The mission included four space walks and the installation of a two-tonne addition to the International Space Station.

Finally after their fourth unscheduled spacewalk, Discovery astronauts have successfully retracted a stubborn solar panel on the International Space Station.

Indian-American astronaut Sunita Williams is all set for an unscheduled fourth spacewalk along with other members of the Discovery crew on Monday to retract the P6 port solar array on the International Space Station.

Only seven other US women and a single Russian woman have participated in the 281 spacewalks taken since 1965.

41-year-old Sunita, who became the second woman of Indian descent to venture into space after Kalpan Chawla, said she was all "excited" to go out and check the planet.

Bob Curbeam and Christer Fuglesang began their spacewalk, the second of their 12-day space shuttle mission, at 1.41 pm CST, and finished a full hour earlier than scheduled.

Two astronauts of space shuttle Discovery have stepped out into space completing the first of the three spacewalks aimed at extending and rewiring the International Space Station.

Sunita replaced German astronaut Thomas Reiter on the ISS, who will return to earth after a five-month sojourn in space.

Trained to remain aboard the space station until July, Williams will also join space station commander Mike Lopez-Alegria for three spacewalks early in 2007.

NASA says the Discovery shuttle will be on the most complex mission yet -- to give the International Space Station a new electricity system. The STS-116 will drop off Sunita for a six-month stay at the space lab.