Popping out for a few hours on Thursday would have left the outpost empty and was originally deemed a Russian risk that NASA objected to.
   
On previous spacewalks, a third astronaut has always remained behind in case of some emergency - such as a stuck hatch or power failure.

But the grounding of US space shuttles has left the station with only two occupants.
   
Five hour mission

The station's British-born commander, Michael Foale, and Russian flight engineer Alexander Kaleri wore Russian spacesuits as they floated free of the airlock on a five-to-six-hour mission - only to return much sooner than planned.
   
Their job was to retrieve some experiments, set up other experiments and make early preparations for the arrival of a new European Space Agency cargo ship scheduled to fly for the first time later this year. 
   

"Our Russian colleagues were very helpful in helping us think through the scenarios and what the response to those might be"

Sally Davis,
NASA Flight Director

NASA officials acknowledge they first balked when their Russian counterparts requested the outing last summer, saying it would be better to wait until US space shuttles, grounded after the Columbia accident last year, were once again cleared for flight.
   
Improved relations

Cultural differences have sometimes marred relations between the two senior partners in the 17-nation venture, but NASA Flight Director Sally Davis said that once both sides sat down to iron out problems, they set a new bar for cooperation.
   
The Russians, with their long experience running space stations, have made dozens of spacewalks while leaving their Mir and Salyut stations empty, but the Americans were unprepared and had to develop contingency plans for every conceivable emergency.
   
"I think for us it was a matter of getting comfortable. If we had an off-nominal situation, exactly how we were going to respond," said Davis.
   
"In fact, our Russian colleagues were very helpful in helping us think through the scenarios and what the response to those might be. When you're working on technical problems like that, the cultural differences almost disappear."