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Does SpaceX have any concerns about the Kessler Syndrome [0] or any plans to mitigate it?

[0] https://en.wikipedia.org/wiki/Kessler_syndrome

Of course they do, it's a well-known problem for the satellite industry. From the technical addendum:

> Each satellite in the SpaceX System is designed for a useful lifetime of five to seven years. SpaceX intends to dispose of satellites through atmospheric reentry at end of life. As suggested by the Commission,50 SpaceX intends to comply with Section 4.6 and 4.7 of NASA Technical Standard 8719.14A with respect to this reentry process. In particular, SpaceX anticipates that its satellites will reenter the Earth’s atmosphere within approximately one year after completion of their mission – much sooner than the international standard of 25 years. After the mission is complete, the spacecraft (regardless of operational altitude) will be moved to a 1,075 km circular orbit in its operational inclination, then gradually lower perigee until the propellant is exhausted, achieving a perigee of at most 300 km. After all propellant is consumed, the spacecraft will be reoriented to maximize the vehicle’s total cross-sectional area, a configuration also stable in the direction of aerodynamic drag. Finally, the spacecraft will begin to passivate itself by de-spinning reaction wheels and drawing batteries down to a safe level and powering down. Over the following months, the denser atmosphere will gradually lower the satellite’s perigee until its eventual atmospheric demise.

http://licensing.fcc.gov/myibfs/download.do?attachment_key=1...

Interesting. Thanks!

> "for a useful lifetime of five to seven years"

Isn't that a relatively low lifetime for so many satellites? Doesn't that mean they'll need to make a lot of launches just to keep the fleet operational?

I think the idea in the first place is to lower the per unit cost. Then spending millions more for longer life doesn't make as much sense.

Depends on how they do it. The lifetime may be low because it doesn't carry much fuel. But if it's small enough they can launch dozens at a time.

This plan is obviously predicated on viable first stage reuse. Estimates vary (and I'm sure even SpaceX doesn't know what the eventual number would be), but it's conceivable that their per-launch cost would be in the low double digit millions. These are also relatively small satellites, so you can pack quite a few of them on a dedicated launch, as well as sending one or more uphill as secondary payloads for launches that have useful trajectories.

Yes. They are going for a very different model compared to "traditional" comsats. Instead of launching very heavy, very expensive birds that need to last for 10-20 years (to justify the huge development and launch costs), they want to launch cheap and light satellites that can be replaced much more quickly.

As someone stated above, this all hinges on first stage reuse proving to be viable. If a customer buys a flight and they recover and reuse the booster, it's almost a "free" flight for them.

They're building a Redundant Array of Inexpensive Satellites.

My best guess is that they're actually going to use the ITS first stage for this. If that's true, we may see as many as 500 of these launched in one go, with a reusable first stage.

I think Kessler syndrome is still likely to happen despite the best intentions and efforts of all players involved. a 1,000km circular orbit is very, very stable, so if something goes wrong and the satellite doesn't deorbit itself properly, it will be there a very long time. If there are on average 4000 of these at a time and only .1% of them malfunction in this way, that's still 4 per year.

Well, eventually we will get Kessler syndrome at some low altitude orbit. But at a rate of 4 satellites per year, we can stay complacent for a couple of millennia.

But yeah, expect this number to grow fast as more people do stuff like that. It will be a problem eventually.

Things in very low earth orbit will re-enter on their own, if left unattended, from atmospheric drag.... At orbits of 450-600 km or less the lifetime of any satellite is very much finite. Satellites in much higher (like the MEO O3b satellites) will not re-enter due to atmosphere drag even on a 500+ year time scale.

In my opinion, the Kessler Syndrome, or a Carrington Event, are the two most underrated yet likely causes of TEOTWAWKI.

The End Of The World As We Know It. (I had to google. Interestingly, my Mac’s dictionary has TEOTWAWKI as an alias for “Survivalism”.)

AIFF: And I feel fineeeee!!

For the uninitiated (incld. myelf...), "The end of the world as we know it."

Why would a Kessler cascade be so devastating? Most of our comsats and all our GPS satellites are above LEO.

But would it prevent launching any more?

It would completely fuck up the viability of all earth-sciences and imagery satellites (Hello google earth, google maps, bing maps, etc) which mostly orbit as low as reasonably possible and in 90 degree inclined polar orbits.

It would also kill Iridium (either the current generation of satellites, or the next generation which will be in generally the same orbital configuration) because it depends on low earth orbit, highly inclined polar orbit satellites. Iridium is incredibly important to maritime users and aircraft users, in addition to its massive US DoD use.

What would you say the probability of something going wrong and leading to Kessler syndrome is, if we have 4k more (or even 10-20k more) satellites?

I'm sure SpaceX isn't the only player thinking of adding a lot of cheap satellites in orbit

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