This is a linkpost for https://www.forethought.org/research/space-debris-and-launch-denial
Thank you for looking into this in depth! My apologies, I have only skimmed the report so far, but I have a few questions:
(1) Suppose someone used 100 starship launches to put optimal debris into orbit. Suppose someone else had capacity for 1000 starship launches. Could they just... Put armor on their spaceships/satellites &/or build them with redundant structures so they can take a hit or two? This would increase the weight of course but maybe that's fine since there's plenty of launch capacity?
(2) My understanding is that if you orbit closer to earth, atmospheric drag becomes a problem. But it is less of a problem for objects with lower surface area to mass ratios, which inherently advantages larger objects. So... Couldn't you just have fewer, bigger, armored satellites that orbit closer to earth where the little debris can't go?
(3) Another strategy of course would be to boost out to a high orbit away from all the debris. It seems you considered this strategy and calculated that with e.g. 40 starships of debris it wouldn't work. What's the difference in difficulty between trying to block boosts to normal orbits like LEO vs trying to block something going into a very high orbit or escaping orbit entirely? Does it take e.g. an OOM less debris to block the former vs. the latter? Five OOMs?
Thanks for the qs!
I guess an overall vibe I should convey a bit more is: before investigating deliberate space debris, it seemed like it could be a very big deal for macrostrategy. Having investigated it, I think it's much less of a big deal (but still probably underrated by the world). I also think there could be much better launch-blocking strategies which don't involve debris.
If one rocket collides with 7 bits of debris on average (and collisions are always catastrophic and Poisson distributed), you need to send about 1,000 launches for >50% chance at least one makes it. But after roughly doubling the amount of debris, so one rocket collides with 15 bits of debris on average, you need more than 2 million launches.
Here's a possible launch-blocking strategy: Orbital lasers and/or kinetic interceptors.
You have a dense grid of laser satellites in orbit. Those on earth trying to get up into space face some disadvantages:
If they stay down on earth and shoot up at your satellites, while your satellites shoot back at them e.g. with lasers and kinetic interceptors, the gravity well gives you an inherent disadvantage. Your stuff has to climb out of the gravity well to hit the satellites whilst their stuff just has to fall down at the right angle. Plus also, the atmosphere and day-night cycle makes your solar panels much less efficient than theirs, so in a war of lasers they might just be able to outproduce you, plus the atmosphere makes the lasers inefficient anyway.
If they try to power up into space to fight you there using rockets, well, a big rocket can be blown up by a small bullet or laser burst as it exits the atmosphere and tries to accelerate to orbital velocity. Very vulnerable. If you try to armor it, you need to armor not just the payload but the rocket itself, which will be like an OOM bigger than the payload, plus the armor might weigh the thing down a lot reducing payload size.
A counterpoint is that you have to spread out your satellites in a grid whereas they can launch their entire fleet all at once in a single location to try to break through the grid. But yeah.
1. In my opinion one of the likeliest motivations for deliberate debris would be as part of an escalation ladder in the early stages of WW3. Whichever player has weaker satellite intelligence / capabilities would have an incentive to trigger a cascade in order to destroy the advantage of their opponent. The point effectively is that space conflict is very strongly offense dominant because of debris cascades, and we know that in general offense dominant dynamics tend to be very unstable.
2. Related to your discussion of totipotence, another dynamic I could imagine in the future is MAD dynamics between a moon colony and earth, where each side has the capacity to create a debris cascade for the other. One concern is that there will not be second strike capability, and so the dynamic could be unusually unstable.
3. One concern is that space colonization is extremely trajectory dependent, so that initial forays into space colonization could have massive impacts on the far future. If so, there may be good reasons to delay space colonization as long as possible, as a "long reflection." A debris cascade would cause a long reflection, by forcing space colonization to pause until new technologies for escape are invented. On the other hand, space colonization is also very important to hedge against catastrophic risk. So the disvalue of debris cascades may be controlled by the relative prioritization of existential risk versus better future dynamics.
On (2), I think I say a bit about this in the piece, but my guess is that it's not much easier to launch debris from the Moon into Earth orbit, than to launch it from Earth into Earth orbit. Although the Moon has the "high ground" in some sense, you need to decelerate the debris to settle into low orbit, which requires some kind of active thrust near periapsis. My sense is that launching debris from Earth to orbit around the Moon is even harder — both because Earth is stuck in a bigger gravity well, and because the Moon is gravitationally lumpy.
(3) is an interesting point. But, as I say, I don't think a debris cascade is very likely to actually trap civilisation on Earth for any meaningful amount of time. Somewhat more likely is if a first-mover used it to make catching up more expensive, after they themselves escape Earth. And more likely still is that it's (as you say) conflict promoting for more prosaic natsec reasons, or the result of a conflict and ∴ evidence civilisation is in a bad state. Either way, it seems good to prevent on trajectory-improving grounds too, in my view.
Nearly 15,000 tons of artificial objects are orbiting Earth. By count, the vast majority of those objects are tiny pieces of debris. This raises some worries about what happens when even more space debris accumulates — worries which get even bigger if we see an industrial explosion and rapid tech progress quite soon.
One question is just how bad things could get as the amount of space debris ‘naturally’ grows. Another question, which hasn’t been discussed nearly as much, is what happens if people deliberately try to create huge amounts of space debris. I investigated both questions.
More debris means more collisions with satellites, launch vehicles, and (crucially) other bits of debris. More collisions generates even more debris, by fragmenting larger objects into smaller ones. If that process blows up, it’s called ‘Kessler syndrome’. It’s a hot topic, especially because launch activity has increased so much recently.
Kessler syndrome isn’t guaranteed to happen, since debris eventually falls back to Earth through drag. But some very crude models of debris suggest that a runaway increase is surprisingly hard to rule out, if we don’t get much better at cleaning it up.
This would be very costly, because it would make it less practical to operate satellites in preferential (the most useful) orbits. But it wouldn’t be the end of the world. First, it would happen over months to years — enough time to adapt. Second, models of debris are already fairly sophisticated, so we’d likely spot an “inflection” point on the horizon before it shocks anybody. Third, we haven’t tried very hard to get effective cleanup and avoidance tech. Scenarios where orbits get really crowded are also probably scenarios where that tech is much improved.
We can also look at how bad the aftermath of Kessler syndrome would be, once we hit peak debris. As I said, it would make it much more expensive to operate satellites, because they’d keep getting destroyed. An even more extreme possibility is that launches themselves could become practically impossible, including launches beyond Earth — maybe passing through the cloud of orbital debris is like running across a street in the rain and hoping to stay dry. That would be a big deal. Fortunately, I don’t think Kessler syndrome would naturally create nearly enough debris to block launches, even with worst-case assumptions.
Space debris and space traffic management are classic public goods and commons problems, so they’re predictably underinvested in, and that’s bad. But I don’t expect ‘natural’ kinds of Kessler syndrome could get so bad that they could dampen humanity’s long-run prospects.
But what about the second question? What if someone wanted to cause there to be more debris in key orbits? If they could somehow generate so much debris that launches through orbit are practically impossible, they could then secure a ‘first-mover advantage’ for themselves: leave Earth first, then seal off the possibility of catching up for many years, effectively grabbing space for themselves in the meantime. That would be big if true.
One strategy to generate more debris is by launching kinetic anti-satellite weapons at active or defunct satellites already in orbit. On collision, they generate huge amounts of debris (spikes in the first graph are caused by single ASAT tests). But a more effective strategy could be to literally lift debris into orbit, perhaps sand or ball bearings, and release it. I think this could get a lot worse than accidental kinds of Kessler syndrome, especially because the size distribution of the debris could be optimised for destruction.
Fortunately, outside of very worst-case assumptions, I don't think this would be enough to make launches through orbit impractical, although I do think it could make preferential orbits totally inhospitable. And a bad actor would need to carry out the plan covertly before they’re stopped, so they’re limited by what they can launch in a short time window.
Moreover, launch vehicles don’t currently have tough shielding, because debris collisions are so unlikely. Better shielding could make it much harder to knock them out, at a big but manageable weight cost.
I still worry that a rogue actor could inject space debris into orbit for other reasons. But I do think there are some straightforward options for mitigating that strategy, like more thorough payload inspection.
All this is not to say that much better ‘launch denial’ techniques don’t exist, that is some way a powerful first mover could themselves leave Earth, but block others from doing the same. Militaries already think about this question in the context of blocking ICBM launches, especially in their boost phase.
You can read the full article here.