Space junk is everything from spent rocket upper-stages that measure metres across, to lost bags of tools let go by careless astronauts, to shattered Chinese satellites to flecks of paint moving at 25 times the speed of sound. Under the wrong circumstances any piece of junk could kill a perfectly good satellite or even an unlucky space-walker. How should we prevent dead satellites from adding to this dangerous cloud of debris?
Dr Kristen Gates has one idea, and it's beautiful and simple. It's dubbed GOLD - the Gossamer Orbit Lowering Device - and it's just been revealed at the "Artificial and Natural Space Debris" session of the AIAA Astrodynamics Specialists Conference.
GOLD is not much more than a football-field sized balloon (made of gossamer-thin but super-tough material, a little like solar sails) that is flown into orbit deflated in a suitcase-sized box and then fastened to a dead satellite. It's then inflated to maximum size and the huge bulk of the balloon massively increases the atmospheric drag that satellites experience up there in the void. This drag is due to the rare molecules of gas that hover around above the fringe of the atmosphere, and it's the same drag that resulted in the premature deorbiting of the famous Skylab satellite in the 1970s, when the mechanics of orbital drag weren't as well understood. The drag acts to slow a satellite in its orbital path, and then simple orbital mechanics means the satellite descends into the atmosphere where the denser air heats it to the point it burns up.
GOLD has numerous advantages: It's cheap, it can be built into rocket upper-stages before they're launched so that new rockets never pose a space junk threat and its proposed material is tough enough that even though the balloon envelope will definitely be damaged by space junk itself, it'll never tear and generate more junk by itself.
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