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The International Space Station may soon have its first policy allowing crew members to intentionally pitch unneeded gear overboard. This may temporarily increase the amount of space junk orbiting Earth, but scientists say it will pose no extra danger to the crew or other spacecraft.

Tools and other gear have accidentally floated away during spacewalks. But NASA has shied away from intentionally jettisoning gear off the ISS in the past because of the threat of space junk hitting the station or other spacecraft.

Even tiny flecks of paint have cracked the windows of the space shuttle orbiter because they zoom around Earth at thousands of kilometres per hour.

“We understand that throwing things out is not something you want to do,” says Nicholas Johnson, NASA’s orbital debris programme manager at the Johnson Space Center in Houston, Texas, US.

But NASA began to consider a change to its policy when the space shuttle fleet was grounded to improve its safety after the Columbia accident in 2003. During that time, garbage and used equipment started to accumulate on the station, and managers began talking about the possibility of pitching things overboard.

Now for the first time, NASA managers have ironed out the first real policy on this issue. It will take effect if it is approved by the station’s other international partners – Russia, the European Space Agency, Canada and Japan.

Initial reluctance

That could require some getting used to, especially for the astronauts themselves. “There was an initial reluctance on the space station’s part to throw things out because we have indoctrinated them so well,” Johnson told New Scientist.

“There are some cases where throwing things out Â… may be the best undesirable occurrence,” he says. “[But] we’re not going to start throwing things out the door on a routine basis.”

Objects that could be released from the ISS include things that could be dangerous to send back to Earth on the shuttle or another space vehicle, things outside the station that would take too long to retrieve during a spacewalk, things that actually endanger the ISS, and things that are specifically designed to be jettisoned from the station.

According to the new policy, the crew would release an object on a spacewalk by pushing it “behind” the station to speed up the separation between the ISS and the object and to decrease the amount of time it spends in orbit. Ideally, the crew would do this from the rear of the station, since the object would be least likely to strike the station if released there (see Space junk: a short history of station litter).

Longest drive

“It seems like it’s a reasonable thing to do,” says William Ailor, director of the Center for Orbital and Reentry Debris Studies at the Aerospace Corporation, a non-profit research firm in El Segundo, California, US.

The new policy proposal comes just as Russia is about to conduct a spacewalk in which cosmonaut Mikhail Tyurin will hit a golf ball from the ISS in a promotional stunt for the golf company Element 21.

During the swing, which is currently scheduled for a spacewalk on 22 November, he will probably achieve the longest golf drive in history – even though he will be decked out in a bulky spacesuit with limited mobility.

“The shot’s going to be more of a swat than it is a full backswing,” says NASA’s deputy ISS programme manager Kirk Shireman.

NASA found that there was no threat of the 3-gram golf ball hitting the station at the time of the swing or on a later orbit – it will quickly burn up in the atmosphere. “We don’t see any issues at all. It’s something that will come down within a matter of days,” Johnson says.

Then, as early as next year, ISS astronauts may jettison some ammonia tanks weighing a total of 500 kilograms.

Track and avoid

The tanks are attached to the station’s P6 truss segment, which will likely be moved to a new position on the station next year. NASA wants to release the tanks because they may not be attached securely enough to withstand the move and were not designed to stay in space for a long time.

The tanks are dense enough they will probably stay in space longer than the golf ball before they burn up in the atmosphere. But large objects are also easier for ground stations to track – the US Space Surveillance Network can track objects roughly the size of a grapefruit. “Being able to track an object also means that you can avoid it,” Ailor told New Scientist.

Jettisoned objects – particularly such large ones – should have less than in a 1 in 10,000 chance of breaking up before they re-enter the atmosphere, according to the new policy, since that would create more pieces of space junk. The risk that an object could survive re-entry and harm someone on the ground should also be less than 1 in 10,000.

Journal reference: Advances in Space Research (doi:10.1016/j.asr.2006.09.006)