Cancellation
Construction of the prototype was some 85% assembled with 96% of the parts and the launch facility 100% complete when the program was canceled by NASA in 2001, after a long series of technical difficulties including flight instability and excess weight.
In particular, the composite liquid hydrogen fuel tank failed during testing in November 1999. The tank was constructed of honeycomb composite walls and internal structures to lower its weight. A lighter tank was needed for the craft to demonstrate necessary technologies for single-stage-to-orbit operations. A hydrogen fueled SSTO craft's mass fraction requires that the weight of the vehicle without fuel be 10% of the fully-fueled weight. This would allow for a vehicle to fly to low earth orbit without the need for the sort of external boosters and fuel tanks used by the Space Shuttle. But, after the composite tank failed on the test stand during fueling and pressure tests, NASA came to the conclusion that the technology of the time was simply not advanced enough for such a design. This conclusion is heavily disputed in the alt.space community, who blame the program's failure on NASA's preference for researching new materials and technologies rather than using older more reliable ones—for example, use of composite hydrogen tanks instead of aluminium-lithium. While the composite tank walls themselves were lighter, the odd hydrogen tank shape resulted in complex joints increasing the total mass of the composite tank to above that of an aluminum-based tank.[5]
NASA had invested $912 million in the project before cancellation and Lockheed Martin a further $357 million. Due to changes in the space launch business—including the challenges faced by companies such as Globalstar, Teledesic, and Iridium and the resulting drop in the number of anticipated commercial satellite launches per year—Lockheed Martin deemed that continuing development of the X-33 privately without government support would not be profitable.
After the cancellation, engineers were able to make a working liquid oxygen tank out of carbon fiber composite.[6]
Recently Lockheed Martin has been testing a new 1/5 scale rocket described to be similar in capabilities and design, known now simply as a "Space Reusable Launch Vehicle". Two tests have been conducted secretly at the Spaceport America in New Mexico. The first on December 19, 2007 was billed as a complete success, while the August 12, 2008 launch ended in an irreparable crash after 12.5 seconds of flight.[7][8] A third test on October 10, 2009, was another success.[citation needed]
