Indian-American astronaut Sunita Williams [Images] 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 [Images].

Mission Specialist Robert Curbeam who participated in all three of the previous spacewalks, and Christer Fuglesang, a spacewalker on the first two, will conduct the spacewalk.

The spacewalk will not go beyond six and one half hours, Tricia Mack, NASA's [Images] lead STS-116 spacewalk officer, said on Sunday.

Curbeam will be the first shuttle astronaut to perform four spacewalks in a single orbiter flight, but is a veteran of extravehicular activity and currently ranks 13th on the list of all-time spacewalkers, NASA officials said.

Most of Sunday was spent getting ready for a fourth spacewalk during Discovery's mission to the International Space Station.

The excursion, which was added on Saturday, didn't provide any respite to the crew members, despite it being a rest day.

Throughout the day, astronauts prepared tools and spacesuits for use by the spacewalkers. Flight controllers put the finishing touches on the spacewalk's timeline for review by the crew.

Overnight, Curbeam and Fuglesang will sleep in the Quest airlock for the pre-spacewalk campout procedure. During a campout, the pressure is lowered in the airlock to the pressure normally found on Earth at 10,000 feet above sea level.

The procedure protects against decompression sickness as spacewalkers go to even lower pressure in the spacesuits for the spacewalk.

During the spacewalk, Curbeam and Fuglesang will attempt to free up the array for retraction with several techniques -- pulling guide wires, flipping grommets, and pushing panel hinges. If necessary, the spacewalkers will shake the panel.

Another objective of the fourth spacewalk is to collect additional information that could prove useful when the opposite side of the array is retracted on STS-117 in March.

The fourth spacewalk resulted in an extra day at the station for the Discovery crew. Discovery is scheduled to undock on Tuesday. Landing is now targeted for Friday at Kennedy Space Center, Florida [Images].

On early Sunday, Mission Specialists Bob Curbeam and Expedition 14 Flight Engineer Sunita finished rewiring the International Space Station during a tedious 7-hour, 31-minute spacewalk.

They successfully finished rewiring the orbital outpost from a temporary power source to a permanent one.

Since Sunita and Curbeam finished the work smoothly ahead of schedule, they also shook a balky solar array wing in hopes of completing its retraction.