NASA officials said Thursday that operations aboard the international space station were growing increasingly difficult to maintain, citing deterioration in some of the craft's environmental systems and exercise equipment.
Space shuttle flights to the orbiting laboratory were suspended Feb. 1 when the shuttle Columbia disintegrated, leaving limited capability to deliver crews, equipment and supplies to the space station. NASA does not expect to resume shuttle flights for possibly another year.
"We are getting a glimpse at just how difficult it is to fly the station," said William H. Gerstenmaier, NASA's space station program manager. "It is an extremely complicated spacecraft, flying in a very hostile environment. It is not an easy thing we are doing."
NASA is relying on manned and unmanned supply missions by its Russian partners, but such flights cannot match the huge capacity of the shuttle. Assembly of the station has been suspended, and the normal crew cut back from three astronauts to two.
American astronaut Michael Foale said Thursday that he did not see any safety or health threats on the space station. Foale and his crewmate, Russian cosmonaut Alexander Kaleri, arrived at the station this week to begin a six-month mission. They will replace Ed Lu and Yuri Malenchenko. NASA officials said it appeared the two departing astronauts were in fine health.
NASA is paying close attention to the station's environment because some of the facility's air-quality monitoring equipment broke several months ago. The agency plans to examine air samples brought back with the returning crew.
"We don't think anything is wrong with the atmosphere, but we can't say that with assurance," Gerstenmaier said.
In making the decision whether to launch Foale and Kaleri or cancel the flight, NASA officials weighed the consequences of letting the station go unmanned for a period of time.
Environmental and health officials initially recommended against the continued habitation of the station about two months ago, but they changed their position after program officials addressed their concerns, Nitza Cintron, NASA's chief of medicine, said at a news conference Thursday.
Gerstenmaier said nobody supported the idea of allowing the station to go unmanned because it raised the risk that any equipment failures could lead to a degradation in the overall condition of the craft.
A number of experts warned in February that the grounding of the shuttle fleet could pose serious risks to the space station, which will cost an estimated $100 billion to complete.
The issue prompted a reprimand of NASA by House Science Committee Chairman Rep. Sherwood L. Boehlert (R-N.Y.), who said space officials had repeatedly assured him that the shuttle grounding did not threaten the space station. "Clearly that was not the case," Boehlert said.