Atlantis Shuttle starts unloading as collision with Soviet space debris is unlikely, NASA says

Astronauts continued organizing the unloading of a year's worth of supplies at the International Space Station after NASA said on Monday that a piece of Soviet space debris was unlikely to collide with orbiting lab.

The U.S. space agency confirmed it was tracking the space debris on Sunday, just moments after the shuttle Atlantis docked on its final mission, and warned

While engineers first warned that a manoeuvre with the shuttle's thrusters might be necessary to avoid a collision, they later on played down earlier concerns after studying the routes of both the object and the shuttle.

"We got some updates since the docking yesterday and everything indicates that the debris will be well clear of the station," said flight director Jerry Jason, adding it was expected to pass 18 kilometres from the lab.

"So we are not going to take any action to move out of the way," Jason said.

NASA also insisted that similar events are not uncommon and that 500,000 such objects are being tracked in the Earth's orbit.

The space agency also revealed that this particular piece of space junk was part of Cosmos 375, a satellite launched in 1970.

"The original concern was that the way we were docking was going to push us a little closer to the debris," said Jason.

But the act of the shuttle latching on at the station slowed the velocity and "changed our orbit enough that it did not become a concern for the debris."

Meanwhile, the four U.S. astronauts who arrived aboard Atlantis began work with their six colleagues at the ISS to transfer a year's worth of food and spare parts - nearly five tons' worth - to the orbiting outpost.

Other supply ships from Europe, Japan and Russia will be able to stock the ISS when the shuttle program retires after Atlantis's mission, but the amount of cargo space available aboard the shuttle is unparalleled.

The Raffaello multipurpose logistics module was lifted out of the shuttle's cargo bay and placed with the help of a Canadian robotic arm onto the space station's Harmony node, NASA said.

The container is "packed with 4,265 kilograms of spare parts, spare equipment, and other supplies, including 1,215 kg of food, that will sustain space station operations for a year," NASA said.

In the next few days, the crew is expected to transfer items from the Raffaello to the station and move more than 2,540 kg of old station gear, including a failed ammonia pump, back into the module for return to Earth.

"It is pretty much all hands on deck," said Jason. "It is going to be a very busy time period."

A six and a half-hour spacewalk by American ISS crew members Ron Garan and Mike Fossum, is also set to begin at 8: 44 a.m. on Tuesday and will see the astronauts move the failed ammonia pump.

It will not be the first time that Garan and Fossum step out for a spacewalk, as in June 2008, they were paired together on three spacewalks as part of the STS-124 mission that delivered the Japanese Kibo lab to the ISS.

They will also attach a Robotic Refueling Module to the ISS.

The shuttle's return to Earth is currently scheduled for July 20, though NASA may add an extra day to the mission.

"Things are looking good for an extension day, though the official decision will be made by the mission management team tomorrow or Wednesday," said Jason.