Two US astronauts completed the fourth and final spacewalk of the Atlantis mission, setting the stage for the shuttle's return to earth later this week, which will bring home Indian-American Sunita Williams after her six-month sojourn at the International Space Station [Images], a record for a woman.

During the six-hour, 29-minute spacewalk on Sunday, mission specialists Patrick Forrester and Steven Swanson successfully completed all the tasks assigned to them, including the activation of the ISS' new truss segment.

They also installed a new set of solar panels and a shield to protect the station against meteors, besides removing an antenna for satellite navigation.

Attention now turns to the departure of Atlantis, which is slated to undock from the ISS on Tuesday and return to earth on Thursday.

Williams, who on Saturday broke the record for the longest uninterrupted space flight by a woman, will be among the seven-member crew making the flight back.

'Suni', as she is called, came to the station in December in her first space flight. She will be relieved by Clayton Anderson, who came up with Atlantis and will remain on the ISS until October.

However, mission managers may yet decide to add a day of docked operations for the Atlantis crew if the Russian navigation computers do not perform adequately during a test on Monday morning.

The astronauts on Friday fixed the ISS computers after a 48-hour systems breakdown by bypassing a power switch with a jumper cable.

Also, Atlantis' thermal blanket was fixed on Saturday, clearing the way for its return flight to earth after a 13-day mission that was extended by two days due to the damaged thermal protection system.

Undertaking the spacewalk on Sunday, Forrester and Swanson first prepared the Starboard 3 and 4 (S3/S4) truss segment of the ISS, which was installed on June 11.

Most of the work centered on activating the Solar Alpha Rotary Joint, which will allow tracking of the Sun.

They then installed a computer network cable on to the Unity module and removed a Global Positioning System antenna.

The two astronauts also finished the installation of a piece of debris shielding on the Destiny laboratory.

Mission Specialist Jim Reilly coordinated the spacewalk and Pilot Lee Archambault operated the robot arm.