Page last updated at 16:56 GMT, Thursday, 12 March 2009

Junk alert for space station crew

ISS (Nasa)
The crew had to move into the Russian Soyuz capsule

The crew of the International Space Station has been forced to shelter in the Russian Soyuz capsule after a close call with a piece of space debris.

The three crew members are now out of danger and have returned to the ISS, Russian mission control officials told Reuters news agency.

Nasa said news of the debris threat had come too late for flight controllers to move the space station out of the way.

The scare comes just over a month after two satellites collided over Siberia.

Officials said the decision to move the astronauts had been a precaution and that the probability of an impact with the ISS had been low.

The space station's operating rules require crew members to be evacuated when debris is detected within a set distance.

Russian Yury Lonchakov and Americans Michael Fincke and Sandra Magnus took refuge for about nine minutes in the Soyuz TMA-13 escape capsule.

Tiny fragment

"The crew have returned to the station. They are in absolutely no danger and the debris has already passed by the station," a spokesman for Russia's mission control said after the incident.

Nasa Spokesman William Jeffs says the evacuation was a rare event

"They didn't even close the hatch between the station and the Soyuz."

They were told the time of closest approach to the station would be 1639 GMT (1239 EDT).

The debris was about 1cm (0.3in) in size and part of an old "payload assist motor" that was previously on either a Delta rocket or on the space shuttle, Nasa public affairs officer Laura Rochon told journalists.

"The crew is safe and back in the space station and they are resuming normal operations," Ms Rochon added.

A Nasa spokesperson told BBC News that the space agency had been notified about the possible threat last night. The short lead time forced officials to move the crew into the capsule rather than manoeuvring the space station out of the way.

Expedition 18 crew (Nasa)
Two Americans and one Russian are aboard the station
The reason for the short notice is unclear, but the small size of the object and its erratic orbital path may have been factors.

"It's a bit like a swarm of bees in a beehive up there," said William Jeffs, a spokesperson at Nasa's Johnson Space Center in Houston, "the trajectories can sometimes be erratic."

It is unclear how many times crew members had been told to enter the Soyuz, but officials said this was "not the first" occasion. Flight controllers have moved the ISS eight times over the past 10 years in order to avoid debris.

Growing threat

Objects in orbit travel at tens of thousands of kilometres per hour. At these speeds, even a small piece of debris can knock out a satellite or, potentially, cause damage to the space station.

Experts recognise a growing threat to satellites and manned spacecraft from orbital debris and several events over the past three years have drawn attention to the problem.

On 10 February, the US Iridium 33 communications satellite collided with Cosmos 2251, a retired Russian intelligence comms sat.

Space debris (Esa)
About 18,000 objects bigger than 10cm are orbiting Earth

The chances of such an event had been estimated at millions or billions to one. The impact produced two expanding clouds of debris in intersecting orbits.

In January 2007, China caused international alarm when it destroyed one of its defunct satellites in a missile test. The US military estimates that this event created 2,500 new pieces of debris in orbit.

In total, there are said to be about 18,000 pieces of orbiting junk larger than 10cm in size.

On Wednesday, Nasa postponed its launch of the space shuttle Discovery from Florida when a hydrogen leak was detected during fuelling.

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