The debris would be harmful to other satellites in orbit. Since it introduces significant risk, they cannot just shoot them down without a good reason.
Yes, this is true, but for this to not be a problem, it also has to suppose that those higher-flying bits of debris don't subsequently collide with other higher-flying satellites.
Right now the economics for this don't add up. The risk of collision is quite low compared to launching "extra" satellites with the sole purpose of finding and tracking another satellite. It is also much more difficult to target an arbitrary piece of debris. If the incoming debris is in a similar orbit (both altitude and inclination) then it requires less fuel to be able track and find it. If the incoming debris/satellite is in a different orbital plane it requires a huge amount of fuel in order to change orbital inclination [0]
A few problems holding a solution like that back right now:
1) It takes a ton of fuel to change your orbit once you're in space, and space is _really_ big (even just the orbital ranges we're talking about). It's just not currently feasible for a ship like that to capture debris and then use _more_ fuel to bring it back down.
2) Relative velocities of some debris are so large (and they are so spread out) that it's not yet feasible to capture it and bring it back with any current approach.
Dead satellites are mostly dangerous for the scattered debris they _might_ become if something hits them/they bread up. So while bringing them back is important, it's not as immediate a danger as things that have already broken up.
Basically, we don't have any approach that would make a major difference, even if money was no object (which it is).
There are on the order of... 10s of thousands of intentional satellites.
There are millions of pieces of debris.
It's useful for preventing future debris from dead satellites perhaps, but doesn't address the large number of existing objects which are currently the problem.
How would that work? A rocket launches into orbit an unmanned satellite capable of autonomously intercepting the orbit of debris in order to collect it and then deorbit itself? Seems extremely expensive for little benefit.
It's my understanding that atmospheric drag and orbital perturbations due to the gravity of other celestial bodies cause satellites to need station keeping maneuvers just to avoid crashing into the Earth. So it seems to me that this debris problem will eventually take care of itself.
Good point, and indeed they can't, but they can cause a mess by shooting down a few. The other satellites will have to evade the debris which will cause headaches to the operator company.
This is in LEO so the damage would be limited - these are designed to decay and fall out of orbit in a few years - and so would most debris.
Most communication satellites (currently) have much higher altitudes, where such an event would be much worse as the debris would stay in orbit for much longer.
I thought so too, but apparently this is not universally true. Some of the debris can be put in an orbit with a longer lifetime than the original satellite. I got into a long twitter argument with experts in this field, and I was proven false: some of the debris can have longer orbital lifetime and go to higher orbit.
Satellites don't just cross their paths by magic. If their orbits don't intersect, they can't collide. Satellites don't collide with each other, it has never happened.
Satellites do collide with debris, but that's a different issue. Furthermore, they don't need a guarantee that they can be put into a graveyard orbit - the proposed satellites (and even any debris, if they'd explode for whatever reason) will be in a graveyard orbit from day one until they stop being pushed up and deorbit.
Here is my intuition: let's say two satellites impact at high relative speed to reach other in LEO. All orbits of the debris have to pass through the impact point (since all debris comes from the point of impact). Any fragments on an orbit that go much higher will have the other end of the orbit intersect the earth's atmosphere. For debris to remain up the longest, it needs to have a very circular orbit (whether retrograde, polar, whatever).
Disclaimer: I don't really know anything about the topic, so if there is something I am missing, then hopefully someone corrects me!
> "If you can decommission debris you can decommission satellites. This has obvious military applications. In fact to properly do this you actually have to get pretty close to other satellites without colliding. By solving the debris problem you're solving a lot of the same problems you need for these military applications."
I'm not sure that's entirely true. Having a collector satellite match orbit with the debris and grab is one way to get rid of it, but I suspect in most cases it's good enough to just position a satellite with, say, a big steel plate in a path that intersects the debris' path and deflect it at the right angle so it returns to Earth. (If you're really clever you might use the impacts to deflect the interceptor satellite into roughly the right orbit to intercept the next piece of debris.)
There might also be ways to "catch" debris with moderately high relative velocity with the collector satellite. I imagine there's limits to the size of thing you can capture that way and the maximum relative velocity if you want to be pretty sure you can catch it without creating more debris.
Maybe the least sophisticated way to deorbit debris would be to just have an object with relatively low mass but very high surface area (e.g. an artificial "asteroid" made of aerogel) in an orbit that gives it the greatest probability of hitting any average piece of space junk, and then you wait for things to hit it by chance. The things that hit it lose momentum and hopefully fall back to Earth.
First, many satellites share an orbit - for example, the whole GEO is a single orbital path, and it has hundreds, something like 25% of all the world's satellites spread over that path; and any junk that intersects that orbit is a threat to all of them, not any one in particular.
Second, a random piece of space junk is likely to be in a weird orbit where no satellite would want to be, but that potentially crosses/intersects many orbits where we would like to put satellites or have already done so, so again, it threatens many satellites (or "orbital slots"), not any one in particular. An orbit that's "clean" for this rotation might intersect a piece of space junk in the next rotation or a month afterwards; that junk is not "in that orbit" but it's still a threat to that orbit and many others because its path is crossing these orbits.
You could assign responsibility to sources of particular pieces debris; but there simply aren't cleanly separable areas of space for orbits to which you could assign responsibility like we do for radio spectrum.
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