If there is so much space junk floating around the earth, how come no spacecrafts returning to earth are hit?
In: 3
The distances between debris is vast. We know where most of it is, it’s orbit route, and how to avoid it.
Imagine there are grains of sand flying around a giant beach ball. There could be a million gains of sand flying around it and you would still see the ball clearly and there would be plenty of room to not touch any of the sand. Besides, any junk worth tracking is being recorded and taken into account for any missions.
Most space junk is tracked. If a astronaut drops a wrench while doing a space walk, it’s someone in NASA’s job to plot that wrench’s orbit until it reenters the earth’s atmosphere (if ever). If these orbits are projected to cause a collision with another satellite, they can usually use what fuel they have left to move out of the way to avoid hitting it.
That said, satellites don’t have infinite fuel. Eventually they’ll lose the ability to avoid predicted collisions. Usually before this happens there is a plan in place to use what fuel it has left to crash into a vacant part of the Earth. That doesn’t always work out as plan, and older satellites didn’t even make such plans.
On top of this not every single thing floating around the earth is tracked. Some objects are just too small and numerous, or NASA just doesn’t know of it’s existence yet. It’s not really practical for NASA or other space agencies to notice and track a piece of paint that flaked off a satellite. [Yet even such a small thing can cause real damage](https://www.theverge.com/2016/5/12/11664668/iss-window-chip-space-debris-tim-peake) without wind resistance to slow it down.
Another comment explained how NASA works hard to avoid collisions, but the ISS has had a few collisions including one that went through the big manipulator arm so the reality is that we’ve just been lucky enough not to have anything catastrophic happen yet.
There are a few designs being tossed around I think for way to try and clean up the junk that isn’t going to de-orbit on its own any time soon which will get more and more important as time goes on
Space is big. About 20,000 objects are large enough to be tracked. If you would distribute 20,000 objects uniformly over the surface of Earth then you get one every 25500 km^(2), that’s about the size of Wales or Vermont. What is the chance that you randomly run into e.g. one particular car parked anywhere in these places? To make things worse (or better, for spacecraft), in space things can pass each other at a different altitude. Imagine we replace Vermont with a massive parking garage, taking up the same space but having 200,000 floors. Somewhere in that parking garage is a single car. You are unlikely to find that car even if you actively search for it your whole life. Spacecraft do the opposite, of course, if they would get close to one of these objects they do maneuvers to avoid them.
It’s estimated that there are up to a million objects larger than 1 cm, with only 1 in 50 of them tracked. These could still be catastrophic on impact, so let’s fill the parking garage with 50 cars. Would you find one now? It’s still very unlikely.
There are even more smaller objects, but impacts of them are rarely catastrophic. They might damage some individual components. The ISS has a few holes in its thin solar panels, but that’s not an issue for the station overall. Spacecraft that carry people are shielded against these smaller impacts.
“Space is big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space.”
Douglas Adams, The Hitchhiker’s Guide to the Galaxy (Hitchhiker’s Guide to the Galaxy, #1)
As others have said, there may be a ton of debris up there, but the chance you’ll actually hit something is very small because space is just that big.
Latest Answers