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Let's say an evil dictator decide to deliver a payload to a retrograde "GEO" orbit.

I suspect the first inevitable collision would quickly produce a Kessler syndrome.

Is there anything that would allow us to detect it in time, and what could we realistically do about it?

NB: Yes, technically a GEO orbit cannot be retrograde, but you get the idea.

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  • $\begingroup$ A retrograde bag of hammers (or spanners) would indeed be an evil, but not stupid payload. $\endgroup$ – uhoh Apr 17 '17 at 2:31
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    $\begingroup$ "Retrograde circular equatorial orbit at geostationary orbit altitude," or more conveniently RCEO-GA. $\endgroup$ – Russell Borogove Apr 17 '17 at 3:59
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    $\begingroup$ Such an action would be tantamount to declaring war on the whole world. The evil dictator wouldn't have long to enjoy his victory. That's what prevents this sort of plan. $\endgroup$ – Hobbes Apr 17 '17 at 10:02
  • $\begingroup$ Kessler syndrome is accidental, I can arrange a more effective initial distribution. As an evil dictator, I'd deliver thousands of ball bearings in similiar but not exactly RCEO-GA orbits. I don't need to hit anything especially hard, since the hits will be fast. But I want to hit as many satellites as possible. $\endgroup$ – MSalters Apr 19 '17 at 14:42
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Its not that obvious that placing an object in a retrograde orbit would quickly produce a Kessler syndrome. It may happen in the long run, but could take a while:

  • I don't think the first collision is so inevitable. At GEO the chance of a collision is much lower than LEO and the debris threat in GEO presently comes less from large tracked objects as these can be avoided. The aggressor object would have to be actively steered for the first collision.
  • a collision would result in a shower of retrograde fragments but these fragments are themselves now uncontrolled and unable to steer to the next victims
  • there have already been a number of posigrade GEO breakups (perhaps a dozen though I'm sorry I don't have a reference to hand). These have been detected by the existance of clouds of debris.
  • any pre-existing debris clouds already pose a reduced risk compared to a retrograde threat, but only in the sense that risk = probability * magnitude. Pre-existing posigrade debris clouds would have the same probability each but lower collision effect magnitude, as their relative velocity is much lower.

This leads us to the conclusion that the event rate (the probability side) should already be apparent if the additional events (say an additional 10%) of a retrograde mission were to be a major problem.

I think the same measures that are being advocated for LEO would be appropriate, though adjusted for the GEO conditions:

  • consideration of sensors specific to the dangers
  • removal of decommissioned objects to disposal orbits
  • sharing of orbit data

If anyone happens to be at the European Space Debris Conference this week, this might be a good time to chip in with thoughts about the event rates of small impacts to date in GEO.

EDIT in response to comments:

GEO has a lower probability than LEO because of the lower spatial density of objects. This is relevant to the line of thought here because I am suggesting a hypothesis as follows (apologies for the following rather slack formal logic):

  • premise A - we add one retrograde break-up and expect to see a kessler syndrome

  • premise B - a retrograde break-up would mean that each secondary particle could have a much greater impact magnitude but no different an event probability compared to a posigrade particle

  • premise C - there have already clouds of debris in GEO resulting from posigrade break-ups

  • premise D - each cloud has the same distribution of fragments and velocities (this isn't that important it just simplifies things)

  • Inference E: taken from premises A, B, C, D - the existing break-up clouds should already have produced lots of impacts, though with magnitude less than a retrograde one

  • premise F (granted, this is like proving black swans don't exist) - we would have become aware of E, if it had happened from civil public satellite owners

  • Inference G: A and F are inconsistant with one another and suggests that A is unlikely to be true.

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  • $\begingroup$ Could you develop on why collision are much less likely in GEO ? To me; it seems that each GEO satellite, while moving in concert and thus not on collision course towards each others like in LEO; the fact that they are all more or less aligned makes it easy for retrograde objects to destroy them all. $\endgroup$ – Antzi Apr 18 '17 at 9:12
  • $\begingroup$ @Antzi: Your retrograde object won't be in the same orbit after the first collision. It will be a cloud of debris in various retrograde orbits, many of them intersecting the atmosphere. $\endgroup$ – MSalters Apr 19 '17 at 14:38
  • $\begingroup$ @Antzi I think I see your line of query. I've added an explanation, I can see its not water-tight but hopefully it clarifies my thoughts. $\endgroup$ – Puffin Apr 19 '17 at 20:48
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Per this question, it takes about 6 hours from launch to reach that orbit, and it's hard to imagine that another space agency could detect and realize the threat and program an early interception trajectory in time to take it out even if they happened to have a launcher on the pad capable of doing so.

If the offender was simply injected into equatorial retrograde orbit at geosync altitude, it might not hit anything immediately, but it would now be harder to take it out safely without turning it into Kesslerish debris, effectively giving it the initial collision for free. Carefully ablating one side of it with a great big laser could push it out of position, perhaps.

If the offender was a guided, self-propelled spacecraft, I don't think there's a chance of stopping it. Ground-based guidance could put it on a close enough course that onboard radar could finish the job.

About the only way I see a chance is if the launch trajectory is actively controlled from the ground, with insufficient onboard location capability for the spacecraft to get into position on its own. Then, conceivably, once the retrograde transfer orbit was understood by other nations, a massive military strike against the launching agency's communications uplink could take out the threat, but no half-competent evil genius would neglect that consideration.

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  • $\begingroup$ I wonder if you could add an analysis of — upon detection — immediately instructing one or several GEO spacecraft to thrust out of GEO to a lower orbit, and trying to make something happen before the highly vulnerable GEO altitude is reached? I don't know what the something could be, but I suppose it would be along the lines of a somewhat messy collision to avoid a potential Kessler-esque event at GEO? It would have to be something with plenty of old fashioned chemical thrust, and not this new, fancy, wimpy electric stuff, and ideally some fancy cameras and/or radar... $\endgroup$ – uhoh Apr 17 '17 at 4:42
  • $\begingroup$ ...which of course there is nothing of the sort up there anywhere. $\endgroup$ – uhoh Apr 17 '17 at 4:48
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    $\begingroup$ Besides having the high thrust, sufficient delta v, and intercept guidance capability it would have to start off in a particular range of longitudes. I'm skeptical that camera guidance would be sufficient (as opposed to active radar) -- although I guess I can just barely conceive of a comsat with software-defined radio turning its transmitter and receiver to the same frequency for use as a tracking radar... $\endgroup$ – Russell Borogove Apr 17 '17 at 15:27
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    $\begingroup$ (There might be a good nerd thriller novel in here somewhere.) $\endgroup$ – Russell Borogove Apr 17 '17 at 15:28
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If such a weapon is launched, it makes no sense to let it break up naturally. A most effective payload would be 50-100.000 small steel projectiles, each 50-100g (0.1-0.2 pound), painted black. It would quickly expand into a cloud 200-300m wide, invisible optically and on radar, with projectiles spaced about 1m apart, guaranteeing destruction of almost any satellite that encounters it at a relative speed of 6Km/s. Each projectile would deliver the equivalent energy of 0.5kg of TNT. The cloud will circle GEO every 12h knocking everything offline in an ever expanding steel net.

The defense would be to move the satellite to a safe orbit for a few days until the natural precession of GEO would move the cloud away. But given the few hours available to react, it seems implausible too many satellites would be saved.

Kesslerization is not really desirable from a weapon effectiveness point of view since the debris would have significantly different speeds quickly falling away from GEO.

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