For those unaware, the term 'Kessler Syndrome' refers to a scenario in which space-borne debris reaches a 'critical mass', destroying spaceborne satellites which in turn produce more debris which in turn produces more debris, until eventually Earth is enveloped by a debris field that renders any space-borne operations difficult to impossible.

Let’s say that tomorrow, NASA scientists calculate that nearly every installation in LEO (ex. communications and military satellites, the ISS) will be rendered inoperable by an expanding debris field within two weeks. Within this timeframe, how should they best prepare? How would they ‘cure’ the debris field, if a ‘cure’ is even possible? And finally, will such a ‘cure’ even be possible in the inevitable panic following the loss of the world’s communications technology?

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – L.Dutch
    Commented Aug 27, 2018 at 5:42
  • $\begingroup$ Preventing the Kessler Syndrome is not the objective, but the criteria, of the solution to the real problem, and maybe the OP might want to consider this. The real problem being addressed is the over-crowding of the orbits. There are just so many places to put a satellite, and those places are being rapidly used up. Keeping a non-functioning satellite in such a spot will not be tolerated by entities that need the spot. So they need a way to remove non-functioning and competitors' satellites without leaving a debris field behind. The debris field will take out their own new satellite. $\endgroup$ Commented Aug 28, 2018 at 16:19
  • $\begingroup$ So preventing the Kessler Syndrome is a criteria of a good solution for freeing up orbital spots from satellites you do not want to be there. Removing 'space junk' is a red herring, meant to make designing machines to clear out the competition palatable to the public. $\endgroup$ Commented Aug 28, 2018 at 16:19
  • $\begingroup$ Just read this answer about projects to clean up orbiting debris. You probably have already found an answer to your question, but if not, it might be helpful to read about real life ideas that are being used to solve the problem. $\endgroup$
    – John Locke
    Commented Mar 2, 2019 at 1:50

3 Answers 3


If you were to send up a large rocket with a bucket-like attachment on top, it could orbit slightly slower than any space junk and catch it. Then it could fire its rockets and drop below orbit velocity so all of the trash it had collected would burn up in the atmosphere. If you add a power source, you could have a giant magnet instead.

This is not a full solution and would be very expensive, but a few of these rockets could help protect existing satellites from being destroyed by clearing the debris field approaching them.

Another option is a spaceship that can run on space junk. That would have the bonus of requiring less fuel to bring to space because it could get the fuel it needed from the space junk.

You could have nanobots in space to eat up all of that junk if you wanted.

If you want to fight chain reaction with chain reaction, you can use the space junk you collect as electricity to power a magnet that attracts more space junk which provides more power and so on.

  • 1
    $\begingroup$ This is not a hard science answer. $\endgroup$
    – kingledion
    Commented Aug 26, 2018 at 12:21
  • $\begingroup$ If you look at the article I linked to, this is entirely plausible. The nanobots are a bit more far-fetched, but still within the scope of possibility for a distant-/near-future society. I think the OP may have gotten confused, because they are using the hard science and the science fiction tags. Maybe a large rocket with a bucket or magnet is inefficient, but it definitely isn't impossible. $\endgroup$
    – John Locke
    Commented Aug 26, 2018 at 12:27
  • $\begingroup$ First off, this setting from the OP is 'tomorrow:' no nanobots. Second, hard science must be backed by equations, citations etcetera. You must demonstrate that a magnet can be used on space debris (it can't most of it is not ferrous), you have to say how much power you need in your power source, how big is the bucket, how long the rockets burn, etc. Hard-science is facts and numbers, not wishy washy ideas. $\endgroup$
    – kingledion
    Commented Aug 26, 2018 at 12:32
  • $\begingroup$ The description of the science-based tag says "For questions that require answers based on hard science, not magic or pseudo-science, but do not require scientific citations." $\endgroup$
    – John Locke
    Commented Aug 26, 2018 at 12:37
  • $\begingroup$ But there are two conflicting tags, shouldn't we ask the OP which they want to use? $\endgroup$
    – John Locke
    Commented Aug 26, 2018 at 12:43

Phalanx autocannons in space.

phalanx autocannon http://rpdefense.over-blog.com/tag/ciws/


The basis of the system is the 20 mm M61 Vulcan Gatling gun autocannon, used since 1959 by the United States military on various tactical aircraft, linked to a Ku-band radar system for acquiring and tracking targets. This proven system was combined with a purpose-made mounting, capable of fast elevation and traverse speeds, to track incoming targets. An entirely self-contained unit, the mounting houses the gun, an automated fire-control system and all other major components, enabling it to automatically search for, detect, track, engage, and confirm kills using its computer-controlled radar system. Due to this self-contained nature, Phalanx is ideal for support ships, which lack integrated targeting systems and generally have limited sensors.

Phalanx autocannons are mature technology. They track incoming projectiles with radar and then destroy them with a barrage of bullets. You would need to tweak the aiming algorithm for space conditions but it is easier in space - no air resistance and no wind. Radar works better in space than on land. Incoming fragments will have huge radar profiles and will be obvious many km out. These fragments will be fast, but not asteroid fast because if they were they would leave orbit. That is well within the ability of Phalanx to see and destroy.

In your scenario you have some notice. These Phalanx systems are ready to go. Tweak them for space and send them up in satellites or old shuttles or whatever you have got. When the phalanx bot detects incoming that matches the profile of space junk, it shoots it. If the thing is hit, it slows, and if it slows, it drops out of orbit. I could imagine that with the sort of lead time the bot will have in space, it might take more of a sniper approach than the "wall of lead" - 1 shot at a time, assess for a hit, then take another shot if target not hit.

With more time you could outfit the Phalanx with lasers, which would sidestep issues of ammo and also the possibility that spent bullets themselves might be a threat. Vaporizing an incoming target will cause it to become an expanding cloud, with less kinetic punch if it hits.

If calculations show that spent bullets might actually be problematic, make them out of ice or plastic or frozen mercury - things which will not persist long.

  • 4
    $\begingroup$ Oh, great. Instead of having one big piece of debris, you have hundreds of smaller pieces AND thousands of bullets added to the fray. $\endgroup$ Commented Aug 26, 2018 at 16:04
  • $\begingroup$ @JustinThyme If you hit an orbiting piece coming towards you, you slow it down. If it slows it drops into lower orbit. If it drops and hits atmosphere it slows further and falls to earth. $\endgroup$
    – Willk
    Commented Aug 26, 2018 at 16:09
  • $\begingroup$ But you also have the hundreds of bullet that you shot at it now floating around. $\endgroup$ Commented Aug 26, 2018 at 17:08
  • $\begingroup$ @JustinThyme - it was in anticipation of your arrival that I put in that last sentence when I wrote this answer. $\endgroup$
    – Willk
    Commented Aug 26, 2018 at 17:32
  • $\begingroup$ Perhaps you are not aware that one of the main sources of 'space junk' is the coolant from decommissioned nuclear reactors? Ice, plastic. and frozen mercury are perhaps even more problematic because they are all a danger to navigation but less detectable than metal. If a paint flec can produce an impact crater on the ISS observation dome, so too can a piece of plastic. $\endgroup$ Commented Aug 26, 2018 at 18:14

The Kessler Syndrome dispels belief so drastically that, well, the answer might just as well too.

Launch huge expandy-foamy-sticky-slime balls into earth orbit. Once in orbit, the balls would expand into gigantic foam sticky balls (made mostly of empty bubbles), maybe a few km.s in diameter. They would sweep their orbits, with all of the space debris sticking to them and becoming embedded by fibrous sticky strands that make up the foam. Eventually, the balls would accumulate so much junk inside of them, that they would become really, really heavy. They would drop out of orbit, and descend to earth. They would, of course, then burn up, taking their accumulated load of space junk with them into a fiery oblivion.


The issues that the mythology behind the Kessler Syndrome does not address is that these collisions are fission, not fusion. That is, the particles get increasingly smaller, not bigger. It is a self-limiting phenomena. Eventuality, the orbit is filled with very tiny, but very numerous, survivable particles. The second issue is that, every collision results in either a loss of velocity, or an increase in velocity. Overall, the net energy of the particles decreases. The orbits become increasingly unstable, and are erratic. The particles will have their descent into the atmosphere quickened. Third, the calculations of the energy of impact all assume that the particles end up with zero velocity, whatever that means. Particles that go right through, are defected, or just glance off do not produce anywhere near the 'released energies' quoted. Fourth, the premise ignores that fact that satellites are now 'hardened' against expected impacts. They are able to absorb the impact energies. And lastly, the problem is minuscule compared to how much space junk hits earth.

60 Tons Of Cosmic Dust Fall To Earth Every Day

Until now, scientists didn't know how much of this cosmic dust was gathering on Earth (though they know rather a lot about how much is up in space). Researchers guessed that anywhere between 0.4 and 110 tons of the star stuff entered our atmosphere every day--that's a pretty wide range. But a recent paper took a closer look at the levels of sodium and iron in the atmosphere using Doppler Lidar, an instrument that can measure changes in the composition of the atmosphere. Because the amount of sodium in the atmosphere is proportional to the amount of cosmic dust in the atmosphere, the researchers figured out that the actual amount of dust falling to the earth is along the lines of 60 tons per day.

from https://www.popsci.com/60-tons-cosmic-dust-fall-earth-every-day

The problem is analogous to the 'Y2K' problem that was hyped at the turn of the century. It had some factual merit, but please, airplanes falling out of the sky on Jan.1,2000? Over-hyped by far.


What is missing from the question, especially for it to be science-based, or even hard science, are any criteria. So, here are a few potential criteria. The solution, of course, could not make the problem worse, by producing even more stuff. Second, the solution would have to be capable of handling or dissipating the potential and kinetic energy of any 'captured' particle, so that no further destruction or damage is done. Third, by far the greatest problem is junk that is smaller than one cm. Any solution that does not handle this should be a non-starter. And fourthly, the solution should be compliant with existing knowledge and information about the problem.

The mean number of fragmentations per year accounts to 4.9 (SD = 2.8) with no sign of regression or fundamental change. However, there was a slight decrease in fragmentations for three years after the introduction of the Inter-Agency Space Debris Coordination Committee (IADC) Space Debris Mitigation Guidelines in 2010. An examination of the fragmented mass over the years is shown in Figure 2b. It is shown that most of the objects that experienced a breakup had a mass less than 500 kg. Looking at the other extreme of the histogram, there are two events with a fragmentation mass of 26,000 kg and 30,000 kg. These events happened in the late 1960s during the Apollo program, but, due to their low event altitude of below 300 kg, almost all fragments re-entered into Earth’s atmosphere and consequently do not contribute to the space debris environment in the long term.

from http://www.mdpi.com/2226-4310/5/2/37/pdf

So a huge ball of space foam would be ideal for trapping these small particles. The volume would be great enough to cause slow deceleration, any small particles that were released would also be trapped, the ball is big enough to be visible, and thus not a navigation hazard, and it is self-healing. Larger particles would just blow through it, and the gap would close.

However, such a material and such a method does not currently exist. The foam could never 'solidify', as it would then be subject to fracturing and thus contributing to the problem. The foam would also have to be sticky, and it would also have to consist of long polymers, such that they would bind and hold together, but also be able to slide along each other, so as to absorb the collision energy. Thus, the answer is just as conjectural as the question.

  • $\begingroup$ nasa.gov/centers/wstf/site_tour/… NASA disagrees with your objections to the theory. $\endgroup$
    – case
    Commented Aug 26, 2018 at 0:16
  • $\begingroup$ From your own reference 'Once collisional cascading begins, the risk to satellites and spacecraft increases until the orbit is no longer usable.' It is the orbit that becomes saturated, not the orbit of every satellite up there. The Kessler Syndrom has been exaggerated so badly that it is now mythology.and its supposed 'application' in sci-fi defies belief. The OP specifically states 'Earth is enveloped by a debris field that renders any space-borne operations difficult to impossible.' $\endgroup$ Commented Aug 26, 2018 at 2:47
  • $\begingroup$ @JustinThyme You cannot ignore the fact that there are satellites on different orbital inclinations but similar altitudes, with speed differences of kilometers per second. In fact, that would be how the Kessler cascading would start in the first place as the objects in orbits of similar inclination and eccentricity often don't have enough kinetic energy to cause significant amount of debris. $\endgroup$ Commented Aug 27, 2018 at 5:07
  • $\begingroup$ @0something0 If you can come up with any credible source that empirically demonstrates that the Kessler Syndrome THEORY is in fact supported by reality, please post it. In point of fact, it is not even a theory, more like a hypothesis. $\endgroup$ Commented Aug 27, 2018 at 13:29

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