But it will live on forever in fiction: In Dan Brown's "Angels and Demons" it was used to fly Robert Langdon, the book's hero, from the U.S. to CERN in Europe in record time.
http://en.wikipedia.org/wiki/Lockheed_Martin_X-33--snip
The X-33 was a technology demonstrator for NASA's "next-generation" of space launch vehicle named Venture Star.
Construction of the prototype was some 85% complete when the program was cancelled 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 had to be composite to be light enough in order for the craft to operate, but NASA came to the conclusion that the materials technology of the time was simply not advanced enough for such a design.
NASA had invested $912m in the project before cancellation and Lockheed Martin a further $357m. Lockheed Martin deemed that the business case to continue development privately without government support was unviable.
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The Orbital Sciences X-34 was intended as a low-cost testbed to demonstrate "key technologies" integratable to the Reusable Launch Vehicle program.
It was intended to be an autonomous pilotless craft powered by a Fastrac rocket engine capable of reaching Mach 8, and performing 25 test flights per year. However the unpowered prototype had only been used for towing and captive flight tests when the project was cancelled in 2001 on cost grounds.