Shuttle - ISS watch space junk and get ready to move out of way

from ABC News science summary (http://www.abcnews.com/)

NASA has been notified that space debris will pass close to the space station/space shuttle Tuesday, when the one spacewalk of this mission is scheduled. Mission Management Team Director Leroy Cain says it is too early to tell what, if any, evasive maneuvers are required. They have teams working around the clock to determine whether there's a real threat to the spacecraft

The space shuttle would use its thrusters to move the space station out of harm's way.
Mission managers have an imaginary safety zone around the two spacecraft. It's shaped like a pizza box, 25 kilometers by 25 kilometers by 2 miles.
"There is a lot of junk in orbit, there are a lot of objects being tracked," Cain said. "Fortunately we have a good process for dealing with it, we have a number of spent rocket bodies, and over time these things drag down from their original orbits."
This news came after an emotional, complicated rendezvous by Atlantis with the station, the last the two are scheduled ever to make. With shuttle commander Christopher Ferguson at the controls, Atlantis pulled up beneath the station, did a slow back flip so that station astronauts could photograph its heat shield for possible damage, and then came in for docking.
The astronauts' job was complicated by a computer glitch. One of Atlantis' five main computers unexpectedly turned itself off during the rendezvous. NASA said it did not threaten the mission, but there might be trouble if a second computer quit.
There is no word yet on the size of the object, or if it is related to a close call two weeks ago, when the ISS crew had to shelter in their Russian Soyuz return capsules. That debris came within 1,000 feet of the space station.
NASA expects any maneuvers would be made Monday night and doesn't know yet how this will affect Tuesday's spacewalk.
The item NASA is tracking is from a Soviet 1970s rocket -- its orbital debris catalog number is 4664. The incident from two weeks ago caught NASA by surprise -- and mission managers are uneasy about having 10 people on board the space station with only two Soyuz escape vehicles that seat three crewmembers each.
The space shuttle can't undock and escape that quickly and its size and sensitive heat shield make it a vulnerable target.
It is a mess up there in orbit -- there are approximately 19,000 objects larger than 10 cm, and about 500,000 particles between 1 and 10 cm in diameter. The number of particles smaller than 1 cm is probably in the tens of millions.
Junk larger than 10 cm is tracked routinely by the U.S. Space Surveillance Network. Objects as small as 3 mm can be detected by ground-based radar, providing a basis for a statistical estimate of their numbers Most of the space junk orbiting up there came from satellite explosions and collisions.