This is a big problem that many people are still trying to figure out, because there is a lot of junk out in space, and it is incredibly dangerous.
As of September 2012, we are currently monitoring 21,000 individual pieces of stuff orbiting the planet which are larger than about 2 inches. Anything this size which is going fast enough to stay in orbit poses a significant threat to satellites, spacecraft, and space stations. The ISS will regularly maneuver out of the way of space junk if we see it coming soon enough. If there isn’t enough time to move the whole ISS, then the crew members of the ISS have to take shelter in one of the Soyuz capsules which are attached to the ISS in case an emergency evacuation is needed.
The two inch limit on tracking isn’t an indication that there aren’t any pieces smaller than that, or that we don’t have to worry about the little ones; we simply can’t spot them from the ground. We fully expect there to be around 100 million more objects out there in the < 0.5 inch category. Even paint chips at orbital speeds can cause significant damage to a spacecraft. A few of the space shuttle missions had paint flakes impact the windshield of the craft, which is an unsettling sight to say the least.
I can tell you the worst way to clean up a dead satellite, which unfortunately happened in 2007; the Chinese military decided to test their anti-satellite technology on one of their dead weather satellites. This test successfully exploded the dead satellite, and created over two thousand new pieces of space debris, which, at the time, increased our space junk tally by 25%. (We had another spike in the space debris population after a dead, but intact, Russian spacecraft managed to collide with a not-dead privately owned satellite – that produced another 2000+ large pieces of debris.)
There have been a few suggestions on how to get the stuff that’s already up there down; some options are more passive than others; the space station Mir ran an experiment in 1996 where they attached pieces of gel onto the outside of the space station to see what kinds of microscopic space junk they could catch. (As an entertaining side note, this was part of the Mir Environmental Effects Package, or MEEP. This is definitely funnier now than it was in 1996.) They found a lot of liquid droplets, soap, and tiny paint fragments, along with pieces of broken spacecraft, and tiny electronic fragments. This was instructive, but not particularly effective for cleaning out the reservoir of stuff surrounding our planet.
The best method to date to keep the skies clear is to make sure that when you put a spacecraft up in space, it comes with a way to come down again. Usually this means that the craft should have a way to intentionally slow itself down enough to re-enter the atmosphere, which will allow most of the small pieces to burn away in the atmosphere due to the heat of re-entry. Large pieces may make it down to the surface, which is why the ‘intentional’ part of slowing down is important. Generally we like to dump the large pieces in the Pacific Ocean, since there aren’t any dense population centers in the middle of the ocean. If a spacecraft falls back to earth after it is 100% dead and unable to be controlled, then there’s no way to modify where it winds up falling, and it might come down on your favorite city. The standard way to slow yourself down is with a rocket, but there have been proposals to do this with a solar sail type contraption; at the end of the craft’s life, it could unroll the sail, which would then help to slow down the craft so it could fall back to Earth more quickly.
But those are only options for spacecraft which haven’t yet been launched, or have thought ahead more than most, and it doesn’t help get rid of the dead satellites we can’t communicate with, or any of the broken pieces of satellite shrapnel. For those, the only option is to send up some kind of clean-up satellite which can help slow down all the miscellaneous pieces. Again, there have been many proposals; the most plausible involve grabbing onto dead spacecraft somehow (perhaps with a net), and then de-orbiting as a pair (like e.Deorbit).
Unfortunately, we can’t just go up and push every dead satellite down to Earth; not only is this impractical in the extreme, all of the privately owned satellites are still privately owned regardless of whether or not they still work, and burning them up in the atmosphere would be burning someone else’s property, even if it doesn’t work anymore. For now, until some of these cleaner satellites can get up there and start pulling down some of the pieces, our main goal with space debris is simply to not produce any more than we already have.
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