Hacker News Reader

Comment by branko_d | Hacker News Reader

Kessler syndrome:

"...is a scenario in which the density of objects in low Earth orbit (LEO) due to space pollution is high enough that collisions between objects could cause a cascade in which each collision generates space debris that increases the likelihood of further collisions"

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

So destroying a subset of satellites might create enough debris to cascade-destroy the rest of them. But that would not be limited to SpaceX satellites, and would effectively lock-out human species from accessing space for some time.

View on HN

Kessler syndrome is kind of a middlebrow concern people love to bring up because they heard about it one time, but I have yet to see any argument that it is a realistic problem for Starlink based on real calculations. The number of Starlink satellites is large compared to previous constellations, but still tiny compared to space which is of course vast. The low orbits used by Starlink are automatically cleaned up by the atmosphere. And even if there were debris clouds in low orbit it wouldn't lock out space access as it would still be possible to launch into higher orbits. The probability of collision is negligible if you're only passing through.

for a brief period, it might even work as an ICBM defence shield for the whole planet. Imagine every single rocket aborting due to debris for 1-2 years( a guess)

You're underestimating how huge the surface area of the sphere these satellites are orbiting, and how little material they have. Even if you somehow blow them all up, they won't shield you from ICBMs.

And if the debris field somehow was dense enough to provide such a shield it would block out enough sunlight to cause the death of most life on the planet I suspect.

On the positive side, a solution for global warming.

If you blow up all starlink satelites, the resulting debris will start taking out other satelites.

… … … you mean it will cause Kessler Syndrome?

It seems that there's a threshold that would have to be hit to trigger that process. Do we have any idea whether starlink satellites, whether intact or as debris, would be anywhere close enough to that threshold to trigger the runaway process?

It could be true that the phenomenon exists conceptually, but that were nowhere near remotely close to triggering it, and that people are vastly underestimating the size of space.

If you blow up all the Starlink satellites, the little pieces start reentering the atmosphere most preferentially in very short order.

Kessler syndrome is more complicated than just "satellite debris bad". At the altitudes the Starlink satellites are at, it is a near non-concern. There is a causal link there... we can afford to put up lots of little satellites at that altitude for that exact reason, and that's exactly why they are where they are. That it's also less energetically expensive to launch is just a bonus.

ICBMs don't stay in space for long enough to be impacted.

> Kessler syndrome

Makes for pretty good anime though:

* https://en.wikipedia.org/wiki/Planetes

It makes more sense in their case, as they have a couple more magnitudes more orbital infrastructure. So much more stuff to hit and much much more mass to cause trouble.

Starlink satellites are orbiting fairly low and atmospheric drag would clear the remnants within 3-5 years.

Say the earth is a smooth featureless sphere and there are 36000 basketballs bouncing around, and say they all broke into 100 tennis ball size fragments. You’d still never expect to run into a single one. And that’s on the surface, there’s a lot more space up in space.

As a side note, if you’re interested in Kessler Sundrome and haven’t read Seveneves yet, you need to get on that. :)

By some time you mean some hundreds of millions of years, it’s not plastic in earth/ocean or uranium which degrades relatively quickly in comparison, there is not much of degradation in orbit.

Well, I heard by from someone, but I stand corrected, nasa [0] says:

  Debris left in orbits below 370 miles (600 km) normally fall back to Earth
  within several years. At altitudes of 500 miles (800 km), the time for orbital
  decay is often measured in decades. Above 620 miles (1,000 km), orbital debris
  normally will continue circling Earth for a century or more.

[0] https://www.nasa.gov/news/debris_faq.html

Reply on news.ycombinator.com