NASA has revived plans to fly its X-37 experimental space plane in orbit for 270 days, a requirement that originally was set by the U.S. Air Force as a way to begin proving the feasibility of orbiting Earth with camera- and bomb-laden space planes for months at a time.

The Air Force withdrew from the X-37 program in 2002. At that time, the 270-day requirement then “floated to the side,” said  Daniel Dumbacher, NASA’s X-37 project manager.

Now, however, NASA has decided to restore the 270-day requirement as a way to test new, scientific remote sensing instruments, Dumbacher said. “I would not say that we’re defining a military requirement,” he said. “The 270-day requirement was revived for the purposes of making X-37 more applicable and useful to other parts of” NASA.

NASA is negotiating with Boeing to include the 270-day requirement in a modified contract that NASA hopes to have completed by early 2004, Dumbacher said. The X-37 orbital flight would take place in late 2006.

In 2002, U.S. Air Force Secretary James Roche pulled his agency out of the X-37 program when Air Force engineers warned that the plane, then in development at Boeing’s facility in Palmdale, Calif., was becoming too heavy to meet the service’s needs.

NASA has since decided to restrict that original version of the X-37 to drop tests from a NASA B-52 bomber. The agency has asked Boeing to build a second, orbital version of the X-37 that would have the ability to stay in orbit for 270 days, as initially envisioned under the joint program.

The X-37 is a winged vehicle that resembles a miniature space shuttle orbiter. It will demonstrate 25 innovative aerospace technologies under NASA’s Orbital Space Plane program, an effort to develop a crew rescue alternative for the international space station by late 2008.

X-37 advocates are concerned that if NASA chooses a wingless capsule as the best way to carry astronauts home in an emergency, their project will be vulnerable to cancellation.

By reviving the 270-day requirement, NASA managers might be trying to draw the Air Force back into the program, said Theresa Hitchens, a senior analyst at the Center for Defense Information in Washington. Hitchens said it would be difficult to justify the long-duration requirement on the grounds of testing remote sensing instruments.

“You could do that on a micro-satellite,” she said. “I don’t get the justification for testing that kind of instrument on that kind of platform.”

When the Air Force decided to withdraw from the X-37 program, military space plane advocates insisted the decision did not indicate a lack of support for the concept of a military space plane. They said the decision was tied specifically to changes in the design of the X-37. The Air Force’s 270-day requirement stemmed from a proposed space warfare strategy of global strike that Air Force space planners have pushed hard inside the Pentagon in recent years.

The strategy hinges on developing a fleet of unpiloted space planes called Space Operations Vehicles that would be capable of staying in orbit for months at a time, according to Air Force officials. The space vehicles would be loaded with smaller re-entry vehicles, called Common Aerospace Vehicles, or CAVs. These re-entry vehicles would carry as many as 10 500-pound conventional bombs.

The CAVs would protect the bombs from the intense heat of re-entering the atmosphere, an Air Force official explained. The bombs would be identical to those carried by Air Force fighter planes, hence the word “common,” this official explained. Targets could be struck quickly nearly anywhere around the globe without having to position aircraft to forward positions.

Pentagon and Air Force leaders have made no decision about developing or deploying a Space Operations Vehicle, said Air Force spokesman Mike Kucharek. In fact, some Air Force strategists have proposed installing the conventionally armed Common Aerospace Vehicles on Intercontinental Ballistic Missiles as an alternative, he said.

Kucharek also said that the Air Force did not have a hand in adding the 270-day stay back to the X-37 program.

“The 270-day on-orbit requirement is a NASA requirement,” Kucharek said. “It happens to coincide with the Air Force requirement in the original X-37 cooperative agreement. There was no Air Force input that revived the requirement, only the desire by NASA to have a vehicle capable of a broader range of activities for NASA application.”

Meanwhile, German aerospace companies are looking for a role on either the Orbital Space Plane or the X-37 project. At the request of NASA Administrator Sean O’Keefe, U.S. contractors met their German counterparts in Huntsville, Ala. Sept. 18-19 to discuss industry-to-industry opportunities in reusable space transportation. German companies would like a role in X-37 — and potentially the Orbital Space Plane — supplying thermal protection system technologies developed under the canceled X-38 program, according to a German aerospace source.

Volker Roth, Boeing’s Orbital Space Plane deputy program manager acknowledged meeting with German aerospace officials and said that Boeing was seeking U.S. State Department approval to continue technical discussions with the German firms.