By Paul Hoversten

Special to AviationNow.com 02/01/03

The loss of space shuttle Columbia and its seven astronauts throws into question the continuing manned operation of the International Space Station, which marked its second year of permanent human habitation last Nov. 2.

NASA officials vowed Saturday to find out why the shuttle disintegrated high above Texas at more than 18 times the speed of sound on approach to landing at Florida's Kennedy Space Center.

"We want to find out what happened, fix it and go on," NASA Associate Administrator Bill Readdy, a former shuttle commander, told reporters.

In a televised address from the White House, President Bush pledged support for space exploration. "The cause in which [the Columbia crew] died will continue. Our journey into space will go on," Bush said.

But if the shuttle fleet is grounded for a significant period -- as happened with the 2.5-year downtime after the 1986 Challenger -- it could mean the imminent return of the three-man crew aboard the station.

"I feel the crew on the station will have to come down before another [shuttle] crew goes up," former astronaut Buzz Aldrin told NBC-TV.

The station crew -- Commander Ken Bowersox, Flight Engineer Nikolai Budarin and Science Officer Don Pettit -- could return home aboard a Russian-made Soyuz parked at the orbiting outpost.

Called Expedition Six, the crew arrived at the ISS in November and was due to return to Earth aboard the next shuttle flight, Atlantis on STS-114, in March or April. Atlantis was scheduled to bring their replacements, the Expedition Seven crew.

Shuttle program manager Ron Dittemore said the station crew had enough supplies to remain on orbit until June. A replacement Soyuz is scheduled to be launched this spring to replace the one now docked at the station. The current capsule's six-month orbital lifetime runs out at the end of April.

"I hope we can get this resolved soon?but in the near term, we have months of resupply capability for the station," Dittemore said at a briefing from the Johnson Space Center in Houston.

For now, the station crew is preparing for the arrival of a new unmanned cargo ship, Progress 10, which is scheduled to launch from Baikonur on Sunday and arrive Tuesday. The crew jettisoned the Progress 9 cargo ship on Saturday after loading it with trash and other unneeded items.

The station also depends on the shuttle fleet for assembly missions and crew supplies. Modules designed for the station, in most cases, are carried inside the shuttle's cargo bay.

NASA is designing a spacecraft, called the Orbital Space Plane, to serve as a crew return vehicle for the station but it won't be ready until at least 2010.

The station can survive without a live-aboard crew and can be flown in a "safe mode" by ground controllers in Houston. NASA has contingency scenarios for such an outcome.

But a vacant station would also threaten the results of scientific experiments now in place and astronauts still would be needed to visit to perform periodic maintenance on the station's systems.

Sources from Rosaviakosmos, the Russian Aviation and Space Center, were quoted by the news agency RIA Novosti as saying Russia's manned and cargo spacecraft are ready to support station operations for the time being if the shuttle fleet is grounded.

Progress vehicles could take over the shuttle's role of boosting the space station, as they did for Russia's former Mir station, but their launch rate would have to be increased. However, Progress and Soyuz spacecraft have a two-year manufacturing cycle, so additional cargo launches soon are unlikely.

Russian officials have previously discussed outfitting a backup FGB station module to carry five tons of fuel and provide orbit boosts, but have not produced a new plan for that in the wake of the Columbia loss.

Correspondent Dmitry Pieson contributed to this report from Moscow.