Washington  - Two astronauts from the space shuttle Discovery successfully completed a third and final spacewalk Sunday outside the International Space Station (ISS).

US astronaut John "Danny" Olivas and Swede Christer Fuglesang began the spacewalk at 2039 GMT and ended it seven hours and one minute later, US space agency NASA said.

The two deployed a payload attachment system on the starboard truss and replaced a failed rate gyro assembly. They also installed two Global Positioning System antennas, replaced a remote power control module and installed an insulation sleeve on a cable inside the truss.

On Friday, Olivas and Fuglesang completed a six-hour spacewalk outside the ISS, installing a new ammonia tank used in the cooling system.

The pair removed an 816-kilogram ammonia tank from a cargo carrier attached to the station and moved it with a robotic arm to its home outside the station. The tank was the largest item ever moved by astronauts during a spacewalk.

The planned 13-day mission is designed to transport new equipment and experiments to the space station to boost its capacity as an orbiting laboratory.

The crew of six US and a Swedish astronaut brought two "racks" for scientific experiments and a freezer to store experiments set to be sent back to Earth. One of the racks will be used to conduct research on metals, semiconductors, crystal, glass and other materials in microgravity. The other will be used to study liquids and gels in space. (dpa)