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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

#41

Post by Cogito »

onethought wrote: post #3

Is this really a thing... orbit is a vastly bigger place than the earths surface... you’d have to try pretty hard to hit that junk wouldn’t you?

The issue is not in passing through the junk - that's like passing through the asteroid belt. We don't (or at least used to not) even plan a specific path through the asteroid belt, as the chance of hitting anything on the way through is so low.

The problem is if you want to stay in an orbit alongside the junk.

The dynamics of orbital mechanics are interesting, to say the least, but it in no way maps to the surface of some sphere.

A somewhat useful analogy is to imagine two circular racetracks, that intersect with each other in two spots. Each racetrack is like an 'orbit', and racecars going around them are satellites.

Make the racetracks really big, and put a car on each track. Have the cars drive around non-stop forever. The chance of them hitting each other on any lap is extremely small. However, if you let the cars go for a long time, and one of them completes a lap a little bit faster than the other, the times that they both cross the intersection will slowly get closer and closer together. Eventually, they will crash. If you put more cars on the track, the chance of two of them colliding increases. If everyone time they crash they create lots of baby cars, well you get Kessler Syndrome.

This is only a problem for these racetracks because they touch. We protect against this in the orbital world by keeping satellites in different orbits, that don't cross. The problem is that the orbits can shift over time due to gravitaional inconsitencies, and solar flares causing the atmosphere to bleed off into space, and the moon, etc. With lots of long lived satellites in low earth orbit, the chance for a crash increases. But even if we do get lots of baby satellites the other orbits farther out will remain useable (like geostationary orbits), you just have to be a little careful when crossing the low earth orbits on the way out.

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

#42

Post by steerablesafe »

JshWright wrote: post #31
mdotshell wrote: post #23

Earlier quoted context omitted.

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.

This is in fact correct, orbital velocity is sqrt(G*M/r) for circular orbits.

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

#43

Post by sandworm101 »

tomhoward wrote: post #17

Fun fact: A hobby satellite my father helped build as a way to justify procrastinating during university in the late 60s is now low Earth orbit space junk. He says he's rather embarrassed to have learned, post launch, that it would likely remain in orbit for 100,000 years. https://en.wikipedia.org/wiki/Australis-OSCAR_5 http://centralblue.williamsfoundation.org.au/oscar-5-the-fir... https://www.youtube.com/watch?v=hj…

Your father's satellite is very high (1400km, 1000km above the ISS) at the edge of what is classified as low earth orbit. It will be up there for a long while but the chance of it ever hitting anything is infinitesimal.

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

#44

Post by Cogito »

gruez wrote: post #40
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.

Remember that, assuming circular orbits (which is fine for this discussion, I think), you have to fit satellites on great circle paths next to each other. For a single great circle you can fit a significant number of satellites in a chain, but turns out you don't want too many like that as all your satellites cover the same part of the earth.

All great circles on a sphere will intersect in two places, which assures a collision if you have satellites in them both (without active avoidance). So you have to separate the great circles on to different sized spheres, or add a little eccentricity to make sure the rings don't touch.

There is still a lot of space, but comparing to the size of the surface of the earth is not very informative when dealing with orbital dynamics.

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

#45

Post by gchamonlive »

marsokod wrote: post #36
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…

I see, thanks for taking the time to answer me =D

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

#46

Post by AlanSE »

Cogito wrote: post #37
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".

It was extremely good for its time. For instance, the creators asked scientists to estimate the efficiency of solar panels at the time, and computed the area needed for the space stations they drew. Truly incredible that they went to these lengths.

Nonetheless, it is very dated. Fusion power looks a lot worse today than it did back in 2003. The fusion-powered space Jovian exploration ship would be right at home in today's sci-fi (just as much the future today as then), but He-3 as a reason to go into space as been eviscerated. People who still (unrealistically) hope for a fusion game-changer are more often touting proton-Boron, and He-3 doesn't even fundamentally change problems of ignition conditions and radiation, it just mitigates it.

They also didn't do much to predict radical reduction in launch costs. In the PlanetES world, it still felt very expensive to get into space. They didn't go unless they had a corporate sponsor or were filthy rich. I don't even remember anything that hinted at booster re-usability, which is now (astonishingly) reality.

There's also the obvious fact that sending people to do trash pickup was always more Hollywood than reality. They knew that then.

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

#47

Post by JulianMorrison »

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?

It might help to put it in a suborbital trajectory, so it would basically go up, squirt, expand to a huge size, and drop back down, being hit by the intended object as it falls. You'd need a lot of foam to knock significant delta-v off the junk, and it would be catastrophically smashed by the thing impacting, but most of it would drop straight back down, and the bits blasted into orbit would be small and light enough to deorbit themselves.

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

#49

Post by simonh »

sandworm101 wrote: post #43
tomhoward wrote: post #17

Fun fact: A hobby satellite my father helped build as a way to justify procrastinating during university in the late 60s is now low Earth orbit space junk. He says he's rather embarrassed to have learned, post launch, that it would likely remain in orbit for 100,000 years. https://en.wikipedia.org/wiki/Australis-OSCAR_5 http://centralblue.williamsfoundation.org.au/oscar-5-the-fir... https://www.youtube.com/watch?v=hj…

Your father's satellite is very high (1400km, 1000km above the ISS) at the edge of what is classified as low earth orbit. It will be up there for a long while but the chance of it ever hitting anything is infinitesimal.

Infinitesimal over 100,000 years? I'm not losing any sleep over it personally, but that's a long time.

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

#50

Post by MauranKilom »

gchamonlive wrote: post #39
copperwater69 wrote: post #13

Earlier quoted context omitted.

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.

> 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.

At those speeds, everything is "flexible" in the sense that even metal just flows in a fluid-like manner (see picture linked in the comment).

Also, the material would have to somehow convert the energy of an entire car crashing into it at full speed. Except the car is only an inch wide.

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