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Review: Promise Denied


Promise Denied: NASA’s X-34 and the Quest for Cheap, Reusable Access to Space
by Bruce I. Larrimer
NASA, 2020
ebook, 410 pp., illus.
ISBN 9781626830516

If, in 1995, you told people in the space industry that in a quarter-century there would be partially reusable launch vehicles in operation commercially, the news might have been a little bit of a disappointment. The mid-1990s were the heyday for reusable launch vehicle concepts, particularly single stage to orbit (SSTO). The DC-X Delta Clipper, developed by the Pentagon and later transferred to NASA and renamed the DC-XA Clipper Graham, was making test flights in New Mexico, demonstrating vertical takeoff and landing. NASA had ambitions for an even more capable RLV demonstrator, the X-33, that Lockheed Martin won the contract to develop with plans to turn it into a commercial SSTO vehicle, VentureStar. Certainly by 2020 RLVs would be commonplace, flying daily!

But the DC-XA crashed and burned—literally—when a landing gear failed to deploy at the end of a test flight in 1996. The X-33 suffered a more figurative crash and burn after a series of technical problems led NASA to terminate the program before the vehicle could make a first flight. Coupled with the problems private RLV ventures faced, both technical and financial, that RLV era came to end about two decades ago.

Often overlooked is another NASA program to develop RLV technologies, the X-34. It has its share of technical issues, but made more progress than the X-33, including a series of captive-carry flights and runway tow tests. NASA nonetheless also canceled the program before its first free flight. In Promise Denied, a NASA history book written by Bruce Larrimer, the X-34 gets some long overdue attention.

While many people recall the X-34 as a project where Orbital Sciences Corporation developed a suborbital winged reusable vehicle that could be air-launched, there were, Larrimer reminds us, two X-34 programs. The first was a joint venture between Orbital and Rockwell for an air-launched reusable vehicle that could, with the assistance of expendable upper stages, launch small satellites. (Orbital had been working on such a concept as an internal effort, called Project MALIBOO, or Manned Air-Launched Intermediate BOOster, since the early 1990s. That effort included Burt Rutan, who suggested that the carrier aircraft could have dual fuselages to allow the rocket to be carried between them, an approach Orbital didn’t pursue but which Rutan, of course, did.)

That joint venture, called American Space Lines, won in early 1995 a NASA cooperative agreement, with fixed-price, milestone-based payments. It anticipated developing two vehicles: a smaller X-34A that could be launched from Orbital’s existing L-1011 aircraft used for Pegasus, and a larger X-34B that would be carried on top of a Boeing 747, like the Shuttle Carrier Aircraft. By late that year, though, the effort was already in jeopardy, with disagreements on what engine to use on the X-34B. Rockwell wanted to use the Rocketdyne RS-27, while NASA favored the Russian RD-120 engine, which Pratt & Whitney was offering at a steep discount. Orbital had doubts about the market for the X-34B. By early 1996, the joint venture had collapsed and the original X-34 was dead.

NASA, though, revived the X-34 months later, but in a different form. The new X-34 would be a hypersonic technology demonstrator, capable of flying to Mach 8. Orbital won the competition for this “technology testbed demonstrator” in August 1996 and started work on a design that could launch from its L-1011. (Larrimer credits Orbital’s success in winning the new X-34 contract to the head of its advanced systems group, Mike Griffin.) It would be powered by Fastrac (aka MC-1, or Marshall Center 1), an engine under development at the Marshall Space Flight Center.

X-34 did have technical issues in its development, including second thoughts about the engine choice, but the program appeared to be making better progress than the larger, and more troubled, X-33. But NASA started to have doubts about the program in the fall of 1998, when it considered not requesting funding for it in its fiscal year 2000 budget proposal then under development. NASA restructured the X-34 project in June 2000 and, in March 2001, announced it would not continue funding either X-33 or X-34 as part of its new Space Launch Initiative program.

Larrimer believes that the multiple space mission failures NASA suffered in 1999—the WIRE astronomy satellite, Mars Climate Orbiter, and Mars Polar Lander—played a key role in NASA’s decision to end the X-34 before its first flight. The experimental vehicle lacked redundancy in many systems, and while NASA had anticipated the risk of failure earlier and authorized development of an additional X-34, those mission failures led to decisions first to develop more redundant systems, and then cancel the program outright. But Larrimer also questions whether NASA was ever really committed to the program after the original X-34 effort collapsed, or perhaps lost interest once the X-33 ran into serious problems.

He laments the fact that the X-34 never flew, a view shared by Rutan, who in 2001 offered to fly them himself. “There was nothing gained and much lost by the failure to carry through with flight-testing of the robotically piloted X-34 Technology Demonstrator vehicles that were already built and ready for flight testing,” Larrimer argues near the end of the book.

Promise Denied is a thorough review of the program that relies heavily on documents from the program along with some interviews and media accounts. That sourcing can be a little sloppy though: in one case he confuses publications (SpaceDaily and Spaceflight Now), and on a couple occasions attributes to SpaceRef newsletters called “Space Access Updates” that were, in fact, authored by the Space Access Society, an advocacy group (and thus missing an opportunity to probe the role such groups played in supporting, or sometimes opposing, RLV programs of that era.)

“Failure to carry through with the X-34 program truly represented a promise denied,” Larrimer writes at the end of the book (emphasis in original.) Yet we have seen reusability start to make a comeback, as SpaceX routinely reflies Falcon 9 first stages and begins testing the fully reusable Starship vehicle, while Blue Origin works on its New Glenn vehicle with a reusable first stage and other companies, from Rocket Lab to ULA, investigate reusing parts of their vehicles. It’s not the future envisioned 25 years ago, perhaps, but it now seems less of a promise denied than a promise deferred.


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