The two International Space Station astronauts completed the spacewalk Monday for installing antennas to enable the European Space Agency to send its first cargo ship to the station.

US astronaut Leroy Chiao and his Russian crewmate, Salizhan Sharipov, also released a baby experimental satellite called Nanosputnik during the 4.5 hour mission, which ended more than an hour earlier than planned.

This was their second spacewalk that left the space station empty in a couple of months. They worked most of the time on preparing the docking mechanism for the first European Automated Transfer Vehicle (ATV), which is due to be launched next year.

The ATVs can carry much bigger loads of food, equipment and fuel than Russia's Progress cargo ship. Russian manned and cargo vehicles have sustained the operation of the space station for more than two years since NASA grounded its shuttle fleet after the Columbia tragedy.

The two astronauts will be replaced by a new two-man crew next month. They have so far spent 165 days in orbit.

In the past several weeks, Chiao and Sharipov had seen multiple breakdowns in the station, including a circuit breaker that cut power to one of the gyroscopes needed to stabilize the station. The breakdown left the space station running on only two gyroscopes, the bare minimum.

NASA has said it plans to resume the shuttle flight from May or June. Visiting shuttle astronauts will then deal with the circuit breaker.