Endeavour astronauts go for first space walk
They are repairing one of the station's orientation controls.
Earlier in the day, NASA engineers spotted damage to the protective surface of the space shuttle Endeavour which has docked at the International Space Station.
The team says the small tear may have been caused by ice or foam insulation that broke off the fuel tank after lift-off.
The damage was revealed by close-up photographs taken by two Russian astronauts from the space station.
On Sunday the crew will use a robot arm and lasers to inspect the hole. NASA says it may need to be patched during a space walk.