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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.
I thought they were just in the early stages of establishing a ring-world, in terrestrial orbit. Oh well...
There will of course, be no such mission, headed by NASA, or any other fraction of the Federal United States. That banana republic operates on such a scale, only when there is substantial room for contractor and supplier rip-off. If Cringeley can figure a way for DynaCor to pocket a billion on the side, instead of increasing fuel efficiency in spaceflight? It'd happen next year.
"Speaking the Truth in times of universal deceit is a revolutionary act." -- George Orwell
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.
Anyone remember Quark, a space garbage scow show from the 70's? :D
It's nice to see it's time...
Only the timescale. "Sooner or later" can be in the decades to centuries range, which is minimally useful for most of us now living.
The risk of snagging one of the numerous live satellites would certainly be a problem. Re-entry, though, could be handled by picking an unloved chunk of ocean(hardly a limited resource) and just aiming for that.
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.
The problem with space junk is that there's thousands of piece of it flying around that can damage spacecraft, re-entry isn't really the problem. That's actually preferable to losing a few of your spacecraft to loose pieces of material in orbit.
Sigs are too short to say anything truly profound so read the above post instead.
We'll just tell them that it is our new orbital anti-whaling weapon...
Wouldn't something like a big ass electromagnet be useful? I mean, compared to a net... or something along the lines of giant flashlight (to push crap into earth)
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?
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.
Can you be Even More Awesome?!
That's not a bad idea. The real questions would be how much of a drag force could you create at a given distance? The junk is distributed in a cloud around the planet so encounters with junk could be hundreds of meters? Kilometers? Getting closer would require propellant. The field strength is limited by the amount of power you can generate, which ain't much from solar cells. The end effect is it may be completely infeasible because of scale. I wouldn't know how to work the numbers, but maybe someone else does.
AccountKiller
This is part of Slashdot's comedy posting allotment.
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).
It's not quite that simple. If the orbit is elliptical then two orbits can intercept even though they have different energy level (average heights). If the two objects in the two orbits join then the one in the higher orbit will lose energy and the one in the lower orbit will gain energy (which corresponds to average height). The resulting object will have the same momentum as the vector sum of the momentum of the two objects, which will give it a new orbit. If you start in a low and highly eccentric orbit, after a number of such collisions you may end up in high and relatively circular orbit (or not, depending on the collisions). Cringely is broadly right that it is probably possible to design an orbit such that the net eventually collects everything. Unfortunately, 'eventually' in this case can mean several million years, possibly longer.
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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.
Perhaps Cringely doesn't have a clear idea what sort of debris we are dealing with here.
No, he doesn't seem to have a clear idea of what debris is, or what orbital energy is, or how orbits work, or how BIG space is.
It is reasonable to clear debris up from Earth orbit... but not the way he proposes.
I'm afraid I have to agree with the people saying that this is not a workable idea. He needs to put some numbers to it. He's going to catch basketball sized objects in a net? Have he thought about what happens when a massive object hits something at several miles per second? I'd say, picture trying to catch a howitzer shell in a net, but, actually, artillery shells are snail-paced compared to orbital velocities. Here's a comparison: imagine that you're catching dynamite, and it explodes the instant you touch it, sending out shrapnel in all directions. Got that in your imagination? OK, it's a lot worse than that. (And if the answer is, well, make sure you come up on it at slow relative velocity... that means that you have to essentially match orbits with each piece of debris. This is unrealistically expensive in terms of delta-V.)
Also, has he thought about the relative size of the net needed to sweep out a few trillion cubic kilometers of space?
http://www.geoffreylandis.com
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.
You may wish to refine your knowledge of inductance 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.
Sigs are too short to say anything truly profound so read the above post instead.
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.
36000km/s is about c/8.
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!
Good point. Probably should be km/h?
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.
Speed is relative. If the net is moving in the same direction in the same orbit at a lower speed, impact speed is far less than travel speed and force can be distributed over time.
The notion of capturing energy from objects already in orbit is intriguing - but I doubt that "tacking" is sufficient to explain how this works. Tacking occurs when two fluids are connected by airfoils; moreover, the essence of tacking requires the deflection, or bouncing, of the fluids - not the collection of same.
So, in what way could you approach an object and steal its energy. But before that question, what does it mean to steal energy from these captured items? If the trash ends up a part of the garbage scow's orbital dynamics, then "stealing" energy is moot - unless the trash is ejected into a less energetic orbit, the scow cannot end up with a more energetic orbit - which of course defined the solution. The desired "net" may be an electromagnet on a long wire. The intercept is made with a near miss, such that trash and the scow end up like a double-star, tumbling around a common axis - then the electromagnet is released in a moment when the trash is tumbling counter-orbital, leaving the trash in an inferior (and hopefully terminal) orbit - and the scow in a new trajectory of choice - based largely on the intercept angle (to establish the tumble plane) and the release timing to select the angular acceleration.
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
You could try reading the summary next time.
You must be new here. We don't read the summaries, let alone the friendly articles. Hell, any day now I expect most /. readers will stop reading the headlines, too, and every article will be a homogeneous mishmash of vim vs. emacs arguments, libertarian propaganda, and goatse links.
Not that I have a problem with this, mind you.
"Destroy science and religion. Science would re-emerge exactly the same; but not religion." - Penn Jillette, paraphrased