No Quick Fix Spacewalk for Disabled ISS Gyroscope

NASA engineers and technicians lower a control moment gyroscope - a replacement part to be installed at the International Space Station during an STS-114 spacewalk - into a carrier. The gyroscope is part of Discovery's cargo during NASA's first return to flight mission. CREDIT: NASA/KSC.

The current crew of the International Space Station (ISS) will not make a special effort to replace a faulty circuit breaker that hobbled one of three gyroscopes used for orientation this week, NASA's ISS program manager said Thursday.

Instead, ISS Expedition 10 commander Leroy Chiao and flight engineer Salizhan Sharipov will go ahead as planned with a March 28 spacewalk to install antennas and other equipment to the exterior of the space station.

"It will not impact [the spacewalk] at all," said NASA ISS program manager Bill Gerstenmaier of the circuit breaker glitch during a teleconference with reporters. "We're perfectly fine with using two control moment gyroscopes for that EVA."

The space station requires a minimum of two functional U.S.-built gyroscopes to maintain its position in space without switching to propellant-driven Russian thrusters.

Gerstenmaier said that a known fault with a single transistor within the circuit breaker, known as a Remote Power Control Module (RPCM), apparently caused a power loss an ISS gyroscope Wednesday. The fault is identical to an earlier glitch that forced Expedition 9 astronauts to make an unplanned spacewalk repair last year.

"When we made the change out we knew the transistor had a fault in it and we assumed it could show up again [and] we were hoping it wouldn't be the case," Gerstenmaier said. "But it looks like it is."

Space station officials said they will continue to examine other ISS systems to make sure the circuit breaker is the only failure.

A spacewalk for another day

ISS managers said the earliest the RPCM could be replaced could be during the next space shuttle flight, STS-114, aboard Discovery, since a two astronauts on that mission are already planning to replace a broken gyroscope. If that falls through, the spacewalk repair could be reset for later this summer, they added.

"It certainly is possible and doable," said NASA astronaut Michael Fincke, who spent six months as ISS flight engineer during the Expedition 9 mission and helped make the initial RPCM fix. "It should go even smoother and faster them."

The RPCM glitch is one of several currently afflicting the space station and its crew, ranging from broken exterior lights to a finicky Russian oxygen generator and a broken toilet, both of which were repaired earlier today by Sharipov.

"The things that are going on at the space station are normal," Fincke said, adding that Expedition 10's Chiao and Sharipov are doing a fine job of balancing the demands of maintenance and science aboard the ISS.

Also today, NASA officials released their Implementation Plan for the International Space Station Continuing Flight, a 210-page document addressing ISS-related issues for the agency's shuttle return-to-flight effort.

"We tried to be as thorough and creative with these things, to look at what's going on at the station, to keep it operational," Gerstenmaier said.

• Complete Coverage: ISS Expedition 10