Art Stephenson, head of Marshall Space Flight Center, is retiring.

I certainly won't miss him. He was a prominent one of the many "authoritative" voices at NASA who make false claims about the technology state, that make it harder to raise money for commercial launch vehicles.

Art Stephenson, director of NASA's Marshall Space Flight Center, said that both the X-33 and X-34 may have failed because they were too ambitious. The X-33 in particular was originally meant to be a subscale model of VentureStar, a single- stage to orbit reusable launch vehicle proposed by Lockheed Martin. Although the designs of the X-33 and VentureStar diverged to a degree over time, the company planned to use some of the technologies tested by the X-33 into VentureStar.

"We have gained a tremendous amount of knowledge from these X-programs, but one of the things we have learned is that our technology has not yet advanced to the point that we can successfully develop a new reusable launch vehicle that substantially improves safety, reliability and affordability," he said.

This is utter Bravo Sierra.

The failure of the two programs is indicative of nothing other than NASA capability to mismanage, and no grand or general conclusions about technology readiness for reusable space vehicles could be reasonably drawn from them. If that's what he learned from those program failures, he needs to go back to school, and learn a little epistemology. Now that he's retired, maybe he'll have time, and will stop doing so much damage to our future in space.

When trying to see what went wrong with the VentureStar, it may be beneficial to look back at the competing design proposals to see if any of those might have faired any better. Much as with the USAF YF-22 / YF-23 fly-off - the better plane often looses. From what I can recall, there was only one other rocket proposal to choose from - a McDonnell Douglas single-stage-to-orbit rocket that took off from a runway (I may be wrong). Would this alternative faired any better than the more venturesome VentureStar?

There were two competitors--the McDonnell Douglas VTVL concept (a follow-on from DC-X) and a Rockwell concept that looked like a self-contained Shuttle, which was VTHL.

The Rockwell concept was probably the most conservative, but the real mistake was downselecting to a single concept so early.

I heard once that one of NASA's main jobs is to be sort of an R & D for America's aerospace industries. If that's true why aren't they passing on all the lessons from the failed programs? Perhaps someone else can get the aerospike engine to work without cracking the fuel tanks and sapping the taxpayers.

They haven't done that since the NACA days. NASA primarily does R&D for itself. It's not at all obvious that aerospike, or any of the technologies that went into X-33 were necessary for low-cost launch.

During the mid 1980’s the DoD forced GE to hand over the design of its amazing F404 engine to P&W: stating that it was in the nation’s interest to have two manufacturers of such a critical engine. Sharing there F404 engine design (an absolute marvel compared to the benchmark set by the J79 that powered the F4 Phantom) with a rival was not what GE wanted to do, but was forced to do because the DoD basically said – they paid for the engine and it is there right to give the designs to whomever it chooses. So there is precedence for what you suggest – having whomever developed the aerospike engine share their data with another company. I do know about the composite tank having problems but did not know the aerospike engine had troubles too.

Actually I don't know if the aerospike had problems or if it failed purely because the fuel tank problems. If there isn't an actual issue with the aerospike its a crime not to spread the info around, I think a few of the small developers are avoiding liquid hydrogen because its too difficult to handle anyway so they wouldn't have the same fuel tank problems.

I don't see NASA sharing anything though.

My understanding is that the linear aerospike functioned plenty well, and was in continued use for some time after the cancellation of X-33 as a hot-fire testbed for electromechanical actuators (another technology being developed on/for X-33).

I'm told the problem wasn't that the linear aerospike was a overt failure (though there were sticky problems with the manufacture of the ramps, as I recall), but that it couldn't have worked as advertised. The performance penalties associated with numerous small thrust chambers meant that it was handicapped from the start (thrust chambers do not scale down in a linear fashion, due to the limitations of real-world materials, so the thrust-to-weight ratio of an individual thruster is lower than that of a conventional bell-nozzle engine). The idea was to make up for the inherent engine performance hit through the overall propulsion system weight savings due to elimination of engine gimbaling (and the associated claptrap, like flex lines, actuators, point-loaded thrust structure, etc.) which the aerospike enabled.

As for using the linear aerospike engines on another vehicle...well, maybe, if you can make the structure-performance tradeoff work, and you don't mind making your vehicle somewhat oblong in cross-section. Alternatively, one could apply the lessons from the production of flightworthy linear aerospikes to annular aerospikes, which could be flown on the usual cylindrical launch vehicles. But again, can such a launcher be designed to be worth the tradeoff involved?

Btw, ISAS has got composite LOX and LH2 tanks on their RVT vehicle, and by reports they seem to be working. They arent odd-shaped like on X-33 though.
Another series of flight tests are planned to start in June after recent successful static test firings of the improved engine.
http://www.isas.ac.jp/e/new/release/2003f/04_03.html

Rand,
Much like the helicopter still uses the somewhat inefficient tail rotor many years after its predicted demise, I think most future launch vehicles will have some type of stages. Single-stage-to-orbit SSTO may have been the real hang-up here. It seems that although there were only a handful of proposals for this new shuttle, they pretty much covered the gambit of SSTO designs. Back in the 70’s there were page after page of concepts for the proposed shuttle because stages offer a great deal more flexibility. SSTO may work with a sled launch, but that in itself is like an initial stage. Just don’t think you can get past stages and be able to deliver a big payload.

Rockwell RLV/X-33 SSTO proposal did look really nice! Quite a bit larger than the VentureStar it appears!

VentureStar used one other new approach that I never heard too much about. It did not have to use tiles like the shuttle because its size would somehow disperse the heat. Does anyone know if this aspect was workable as advertised?

Not exactly. There were plenty of "tiles" on X-33 (and there would have been many many more on VentureStar), but they were a metallic honeycomb rather than ceramic. Really, they were more like large panels (~18" square) than tiles, as they were mounted on standoffs rather than bonded to a substrate. The upper surface was a composite shell covered with felt (Nomex?), much like the Orbiter payload bay doors.

I've recently seen the honeycomb pannels, but did not know that they would have used them on VentureStar. They sound like a real breakthrough!

I know a lot of very high temperature materials were recently developed for the "Integrated High Performance Turbine Engine Technology (IHPTET) program." Turbine engine temperatures are the key to efficiency and 3-4,000 degree temperatures seemed to be their goal - well over the 2,000 degree temperatures of today. F-22 and F-35 engines are made of this and so is the Eurofighter Typhone's. They can actually grow a single crystal into a fan blade by rapidly freezing one end as it comes out of the mold!!!

Rand's point is an excellent one, and it bears repeating: X-33 and X-34 were not failures of technology; they were failures of management.

NASA feels for instutitional reasons it cannot admit this, and so claims the "technology wasn't there" instead. Of course, the price we all pay is that now we as taxpayers get to buy into another scheme whose only virtue is that it doesn't look like the last scheme....

NASA likes to claim that X-33 proves that SSTO is impractical. But, remember, X-33 was not SSTO...it was built to do Single-Stage to Utah. Does NASA seriously contend that a reusable Mach 12 rocket is not physically possible? Not according to the last SLI viewgraphs I saw. Obfuscation and cover, only.

The claim becomes downright hilarious with respect to X-34. The technology isn't there? Really? To go Mach 8, air-launched, just like the X-15 only a Mach number faster? We can't do that? Puh-leeze.

The real story is that in both cases, NASA picked the most difficult-to-build vehicle because it would buy the most technology development, then failed to manage it properly. Cost ballooned, schedules slipped, and eventually the program was cancelled.

When OSP breaks down the same way -- and it will -- we will then be told that the X-20 (or an Apollo capsule!) are just too darn difficult to build with today's technology. They'll be wrong then, as they're wrong now.