Space junk has threatened seven astronauts aboard the International Space Station (ISS) – home to four Americans, one German and two Russians, forcing them to seek shelter in their docked capsules and disrupting their work.

The US Space Command said on Monday that it was tracking a field of orbiting debris, the apparent result of a satellite breakup. The situation had the debris coming uncomfortably close to the space station on subsequent orbits, and required the astronauts to close and then reopen several compartments, including the European lab, every 1 1/2 hours until bedtime.

Experts say anti-satellite weapons that shatter their targets pose a space hazard by creating a cloud of fragments that can collide with other objects, which in turn can set off a chain reaction of projectiles through Earth’s orbit.

“We are actively working to characterize the debris field and will continue to ensure all space-faring nations have the information necessary to maneuver satellites if impacted,” US Space Command said in a statement.

Mission Control said the heightened threat might continue for several more days and continue to interrupt the astronauts’ science research and other work. Four of the seven crew members arrived at the orbiting outpost Thursday night.

The US military said it was aware of a “debris-generating” event in outer space and one official said it appeared that Russia had carried out an anti-satellite weapons test.

The US Department of State said Russia tested an anti-satellite missile against one of its own satellites, which generated debris, jeopardised outer space and showed that Russian opposition to weaponisation of space was hypocritical.

“Russia’s dangerous and irresponsible behaviour jeopardises the long-term sustainability of … outer space and clearly demonstrates that Russia’s [claims] to oppose the weaponisation of space are disingenuous and hypocritical,” State Department spokesman Ned Price told reporters Monday, saying the Russian missile generated more than 1,500 pieces of “trackable orbital debris”.

Britain’s defence minister Ben Wallace echoed that on Monday.

“This destructive anti-satellite missile test by Russia shows a complete disregard for the security, safety and sustainability of space,” Wallace said in a post tweeted by the defence ministry.

NASA astronaut Mark Vande Hei, who is midway through a yearlong mission, called it “a crazy but well-coordinated day” as he bid Mission Control good night.

“It was certainly a great way to bond as a crew, starting off with our very first workday in space,” he said.

The Space Command said it was working with NASA and the State Department.

Earlier in the day, the Russian space agency Roscosmos said via Twitter that the astronauts were ordered into their docked capsules, in case they had to make a quick getaway. Later, the crew was “routinely performing operations”, the agency noted.

“Friends, everything is regular with us!” tweeted the space station’s commander, Russian Anton Shkaplerov.

But the cloud of debris seemed to pose a threat on each passing orbit – or every 1 1/2 hours. German astronaut Matthias Maurer was told to move his sleeping bag from the European lab to a safer location for the night.

Some 20,000 pieces of space junk are being tracked, including old and broken satellites. Last week, a fragment from an old Chinese satellite – the target of a missile-strike test in 2007 – threatened to come uncomfortably close to the ISS. While it later was dismissed as a risk, NASA had the space station move anyway.

The US military is increasingly dependent on satellites to determine what it does on the ground, guiding munitions with space-based lasers and satellites as well as using such assets to monitor for missile launches and track its forces.

(Al Jazeera/News Agencies)

•PHOTO: The United States military said it was aware of a ‘debris-generating’ event in outer space, and one official said it could be the result of a Russian anti-satellite weapons test [File: NASA via AP]

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