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There is a whole bunch of space junk; Wikipedia says there are about 19,000 pieces of junk being tracked. With no clouds, solar energy is readily available, so the biggest missing ingredient for gaining altitude once you are in orbit is reaction mass. Normally you have to launch any mass with you that you want to use; the current cost-per-Kg to send mass into LEO is between 4,000 and 13,000 US$.

There must be tons of space junk floating around in orbit. Have there been any studies or experiments using space junk as reaction mass to gain orbital lift or modify orbit/travel?

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    $\begingroup$ Only if it is made from Hemp. The amount of materials needed to process 'junk' into usable propellant would (in my guesstimation) far exceed the reaction mass that could be gained from it. $\endgroup$ – Andrew Thompson Oct 4 '13 at 18:04
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    $\begingroup$ @Andrew You do not need to process it at all, just need to accelerate it! $\endgroup$ – Volker Siegel Apr 14 '14 at 5:04
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    $\begingroup$ @VolkerSiegel "..just need to accelerate it!" After matching trajectories with it, to capture it in the first place. Then there is the matter of exactly how you intend to accelerate any matter gained. $\endgroup$ – Andrew Thompson Apr 14 '14 at 5:38
  • $\begingroup$ @Andrew Yes, agreed. I was thinking about the need to process the captured junk, and I think there is no need to spend material on it. Like to spend solar energy to vaporize material, whatever it is, and accelerate that vapor. Similar to the second variant in the selected answer. $\endgroup$ – Volker Siegel Apr 16 '14 at 10:06
  • $\begingroup$ Doing Hohmann transfers between those objects would be exceedingly expensive too, not to mention hard to prioritize and calculate. $\endgroup$ – Magic Octopus Urn Sep 23 '18 at 14:28
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Contrary to what seems to be a popular belief in this thread, I'm going to say yes, you could use space junk as your reaction mass. Technically, it would of course be rather challenging, but assuming you could gain more thrust from, oh don't know, maybe superheating metal into plasma and ejecting it by your ion propulsion system, than the momentum you would lose by capturing this mass, you'd be eventually on your way faster than you started with.

You assert correctly in your question that reaction mass is expensive to get to orbit, and since there is rather large mass of it there without any function whatsoever, it is natural to ask if it could be reused to any advantage. Indeed, we have many similar questions on our site, and some rather impressive answers for them, too. Now, thinking of how we could transfer all this useless mass into something useful like reaction mass to propel your spacecraft, here are a few options:

  • Use it as is or break into smaller pieces, and either accelerate metallic pieces you gathered with the help of a railgun, hook onto it with tether to achieve momentum transfer, or repel from the whole piece of the space junk magnetically with the use of strong electrically powered magnetic field generator.
  • Superheat it with the use of a solar powered furnace and use superheated metallic gases as your reaction mass at your exhaust. Alternatively, you could ionise superheated gases and use them as your reaction mass for your ion thrusters.
  • Reuse remains of propellants in defunct and abandoned upper stages directly and replenishing your fuel and oxidizer tank levels. This is of course assuming same propellant components can be salvaged from space debris that your thrusters are built to use.
  • Launch lighter from the start, and count on collecting some of these space debris to use as your radiation shield, harden your outer shell or otherwise find use for this mass you didn't have to bother launching into orbit and saved a great deal on your payload mass.

Not a complete list at any length, and there are countless other ways provided you have technology and ways to generate required energy, limited by our imagination and technical capabilities to actually exploit this space junk and find some use for it. None of these techniques mentioned would be easy, and you would likely want to identify and track specific pieces of space debris you'd later target to reuse, but short of having to spend more of your inertia to capture this mass than you can later produce trust from it, and of course not unwittingly deorbiting in the process, yes, you could get higher with space junk. And I don't mean this in psychotropic sense.

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Short answer: No.

You could use some of the mass in LEO, except that most of the space-junk is metal. We can't burn that easily to produce any thrust. Some sort of magnetic accelerator might be productive, but that's WAAAYYY in the realm of science-fiction, not to mention hard to use once you get past low-earth orbit.

Secondly, while the 19,000 number seems high, it's not like there's a huge cloud of stuff hanging in orbit - it's REALLY diffuse and hard to find, let alone capture and use. Keep in mind, the stuff in orbit is generally going at orbital speeds - in the ballpark of 5-10 km/second. You'd end-up chasing-down a defunct satellite or something and it just wouldn't work well.

Now, if there was some space-junk that happened to be a full tank of rocket fuel, then it might be worth the effort. I don't think there's too many of those at the moment.

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    $\begingroup$ "Now, if there was some space-junk that happened to be a full tank of rocket fuel, then it might be worth the effort. I don't think there's too many of those at the moment." -- Worth noting that even when this does happen, they don't tend to stay in-tact for very long. $\endgroup$ – user29 Oct 4 '13 at 18:52
  • $\begingroup$ @Chris: Why do they not stay intact long? Is the fuel corrosive? $\endgroup$ – Everyone Oct 4 '13 at 19:07
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    $\begingroup$ @Everyone In general, upper stages are not meant to last very long, so a stranded upper stage full of propellant will eventually explode. As to what, exactly, happens in a physical sense, I'm not completely sure... $\endgroup$ – user29 Oct 4 '13 at 19:16
  • $\begingroup$ Stupid question: Is burning really necessary though? Isn't a thrust essentially just exhausted_mass × exhaust_velocity? Is there no other way to accelerate the debris to high enough velocity other than via burning? For example, with some sort of railgun mechanism? (let's ignore for the moment of the feasibility of collecting enough debris, remolding them into shape, and safety of slinging projectiles towards the earth) $\endgroup$ – Lie Ryan Oct 5 '13 at 7:45
  • $\begingroup$ @LieRyan - Like I said in my answer, you could use magnetic acceleration (i.e. railguns) - but that's quite heavy, power-consuming, and not really useful once you're past low-earth-orbit. E.g. if we wanted to go to Mars, there's not a huge cloud of space-junk to 'boost' with along the way. Fundamentally, yes, your idea is correct, it's just that something we can 'burn' incrementally when we need to is WAY more useful that a one-shot kinda thing. $\endgroup$ – john3103 Oct 5 '13 at 12:31
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If we are ever able to scale up the effect of tractor beams beyond the microscopic level, using a tractor beam on a massive object--in theory--should alter your trajectory.

Tractor beam research is currently in its infancy, but has been effective on the microscopic level.

Sources:

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  • $\begingroup$ The interesting thing about this solution, if it is ever viable, is that it relies more on a "pull" than the "push" of conventional propellant. $\endgroup$ – called2voyage Oct 4 '13 at 18:33
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JSPOC is currently tracking around 22,000 objects, at least, unclassified objects. That number is fairly low actually, compared to the vastness of space. As of writing this post, Flight Radar says there are over 5000 planes in the air, and it's quite early on an East Coast Saturday morning. Also adding in the fact that most planes are larger than satellites, and that satellites are uniformly spread across the globe, while planes aren't, and you've got somewhat of a picture as to how rare space junk is in space.

That being said, how likely is it that you will have a close encounter with space junk? Not very likely. From my experience, a single satellite will pass within a few hundred meters of a trackable piece of junk only once maybe a few times a year. Then keeping in mind that you actually have to be much closer in velocity to take advantage, and, well, you've got a lot of problems. You might be able to latch on to a larger piece of space junk and use it for some purpose, but the material wouldn't be ideal, and the orbital rendezvous problem is difficult still, although it is manageable.

You probably could de-orbit a spacecraft by sticking out some large wings meant to withstand the impact of small space junk, which would slow you down gradually. But the same effect will be had by air resistance.

Bottom line is, you're more likely to find use out of fixing old satellites, rather than using them for fuel. Use them for spare parts, putting in new batteries, fuel, etc. But you're probably not going to get anything significant out of them in terms of propulsion.

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  • $\begingroup$ Keep in mind that the 22,000 number is limited by the size of objects JSpOC can reliably track. Also, it's not true to say "satellites are uniformly spread across the globe", as there are clear peaks in certain orbit regimes. $\endgroup$ – user29 Oct 5 '13 at 15:35
  • $\begingroup$ @Chris: The first point I think is still valid because small debris isn't going to have a large potential for propulsion. Furthermore, it is true that they aren't spread across the globe, but satellites will be more uniformly spread than, say, airplanes. $\endgroup$ – PearsonArtPhoto Oct 5 '13 at 15:54

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