A circuit breaker on the international space station tripped for the second time in less than a year early yesterday, disconnecting one of the main gyroscopes that the orbiting laboratory uses to control its position in space.
NASA spokeswoman Kylie Moritz said the shutdown did not disturb the station, because two other gyros were still operating, and had no effect on the activities of crew members Leroy Chiao and Salizhan Sharipov, who are five months into a planned six-month stint aboard the station.
Moritz said in a telephone interview from Houston late yesterday that engineers at the Johnson Space Center there were trying to reset the circuit breaker electronically and would continue to troubleshoot the problem today.
Moritz noted that there is a spare circuit breaker -- known as a "Remote Power Controller Module" -- aboard, and that the crew could swap it for the failed one during a spacewalk if necessary. Astronauts installed a new circuit breaker after a similar failure almost a year ago.
The space station carries four "control moment gyroscopes" and needs two to keep itself steady without using thrusters. One gyro failed three years ago, but the replacement has not been installed because it must be carried up aboard the space shuttle, grounded since the 2003 Columbia disaster.
The shuttle Discovery -- carrying the gyro -- is scheduled to fly sometime during a three-week launch window that opens May 15. Discovery's scheduled rollout to its Kennedy Space Center launchpad has been delayed two weeks while engineers conduct further tests on the main landing gear and prepare the heat shielding around the landing-gear doors.
NASA spokesman Kyle Herring said the agency builds "a number of contingency days" into the shuttle preparation as standard procedure. A two-week delay will not affect the timing of the launch, he said.