Live In Orbit: Spacewalk On Tap After Near-Miss

Spacewalking astronauts will venture outside the International Space Station Saturday on an excursion that will come a day after space junk buzzed the orbiting outpost.

Shuttle mission specialists Danny Olivas and Christer Fugelsang plan to prep the complex for the arrival next year of the U.S. Tranquility module -- the last large American station section.

The spacewalkers also aim to swing a spare parts pallet into position, swap out a faulty circuit breaker and replace a gyroscopic assembly that keeps the station positioned properly in space.

It will be the third and final outing during Discovery's station visit.

"We have two under our belts," said Olivas. "But the two behind us doesn't mean that third one isn't going to be as much or even more of a challenge. This late in the mission, we just have to keep ourselves focused."

Discovery astronauts are in the midst of a 13-day round trip to the station.

The crew has hauled 90 percent of an 8.5-ton load from a shuttle-launched Italian moving van into the station. They also are 60 percent done with packing trash and surplus gear for the trip home.

The spacewalk today will be the 133rd performed in the assembly and maintenance of the station, a daunting job that began when the first two building blocks were linked in low Earth orbit in late 1998.

The outing will come a day after a large piece of debris from a European Ariane rocket zoomed within less than a mile of the station.

U.S. Space Command tracks space debris and provided data that showed no evasive action would be required by the joined shuttle-station complex.

"We calculated a probability of collision of zero. So we knew we were okay," NASA flight director Ron Spencer said. "We were very confident in our tracking of it, so we knew it was going to be a near-miss without a threat of collision."

Here's a look at the upcoming day in space:

++11:59 a.m.: Shuttle crew wakes up.

++12:34 p.m.: Spacewalk preps pick up.

++4:34 p.m.: Cargo transfer between shuttle and station.

++4:49 p.m.: Spacewalk No. 3 begins.

++11:19 p.m.: Spacewalk No. 3 ends.

++3:29 a.m. Sunday: Shuttle crew sleeps.

Discovery is scheduled to land at Kennedy Space Center next Thursday.