How do you design them to not cause that problem? Except for choosing an orbit that degrades relatively quickly.

By choosing an orbit that degrades quickly. And possibly making the sattelites disposable.

> Except for choosing an orbit that degrades relatively quickly.

You answered your own question.

More specifically, a Kessler syndrome is the problem that occurs when satellites collide and shatter into clouds of sand-sized particles, and then the sand-sized particles impact more satellites and shatter them, leading to a cascade that clears the whole orbit. Because small things deorbit faster than large things (square-cube scaling), this simply cannot happen at orbits that are low enough, at the Starlink deployment orbits if there was a catastrophic collision, most of the material would be out of orbit in a matter of days. At the even lower orbits of V2 constellation, most of the material will be out of orbit in a matter of hours.

The reason Kessler syndrome gets mentioned with Starlink is that the original system design had the early sats at 1100km and most of the constellation at ~800km. This would have been really bad, because that's about the worst possible orbit for collisions, as it's just high enough not to be swept clean by the atmosphere, but low enough that orbital velocities are very high and collisions are more likely. After the concerns were raised, SpaceX modified their design to be not dangerous.

To augment: sand-sized particles have a massive area/mass ratio, which is the main determinant in how quickly things deorbit. An unpowered Starlink satellite will deorbit naturally in 5 years. A sand sized particle in a Starlink orbit will deorbit naturally within a single orbit (90 minutes).

And more augmentation: sand size particles aren't the concern anyways. Satellites get hit by sand size meteors regularly. The space station is protected by Whipple shields. Satellites aren't, so sometimes they are partially or fully disabled by a sand size particle, but they never disintegrate because of one.

Particles under 1cm in size don't cause Kessler because they're too small. Particles over 1cm in size don't cause Kessler because they are big enough to be tracked and actively avoided.

The satellites are equipped so that they can not only correct their orbit themselves, but also deorbit whenever SpaceX decides that it is their end of life, rather than just be abandoned.

Thanks for actually answering my question. :)

Everyone else is busy telling me I already answered it myself but you added the information I was asking for. :/

By choosing an orbit that degrades relatively quickly.

Yes, they're designed not to cause the problem, but wouldn't they feed the problem, if it's ever caused by someone else?

How? If they're in a low orbit how can they get higher to pose a threat? If they collide with something that is en route to a higher orbit, then the collision takes place in this low orbit, and any debris will also be in that low orbit?

They're operating around 500 km, which is not the lowest of orbits. There's stuff below, including people in the orbit.

As long as the satellites are under 600km or so they will deorbit on their own in under 5 years. So in the worst case scenario caused by Starlink we would not be able to access space for 5 years which while not great is not the end of the world either.

The time to deorbit is not linear. So this 500km orbit is fine while 700km orbit would get us ~25 year deorbit time. 800km over 80 years and so.

generally when two satellites collide some debris can be shot at a higher orbit which will take forever (or will not) reenter atmosphere.

See the scatterplot of debris for the Chinese collision test of 2000: https://en.wikipedia.org/wiki/Space_debris#/media/File:Gabba...

See this video for evolution of debris and altitude over time: https://www.youtube.com/watch?v=mQT5aMa_7iI

The Chinese test also happened around 350km higher then Starlink satellites (850km). The natural deorbit time at that altitude is already over 100 years vs under 5 years at 500km.

Also it was literally the worst possible collision being an intentional head on collision. Satellites accidentally hitting each other on orbit are very unlikely to hit each other head on as it is very uneconomical to put satellites in a reverse orbit that low (there is a reason why we do rocket launches towards east if possible)

> generally when two satellites collide some debris can be shot at a higher orbit which will take forever (or will not) reenter atmosphere.

The lowest point of the new orbit (perigee) is guaranteed to be no higher than the point of collision. Fragments after the collision have no further propulsion, so their new orbit must initially include the point of collision, and can only decay from there. This can also be seen on your scatterplot.

Moreover, the time to decay is most strongly influenced by the perigee, as the atmosphere is the strongest there. If a satellite on an low orbit (decay in decades) explodes, those fragments that "reach a higher orbit" will still (due to the low perigee) decay back to a near-circular orbit in decades. A collision can increase the lifetime for some of its fragments, but not by multiple orders of magnitude (unlike a circular higher orbit).

Your video link also nicely shows that fragments with a low perigee will decay quickly, no matter how high their apogee is.

Yes, this is true, but for this to not be a problem, it also has to suppose that those higher-flying bits of debris don't subsequently collide with other higher-flying satellites.

Debris orbits like anything else. Regardless of the orbits of the colliding objects, the orbit of any debris is only really constrained to intersect the point of collision. For some debris, the point of collision could be the lowest point in its new orbit, meaning it could take longer to reenter and could collide with other stuff higher up until then. On the other extreme, some debris could essentially fall straight down to earth immediately.

No collision of 2 surfboards is going to loft debris high enough to be in a stable orbit. If the common point of orbit is 500km, all of that debris will de-orbit. The only propellent on those things is krypton, so if they collide it is only going to be mechanical effects on the debris. In my search I have not found a single reputable source claiming starlink could contribute to kessler syndrome, only clickbait articles.

The debris orbits from an initial collision don't have to be stable to allow a chain reaction that produces debris in more stable orbits. Debris from even a single low altitude collision/disintegration could collide/disintegrate later at a higher altitude, producing debris with a higher periapsis than any of the original bodies.

There are many factors in whether this matters practically, so I'm not passing judgement on that. None of this is specific to Starlink.

Nope, the satellites are flying so low that they will reenter the atmosphere and burn in few years no matter what happens .

what a laughable sentence, there have been at least 2 near misses last year between starlink satellites and Tiangong. Also, if there's a collision, the smaller parts and debris would remain in orbit far longer than expected (hence causing more incidents).

It is not laughable, Starlink satellites are in a low enough orbit that they will automatically deorbit due to air drag. They will not contribute to Kessler Syndrome.

>SpaceX said that a large part of Starlink satellites are launched at a lower altitude of 550 km (340 mi) to achieve lower latency (versus 1,150 km (710 mi) as originally planned), and failed satellites or debris are thus expected to deorbit within five years even without propulsion, due to atmospheric drag.

https://en.wikipedia.org/wiki/Kessler_syndrome