The crew of the Space Shuttle Discovery will have to wing it when they start a fourth spacewalk Monday.
Astronauts spent months in training for the mission's three scheduled spacewalks. But, the additional one wasn't planned until Saturday.
NASA approved it so astronauts could try to fully retract a solar panel on the international space station has refused to close during the mission. The crew has been preparing spacesuits and repositioning equipment in advance of the spacewalk.
They are scheduled to start Monday afternoon. The spacewalk will delay Discovery's return to earth -- the shuttle won't make it back to Kennedy Space Center until Friday. They have already moved cargo from the international space station to the shuttle for the trip back home.