Astronauts prepare for 11th day in orbit

The crew of Discovery is schedule to wake up in about half an hour for its 11th day in space.

NASA engineers should decide today if the crew will take part in a fourth, unplanned spacewalk to fix a stuck valve.

The spacewalk would take place Friday in an attempt to free the nitrogen valve on the International Space Station.

Engineers sent the valve a series of commands Wednesday and plan to continue trying to free the valve electronically today.

The valve controls the flow of nitrogen, which pressurizes the ammonia cooling system. Engineers are studying whether the cooling system can be effective with the valve closed.

Another option would be to have the ISS crew perform a spacewalk after Discovery departs.

As of now Discovery is set to leave the ISS on Saturday morning, but that could change if a fourth spacewalk is ordered.

Originally this was a 13-day mission, but a day was added mid-trip. If the fourth spacewalk takes place it could become a 15-day mission.