Washington: The US space agency is tracking a piece of space junk that could be on a path toward the International Space Station, where the shuttle Atlantis has just docked on its final mission, NASA has said.

However, NASA is not ready to say for sure whether the object is projected to collide with the shuttle and station, though the paths were likely to cross on Tuesday, said Deputy Manager of the space shuttle program LeRoy Cain.

"What we were told today is very preliminary," Cain said on Sunday. "It is a potential right now,"

Cain said he was unaware what size the object may be, but expected more information later Sunday or Monday.

Tuesday is the scheduled day for a spacewalk by two US astronauts aboard the ISS as part of Expedition 28.

On June 28, a piece of space debris narrowly missed the ISS in a rare incident that forced the six-member crew to scramble to their rescue craft, space agency officials said.

The high-speed object hurtled toward the orbiting lab and likely missed it by just 1,100 feet (335 meters). The crew moved to shelter inside two Soyuz spacecraft 18 minutes before
the debris was expected to pass, NASA said.

"It was probably the closest object that has actually come by the space station," NASA's associate administrator for space operations, Bill Gerstenmaier, said afterward.

"We didn't have any information that it was coming until it was very, very close."

The size of the space junk remains unknown and no harm was done by its fly-by.

Atlantis' completes first full day in orbit

The space shuttle Atlantis hasn't performed like a ship ready for retirement. The first full day of the final flight of the aging space shuttle fleet has been practically flawless.

NASA officials say the unusually small four-person crew of Atlantis worked through lunch on Saturday and finished their tasks in near record time.

After Friday's launch, the astronauts inspected the shuttle's heat shield for launch damage and prepared for Sunday’s docking with the International Space Station.

So far, Atlantis doesn't even have minor glitches. The worst problem is that the crew could not find an eye chart for a vision test, something that caused a chuckle among ground controllers.

Flight Director Kwatsi Alibaruho said the lack of problems allows engineers to enjoy the final flight more.