Washington, Sep 6 (DPA) Two astronauts from the space shuttle Discovery began a third and final spacewalk Saturday outside the International Space Station (ISS).

US astronaut John 'Danny' Olivas and Swede Christer Fuglesang began the scheduled six-and-a-half-hour spacewalk at 4.39 p.m. (2039 GMT), US space agency NASA said.

They were to deploy an attachment system that will be used to hang spare parts on the station's truss. They were also to replace a device designed to help the station determine its position relative to the Earth.

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

The pair removed an 816-kg ammonia tank from a cargo carrier attached to the station and moved it with a robotic arm to its home outside the station.