AFTER decades of being treated like a cosmic junkyard, the space around our planet is starting to resemble a shooting gallery. The UN is concerned about the spiralling risks of junk colliding with satellites and spacecraft and has now issued guidelines asking member nations to limit the amount of rubbish they leave in space.
Although the recommendations are voluntary, they represent the first international agreement to deal with the problem. 鈥淭his is a very important milestone,鈥� says Walter Flury, space debris protection manager for the European Space Agency.
Until now, spacefaring countries have been dumping debris with gay abandon. Since Sputnik was launched in 1957 about 4500 rockets have followed, each generating its own junk, and there are now thought to be tens of millions of pieces of debris in orbit around the Earth, nearly 10,000 of which are likely to be more than 10 centimetres across.
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During the early years of space launches, junk was not considered to be a significant problem because it was simply adding to dust and rocks that were already there, says Richard Tremayne-Smith, Britain鈥檚 delegate on the UN committee. 鈥淚t wasn鈥檛 pristine, it was already a hazardous environment,鈥� he says.
But it has become clear that any debris can be a serious hazard. Space debris is being considered as one possible cause for the shuttle Columbia鈥檚 catastrophic disintegration. While the smallest objects that can be tracked reliably are 10 centimetres across, a NASA report published in 1997 concluded that a piece just a few millimetres across could be fatal (快猫短视频, 15 February, p 8).
If nothing is done, the amount of debris is likely to increase exponentially over the next few decades and the risks could spiral out of control. 鈥淥ne should take measures now, even though the risks are currently small,鈥� says Flury.
It would be difficult and expensive to clean up junk already in orbit, but it should be relatively easy to control what is produced by future launches. So the UN guidelines, agreed in Vienna last week, advise spacefaring countries and companies how to do just that.
Some of the worst culprits 鈥� generating up to 40 per cent of the junk 鈥� are the upper stages of rockets, which can explode after they have been discarded. The new guidelines advocate simply venting any remaining fuel from the rockets鈥� tanks to minimise the risk of explosion. Another recommendation is to shift satellites that have served their term into 鈥済raveyard orbits鈥� so the remnants do not interfere with functioning craft. At the moment this only happens in about a third of cases, says Flury. 鈥淭he rest are either left in their current orbits or placed in orbits where they can still encroach on active satellites.鈥�
A further 10 per cent of the debris is made up of exploding bolts, lens covers and other objects deliberately released by spacecraft or satellites during their missions. Instead of tossing them into space, the guidelines recommend attaching them with hinges or tethers.
Tremayne-Smith says the recommendations are an important first step towards solving the problem of space junk. 鈥淛ust producing the guidelines has made a big difference,鈥� he says. 鈥淭hose countries all had a different understanding of what was involved. They now have the same understanding.鈥�
The next step could be to make the guidelines legally binding. There are no plans for this at the moment, but it might be necessary if owners of satellites damaged by space junk start trying to sue those who are not abiding by the guidelines, predicts Tremayne-Smith. 鈥淚t鈥檚 never happened, but it鈥檚 possible.鈥�