The Space Garbage Scow, ala Cringely 221
An anonymous reader writes "Robert X. Cringely once again educates and amuses with his take on how we could clean up the garbage that's in orbit around Earth. I cannot vouch for his math, but it makes sense to me. Quoting: 'We’d start in a high orbit, above the space junk, because we could trade that altitude for speed as needed, simply by flying lower, trading potential energy for kinetic. Dragging the net behind a little unmanned spacecraft, my idea would be to go past each piece of junk in such a way that it not only lodges permanently in the net, but that doing so adds kinetic energy (hitting at shallow angles to essentially tack like a sailboat off the debris). But wait, there’s more! You not only have to try to get energy from each encounter, it helps if — like in a game of billiards or pool — each encounter results in an effective ricochet sending the net in the proper trajectory for its next encounter. Rinse and repeat 18,000 times.'"
Quark! (Score:2, Interesting)
Anyone remember Quark, a space garbage scow show from the 70's? :D
It's nice to see it's time...
Re:Wouldn't that be bad when it re-enters? (Score:3, Interesting)
Metal (Score:3, Interesting)
Re:Cringely is an idiot. (Score:5, Interesting)
A better idea might be to use the concept of induction to our advantage. Create a satellite that creates a several kilometer diameter magnetic field bubble and fly it through the debris at high velocity. THe debris is most likely conductive and would have a current induced in it causing a drag force against the janitorial satellite. The orbits that cause the most drag are ones that run counter to the craft so they'll probably be nudged into a lower orbit by the drag. The janitorial satellite will use solar power and a space tether to stay in its current orbit. Any satellites that need to stay up there and aren't considered debris can be tracked much more easily and you could just shut the EM field down upon close encounter with them.
The craft would use very little propellant and would probably work better than a net anyway. Just have a few craft like these flying around and acting like an immune system that kills off targets that are a danger to other craft.
Re:Make sure. (Score:3, Interesting)
Use Aerogels to slow objects w/o fragmentation (Score:5, Interesting)
IF (and I know it is a big IF) it were possible to "manufacture" aerogels in space, this material could be ideal for capturing/de-orbiting small pieces of debris that would be too difficult/expensive to chase and capture the traditional way (via space tug or whatnot) but still poses a threat. Aerogels have already proven themselves as capable of capturing extremely fast (although tiny) particles moving at literally astronomical speeds without itself disintegrating. It was used precisely for this reason in both the "Stardust" and "Genesis" probes.
Now imagine instead of the small plates that were on these probes a very large slab tens or hundreds (thousands?) of meters on a side that would, over time, slowly intercept the smaller particles. Larger fragments would still go right through but might lose enough kinetic energy (without fragmenting and making the problem worse) so as to de-orbit themselves. The only thing that might make this remotely possible is the thought that the aerogel is so light (lighter than air) that a really huge piece could be put into orbit without spending billions in launch something heavy. Of course the only way to keep the launch volume reasonable is to MAKE it in space. Once in space, an ion engine would be required to counteract the atmospheric drag (and loss of kinetic energy from the impacts of the space debris).
By "manufacture" I mean the raw material (I guess it some sort of silicate compound) would have to be brought up from earth but since the resulting aerogel is 99.9% empty space, a little could go a long way. I understand that one way to produce it requires a super-critical liquid carbon-dioxide solution; obviously the CO2 would have to be recycled or better yet would be if a means of producing it directly in vacuum. Chemists, any ideas?
Re:Cringely is an idiot. (Score:3, Interesting)
Did you even read TFS?
He's not proposing 18,000 spaceflights manned or otherwise. He's proposing a gigantic billiards shot where all the balls are in motion, salvaging the motion of some of the balls to line up the next one and eventually encounter and sink all the balls in one shot.
Then he's got some weird ideas about orbital energy this "net" concept that seems tricky (although a sufficiently strong, ductile net would increase the target area for intercept and it doesn't matter if the net gets torn to shreds as long as the shreds stay attached), but the underlying idea is interesting, and it certainly doesn't need to be so tricky as to sink all the debris in only one flight with no inter-object maneuvering.
Re:"net"? (Score:5, Interesting)
As long as you're traveling at the same speed and direction as the bulletlike flecks, you don't have to worry about damage. Given that space is a frictionless environment, it's actually fairly easy to accomplish this. We do it every time we dock with the ISS.
Cringley seems to be suggesting traveling slightly slower, as to absorb some kinetic energy in the impact, while preserving the integrity of the net. This sounds pretty cool in theory, although there are a few problems in practice, such as tracking all the tiny bits of debris, having enough fuel to maneuver, and ensuring that you don't get caught between two pieces of junk traveling in opposite directions.
It's a difficult problem to be sure, but I wouldn't write it off entirely.
As an alternate proposal, would it make sense to put huge blocks of aerogel (or a similar substance) into orbit? Junk that strikes the blocks would either get caught inside, or pass straight through (but lose some kinetic energy in the process, leading to its gradual orbital decay or capture). Aerogel itself has a low enough density that loose chunks of it would be relatively harmless to passing spacecraft.
Gain kinetic energy? (Score:3, Interesting)
To drop from a higher altitude to a lower altitude you have to lose kinetic energy, not gain it. Furthermore, everything is not traveling in the same direction. There are many different orbits and junk is in all sorts of them. So some junk you'll never "net" since it's traveling in the same direction as the dejunker, and other junk is traveling exactly opposite and will slam into the net with twice the velocity of the denetter's current orbital velocity. Furthermore if the junk's orbit is 90 degrees to the dejunker, it will never be caught either. Even if the orbital paths crossed, it would probably just destroy or damage the dejunker satellite (paint fleck or rachet wrench).
So it wouldn't seem that his idea stands the common sense test (or physics for that matter). But this is just slashdot and I am not an orbital-mechanics expert. I failed that class at the starfleet academy (or was that temporal mechanics).
Re:Wouldn't that be bad when it re-enters? (Score:5, Interesting)
Who says it needs to re-enter? If the bits of junk are all lodged in a larger net structure which behaves in a predictable manner, it could just be left up there as a sort of orbital junkyard. The proposed designs for a space elevator require a chunk of ballast to keep the tether taught... Why not a bunch of discarded booster shells and such, tacked together? It took a lot of energy to get that stuff up there... Why waste it?
Re:Wouldn't that be bad when it re-enters? (Score:5, Interesting)
At speeds above Mach 8.0, you can drive a pencil through a 100mm armor steel plate - even the pencil tip stays intact and sharp.
At 36,000km/s (equal to Mach 36 at sea-level), the net or carbon fiber construction will not even have a chance to absorb anything. The net itself might be able to absorb this momentum and energy level at a whole, but I seriously believe a metal piece will just blast right through it, instantly shearing the filament at molecular level. The inertia of a single carbon nanotube will probably be all that is needed to cleanly cut it off.
Re:Cringely is an idiot. (Score:3, Interesting)
You may wish to refine your knowledge of inductance [wikipedia.org] which is not dependant on a material being ferromagnetic. Also, the craft is designed to sweep through about 800km^3 of space (10 km diameter bubble) every second and would be capable of cleaning a layer of space covering the whole planet 30 miles thick in a single year. More if the size of the bubble is increased.
Re:Make sure. (Score:4, Interesting)
I remember an SF story over a decade ago where the author (maybe Pournelle?) had a similar sweeper idea and they used aerogels [nasa.gov] to scrub Earth orbit. I say let's call it a trap instead of a net or a sheet, since that describes its function as opposed to its form. That said, I don't think the orbital mechanics would work the way Cringely thought it might. Higher orbits go slower, so the hanging sheet/net (moving at the speed of the orbit of the center of mass of the sheet/tug) is going to be accelerated by impacts from the space junk which will lead the whole thing into a more elliptical orbit, not a shallower circular one. That's not a good way to arrange a slow spiral down to clean up orbits gradually. And that doesn't even begin to consider the stuff in eccentric orbits. So Cringely's idea isn't original, and if he read the same story I did and is subconsciously re-iterating the idea, he's not even getting it right. Now, if you balanced your trap with a larger solar sail and used it to keep your orbit more circular, you might have something.
As for atmospheric drag, if it's an issue for the trap, it will be an issue for anything flying that low. The space junk flying low enough for atmospheric drag to be a factor is a self-correcting problem.
Re:Wouldn't that be bad when it re-enters? (Score:2, Interesting)
This is always annoyed me when they interview scientist for shows about earth impactors.... "You can't just hit it with a missile it would break apart and hit the earth like a shot gun blast"
I agree the larger surface area would be a great benefit to any sort of impact.
Re:Make sure. (Score:3, Interesting)
Hmm, interesting point, and idea. Though I imagine in RL the cost of that much aerogel would be prohibitive, at least at this point.
I think the self-correcting factor comes in 10x, 1000x, etc. flavors, depending on velocity/mass/coefficient/altitude. I think 100,000 years is the figure I heard at one point (no source, sorry) for non-LEO objects. So while your correct that waiting a few decades corrects the LEO problem (or perhaps a few centuries) for nearly anything, the HEO objects would, I imagine, be much more dependent on e.g. a massive drag coefficient to momentum ratio (HEO objects are subject to atmospheric drag... just a tiny, tiny amount.) A sail-like structure is going to dwarf the drag of e.g. a bolt. My idea was that perhaps it would be possible to turn that problem into a mechanism of operation for the device.
But now I'm clearly off into my own SF :)