"It would focus on propulsion, thermal protection and avionics," said NASA Chief Engineer Daniel Mulville. "And if that's successful, then Lockheed believes that in 2003, they would go ahead with VentureStar."

The X-33B program would be run similarly to the X-33 program -- as a government-industry partnership, Mulville said.

Lockheed would be able to gather data from the craft before it makes any commitment to the VentureStar.

"The critical design review for VentureStar would come about the time the X-33B flies," said NASA Deputy Associate Administrator Gary Payton.

"I don't want to underestimate the technology leap from an X-33 to a VentureStar," Mulville said.

The X-33B program would replace some parts of the existing X-33 vehicle with new technologies. It would fly with more advanced flight components -- perhaps substituting some of the metal internal systems with lightweight carbon composites. It would also incorporate a more advanced thermal protection system, as well as a lightweight avionics package developed by the Jet Propulsion Laboratory that is currently slated to ride as an experiment on the first X-33, Payton said.

The new avionics system is 14 pounds lighter, he said, "But it's also cooler, and that cuts down on the coolant you need."

The new technologies, Payton noted, will make the X-33B an even more useful demonstrator for the VentureStar than the X-33.

"I think 'X-33B' is a name unto itself," said Lockheed spokesman Tony Jacob, "the term is sort of getting a life of its own to describe in one term the additional follow-on technology work that could be valuable in getting us from the sub-scale technology demonstrators to the full-scale RLV."

"Once we complete the current X-33 program, the X-33 vehicle itself will remain a very valuable platform and asset," Jacob said.