Astronauts carried out the first of five spacewalks at the International Space Station on Saturday.
Two crew from the Endeavour spent nearly six hours outside the ISS, attaching a large platform - the final piece of a Japanese space lab.
Endeavour docked with the space station on Friday - a record 13 astronauts are now at the ISS.
Saturday's spacewalk was the 127th involved in the construction of the station.
The BBC reports it lasted five hours and 32 minutes, about an hour less than scheduled.
However, communication by the astronauts with their colleagues on the ISS was hampered by heavy static from the microphones in their helmets.
NASA said the problems did not pose a safety risk. The next spacewalk is scheduled to take place on Monday.
The ISS is a project involving 16 nations. NASA has seven missions remaining after Endeavour's to complete construction of the $US100 billion space station and then retire the shuttle fleet.