Problem Cuts Shuttle Mission Short

The space shuttle Columbia and its seven astronauts will return to Earth on Tuesday, 12 days earlier than planned, because of a deteriorating and potentially explosive power generator.

It is only the third time in space shuttle history that a mission has been cut short by equipment failure.

While NASA considered commander James Halsell Jr. and his crew to be in no immediate danger, shuttle managers did not want to take any chances with the generator and, on Sunday, cut short the 16-day science mission.

“The conservative thing to do is land on Tuesday,” shuttle program manager Tommy Holloway announced at a hastily arranged news conference.

Holloway said a landing today was ruled out in order to allow for an orderly return, and because Columbia’s two other electricity-producing fuel cells were working as they should.

The fear was that hydrogen fuel and oxygen in the degraded generator could mix, overheat and blow up if voltage in the unit dropped far enough. Flight controllers had the astronauts turn off the unit Sunday to reduce, if not eliminate, that risk. The crew also shut down all noncritical equipment to conserve power.

While a shuttle can land safely with two fuel cells, it is uncertain what would happen if only one fuel cell was available because of all the vital systems that would have to be shut down for lack of power.

Each $5-million fuel cell uses hydrogen and oxygen to generate electricity for the shuttle’s numerous systems and produces water as a byproduct. National Aeronautics and Space Administration flight rules say that if all three fuel cells are not working properly in orbit, a mission must be shortened.

Engineers have no idea why the fuel cell was slowly losing voltage. The unit has flown before without problems.

A failed fuel cell forced an early landing during NASA’s second shuttle flight in 1981; in that case, the unit was flooded with water. The only other time a shuttle mission was cut short for equipment failure was in 1991, because of a failed navigation unit.

Halsell did not sound surprised when Mission Control radioed up the bad news.

“That’s certainly a disappointment,” Halsell said, “but we know you guys put your best effort forward.”