After partially folding and unfolding the panel more than 40 times, the astronauts abandoned efforts once it was retracted far enough for the new solar panels to move.

The solar panel causing the problems is attached to the P6 tress segment. It is part of the station's backbone but has been temporarily attached to one arm of the station since 2000 - awaiting the P5 tress segment which astronauts installed during their first space walk on Tuesday. The P6 segment will be moved to the end of the P5 segment and the solar panel redeployed in 2007 - completing one end of the station.

Retracting the P6 solar panel marks the start of an intense four-day overhaul the ISS's power systems. The task was the second of three scheduled space walks, although NASA is considering extending Discovery's stay by a day to allow astronauts to venture outside the station for a fourth time to attempt to finish the job.

Discovery was expected to stay at the station until Monday, with a return to earth scheduled for Thursday December 21. NASA engineers are keen to have the ship and crew safely on the ground before New Years Day, as the shuttle's navigation software is not designed to handle the new year roll over.{moscomment}