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.'"
Mod parent up. In addition, tiny specks acting as micrometeorites are probably a much bigger problem than the bigger avoidable pieces. Hitting all that big junk together in a net at orbital speeds will probably result in even more micrometeorites.
I suppose you're catching stuff in a net travelling in the same direction as the junk so it'll be a gentle catch rather than a hard collision. That shouldn't create any more micro bits of shrapnel.
Actually, our boy Cringely wants the net to travel in a polar orbit to catch junk that's mainly traveling in a equatorial orbit. Think of a bit of junk t-boning your net at 17,000 MPH.
This also leads me to think that you'd need less of a 'net' and more of a 'sheet'. One would then wonder, depending on altitude and sheet size, when atmospheric drag becomes an issue.
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.
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
Wouldn't it be bad catching all of the space debris in a giant net, when the net itself will eventually come back down to earth. Individual space junk coming out of orbit isn't as bad since it's not all falling in the same place and it's small enough to mostly burn up in the atmosphere, but if you've got this huge net there's a lot more junk to burn up with a much more localized crash site.
Plus this thing bouncing around like a billiard ball seems likely to catch something that isn't junk...
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.
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.
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!
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.
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.
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...
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
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.
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.
Not only that, but does he realize how LARGE that space is? Can you imagine saying to somebody, take your yacht, and sail around the oceans picking up 18000 pieces that go around with vastly different speeds (and orbits)? Now do this in 3D instead.
Moreover, the delta v's involved are probably quite a lot larger than one would expect.
And as you say, the big pieces are tracked and show up on radar, it is the little pieces that hit unexpectedly.
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.
Low earth orbit starts at ~200km:
Rleo1 = Re + 200km = 6,578km
Low earth orbit extends up to about 2000km ( it's debated. Using nice round numbers )
Rleo2 = Re + 2000km = 8,378km
4/3* PI * ( Rleo2^3 - Rleo1^3 ) = 1.271E12km^3
1.3 trillion cubic kilometers of space to sweep.
Assume a block of aerogel 10 meters on a side - so a frontal area of 100 m^2. That's pretty big, and it won't get any bigger unless we figure out how to manufacture the gel in space:
Agel = 100m^2
= 0.0001km^2
Velocity in leo is around 7.5km/second, relative to the ground.
Vgel = 7.5km/s
Let's assume that we are just trying to sweep the entire volume of space once, ignoring that things are moving etc. Even one sweep of the volume would certainly clean up a lot, if the orbit of the gel is tangent to the orbit of most of the junk. So we just pretend that the block of gel is flying down a tunnel, basically - frontal area times velocity * time equals volume cleaned:
Every velocity in space in orbit is super-bulletesque. It's the relative velocities that matter. I could catch the paint fleks with any old material, if, the relative velocities were reasonably close. Indeed, if you launched me out of a cannon next to a bullet fired out of a rifle, I'd almost be able to catch the bullet with no harm to myself. It's just the launching and the landing that would suck.
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 tr
I would think that if we went 'spongy', it would make sense to send up a few cubic meters of a densely packed raw material and then extrude it in space; after all, the whole point of those materials is how low density they are. One jar of popcorn kernels is easier to transport before they're popped.
Do popcorn kernels pop when exposed to vacuum? I may have solved the issue, right there.
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)
But I think that I would prefer a set of these, and dispense of them after a shorter time (burn it up or capture it for material studies). For starters, imagine accumulating a bunch of that junk together and then losing the ship. It could actually make things worst.
Also, this would be a good use for the tug concept. At some point, a tug will be useful for space. This could help push the concept.
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?
And by massive I mean square kilometres and tens of meters thick.
Aerogel [wikipedia.org] has been shown to be able to pick up even the smallest flecks of material for the Stardust [wikipedia.org] project.
Since it's the smallest things that are the trickiest (huge bits are easily tracked), we need something that will not only absorb the energy of the impact, but also keep the debris in place. Thus, Aerogel is a good fit.
It makes sense to capture and lose the small pieces. BUT, the large ones are lots of material in space that took a lot of fuel to get there. That would be a shame to lose those if they are together. Seems like we can push those into a higher orbit out of the way and then use them in the future.
...means the net will lose speed every time it captures some junk. The author needs to take high school physics again.
Tacking on a sailboat works because the wind is blowing on the sail, adding energy to the whole craft.
Scooping stuff in a net is just an inelastic collision. The momentum gain of the junk will equal the momentum loss of the net. The net's orbit will decay as it captures more and more junk.
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.
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).
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.
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.
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.
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.
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 someon
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.
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 sh
Only make some sort of sense if the summary had described the net as being in _front_ of the spacecraft, so that collisions increase the spacecraft's speed (which is in higher orbit and thus moving slower).
Even so, the net is more likely to cause stuff to break into smaller and harder to track pieces. And definitely bad if the net breaks...
Make sure. (Score:5, Insightful)
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.
Reply to This
Re: (Score:3, Interesting)
Re: (Score:3, Informative)
I suppose you're catching stuff in a net travelling in the same direction as the junk so it'll be a gentle catch rather than a hard collision. That shouldn't create any more micro bits of shrapnel.
Re:Make sure. (Score:4, Insightful)
Actually, our boy Cringely wants the net to travel in a polar orbit to catch junk that's mainly traveling in a equatorial orbit. Think of a bit of junk t-boning your net at 17,000 MPH.
Reply to This
Parent
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.
Reply to This
Parent
Re: (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
Wouldn't that be bad when it re-enters? (Score:2)
Plus this thing bouncing around like a billiard ball seems likely to catch something that isn't junk...
Re: (Score:3, Interesting)
Re: (Score:2)
do not tell that to sea shepherd...
Re:Wouldn't that be bad when it re-enters? (Score:4, Funny)
Reply to This
Parent
Re:Wouldn't that be bad when it re-enters? (Score:4, Informative)
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.
Reply to This
Parent
Re:Wouldn't that be bad when it re-enters? (Score:5, Informative)
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!
Reply to This
Parent
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?
Reply to This
Parent
Re:Wouldn't that be bad when it re-enters? (Score:5, Insightful)
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.
Reply to This
Parent
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.
Reply to This
Parent
Re: (Score:3, Informative)
Re: (Score:3, Informative)
Good point. Probably should be km/h?
Re:Wouldn't that be bad when it re-enters? (Score:5, Insightful)
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...
Reply to This
Parent
Re:Wouldn't that be bad when it re-enters? (Score:5, Funny)
Reply to This
Parent
Cringeley Amuses (Score:4, Insightful)
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.
Reply to This
"net"? (Score:5, Insightful)
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.
Reply to This
Re:"net"? (Score:5, Insightful)
Moreover, the delta v's involved are probably quite a lot larger than one would expect.
And as you say, the big pieces are tracked and show up on radar, it is the little pieces that hit unexpectedly.
Reply to This
Parent
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.
Reply to This
Parent
Re:"net"? (Score:4, Informative)
Radius of the earth:
Re = 6,378 km
Low earth orbit starts at ~200km:
Rleo1 = Re + 200km = 6,578km
Low earth orbit extends up to about 2000km ( it's debated. Using nice round numbers )
Rleo2 = Re + 2000km = 8,378km
4/3* PI * ( Rleo2^3 - Rleo1^3 ) = 1.271E12km^3
1.3 trillion cubic kilometers of space to sweep.
Assume a block of aerogel 10 meters on a side - so a frontal area of 100 m^2. That's pretty big, and it won't get any bigger unless we figure out how to manufacture the gel in space:
Agel = 100m^2
= 0.0001km^2
Velocity in leo is around 7.5km/second, relative to the ground.
Vgel = 7.5km/s
Let's assume that we are just trying to sweep the entire volume of space once, ignoring that things are moving etc. Even one sweep of the volume would certainly clean up a lot, if the orbit of the gel is tangent to the orbit of most of the junk. So we just pretend that the block of gel is flying down a tunnel, basically - frontal area times velocity * time equals volume cleaned:
Vclean = Agel * Vgel
1.27E12km^3 =
t = 1.695E15 seconds
= 5.37018E7 years
= 53 million years.
Reply to This
Parent
Every velocity is super-bulletesque (Score:2)
Every velocity in space in orbit is super-bulletesque. It's the relative velocities that matter. I could catch the paint fleks with any old material, if, the relative velocities were reasonably close. Indeed, if you launched me out of a cannon next to a bullet fired out of a rifle, I'd almost be able to catch the bullet with no harm to myself. It's just the launching and the landing that would suck.
Can you Catch a Cannonball in a Fishing Net? (Score:3)
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 tr
Re:"net"? (Score:4, Funny)
Do popcorn kernels pop when exposed to vacuum? I may have solved the issue, right there.
Reply to This
Parent
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: (Score:2)
Anyone remember Quark, a space garbage scow show from the 70's? :D
It's nice to see it's time...
That was exactly what I thought of when I saw this .. ah the memories of seeing it on TV and the crushing blow when it was discontinued.
Re: (Score:2)
Space junk's like any other problem (Score:2)
Metal (Score:3, Interesting)
Reply to This
Interesting idea (Score:2)
Also, this would be a good use for the tug concept. At some point, a tug will be useful for space. This could help push the concept.
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?
Reply to This
Net? Use massive slabs of Aerogel instead (Score:2)
And by massive I mean square kilometres and tens of meters thick.
Aerogel [wikipedia.org] has been shown to be able to pick up even the smallest flecks of material for the Stardust [wikipedia.org] project.
Since it's the smallest things that are the trickiest (huge bits are easily tracked), we need something that will not only absorb the energy of the impact, but also keep the debris in place. Thus, Aerogel is a good fit.
Gel or Foam? (Score:2)
What about some gel block, or even better some kind of foam?
One other thing (Score:2)
Conservation of energy/momentum (Score:2)
...means the net will lose speed every time it captures some junk. The author needs to take high school physics again.
Tacking on a sailboat works because the wind is blowing on the sail, adding energy to the whole craft.
Scooping stuff in a net is just an inelastic collision. The momentum gain of the junk will equal the momentum loss of the net. The net's orbit will decay as it captures more and more junk.
Re:Conservation of energy/momentum (Score:4, Informative)
Reply to This
Parent
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).
Reply to This
Tacking may not work in Space (Score:3, Insightful)
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.
Reply to This
Re:gravity (Score:5, Insightful)
Reply to This
Parent
Re:Cringely is an idiot. (Score:5, Informative)
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.
Reply to This
Parent
Re:Cringely is an idiot. (Score:4, Funny)
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.
Reply to This
Parent
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.
Reply to This
Parent
Re: (Score:3, Insightful)
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 someon
Re: (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: (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 sh
Re: (Score:2)
Even so, the net is more likely to cause stuff to break into smaller and harder to track pieces. And definitely bad if the net breaks...
Re: (Score:3, Insightful)