NASA is tracking a piece of Soviet space debris that could collide with the International Space Station (ISS), the US space agency said.
The space junk is part of Cosmos 375, a satellite launched in 1970 by the former Soviet Union and which collided with another satellite and broke apart, but details about the size and exact trajectory of the object were unknown, NASA said.
However, the debris could be on a collision course with the station at around 0200 AEST Wednesday, the same day that two US astronauts are scheduled to step out on a spacewalk.
"The team expected updated tracking information following today's docking to help determine if a manoeuvre using the shuttle's thrusters is necessary to avoid the debris," NASA said in a statement.
Word of the debris came shortly after the shuttle Atlantis docked at the orbiting International Space Station for one last time, on its final space voyage before the entire 30-year US shuttle program shuts down for good.
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The shuttle docked at 0107 AEST on Monday, just over an hour after the spacecraft performed its habitual slow backflip so that the ISS crew could take pictures of Atlantis's heat shield before clasping onto the lab, NASA said.
A close call between the orbiting outpost and a piece of space debris happened just two weeks ago, and the astronauts took temporary shelter in their Soyuz spacecraft docked at the station until it passed.
Flight controllers are monitoring more than 500,000 pieces of debris in Earth's orbit, NASA said.
"It is not uncommon. There is a lot of junk in orbit and there are a lot of objects that are being tracked," said deputy manager of the space shuttle program LeRoy Cain.
"What we were told today is very preliminary," Cain said. "It is a potential right now."
