NASA has directed Boeing to throttle back on development of the orbital variant of the X-37 prototype space plane until more money is found for the program, an action likely to delay a re-entry and landing demonstration that was planned for 2006.

The purpose of the X-37 program is to validate new technologies in space and test system performance during orbit, re-entry and landing. NASA says the results of the X-37 flight will aid in the development of the Orbital Space Plane, an expendable-rocket-launched vehicle the agency wants to field by 2008 to serve as a crew lifeboat for the international space station.

NASA officials will not specify how much more money is needed to carry through with the orbital flight, saying only that the $178 million budgeted for the program for 2004 is not enough to both finish an atmospheric test version of the winged X-37 and proceed with work on a separate vehicle designed to go into space.

Daniel Dumbacher, NASA’s X-37 program manager, said Boeing officials were told in late November to concentrate on finishing the atmospheric test vehicle in time for a drop test from an aircraft in late 2004. Although Boeing also was told to continue work on some of the high-risk technologies needed for the orbital X-37, design work on that vehicle is on hold, he said.

NASA plans had called for launching the orbital vehicle in 2006 on either an Atlas 5 or Delta 4 expendable rocket for a 270-day orbital mission, after which it would re-enter the atmosphere and glide in for an aircraft-like landing. Dumbacher said that demonstration will be delayed, but could not say for how long. He said NASA has no plans to scrap the orbital flight.

But officials with Boeing NASA Systems, Huntington Beach, Calif., say it is not entirely clear what the future holds for the X-37 program.

Paul Geery, Boeing’s X-37 program manager, said the company has a “reasonable commitment” but “not a strong commitment” from NASA that the orbital vehicle will be built. For that reason, he said, the company cannot afford to press on with development work on the orbital vehicle while NASA works out the funding issues.

“If there was a guaranteed order in the works, it would be no problem,” Geery said in an interview. “But we are still in the negotiation phase of whether we restart” in 2004 or 2005, he said. “It’s just a little too unclear for us to make a commitment.”

Geery said Boeing intends to reassign about 100 of the roughly 400 engineers working on the X-37 to other programs within the company by the end of February. Most of Boeing’s X-37 jobs are in Huntington Beach, Calif., with the rest in Palmdale, Calif.

Geery said the cost of the X-37 atmospheric test vehicle has grown, but would not say by how much. He attributed the cost growth to a number of factors, including a several-month delay in getting under contract in 2002 and the need to  strengthen X-37’s wings. Geery said that redesign effort is complete.

NASA’s involvement in the X-37 dates back to 1998, when the project was selected as the first of a planned series of flight demonstrators dubbed Future X. At the time, NASA agreed to share the X-37’s projected $173 million cost with Boeing and the U.S. Air Force. After the Air Force announced in 2001 that it would stop funding the project, NASA told Boeing that the company would have to submit a new proposal for X-37 to be eligible for additional funding.

After persistent prodding from U.S. Rep. Dana Rohrabacher (R-Calif.), NASA in 2002 awarded Boeing a $301 million contract for two vehicles instead of one. One of those vehicles would conduct a a series of drop tests within the atmosphere, paving the way for the flight of the orbit and re-entry vehicle in 2006.

NASA determined earlier this year that the X-37 orbital vehicle had grown to a projected weight of 5,400 kilograms — too heavy to launch on a Delta 2 rocket as planned. The decision was then made to launch the craft aboard the heavy-lift variant of either the Delta 4 or Atlas 5, both of which are far more powerful but also far more expensive than the Delta 2.

More recently, NASA asked Boeing to design the X-37 orbital vehicle for a 270-day stay on orbit. NASA and Boeing were negotiating a contract modification to cover that requirement when NASA decided to put the orbital vehicle on the back burner.

Dumbacher said NASA is seeking additional money for the X-37 as part of a supplemental budget request for 2004 that the agency is pushing primarily to accelerate the Orbital Space Plane program by two years. He declined to specify how much money NASA is seeking, saying the funding outlook for both programs should be clearer by the time the White House sends its 2005 spending request to Congress in February.

A NASA source said a supplemental request that includes funds for the X-37 and Orbital Space Plane has been sent to the White House Office of Management and Budget.

Because the U.S. Senate adjourned for the year without approving an omnibus spending bill that would fund NASA in 2004, the White House could still amend its request to add more money for the Orbital Space Plane program. But such an action would entail sending the $328 billion spending package back to the House, which approved the measure Dec. 8.

A NASA supplemental could be included next year in one of the emergency spending bills Congress passes nearly every year to pay for U.S. military engagements and disaster relief. Congress also could attach a NASA supplemental to another unrelated bill. In July, for example, Congress added $50 million to help pay for Columbia disaster recovery operations to the legislative branch spending bill.