Circuit Breaker Fails Again Aboard ISS

A circuit breaker has failed aboard the International Space Station (ISS), cutting off power to one of three gyroscopes used to keep the orbital facility oriented properly.

It is the second time in less than a year that the circuit breaker, called a remote power control module (RPCM), has failed, leaving the ISS dependent on two operational gyroscopes - the minimum required - to maintain attitude control.

NASA spokesperson Kylie Clem told SPACE.com that the faulty circuit breaker will be discussed Thursday during a regular scheduled ISS mission management meeting.

While no action by the space station's current crew, Expedition 10 commander Leroy Chiao and flight engineer Salizhan Sharipov, is immediately required, today's glitch mirrors one that occurred on April 21, 2004, less than a day after the Expedition 9 crew boarded the ISS.

The circuit breaker failure occurred this morning in a device that has already been replaced once by space station astronauts. Expedition 9 crewmembers Gennady Padalka and Michael Fincke swapped out the device during one of the four spacewalks of their mission.

Expedition 10's Chiao and Sharipov are scheduled to conduct an unrelated spacewalk on March 28 - aimed at preparing the ISS to receive a European cargo ship - but whether they will have to perform an additional extravehicular activity was not immediately known. At least one spare RPCM is available aboard the ISS.

The ISS actually carries four of the large U.S.-built gyroscopes used to orient itself in space, though one has been inoperable since 2002. The RPCM device functions as both power plug and circuit breaker for ISS gyroscopes and today's glitch has left the station without a spare should another one fail. Russian thrusters, which fire propellant to push the station, can also be used to orient the ISS.

NASA already has plans to ship a replacement gyroscope to the ISS aboard the Discovery space shuttle during STS-114, currently set to launch in mid-May, though the space station must be able to maintain its position for the spacecraft to dock properly.

• Complete Coverage: ISS Expedition 10