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Comment by throw0101a | Hacker News Reader

At what point should we start worrying about Kessler Syndrome?

> The Kessler syndrome (also called the Kessler effect,[1][2] collisional cascading or ablation cascade), proposed by the NASA scientist Donald J. Kessler in 1978, is a scenario in which the density of objects in low Earth orbit (LEO) 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.[3] One implication is that the distribution of debris in orbit could render space activities and the use of satellites in specific orbital ranges difficult for many generations.[3]

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

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I've heard that at least with the SpaceX satellites, they have full plans for decommissioning with these satellites re-entering the atmosphere.

I do agree that this is a real concern though, and we'd hope there's pretty careful consideration, considering the sheer number of satellites being launched. Still, space is big .. really big, even the space just above our planet.

I don't put it past humanity to not fuck up space. After all, look at all the plastics and waste in the oceans. Hopefully all these companies and FCC regulators are thinking far ahead, and require the right designs and safety measures to make sure we don't end up enclosed in a float garbage pile.

Correct on the decommissioning plans. SpaceX lists out in their FCC filings a number of things including how long it will take them to actively de-orbit satellites, how long for them to de-orbit if they lose contact/control, and also how much of the material will survive re-entry.

I have read conflicting things so don't hold me to this, but on article I read said they delayed adding the laser links to the current batch of Starlink satellites because of concerns over how much would survive the de-orbit maneuver.

What I heard they launched them ASAP because otherwise they would lose spectrum license.

This is relevant: https://www.youtube.com/watch?v=yS1ibDImAYU

> I've heard that at least with the SpaceX satellites, they have full plans for decommissioning with these satellites re-entering the atmosphere.

It's not just that they have plans to do so, they're low enough that they'll de-orbit fairly quickly on their own without active control (boost from their ion engines). Something pretty strange would have to happen for them not to eventually burn up.

Isn't the Kessler effect partly about creating further junk from a cascade of collisions? Even if the "junk" were to re-enter the atmosphere eventually, how long would that take? How long would access to space be cut off before the junk were to clear?

I'm not an expert (and expect to be corrected on details here), but I think it depends on the orbit altitude - if it's low enough to suffer significant atmospheric drag, then it'll de-orbit fairly quickly. But if they're at high altitude (geostationary and geosynchronous orbits spring to mind - around 22000-26000 miles), then that's much less likely, although there's a much bigger area to cover at that altitude. But given the damage that even a tiny particle can cause at those velocities, I think it's a real concern with such mass launches.

The smaller any given piece of debris is, the greater it's surface area:mass ratio is, and therefore the faster it deorbits due to drag.

Project Kuiper and Starlink both put the very large, thousands-of-satellites constellations low enough that trash gets cleared quickly enough that even a set of multiple catastrophic collisions is very unlikely to threaten most of the network, and even if they all just blow up, the pieces will fall down shortly and clear the orbit for reuse. For Starlink, drag is actually so high that they are using the solar array as a sail for attitude control.

With right lobbying strategy and targeting lawmakers during campaigns, I have no reason to believe that Amazon cannot influence enough heads in their favor. Are government entities such as FCC are the absolute gatekeepers that we expect them to be? I am highly skeptical. Look how FAA handled Boeing's 737 Max and we ended up with two crashes. A company of Amazon stature and resources can easily influence and overwhelm FCC into giving them green light. For Amazon this is a two fold win; Blue Origin will finally have a purpose, and further domination of Amazon in farthest corners of the world.

Those dense internet satellite constellations will be in low earth orbit, which have relatively fast decay times. So even in the worst case it would only set us back by a few decades while either cleanup solutions are developed or we wait for them to decay naturally.

You can still launch through the debris field into higher orbits because the collision probability will be quite low at any given moment, it just adds up over time for things that want to stay there.

What about debris from LEO collisions moving into higher orbits?

Gravity is directional.

A single impact can't put something into a higher circular orbit-- it can create an elliptical orbit with a higher apogee (max distance), but the correspondingly nearer perigee (closest approach) means that it experiences more atmospheric drag and falls out of orbit faster.

Granted, I don't know the math and this is intuition from Kerbal Space Program, but I'm not sure that's right. Wouldn't two objects colliding at 0° and 90° orbits result in a higher apoapsis and the same periapsis? Wouldn't it be equivalent to a normal impulse? Some pieces of one of the satellites would have more energy than they did before the impact.

You are correct. The result would be an elliptical orbit, though, not the circular orbit that the post you replied to mentioned.

I don't know if the person edited it after you replied, though.

Kerbal Space Program taught me so much, I now realize. I was able to follow and visualize everything in this thread due to that videogame. Neat.

I don't think the perigee needs to be lower? Consider a collision fragment that breaks off tangentially to the orbital path and moves faster than the speed needed to maintain a circular orbit: its new perigee should be the radius of the circular orbit, but the apogee will be higher.

I thought so too, but apparently this is not universally true. Some of the debris can be put in an orbit with a longer lifetime than the original satellite. I got into a long twitter argument with experts in this field, and I was proven false: some of the debris can have longer orbital lifetime and go to higher orbit.

EDIT: Here: https://twitter.com/SpaceJosh/status/1119721780254371840

Always embarrassing to make a fool of myself on the Internet, but losing an argument IS a very effective way of learning.

You said:

> That seems unlikely, as that requires like 11km/s which is more than the sum of the two velocities[...]

Isn't the first problem here that you're assuming a spherical cow in a vacuum physics problem? Two satellites colliding aren't two indivisible pebbles colliding.

They're going to pulverize on impact, and some of the now-expanding debris cloud might even contain combustibles the satellites were carrying.

The debris also won't only collide once, there'll be a series of rapidly occurring re-collisions. Some of those might impart extra velocity on some of the expanding debris.

Galilean cannon?

Higher orbits require higher velocities, which aren't going to be reached by collision debris.

It’s not likely but definitely not impossible.

https://youtu.be/2UHS883_P60

For the sake of completeness, did a little digging, looks like it did happen in fact - https://celestrak.com/events/collision/

Collisions can absolutely eject debris at a higher velocity than either of the initial impactors.

>only set us back by a few decades

Uhhh, that’s quite some time.

It is interesting to think about. Assume for a minute that Starlink and Amazon's project and a handful of others put tens of thousands of satellites into 500-600 km LEO. Two crash, bits of those crash into others, and runaway Kessler syndrome ensues, resulting in space at those altitudes effectively closed off for 25 years. Assume the ISS at 400 km is no longer safe for human habitation, and it's too risky to try to punch larger payloads through to higher orbits. Human space exploration is effectively dead for 25 years. What happens?

On the scale of human history, that's a moment in time. Today, as we learn about the history of colonial Europe, there's lots of exploration, then the 30 Years War in 1618 slowed that down a lot for a while, then things resumed. In 2500 AD, astronauts will learn of the early history of 1900s first flights, and the 2020-2045 setback, and then 400 years of further development.

But in the short term, that's a full career for everyone who just entered the field. Space companies would publish 100 quarterly earnings statements with zero progress, just waiting for the window to open again. I just don't know that modern society has the ability to think long-term for an event like that.

FYI it appears that for a unpowered satellite at 500-600km the average lifetime is around 5 years.

https://space.stackexchange.com/questions/13851/how-long-can...

Think about it in terms of cars. Imagine spread out 3k cars around the surface of the earth. Each car will be thousands of Km away from each other. For example New York has 5 million registered cars. And they manage to use only a fraction of available land dedicated to roads. So I don’t think 3k is anything for a orbit around earth, which is also much bigger than the surface of the earth itself

Edit: I am not saying a collision would not cause the effect that OP referred to. I am saying that 3K satellites in Earth's orbit will be very far apart, so the odds of them colliding in the first place is incredibly low.

It’s not 3000 completely self-container items. It’s 3000 satellites with hundreds and hundreds of parts inside, each of which can splinter into thousands of pieces.

I hope you know about how dangerous space debris is for space exploration. Each of those tiny pieces move faster than bullets around the Earth.

Sandra Bullock in Gravity would disagree: https://www.imdb.com/title/tt1454468/

(SPOILER: The debris from one satellite wiped out all the others, including the ISS)

;-)

But satellite collisions can, and indeed already have, happened: https://en.m.wikipedia.org/wiki/2009_satellite_collision

The bigger issue is all these satellites outnumbering the total number stars visible from Earth. It has astronomers worried.

https://www.nytimes.com/2019/06/01/science/starlink-spacex-a...

Astronomy is fine and all but I think this is more important.

I can't tell if you're being sarcastic or not.

Worldwide satellite internet access provides more value to humanity than identifying stars. Maybe some telescopes should be put on the moon/mars anyway.

I'd tend to disagree with ya on that!

Without astronomy, this whole enterprise couldn't have happened.

All the necessary physics could have been developed just fine even if there had always been a dense fog of debris surrounding the earth past the moon.

The Big Bang vs Cat videos?

One obvious solution is to put them in an orbit low enough that they'll fall back within a few years.

I'm more worried about the future sudden need to stop supporting the existing internet once a few companies decide we should just use their new space internet, that seemsnlike the more profitable longterm play.

It’s the same internet, just like when we switched from dialup to broadband.

Not without net neutrality it isn’t.

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