NASA X-38 program engineers decided to postpone the seventh free flight of an X-38 vehicle at about 10:29 a.m. PDT Friday. The halt came after the X-38, still secured to a wing pylon on NASA's B-52B mother ship, was already airborne.

File image of B-52 with X-38 craft. Photo: NASA

The B-52/X-38 combination returned to Edwards Air Force Base, Calif., where NASA's Dryden Flight Research Center is located.

The mission could be reflown as early as Monday, said John Muratore, X-38 program manager.

The halt was called because of a radio ground equipment problem. Time needed to rectify this could have exceeded the fuel requirements for chase aircraft, so the X-38 flight was postponed.

The X-38 is exploring technologies to enable construction of a Crew Return Vehicle (CRV) to be used as a "lifeboat" attached to the International Space Station. The CRV would be capable of evacuating a full seven-member space station crew and returning them to earth on short notice.