The two international space station crewmen have aborted a maintenance spacewalk because of a faulty oxygen tank on one of them.

Russian ground controllers ordered U.S. astronaut Mike Fincke and Russian cosmonaut Gennady Padalka back into the station shortly after the spacewalk began when the astronaut's oxygen tank began losing pressure.

They were supposed to fix a faulty circuit breaker that has interrupted power to one of the outpost's four stabilizing gyroscopes.

Only two gyros are working, the minimum necessary to steer the facility without resorting to firing steering jets and using extra fuel. The U.S. and Russian space agencies want a third gyro operational as a backup to avoid using the jets.

This spacewalk was to be unusual, because the crewmen wore Russian spacesuits for work close to the American side. The U.S. spacesuits have cooling problems that prevented their use.

This required them to depart from a Russian hatch for a worksite across the station. But the site is out of view of the Russian antennas on the station, which might have caused a risky communications blackout. So the two had been prepared to use hand signals just in case.

It is unclear when the spacewalk will be rescheduled.