What happens to old spacecrafts?

Stuart and Carolin answer a question from Tony that's out of this world

Stuart - It depends if we’re talking about spacecraft such as satellites then you’ve got a couple of choices. You can do the fun thing, which we talked about a little bit earlier which is to dive bomb the back into a planet or into a star. You can bring them back into the Earth’s atmosphere and, most of the time, the majority of satellite will break up as it burns up and gets very hot. If you’re unlucky maybe a few fragments will make it back down to the ground.

The other option is to stick into what’s called a graveyard orbit. You can put them about 200 miles higher up than the active satellites, so about 22,400 miles above the Earth. The idea is basically to put them out of the way. This is a really big problem because we’ve put so many satellites into space, and so many satellites orbiting the Earth that all that rubbish is starting to get in the way. Because these things are moving so quickly and so fast that the impacts of these parts of debris of systems cause huge problems with existing and active satellites that are out there. So it’s something you really have to take care of nowadays.

Chris - Because the particles are whizzing round at ludicrously high speeds and energies, aren’t they? So if you happen to be on a space walk or something it could tear through your spacesuit, it could tear through your spacecraft?

Stuart - Yeah. It’s a huge danger to the International Space Station. If you’ve got a small millimeter size particle doing a thousand kilometres and hour that can go through the side of shielding or something, that’s a big problem.

Chris - Even faster than that in some cases isn’t it Carolin? Some of the particles are moving very, very fast.

Carolin - The space station itself is going about 8 kilometres a second - phenomenal speed. I will just say though, space stations are in quite a relatively low Earth orbit so anything that’s orbiting at that height, if it’s not being continually boosted, will decay and burn up. One of the most recent examples was the astronaut who let go of her toolkit by accident and it drifted away from the spacestation. I can’t remember how many weeks later, but people could actually see her toolkit burn up in space because in orbit it had decayed and then it reached the atmosphere.

At the height of the International Space Station, there is junk around and you're relatively safe. But further up we’re just getting cluttered and you have the immense danger of things colliding. You get this breakaway thing where you have these high impact collisions, bits fly off that are more likely to impact other satellites, and it could be disastrous.

Chris - The height of the International Space Station - 150 kilometers or so up isn’t it - it’s not very high?

Carolin - A bit higher than that, probably about more 350/400 kilometres. Space starts at about 100 kilometres roughly.

Stuart - Every time a supply ship comes up and it docks at the International Space Station they have to boost it a little bit higher to stop it coming back into the Earth’s atmosphere.

Chris - It gives it a bit of momentum to speed it up?

Carolin - Yeah, just a little push.