Space Shuttle STS-121 Discovery sits on the launch pad after the roll back of the rotating service structure at the Kennedy Space Center in Cape Canaveral, Fla., on Friday, June 30, 2006. (John Raoux/Associated Press)

The space shuttle Discovery's December trip is another "construction-and-bus" mission to the International Space Station.

With a lift-off window between Dec. 7 and Dec. 26, the 11-day trip to the station for space shuttle mission number STS-116 will:

• Deliver a new crew member to the station, and bring back one who has been there six months.
• Undertake major renovations to the station's electrical system.
• Allow the crew to conduct a number of experiments.

Bringing German Thomas Reiter of the European Space Agency back to Earth and delivering U.S. astronaut Suni Williams to replace him is a key part of the mission, NASA said. Reiter has been on the station since July. Williams, on her first flight, will remain for six months.

"So, we’re very much looking forward to getting up there, greeting an old friend, Thomas, and then bringing him back home to his family. I just have really good feelings about doing those things," mission commander Mark Polansky said.

No DIY reno

The station has been running on a temporary electrical system since it went into orbit in 1998. It's like using a generator to provide power to a new house until it's linked to the grid, lead space station flight director John Curry said.

An earlier mission in September saw astronauts install two new solar panels to generate electricity. But they're not hooked up to the station, and that's one of the main goals of mission STS-116.

Part of the set-up for the electrical work requires the crew to install a new 1,800 kilogram truss, called P5, outside the station. It is about the size of a small car, and is needed so another truss and solar arrays, which have been in temporary positions for six years, can be moved into their proper position.

Getting the P5 from the shuttle's cargo bay to the spot where it will be bolted down is a tricky procedure involving the robotic arm. When that's done, astronauts will go into space to physically unplug electrical cables and reconnect them so that power can flow from the new solar panels.

That requires NASA to shut off the power in two steps - half each time, so the station is not left powerless. That will require two spacewalks, one for each operation.

"Everything will be fine - if nothing breaks," Curry said.

Potential problems could arise because some of the equipment has been in space for six years, exposed to swings in temperature of between –128 Celsius and 93 C every 45 minutes as the station turns towards and away from the sun.

With that kind of stress, NASA can't be sure that the old parts of the electrical system will work after they're switched back on. If they don't work, the astronauts can't down tools and wait for a repair crew. They'll have to try and fix the problem, or else only half the station will have power.

Science in space: coffee-cup satellites to insomnia

Experiments on this trip - Discovery's 33rd flight and the 20th to the station - range from testing a new composite material for hinges, to assessing how spaceflight affects sleep cycles.

"This information could be vital in treating insomnia on Earth and in space," NASA said.

The drug midodrine will be tested to see if it reduces orthostatic hypotension, the dizziness that affects some astronauts caused by pressure changes as they return to Earth's gravity.

Another experiment will investigate why astronauts have hand-eye co-ordination problems while in orbit.

Components in tiny satellites the size of coffee cups, powered by microelectromechanical systems, will be tested to see if they can be used to inspect space vehicles.

The mission will also deliver materials that will be used in later experiments, along with supplies for the station, including oxygen.

A Green Crew

Discovery's seven astronauts are the greenest crew in eight years when it comes to space flight. Five have never flown in a space shuttle before, but commander Mark Polansky said each has been training for at least eight years.

"I don't consider them rookies," he said.

Here's a quick look at each member of the Discovery crew:

Mark Polanksy, 50, commander

Polansky is making his second mission to space. He was the pilot of Atlantis when it delivered the Destiny lab to the space station in 2001. He was an Air Force trainer and test pilot for 12 years before joining NASA in 1992 and the astronaut corps in 1996.

U.S. Navy Cmdr. William Oefelein, 41, pilot

Oefelein was selected as an astronaut in 1998. He will undock Discovery from the space station and co-ordinate spacewalks and use the shuttle's robotic arm to inspect for damage.

U.S. Navy Capt. Robert Curbeam 44

Curbeam has the most Shuttle experience. He flew aboard Discovery in 1997 and was on 2001 Atlantis flight with Polansky. He will spacewalk three times to rewire the space lab.

Joan Higginbotham, 42

Higginbotham is a former engineer at the Kennedy Space Center before applying to be an astronaut. She will be primary operator of station's robotic arm.

Nicholas Patrick, 42

Patrick, from Britain, is one of two crew members from Europe. He holds three patents in telerobotics, display design and aircraft alerting systems. He will be the primary operator of Discovery's robotic arm and will be in charge of the shuttle's video and computer networks.

Christer Fuglesang, 49, European Space Agency

Fuglesang will be the first Swede in space once Discovery reaches 100 km above Earth. The former Swedish national Firisbee champion will carry a Frisbee into space during one of his two spacewalks.

U.S. Navy Cmdr. Sunita Williams, 41

Williams will replace German astronaut Thomas Reiter on the space lab. She is a former diving officer, naval aviator and pilot instructor.

With files from the Associated Press

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