A piece of space junk appears headed for the International Space Station at the same time that the shuttle Discovery is on its way there, too.

Officials at NASA will decide on Monday if it's necessary to fire the station's engines in order to change its position to avoid a collision with the debris, which is a piece of a Russian satellite.

It is projected that the debris may come within just under a kilometre of the space station early Tuesday.

Astronauts who are currently at the space station had to enter an emergency capsule for about 10 minutes last week when another piece of space junk veered too close.

If the space station is required to change its position, the Discovery, which took off on Sunday, will have to change its course in order to dock there.

The shuttle took off Sunday evening after five separate delays.

The mission has been shortened by a day, which means a planned spacewalk has been cancelled. However, the astronauts should be able to complete between 80 and 90 per cent of their tasks.

"It's not a major setback to us," Bill Gerstenmaier, NASA's associate administrator for space operations, said Sunday evening. "We're able to accomplish everything we want."

Those tasks include dropping off Japanese astronaut Koichi Wakata, who will be the space station's newest crew member. He will replace U.S. astronaut Sandra Magnus.

Other tasks include:

  • Installing the station's last pair of solar wings, which will allow it to run at full power.
  • Delivering supplies and hardware, including a broken machine that turns urine into drinking water.

NASA officials were under considerable pressure to launch the Discovery ahead of a Russian Soyuz rocket launch, which is scheduled for March 26. The Soyuz will deliver a new crew for the space station.

Hydrogen valve problems grounded the shuttle for weeks in February, and then a hydrogen leak during fueling cancelled the launch that was scheduled for last Wednesday.

There were no fueling problems before Sunday's launch, and it appears that no debris came off the external fuel tank during takeoff.

NASA has watched for debris since 2003, when a piece of a fuel tank broke away from the shuttle Columbia. The shuttle exploded, killing all seven of its crew members.

To be sure, the Discovery's crew will spend Monday checking the shuttle's thermal protection system with cameras and sensors, which are attached to the shuttle's robotic arm.

With files from The Associated Press