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Comment by biaachmonkie | Hacker News Reader

Well since it's in LEO and since the sats will have been destroyed or damaged they won't be able to maintain their orbits, so the debris orbit will be decaying from the moment of the incident and should re-enter in a matter of a few months. The scenario I'm sure will be simulated by numerous people/orgs by the time this project is in full swing.

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This is not true of the orbit that the SpaceX satellites are going in to. LEO is a bit of a general term that covers altitudes anywhere from 100 km to 2000 km. While it is true that something at 400 km altitude will deorbit in a few months, they will be orbiting at an altitude of 1100-1300 km. At that altitude it will take hundreds of years from them to deorbit. The drag goes down exponentially as you get in to higher orbits. The FCC filing says that the SpaceX satellites will have enough fuel remaining in order to deorbit the satellite after the satellite has reached its usable mission life.

This was a big concern for NASA though. Their typical guidelines were that commercial satellites have to have >90% reliability to deorbit the satellite. But they want to increase this for the SpaceX satellites because if 10% (~400) of the satellites end up failing then they are effectively up there forever.

Not to mention a struck satellite (probably) no longer has the capability to deorbit, at least not in a controlled manner.

Little pieces of smashed satellites are not obligated by the rules of physics to decay.

An example of how long shit can stay in space: A Saturn V booster rocket is still out there, slowly orbiting the planet: https://en.wikipedia.org/wiki/J002E3

I believe you're thinking about their initial application. They've updated it [0] to an altitude of 550km, so atmospheric drag should still de-orbit broken satellites fairly promptly.

[0] - <https://fcc.report/IBFS/SAT-MOD-20181108-00083>

Thank you, I was thinking about their initial application. Yes, de-orbit times from 550 km are on the order of years to possibly tens of years. The requirement from the FCC is to deorbit your satellite within 25 years after the end of mission.

Edit: Their most recent application only moved the Phase 1 satellites in to the lower orbit. In later phases they are still planning on having more than 1000 satellites at the higher orbital altitude.

Yes, de-orbit times from 550 km are on the order of years to possibly tens of years.

So it wouldn't stop progress for a century, but might it put a damper on things on the same scale as the Great Depression?

SpaceX recently updated their plans to put most satellites between 300 and 400km. That ensures a quick deorbit of the satellites and debris and cuts down the ping times.

Interesting. That does make me feel a bit more secure about the whole thing, but it does raise the question of how much they will need to invest in orbital upkeep/replacement of decayed spacecraft. I can see this getting expensive quick.

Definitely expensive, but it is likely still much less expensive than putting all of the satellites in to the higher orbit. It takes a lot more fuel to get the satellites in to the higher orbit, as well as still having enough fuel to get it back down to de-orbit the satellite.

Plus, in the ~1100 km orbit you are getting in to the lower Van Allen belt where the radiation will degrade electronics much more quickly. This can be mitigated with radiation-resistant parts and more shielding, but it adds a lot more cost.

There are new technologies like air breathing ion engines and electrodynamic tethers, which have the potential to sustain low orbit satellites for years.

they filed that because it's believed that they have mechanical problems on the satellite. Not because they wanted to:

https://mobile.twitter.com/TMFAssociates/status/106076080100...

Isn't the lower orbit even better for them in terms of latency though? So long as the orbit doesn't decay faster than the planned 5 year life span of the sats, it's actually a win.

The lower orbit means the satellite coverage on Earth is smaller now, so they need more satellites to compensate for delivering the same capacity in a given area. It's better in terms of latency, but it's not a significant difference.

Very good point, thanks for responding.

I'd think that only a fraction of the debris will head down into the influence of atmospheric drag. The rest would fly away at an angle that either takes it parallel to the path of the orbit, or higher in the orbit (however short that may last). These satellites, while in a LEO orbital configuration, I would assume would still be high enough to where there is a decent amount of room before significant drag comes into play. Otherwise, it would not be economical to have these in orbit as they would decay and need to be replaced too quickly to justify the cost.

They’re already in place that has enough drag. The satellites will deorbit in months to years without periodic boosts. Debris will come down faster, since they have more surface area relative to their mass. A single impulse always results in an orbit that intersects the original orbit at the location of the impulse, so it’s impossible for a collision to raise debris entirely beyond that altitude.

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