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Decluttering low-Earth orbit: It's time to tidy up space

economist.com

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Re: Decluttering low-Earth orbit: It's time to tidy up space

#31

Post by JshWright »

mdotshell wrote: post #23
f-word wrote: post #19

Suppose you put a largeish amount of polyurethane foam in orbit, possibly around some scaffold to take up even more space, had it inflate when up there and had it absorb any wandering garbage for a while. How long would it take for the giant garbage mound to deorbit and burn?

Because of orbital mechanics, anything that would be traveling faster than the scaffold would be at a higher orbit and wouldn't be able to be caught. The exception to this would be if the object were in an elliptical orbit, which would allow for contact to be made with the scaffold at its perigee, which be impossibly rare.

Faster orbits are lower, not higher.

Re: Decluttering low-Earth orbit: It's time to tidy up space

#33

Post by MauranKilom »

f-word wrote: post #19

Suppose you put a largeish amount of polyurethane foam in orbit, possibly around some scaffold to take up even more space, had it inflate when up there and had it absorb any wandering garbage for a while. How long would it take for the giant garbage mound to deorbit and burn?

I'm not exactly sure how you imagine the collisions to play out. If you think anything gets "stuck" in your foam, you're underestimating the speeds at which objects in orbit move. It's more like shooting a railgun at your impactor. I also recommend Netwon's impact depth approximation: https://en.wikipedia.org/wiki/Impact_depth

For the purposes of deorbiting junk it may be sufficient to just impart some delta-v, but you neither want that to be uncontrolled collisions sending stuff into even more erratic orbits, nor would you want to risk generating even more tiny pieces.

Re: Decluttering low-Earth orbit: It's time to tidy up space

#34

Post by usrusr »

mdotshell wrote: post #23
f-word wrote: post #19

Suppose you put a largeish amount of polyurethane foam in orbit, possibly around some scaffold to take up even more space, had it inflate when up there and had it absorb any wandering garbage for a while. How long would it take for the giant garbage mound to deorbit and burn?

Because of orbital mechanics, anything that would be traveling faster than the scaffold would be at a higher orbit and wouldn't be able to be caught. The exception to this would be if the object were in an elliptical orbit, which would allow for contact to be made with the scaffold at its perigee, which be impossibly rare.

If you'd ever build an artificial "sponge moon" with the goal of assimilating as much spacejunk as possible you'd probably not want to circulate its orbit. But I doubt you'd ever face that decision, given the absurd materials requirements imposed by orbital collisions.

Re: Decluttering low-Earth orbit: It's time to tidy up space

#35

Post by sandworm101 »

What people forget is all the natural junk up there. Space is not "clean". Something like 100 tons of rock, mostly dust, falls onto earth from space every day. That isn't stuff in orbit, but given the capture effects of our moon there is likely a significant amount that does achieve some sort of stability. That amount probably outweighs everything we have ever put up there.

https://astronomy.com/magazine/ask-astro/2014/07/space-debri...

The real problem isn't that space is getting full of our junk, but that our junk is in a very narrow band of orbits that we use for very specific missions: Sun synchronous polar orbits used by imaging satellites. Look at how these orbits all cross paths at the poles. That's the danger zone. While the military cares deeply about these orbits, civilian infrastructure in space (geosynchronous communications sats, GPS etc) are well beyond any real danger. Or, at least they are in orbits where danger from natural debris is vastly greater than from space junk.

Re: Decluttering low-Earth orbit: It's time to tidy up space

#36

Post by marsokod »

gchamonlive wrote: post #11

> In the long term, this accumulation of junk may lead to a chain reaction, known as Kessler syndrome, that would make some low-Earth orbits unusable. I read about it, and it seems a little counter-intuitive for me. I would expect that in a collision in space, some of the kinetic energy would be used in internal structural changes, and not all converted to the resulting motion. Am I wrong here? If not, does it still…

You are right that the collisions will dissipate some of the mechanical energy will be dissipated into heat and technically collisions will reduce the duration it takes for the mass of debris that are in orbit. I am not sure if that has a significant impact on top of the atmospheric drag though.

However, the Kessler syndrome is not about the total mass of debris in orbit, but the number of individual debris. So while before the collision we had 2 nicely aggregated debris, after the collision you will have thousands of small ones.

The small ones will tend to deorbit faster on average, because of the loss of energy mentioned above and also because their aggregated surface area increases, but you still have more debris. And when we are talking about multiple decades/centuries of lifetime, these debris will collide with other satellites, creating a positive feedback loop, increasing the numbers of debris exponentially, at least initially.

Obviously this is just the beginning of the process, which will end up with a maximum number of debris and then a decrease towards zero, but that timeline is extremely long and therefore not really relevant to us.

Re: Decluttering low-Earth orbit: It's time to tidy up space

#37

Post by Cogito »

copperwater69 wrote: post #6

Probably not a HN tier comment, but there's a great anime about space debris cleanup. https://en.wikipedia.org/wiki/Planetes https://www.youtube.com/watch?v=CZ-OyT4ivkM

This anime is brought up in a lot of threads on space debris, and as others attest is excellent. It's a fully fleshed out and plausible future, where people have jobs cleaning up space debris, and it explores many of the issues that may await that kind of work in the future.

Your comment epitomises the golden rule of Hacker News, that you should post "anything that gratifies one's intellectual curiosity".

Re: Decluttering low-Earth orbit: It's time to tidy up space

#39

Post by gchamonlive »

copperwater69 wrote: post #13
gchamonlive wrote: post #11

> In the long term, this accumulation of junk may lead to a chain reaction, known as Kessler syndrome, that would make some low-Earth orbits unusable. I read about it, and it seems a little counter-intuitive for me. I would expect that in a collision in space, some of the kinetic energy would be used in internal structural changes, and not all converted to the resulting motion. Am I wrong here? If not, does it still…

Imagine two objects hitting each other perpendicularly, as opposed to head on. Plenty of momentum could be conserved and thrown out in a median vector. Edit: Not only that, but even if 90% of momentum was lost - it only takes another satellite going in the opposite direction to supply all the energy. Here's what 2 ounces of plastic does at 15,000mph to a block of aluminium. https://imgur.com/gallery/8NwAhgK

It depends on the material. If they are flexible, and deform easily, a lot of energy would be converted into structural damage, I would presume.

> it only takes another satellite going in the opposite direction to supply all the energy

I see, indeed the next collision will supply a lot of external momentum.

Re: Decluttering low-Earth orbit: It's time to tidy up space

#40

Post by gruez »

yottalove wrote: post #38

Elon Musk's SpaceX Starlink: thousands of satellites that can be re-positioned en masse in time of need and meanwhile reserve a spot in the LEO surface. Useful in both communication and in denying the space to other classes of satellites.

>and in denying the space to other classes of satellites.

Is this actually an issue? The earth has a surface area of 500M km^2 so if want 0.5km between each satellite you can fit 500M satellites at one orbit level. A few thousand spacex satellites is a drop in the bucket.

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