 ft.

Unfortunately(!), the paper was reprinted in in AIAA archives and they require being paid for reprints. It was available for free from a NASA archive, but not any more.

 

[hesham]

Also from NASA;
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20010059598_2001093651.pdf

 

[Proponent]

I think using H2 for a propellant makes for a much bigger vehicle. Several studies I have at home indicate hydrocarbon fuels have competitive density impulse values. What do you think?

Absolutely. The volume-specific impulses of hydrocarbons are better. Hydrogen's high specific impulse is a great advantage in some applications, but it doesn't always outweigh the disadvantages of its low density. Also, when it comes to high-speed scramjets I gather it's easier to build an engine that runs on hydrogen than one that runs on hydrocarbons.

I suspect that part of the reason that hydrogen became to be regarded as the best fuel was that people focused on gross lift-off weight (GLOW) as a design metric, and all-hydrogen vehicles generally do have lower GLOWs. GLOW, however, is not the same thing as cost.

Methane seems to be everybody's favorite hydrocarbon these days. Personally I like sub-cooled propane, because it is significantly denser and has a specific impulse within a few seconds of methane's.

 

[Archibald]

Another alternative is Mitchell Burnside-Clapp H2O2... very dense fuel (which make the british Black Arrow the smaller launcher ever)

 

[Proponent]

Another alternative is Mitchell Burnside-Clapp H2O2... very dense fuel (which make the british Black Arrow the smaller launcher ever)

H2O2 is an oxidizer rather than a fuel (although it can also be used as a monopropellant because it can readily be induced to decompose into H2O and O2). Its high density, low toxicity, high boiling point and hypergolicity make it attractive for rocket engines, but it does not apply to scramjets.

EDIT: "It's" -> "Its"