Comment by iracigt | Hacker News Reader

Comment by iracigt | Hacker News Reader

This is concerning to me, but not quite for the reason the article suggests. SpaceX is doing the right thing here by maneuvering and using Very Low Earth Orbits to cap the amount of time a failed satellite can stay up before falling. What if the maneuvers stop though? Say they run into financial issues and cease operations.

25,000 1-in-100,000 collision probability events in 6 months is actually pretty high. Without actively controlling the satellites to avoid you get:

1 - (1 - 10^-5)^(50e3) = 0.39...

chance of collision per year.

SpaceX says Starlink satellites should deorbit in about 5 years if they don't keep actively boosting their orbits. That still means a 90% chance of a collision before deorbit if they stop maneuvering. Those debris would be in low orbits and also decay quickly. You could still to some real damage to any of your neighbors in that time though.

From a regulatory perspective, I sincerely hope the FCC and others are thinking about what contingency plans need to be in place if SpaceX became financially unstable. They've basically guaranteed themselves a government bailout at this point. The UK did that to OneWeb for purely economic reasons. If SpaceX goes under, they're taking LEO with them.

> Say they run into financial issues and cease operations.

Then the last thing they'll do will be to deorbit the satellites.

You also missed a major factor in your calculations -- the odds that a collision will raise the odds of further collisions. And that's zero. The vast majority of collisions are with centimeter size objects, which aren't going to shatter a Starlink. And if you collide with something large enough to shatter a Starlink, then it will remove enough energy from the orbits of most of the objects that they'll deorbit within a single orbit.

It's true that the bigger question is "what is the impact of a collision?". For many of them, the answer is probably nothing. In an industry where 1 in 10,000 makes people uncomfortable though, I think it's enough be to be potential headache. Increasing density of LEO would make that worse. It doesn't need to be a runaway effect to be economically or especially politically problematic.

Proactively deorbiting at EoL is definitely the correct move, but requires enough runway to continue short term operations. I can absolutely picture this being used as political leverage.

I imagine if SpaceX was financially toast and trying to ransom LEO for a bailout then we'd probably just Defense Production Act them and give them a loan for only enough to pay the staff to deorbit the constellation.

It's probably true that energy is removed from the whole system, but I don't think it's correct to say that each piece of resulting debris has lower energy, some do gain energy, or lose very little.

Just to contrive a counterexample, what about a collision from a higher eccentricity object near its perigee? That could be adding a lot of energy I think, no?

Probability question: why is it 50e3 if there are 25e3 potential events?

25e3 per 6 months is 50e3 in 12 months. That's assuming the constellation isn't shrinking, which SpaceX definitely doesn't seem to be doing.

Ah, thank you.

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