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Assuming a planet of similar mass and atmosphere as earth, how much and how often do I need to add orbital debris to prevent space travel?

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    $\begingroup$ There needs to be a little context here. What kind of civilization is doing the dumping? A super-advanced one keeping a new one under it's thumb, a rival planet with similar tech, or inhabitants of the planet itself trying to prevent escape? Is the goal to prevent any escape, or simply thwart attempts to establish space infrastructure? How advanced is the oppressed civilization? $\endgroup$
    – DWKraus
    Jul 6 at 22:13
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    $\begingroup$ Does the oppressed civilization know what the oppressor is doing? Are they actively opposing you dumping/trying to reduce debris? $\endgroup$
    – DWKraus
    Jul 6 at 22:16
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    $\begingroup$ What kind of travel do you have in mind - launching satellites? Going to the moon or other planets? Do you just have to clog up certain orbits or block all launches everywhere? $\endgroup$
    – Cadence
    Jul 6 at 22:31
  • $\begingroup$ Kessler syndrome at it's worst would make space launches unsafe but not prevent space travel if people are willing to take risks. $\endgroup$
    – Peteris
    Jul 7 at 13:22
  • $\begingroup$ Does this answer your question? How long before we're stuck on Earth due to Space Debris? (Kessler syndrome) $\endgroup$
    – Mazura
    Jul 8 at 0:52

4 Answers 4

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No

It may be possible to use Kessler syndrome to stop them from placing stable orbiting satellites (see: Can I render satellite deployment impossible, or at least impractical, by exploiting the Kessler syndrome?). I have an answer there calculating that a deployment of around 12,000 is the minimum for LEO only.

To stop people being able to leave? Nope. The escape vector to leave a planet you need a very slim window to directly go through which you can't stop outside of a Dyson-sphere like construct, which isn't really a satellite at that point. Sure, maintaining a stable orbit isn't really viable and without stable orbits, space flight isn't that useful, but you can't stop space travel just by caking a planet with a minor debris field.

Not to mention that space is huge, there's not really an effective way of stopping a satellite with has decided to orbit past GEO. Sure, it's not a great place to orbit, but it can orbit there. And, remember, once you start oversaturating the debris field, it will hit itself and start knocking itself from the sky, so there's a limit to how much you can saturate that,

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    $\begingroup$ You can still kill everyone inside the thing that tries to leave, by punching enough holes in the life support system. $\endgroup$
    – user253751
    Jul 7 at 11:51
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    $\begingroup$ @user253751 No, the point is that Kessler Syndrome makes collisions inevitable only when the spacecraft and the debris field occupy the the same orbit. If the spacecraft is just "passing through" to a higher orbit or beyond, the chance of collision is low even with lots of debris. $\endgroup$ Jul 7 at 13:46
  • $\begingroup$ How much is "lots"? Surely there's some amount of debris that would make passing through LEO without sustaining damage unlikely. What if I capture a few large asteroids, maneuver them into orbit, then shatter them into a bazillion pieces with nukes? $\endgroup$
    – Ajedi32
    Jul 7 at 17:37
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    $\begingroup$ @Ajedi32 And as for how much is "lots", consider that LEO is really close to the surface, so it covers a surface that is, roughly, the surface of the Earth. Now, consider what would be needed to prevent a rocket from passing through a net that covers THE WHOLE PLANET, and that is more or less what we are talking about. $\endgroup$ Jul 7 at 19:00
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    $\begingroup$ @Ajedi32 You could take a very large asteroid like Vesta and build a ~100m-thick "shell" around the earth in LEO - the problem is you'd need to very carefully stagger orbital rings at different inclinations and altitudes to have any hope of stable orbits (which itself leaves gaps), otherwise collisions will quickly knock much of the material out of orbit. That's why I like the question phrasing of "how often" does debris need to be replenished - you might be able to temporarily block travel with a truly huge amount of haphazardly scattered debris, but it won't last. $\endgroup$ Jul 8 at 19:10
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This is my second most frequently used quote on this Stack:

Space is big.

Really big. You just won't believe how vastly, hugely, mind-boggling big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space. Listen; when you're thinking big, think bigger than the biggest thing ever and then some. Much bigger than that in fact, really amazingly immense, a totally stunning size, real 'wow, that's big', time. It's just so big that by comparison, bigness itself looks really titchy. Gigantic multiplied by colossal multiplied by staggeringly huge is the sort of concept we're trying to get across here.

(Douglas Adams, The Hitchhiker's Guide to the Galaxy)

All the crapola that humanity has put into orbit in the last 70 years hasn't made a dent in our ability to launch ships. But what really stings is that you can't just dump trash — you'd need to actually power your orbital constipation.

The natural spin of things creates rings

If you put enough stuff into orbit that it would stop launches, that stuff would begin bouncing off each other like a drunken llama at a rave. You see, all those stable orbits in places other than the equator exist in no small part because nothing's getting in their way. As soon as you start introducing chaos, the result is for things to settle down and get swept along by Earth's gravitational tidal forces.

Into rings.

Oh, it may take a bazillion years, but it would happen. The only way you can avoid that is to make your blockage intentional with powered satellites that remain in their assigned courses to ensure no launch can happen.

And if you're going to do that, you might as well save yourself some dough and simply arm some of the satellites so they can shoot down the launches.

But I love the idea!

And why do I love it? Because everybody on the planet would be constantly dodging bits and pieces falling out of the sky. It would create an entirely new cottage insurance industry.

It would also cause a boom in investments into geothermal energy, because enough stuff in the sky to stop all launches would (IMO) seriously block out the sun. That means growing mushrooms in caves located under the Yellowstone Caldera to feed the people.

In the meantime your civilization devoted to blocking the planet's inhabitants from leaving has made me rich because I sold all their stock short due to the economic depression caused by the cost of moving so much junk into another planet's orbit! I mean, think about it. How much junk would you need to drop onto the surface to keep people from driving their cars? Now multiply that by a bazillion because the surface area in low orbit is so much larger than the surface area on, well, the surface.

Big. Really, really, really big.

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    $\begingroup$ "because the surface area in low orbit is so much larger than the surface area on, well, the surface" -- isn't it a relatively small difference? About 40% of the surface of the Earth is land, and 60% is water. The total surface of the Earth is about 5.1*10^8 km^2. But the surface area of a sphere with ~400 km radius more (LEO) is only 5.76*10^8 km^2. That's only about 12% more. So the surface area of all of LEO is not even three times that of all the land area on Earth. Not sure that qualifies as "a bazillion" ;) $\endgroup$ Jul 7 at 9:51
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    $\begingroup$ I don't think it would block out the sun that much. Loads of high-velocity bullet-sized objects would be enough; you don't need very many bullets to take down a spaceship, especially a pressurised one with a life-support system. A slight tint to the sky, perhaps, but humans probably wouldn't even notice unless they were looking. (And there's no way you're getting enough material into the sky to affect the sun's W/m² by more than half.) $\endgroup$
    – wizzwizz4
    Jul 7 at 10:05
  • $\begingroup$ +1 for this, and if I could I'd give you an extra for "orbital constipation". :D $\endgroup$ Jul 7 at 14:30
  • $\begingroup$ This question and this answer reminds me of the book Skyward by Brandon Sanderson. $\endgroup$
    – mgarey
    Jul 7 at 14:43
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    $\begingroup$ So you're saying the answer to the OP's question is "once every bazillion years"? The question was "how often", not "how do I make it permanent?" $\endgroup$
    – Ajedi32
    Jul 7 at 17:32
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Short answer it won't work

Reason for that is that at 200km orbits things deorbit quite fast, but it still a viable orbit just more expensive one, from which one can sync with stuff flying around and leave the orbit.

  • different attack and counter attack strategies are possible, but it pretty much all the same as a result debris is not that effective.

It means you have dump a lot quite often and this may be a more of an attack on the surface of the planet as effects go - so in a sense it easier to kill all the life on a planet than block space travel by debris.

Active means like sleeping missiles are much more effective

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Based on other answers saying it's basically impossible to do what you want to do, here's my suggested evil space overlord alternative:

Assumptions: the evil space overlord does not want the civilization to know this is happening. He just wants them to think that space is really dangerous and full of small rocks. The evil overlord also has some kind of scanner/radar-type technology that the civilization is incapable of detecting. (I feel like these are reasonable assumptions otherwise why do any of this. Just shoot them all down blatantly.)

  1. Find out how small of an object the alien civilization can track. NASA currently tracks objects "as small as 2 inches" in low earth orbit. Let's assume the civilization is at the same level here:
  2. Litter a good deal of 1 inch debris around.
  3. Throw in a lot of space guns that fire 1 inch pellets at tremendous velocity.

The idea will be that the civilization will encounter the 1 inch debris and while, as per other answers, it's not able to be dense enough to really create a reliable hazard, it's dense enough that they will notice it.

The guns will then fire on some rule basis:

  • Any ship reaching velocity to escape the planet's gravity well gets shot. "Oh wow bad luck we managed to hit one of those little rocks and it went straight through the engine."
  • Any ship in orbit gets a random chance to get shot, per day. It's a low chance but nothing stays in orbit for years without taking multiple hits.

We have created a vague hazard that's impossible to accurately track and then weighted the die by setting up some guns, which just look like debris, that will fire automatically to keep the threat inflated. It will probably really confound their scientists but short of discovering one of the guns it should keep them contained and befuddled. Might even be most governments just opt out of the space program because it's "too risky" and public sentiment turns against it.

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  • $\begingroup$ Gun = energy. What is supplying the energy for firing the gun? How are the sensors and attitude control systems, used for aiming, powered? What's the method for firing the weapon? Because regardless if they can get into space or not, at some point their observational technology will reach the point where they know something is going on. Also, never underestimate the power of statistical analysis. $\endgroup$ Jul 7 at 17:04
  • $\begingroup$ I was actually thinking after I wrote that that the evil overlord could place the guns virtually anywhere. Flight paths would be entirely predictable so if it takes 8 hours for the projectile to reach the target that's perfectly fine. No reason for the guns to be particularly nearby. (I'm also thinking the civilization is more like 1950s while the overlord is more like "type II civilization" minimum.) Sputnik launched! Oh no, it gets hit by a rock. Second launch. Okay for a few days. Hit by a rock. How many hits before they just go "oh dang space is just too dangerous". $\endgroup$
    – JamieB
    Jul 7 at 18:33
  • $\begingroup$ (I also imagine there is an easy plot device here wherein the civilization will, eventually, realize what is going on. Maybe it takes them hundreds of years because investment in space is vastly reduced. They will probably be very angry about all this when they find out.) $\endgroup$
    – JamieB
    Jul 7 at 18:36
  • $\begingroup$ The evil overlord still has the issue of trying to make the weapons platforms and their power sources undetectable (see: There Ain't No Stealth in Space). Also, there will be an obvious question astronomers will raise: if there's so much debris it has a 100% hit rate, the amount of debris required would be easily calculated. If it doesn't match what they're seeing (even dust creates visible reflections, let alone 1 inch particles), the stats will raise eyebrows. If there's a 99% chance a vehicle should be hit, after 10 launches there's a 35% chance something should have survived. $\endgroup$ Jul 7 at 22:38
  • $\begingroup$ @KeithMorrison - My suspicion: they would never reach that point. The space race on Earth was driven by early Soviet success. Had the first launches met some mysterious doom in space, there would be no political one-upmanship and no "space race". In fact, the naysayers calling it all "a waste of money" would probably win the floor. The scientific inquiry would fall victim to politics as the funding vanishes. Of course, if the debris showed up, say, today, it would raise all kinds of suspicion, with "probably an attack" high on the list. OP never did elaborate. Still, I liked the question! $\endgroup$
    – JamieB
    Jul 11 at 18:14

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