Slashdot Mirror
The Space Garbage Scow, ala Cringely
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.'"
That this doesn't break up any debris into more parts - or cause the "net" to break and provide additional pieces of junk circling the earth.
If builders built buildings the way programmers wrote programs, then the first woodpecker would destroy civilization.
Perhaps Cringely doesn't have a clear idea what sort of debris we are dealing with here
There are, certainly, some big chunks out there; but unpleasant enough(and far more numerous) are the little flecks of paint, bolts, and general fragments of this and that zipping around at bulletesque velocities.
Either this "net" will be made of very close-woven unobtanium, of the sort that we don't yet have, despite decades of interest in the personnel armor industry, or it will have to be a vast spongy particle trap, of the sort whose volume would be completely prohibitive for any available launch mechanism.
Only the timescale. "Sooner or later" can be in the decades to centuries range, which is minimally useful for most of us now living.
You could try reading the summary next time. His proposal was for one flight, not 18000. I imagine his plan is still impractical for lots of reasons (you probably can't get enough impulse from each piece to approach the next one at a low enough speed, etc.), but it's still not as bad as your suggestion of 18000 manned space flights.
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.
Sigs are too short to say anything truly profound so read the above post instead.
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?
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?
I'd mod you up if I had points. Apparently Cringely hasn't thought about how valuable a few hundred metric tons of refined materials would be in orbit. Instead he says "Nope, we have to gather the stuff and bring it back to Earth." He fails to realize that _someone_ would certainly pay for access to all of that material. He also fails to realize that a polar orbit intersecting an equatorial orbit will result in a relative velocity of about 10 kilometers per second, which equates to 50 megajoules per kilogram. Carbon nanotubes or not, nothing is going to withstand such a large amount of energy in such a small area, repeatedly, along with whatever centripetal forces are acquired from off-center hits from debris.
A visionary he might be, but a practical engineer he is definitely not.
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.
Though I completely agree with your overall point, I'm curious if you have a citation for this sentence. The plate and pencil are in relative motion, yet apparently the impact drills a hole through the plate without even dulling the pencil? I tried googling for an experiment like this with no luck. Now I'm just trying to figure out what insane combination of high-speed photography and a hypersonic wind tunnel with a "pencil of death" feature would be required for proof...
Just wanted to point out that for the first time in the history of slashdot, you correctly spelled "losing" and "loose" in the same sentence. The content of your point is good too!
I wonder if this means that if you hurled 100mm armor steel plate @ mach 8.0 at a pencil if the pencil would survive-- perhaps we should be investing in pencil-based armor