After arriving in space for the delivery of a new module for the International Space Station, and the extensive examination of Discovery's external head shield, the astronauts encountered two different problems at the station's solar panel that power it with electric current.

The first unplanned space walk, involved a rotary joint that supports and turns towards the Sun, one of the station's solar panels. Trouble began as astronauts observed vibrations and power peak while trying to move it. On further inspection, they have found metal shavings in the rotary joint, that could have produce permanent damage, though turning a quick easy fix into a failure. The rotary joint had been installed only four months earlier, suggesting they have not been well manufactured.

Now, for the second time, astronauts have to go into space, repair the damaged solar panel that has been ripped while it was unfolded. Until further inspection, they do not know what materials are necessary for the successful repair.

This is one of the most difficult and dangerous spacewalking repair mission ever attempted in orbit. Astronaut Scott Parazynski will take the risk of walking to the damaged solar panel, and try to fix it. NASA has delayed the mission for Sunday, because any earlier attempt would be too risky without a strong safeplan, and saving the ripped solar panel has become Discovery's top priority during its visit to the space station, before re-entry planed for November 6.

The engineers think that the wing has snagged onto a guidewire or a guidewire support while it was unfolded, and is now producing only partial power. Nevertheless, it poses a great risk for the astronaut that will attempt its repair, as electricity generating solar cells cover the whole surface of the wing, and still produce enough energy that could potentially melt part of the tools he's using, that could burn holes into its space suit, or he might be electrocuted.

The trip to the ripped solar panel will take probably between 30 to 60 minutes, and NASA has a policy which prevents spacewalks more than 30 minutes away from the hatch in case of an emergency; still, repairing the station is absolutely necessary...