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by ncallaway 1796 days ago
I think these LEO constellations are actually the least concerning part of space pollution.

There are many more LEO satellites, true, but their orbital placement is such that the satellite's orbit naturally decays in a few years. Which means if a satellite becomes uncontrollable (or is destroyed in some way), the debris will clear in a relatively short period of time.

I'm actually much more concerned about the much smaller number of satellites in medium and geostationary orbits, where the decay time is decades or centuries.

Failed satellites or debris in these orbits will take a very long time to clear, and strikes me as a much larger concern than the larger number of LEO sats

1 comments

This doesn't make much sense. MEO is huge and GEO is only "relatively" small because it's narrow along two of three dimensions we care about†, which has no influence on any debris from a collision and thus it would most likely leave GEO altogether.

Would a volcanic eruption in New York be very bad? Yeah, I guess it would, but, that's not going to happen. Whereas California has several volcanoes that - while we've no reason to expect them to erupt this year - certainly can't be ruled out for our lifetimes, so, makes sense to manage that risk not worry about New York.

† A Starlink, or a GPS bird, has a "ball of yarn" orbit, it doesn't really matter which part of the planet it's over at any particular time so long as we can predict where it'll be for the near future. But the whole point of a Geostationary satellite is its apparent fixed location in the sky from a point on the ground. To do that it needs to orbit at the same rate the Earth spins, limiting the orbital radius to a tight band - and it also needs to orbit over the equator, the result is all GEO birds are in more or less identical orbits, just offset in time.

We're looking at two different axes. You're considering "how much of the orbit is occupied". I'm looking at "how long does a dead or destroyed satellite continue to occupy space".

If we have a collision that causes a significant amount of debris in a medium earth orbit, that debris will continue to exist for a very long time, so a wide portion of that orbit will be unusable or dangerous.

> Would a volcanic eruption in New York be very bad? Yeah, I guess it would, but, that's not going to happen.

That's fair, but I think your analogy might fall down on the comparative risks of damaged or destroyed satellites in LEO/MEO compared to the comparative risks of volcanic activity in CA/NY.

Yes, it's true that there is a larger risk of collisions in LEO with the number of satellites operating there. And it's true with the larger number of satellites, there are more risks of a satellite losing control. But that doesn't mean GEO and MEO satellites are without risk. Just last year there was a significant risk that a GEO satellite had the potential to explode due to a failing battery (https://spacenews.com/directv-fears-explosion-risk-from-sate...).

I'm mostly interested in hedging against worst case scenarios, and the worst case scenario for a LEO constellation is much less problematic than the worst case scenarios for MEO constellations.