For the second time in just under a year, a circuit breaker failed on the international space station Wednesday, shutting down one of the gyroscopes needed to keep the orbiting outpost steady and pointed in the right position.
Despite the early-morning breakdown, the space station continued to cruise along smoothly in orbit and the two men on board went about their normal duties, including repair work on a balky oxygen generator.
The circuit breaker was a new one put in by spacewalking astronauts last summer. In a repeat from one year ago, the failure left the space station with only two functioning gyroscopes, the bare minimum needed for control.
This time, though, the problem could affect NASA’s plans to launch Discovery to the station in mid-May after a two-year grounding of the shuttle fleet. The space station must be steady for a shuttle to dock, and NASA might opt for a wide margin of safety.
The breakdown Wednesday appeared to be similar to what happened in April 2004, when a circuit breaker tripped and cut off power to the same gyroscope. Two months later, two spacewalking crewmen plugged in a new circuit breaker and got the gyroscope working again.
For now, flight controllers will try to command the circuit breaker to close, Mission Control said.
There is at least one spare circuit breaker on board. But there was no immediate discussion of whether the two crewmen would conduct a spacewalk to install it. They are already scheduled to go out on a spacewalk March 28 to perform routine maintenance work.
The station is equipped with four American-made gyroscopes, essentially 4-foot (1.2-meter) spinning wheels. But one of those gyroscopes broke three years ago; it will be replaced by Discovery’s astronauts, who will be making NASA’s first post-Columbia shuttle flight.
Russian thrusters could also be used to steer the station, but they use precious fuel.