HOUSTON (AP) – Anyone who’s ever tried to fold a well-used map can probably relate to the challenge Discovery astronauts face in the next phase of their mission.

One of the station’s solar panels needs to be retracted Wednesday to make room for another panel that will begin rotating for the first time after the rewiring takes place. The panels follow the sun’s movement to maximize the amount of power they can generate for the orbiting space lab.

But retracting a solar array isn’t easy, and NASA managers are wary about putting too much pressure on the array while trying to fold it back into its box.

“A map never goes back to the way you bought it. It just doesn’t,” said John Curry, NASA’s lead flight director for the space station.

NASA has contingency plans if something goes wrong, but managers won’t be certain how the 120-foot-long array will compact until the controllers in Houston start the long, computerized process. It’s expected to take about five hours.

The shuttle crew awoke Wednesday to a recording of “Suavemente” sung by Elvis Crespo. But they didn’t awake in their usual spots.

Flight controllers had asked them to sleep in highly protected areas of the shuttle because of concerns about solar flares. The flares never posed any danger to the crew but are a phenomenon flight controllers keep an eye on.

After a successful first spacewalk on Tuesday, the crew was set to spend much of Wednesday preparing to rewire the international space station, one of their most important tasks.

The rewiring is a vital step in the growth of the space station. Reconfiguring the power system will give the station the capability to provide electricity to laboratories that will be added to the structure in upcoming years.

Discovery’s astronauts have already completed one of the main tasks on the 12-day mission. Spacewalkers Robert Curbeam and Christer Fuglesang, along with robotic arm controllers Joan Higginbotham and Sunita Williams, installed a 2-ton, $11-million addition to the space station truss on Tuesday.

Williams also has officially replaced German astronaut Thomas Reiter in the space station crew. Reiter will return with Discovery after a five-month stay in space.

Two more spacewalks, scheduled for Thursday and Saturday, will be dedicated to rewiring the station from the current temporary power system to the permanent one.

“This is a major milestone for the program,” Mr. Curry said.

The array to be retracted has been part of the station’s temporary power system. It will be moved to its permanent position on a later shuttle mission.

Also on Wednesday, NASA planned to fill cooling loops with ammonia. The pumps on those loops are scheduled to be turned on after the rewiring so the liquid can dissipate heat from electronics in the new power grid.

Discovery is scheduled to return to Earth on Dec. 21. NASA managers on Wednesday cleared the space craft for the flight back, saying dings on its left wing and belly were not of concern. The space agency has been particularly wary of damage to the shuttle’s heat shield since a gash in shuttle Columbia’s wing led its destruction and the deaths of its seven astronauts in 2003.