March 18, 2005

NASA: Space Station Work Put Off for Now

CAPE CANAVERAL, Fla. (AP) -- Astronauts will have to go out and replace a failed circuit breaker outside the international space station, but the work can be put off for a few months because the orbiting complex is holding steady, a NASA official said Thursday.

A circuit breaker popped open Wednesday and cut off power to one of the gyroscopes needed to keep the space station stable and pointed in the right direction. It was a new circuit breaker put in by spacewalking astronauts less than a year ago, to replace one that failed in seemingly identical fashion.

Space station program manager Bill Gerstenmaier said in both cases, the culprit appears to be a bad transistor in the circuit breaker, the result of a design flaw. These circuit breakers have failed 12 times in various components inside and outside the station, he said. They are being redesigned.

"In our quest to make sure we've looked at everything," engineers are analyzing data to make sure the gyroscope itself is not to blame, Gerstenmaier said. This quest is part of the additional rigor put in place following the 2003 Columbia disaster; the station program on Thursday issued a 210-page report detailing its post-Columbia improvements.

"It's curious that the same channel would have the same failure in the same transistor. It's not improbable, but it's curious," Gerstenmaier said. "So we're going to go look and see if there's anything else that could have triggered it."

Wednesday's breakdown left the space station running on only two gyroscopes, the bare minimum needed. The station is equipped with four, but one broke three years ago and will be replaced by visiting astronauts from Discovery, due to lift off in mid-May following a two-year grounding of the shuttle fleet.

Gerstenmaier said the breakdown should not affect Discovery's launch.

The 600-pound gyroscopes - essentially 4-feet spinning wheels - are so big that they cannot fit in Russia's small spacecraft and must be transported via the shuttle. The spare was supposed to go up in 2003, but remained on the ground with the shuttles in the wake of the Columbia tragedy.

Astronaut Leroy Chiao and cosmonaut Salizhan Sharipov will not attempt to replace the circuit breaker when they venture outside March 28 to perform maintenance work, Gerstenmaier said. Rather, Discovery's astronauts may be given the task or the job may wait until summer and be handled by the next station crew.

Discovery, meanwhile, has a new problem that has pushed its move to the launch pad into early April. Liftoff remains scheduled for May 15, but the date is increasingly threatened by all the delays in getting the shuttle to the pad.

NASA is removing all the wire-tray covers in Discovery's payload bay in order to pad the bottom of the fasteners that hold the covers in place. The concern is that the fasteners could rub against the wire bundles and cause chafing.

The problem was first discovered in Endeavour, just this week.


On the Net:

NASA: http://spaceflight.nasa.gov/