Chair Force Engineer

Tuesday, April 11, 2006


Today marks the unofficial 5th anniversary of the death of X-33. At one time, the space plane (shaped like a potato wedge) was NASA's best hope for the post-shuttle era. Like much of the world that existed in the years prior to the 9/11 attacks, the dream of a single-stage spacecraft seems like a blissful illusion when viewed in the present.

The X-33 program began with unrealistic expectations. While the X-33 was only supposed to fly suborbitally, NASA wanted the vehicle's prime contractor to eventually build a commercially-viable, single-stage-to-orbit (SSTO) launcher. The problem was that there was no traceability between a Mach 15 demonstrator and a Mach 25+ orbital system. Further, it's doubtful that the materials and propulsion technologies of the day would have supported SSTO. Even if they did, a fully-reusable two-stage system would have been able to launch more payload for a given liftoff mass.

NASA chose the Lockheed Martin X-33 from three proposals with varying levels of merit. The Rockwell proposal was the lowest-risk of the three: established propulsion system (Space Shuttle Main Engine) and established reentry technique (wings.) McDonnell Douglas & Boeing teamed for what was essentially a bigger version of the DC-X. While DC-X achieved some non-trivial miracles, the larger X-33 concept would have required a lot of miracles to work precisely and correctly.

Lockheed Martin's "Winged Potato" may have been the riskiest of all. It paired a new, metallic thermal protection system with new structual concepts (multi-lobe, composite fuel tanks,) new engines (linear aerospikes,) and lifting-body reentry (with the "winged potato" shape having inferior aerodynamic characteristics to previous designs like the HL-20 and Starclipper.)

NASA was willing to take the risks inherent in the winged potato for one reason: LockMart was willing to put its money where its mouth was, to a degree that Rockwell, McDonnell Douglas, or Boeing weren't. LockMart had even touted its orbital "VentureStar" as a replacement for the shuttle and Titan IV, ready for flight between 2004 and 2006.

I disagree with the assessment of former NASA director Ivan Bekey that X-33 would have been a waste without composite fuel tanks. If anything, the X-33 manufacturing process taught us that the benefits of composites are often outweighed by their drawbacks. If we consigned ourselves to the fact that SSTO wasn't viable, and looked at X-33 as a technology demonstrator for a realistic TSTO, I think there would have been plenty of value in completing and flying the vehicle. X-33's thermal protection system and health-monitoring systems would have been essential technology for any future TSTO spaceships.

In the aftermath of failed programs like X-33 and Orbital Space Plane, the US government has all but abandoned the dream of reusable spaceships. This is a shame, because the technology to do so is already in hand, awaiting a government agency with the funds, time, and will to get the job done. There are two critical demonstrations needed to pave the way for truly reusable space access. The first is a flyback booster that can achieve altitudes greater than 100,000 feet and speeds of Mach 6 or greater during the boost phase, then glide back to base (a feat far more difficult than many are willing to acknowledge.) The other demonstrator would be a small spaceplane (like X-20 or HL-20) launched on an expendible rocket. It would demonstrate a robust heat shield design, integrated vehicle health management, and reliable, reusable propulsion for orbital insertion / maneuvering / deorbit.

Space cadets of the world should not give up on the dreams of reusable rocketships simply because there is no more government support for the idea. While programs like X-33 have left us "Venture-Scarred," reusable rockets will be brought into the realm of the feasible if they are rooted in sound, conservative technical judgement and incremental development. Reusable rockets will initally be very expensive, but the cost of a sustainable means of space access is well worth it.

[EDIT 11 Apr 06, 1930] Rand just disemboweled part of my polemic. Fair enough. There's no doubt that NASA was blinded by "gee whiz" technology during the mid-90's, and the "winged potato" did an excellent job in embodying practically every risky new technology available at the time.

It's also apparent that there existed no market for the VentureStar; while the market for EELV and for small-sat launchers collapsed unexpectedly, NASA and the NRO were the only forseeable customers for VentureStar. Even if the rocket was capable of high flight rates (say, 20 missions per year,) there's no way that flight rate could be justified by sufficient payloads.

While LockMart certainly wasn't willing to bail the X-33 out with its own money, they certainly spent a sizable amount of their personal fortune on the winged potato. I should probably do some research into how much LockMart was willing to bankroll, versus what McDD+Boeing or Rockwell was willing to put up. But I tend to believe that at least the Rockwell people would be wise enough to see that X-33 would never lead to SSTO, and wouldn't put more than a token amount of company funding into it. Even McDonnell Douglas wasn't willing to continue the DC-X series as a private development after the military lost interest, or when the flight article crashed and burned.