Skunkworks has had a boner for LH2 since the 50s, though. At one point they had 90% of the liquid hydrogen in the world in a Burbank hangar next to I-5.
The X-33 was kind of a Kelly Johnson-era "we can make big things happen" project, only without Kelly Johnson. Never mind that the best Ben Rich ever accomplished was the F-117 (which the Serbians jury-rigged into oblivion with a 30-year-old radar system), Kelly Johnson couldn't make hydrogen tanks work either. Rockwell did, but they accomplished it by going one-time-use and tossing the fuckers over the Atlantic.