|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
Mopping up Space Junk
I have a few ideas to throw into the global pot for consideration.
After their useful lives, some satellites can deorbit with chemical or ion rockets or deploy vary large sails to increase their drag coefficient or be perturbed by the solar wind. Another method could be to extend long cables to use the Earth’s magnetic field to induce drag. However, all these require active systems installed on the junk and be commanded to deploy. The only methods for getting rid of space debris is to either go up there and get it, or wait a very long time for it to decay out or hit something else and hope that the resulting debris ends up with lower velocities that will decay quickly and not contribute to the cascade effect. Matching an orbit to be able to retrieve something is horrendously costly in fuel and really not practical except for large or valuable pieces in really inconvenient orbits. My idea would be to scale-up Stardust's aerogel capture system and deploy kilometre-sized megafoams in orbits designed to intersect as many debris fields as possible. While probably not able to capture most debris, one or more collisions could reduce their kinetic energy substantially to aid quicker reentry. Any foam shrapnel produced should be relatively harmless and decay very quickly. I can't imagine any process that could create kilometre-scale aerogels on Earth, let alone in-situ! A few tons of foaming agents could be shipped up in batches and then mixed together when the right quantities are reached. Foams would expand massively in a vacuum if the bubbles in the material could remain gastight under the extreme stretching. Space would be a very harsh environment for foam, as they would deform a lot depending on temperature so some pretty amazing materials would need to be used. Many shapes are possible - either big amorphous blobs, tentacular tangles or more structured lattices. If foams are extruded while being formed they could make long continuous tentacles. These could also be used instead of sails as aerobrakes for deorbiting. I imagine enormous structures could be made in space with just a few tons of materials. They would have to start off in high orbits because their own orbital decay would be substantial. Maintaining altitude and manoeuverability would be difficult using rockets, especially after absorbing unknown amounts of angular kinetic energy from the collisions it is looking for! If the foaming material has a high enough albedo or aluminized, they could provide usable night illumination too. If we make thousands of them, perhaps they could also reduce insolation by a useful amount as well. The foam would have to be environmentally benign for reentry. If it didn't burn up it would shrink massively with increasing atmospheric pressure. If enough survives, it might even preserve anything it caught. NASA know an awful lot about foam now, anyone from NASA like to comment on feasibility? How easy would it be to make foams in a vacuum? Andy Lee Robinson |
#2
|
|||
|
|||
Mopping up Space Junk
Andy wrote:
My idea would be to scale-up Stardust's aerogel capture system and deploy kilometre-sized megafoams in orbits designed to intersect as many debris fields as possible. While probably not able to capture most debris, one or more collisions could reduce their kinetic energy substantially to aid quicker reentry. Any foam shrapnel produced should be relatively harmless and decay very quickly. [[...]] A few tons of foaming agents could be shipped up in batches and then mixed together when the right quantities are reached. Foams would expand massively in a vacuum if the bubbles in the material could remain gastight under the extreme stretching. This is a clever idea. Let's crank a few numbers to see how it works... In article (20 Aug 2002) John Stockton discussed a similarly clever idea, having sounding rockets dump a gas cloud into space (without orbital velocity) just ahead of a debris chunk, so the debris would pass through the gas cloud before the gas cloud dispersed. As John wrote then To drop the perigee of an object in circular long-term orbit by a truly significant amount (so that it becomes no more than a short-term object) will require a change of velocity of the order of, say, 80 m/s, or 1%. To obtain such a change of velocity by hitting what would be an effectively stationary gas cloud would require the object to hit gas totalling around 1% of its own mass. In other words, if the aerogel is too tenuous, then debris won't be decelerated enough by passing through it. What matters here is basically the areal density of the absorber, in grams/cm^2. That is, if you cut a debris-fragment-sized hole through the absorber, the mass of absorber in that hole, m, is given by the product of this areal density, and the hole's area. If a debris-fragment of mass M passes through the absorber, it is then looses a fraction m/M of its orbital velocity. We want this fraction to be at least f=0.01. [In my simplistic analysis, it doesn't matter whether a given areal density comes from a very low-density aerogel that's quite thick, or from a higher-density aerogel that's a bit thinner.] A line or two of algebra reveals that this means the absorber areal density must be at least (4/3)*f*r*rho, where r is the typical radius of a debris fragment and rho is the typical mass density of a debris fragment. Setting rho = 3 grams/cm^3 gives f (in grams/cm^2) = 0.04 * r (in cm). So to deorbit 1cm-and-smaller diameter debris fragments (a 1cm-diameter fragment has r = 0.5cm, and in this crude masses around 0.4 grams) needs an absorber with an areal density of 0.04 grams/cm^2. That's 400 grams/m^2, so an absorber 100 meters on a side has a mass of 4 tonnes. So far, so good. Unfortunately, near-Earth space is *big*, so it takes a lot of absorber area to sweep it in any reasonable time. As Henry Spencer put it in another old post to this newsgroup, (article on 6 Mar 2006), An absorber 100 meters on a side -- a *big* thing to build, especially since it needs a fair bit of mass per unit area -- sweeps out about 7000 cubic kilometers a day. Assuming you put it into a slightly elliptical orbit, with apogee 100_km higher than perigee so that it sweeps out a range of altitudes rather than just one, it's trying to sweep a shell with a volume of 53,000,000,000 cubic km. In 20 years it sweeps about 0.1% of that volume. In other words, our 100-meter absorber just isn't big enough to do the job in any reasonable time. If we want our system to sweep, say, 10% of that volume in 20 years (which is still not really "doing the job in a reasonable time"), then it needs to be 100 times bigger, i.e., 1 kilometer on a side. But now it masses 400 tonnes, so launching it isn't quite such a simple job. Making the system another factor of 10 larger in area, so it nominally sweeps all the target volume in 20 years (i.e., so it's actually a "solution" to the orbital-debris problem, at least in this 100km-wide range of orbital altitudes) means it now has a mass of 4000 tonnes. In other words, while the aergel system can be made to work, it's not going to be small, fast, or cheap. There's also another rather serious issue to worry about, namely the fate of all the non-debris satellites in that range of orbital altitudes. The aerogel probably has to have a substantial delta-V capability (i.e., it has to carry a rockets and (given its huge mass) a *lot* of fuel) to be able to maneuver so as to avoid hitting any known satellites. In fact, it's probably better to divide up that 4000 tonnes and 10 km^2 absorber area into 1000 100-meter-on-a-side 4-tonne absorbers, each with its own maneuvering capability. This way "only" 4 tonnes of absorber (+ rockets + fuel + control/structures/communication/etc) has to be maneuvered each time there's a satellite in the way. [The requirement to maneuver the absorber also means that the whole thing (aerogel + any supporting structure) has to be structurally strong enough to handle the maneuvering g-forces. We probably want to make the maneuvers as gentle as possible consistent with not hitting other satellites.] Someone has probably done a more careful analysis of such a debris-sweeping constellation, but I've never seen it... -- -- "Jonathan Thornburg [remove -animal to reply]" Dept of Astronomy, Indiana University, Bloomington, Indiana, USA "Space travel is utter bilge" -- common misquote of UK Astronomer Royal Richard Woolley's remarks of 1956 "All this writing about space travel is utter bilge. To go to the moon would cost as much as a major war." -- what he actually said |
#3
|
|||
|
|||
Mopping up Space Junk
On May 6, 7:30 am, Andy wrote:
My idea would be to scale-up Stardust's aerogel capture system and deploy kilometre-sized megafoams in orbits designed to intersect as many debris fields as possible. Variations on the theme have been suggested before, like large ceramic fabric disks. While probably not able to capture most debris, one or more collisions could reduce their kinetic energy substantially to aid quicker reentry. Any foam shrapnel produced should be relatively harmless and decay very quickly. I'm not sure I'd trust the foam to be "harmless." The shuttle has had some divots blown out of its windows by paint chips. On the other hand, if there's any solid substance with a chance of being harmless in orbital impacts, it's aerogel. So if it passes muster in simulations and tests, it'd be the material for these debris sweepers. I can't imagine any process that could create kilometre-scale aerogels on Earth, let alone in-situ! Probably something involving an inflateable mold. http://en.wikipedia.org/wiki/Echo_satellite Mike Miller |
#4
|
|||
|
|||
Mopping up Space Junk
On May 6, 7:30 am, Andy wrote:
My idea would be to scale-up Stardust's aerogel capture system and deploy kilometre-sized megafoams in orbits designed to intersect as many debris fields as possible. While probably not able to capture most debris, one or more collisions could reduce their kinetic energy substantially to aid quicker reentry. Any foam shrapnel produced should be relatively harmless and decay very quickly. I can't imagine any process that could create kilometre-scale aerogels on Earth, let alone in-situ! Too late, that was already suggested in a story published in Analog Science Fiction & Science Fact. Earl Colby Pottinger |
#5
|
|||
|
|||
Mopping up Space Junk
On May 11, 6:07 pm, Hipupchuck wrote:
Snip. All you need is a satellite with a targeting laser blaster on it. Have it seek and disintegrate space junk or slow it down so it falls to earth. Nice idea.. but difficult.. molten space junk is still space junk, and fragments of space junk is yet more space junk, and may even take longer to decay if cross-sectional area decreases, eg, a breaking up a flat panel into tiny fragments. If a laser could vapourise or plasmarise a target, then it could be useful, but have watch out for anything else in its path. Boiling random patches of ocean might not be popular! Perhaps solar storms could be seeded to increase atmospheric drag or solar pressure? Cheers, Andy. |
#6
|
|||
|
|||
Mopping up Space Junk
Andy Lee Robinson ) writes:
On May 6, 7:30 am, Andy wrote: My idea would be to scale-up Stardust's aerogel capture system and deploy kilometre-sized megafoams in orbits designed to intersect as many debris fields as possible. While probably not able to capture most debris, one or more collisions could reduce their kinetic energy substantially to aid quicker reentry. Any foam shrapnel produced should be relatively harmless and decay very quickly. I can't imagine any process that could create kilometre-scale aerogels on Earth, let alone in-situ! [...] However good an idea it seemed at the time, letting loose hundreds of millions of fragments was really irresponsible. In such a high orbit with the copper's high density, they could be there for a very long time. However very large, luminous, negligible density megafoam structures are complely different. Their orbits would decay quickly, and more so after absorbing debrital energy with the average resultant against the direction of travel. Just hope they could mop up a useful amount of debris before reentry. Actually I'm under no illusions about the vastness of the volume involved... Even a 1km blob in a 1000km orbit would occupy such a small volume, that 3 million of them would be required to cover just 1% of sky at that altitude, but would be likely to mop up all intersecting debris within a few hundred orbits. [...] So I concede tha the only viable solution is to not pollute in future and to track and avoid for a few thousand years and pray. As impractical solutions go, why not use a cloud of finely divided ice? At least, if it doesn't leave orbit, it will eventially evaporate. --John Park ======================================= MODERATOR'S COMMENT: Please consider trimming your quotes in the future. |
#7
|
|||
|
|||
Mopping up Space Junk
In sci.space.tech message e741088d-ad41-4d99-868a-4a2dbbcd431b@a7g2000y
qk.googlegroups.com, Wed, 3 Jun 2009 00:00:49, Andy Lee Robinson posted: ... Actually I'm under no illusions about the vastness of the volume involved... Even a 1km blob in a 1000km orbit would occupy such a small volume, that 3 million of them would be required to cover just 1% of sky at that altitude, but would be likely to mop up all intersecting debris within a few hundred orbits. ... Firstly, there is the small but important set-of-cases involving impact between two objects of which both are trackable and at least one is manoeuvrable. In that case, dodging is effective. Otherwise, up there we have a large number of useful, easily-damaged objects, going in many directions some more popular than others, and with drifting orbital parameters. And we have a much larger number of useless objects, some shatterable but mostly hard to destroy, going in a similar spread of directions. Collision rate, per pair, is roughly proportional to their combined cross-sectional area and their relative speed. Collisions with useful objects are bad, on the whole. Send up a quantity of unguided "brooms", of any type. Each will have a certain total collision rate with junk; the best that can happen is that the junk is taken aboard, disintegrated into bits with less damage potential, or made to re-enter atmosphere sooner. The worst is that some of the broom adds to the junk. The average will be in between. Each broom will also have a certain collision rate with useful, un- manoeuvrable stuff; most such collisions will be harmful to the useful stuff, and many will create more numerous junk. Brooms will also collide with each other, unless very carefully orbited. Consider all those area-dependent collision rates, and their effects. ISTM inevitable that launching unguided brooms will be of negative benefit - by hitting useful stuff, or by creating more harmful junk. The case is, of course, different for anything that can discriminate between junk and useful stuff, and act on the difference. -- (c) John Stockton, nr London, UK. Turnpike v6.05 MIME. Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links; Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc. No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News. |
#8
|
|||
|
|||
Mopping up Space Junk
Andy Lee Robinson wrote:
On May 11, 6:07 pm, Hipupchuck wrote: Snip. All you need is a satellite with a targeting laser blaster on it. Have it seek and disintegrate space junk or slow it down so it falls to earth. Nice idea.. but difficult.. molten space junk is still space junk, and fragments of space junk is yet more space junk, and may even take longer to decay if cross-sectional area decreases, eg, a breaking up a flat panel into tiny fragments. Breaking up a flat panel into tiny fragments won't prolong the orbital life of the pieces. You could have part of the space junk stay up longer by cutting off pieces with lower mass to cross-sectional area ratio. For instance if you cut off solar arrays to a satellite, the solar arrays will de-orbit relatively fast and the rest of the satellite will be up there longer. It isn't obvious to me what is best, having a smaller satellite (e.g. satellite without solar arrays) staying up there longer or a larger satellite coming down faster, but I would think that in most cases you are better off leaving the solar arrays on the satellite so it deorbits faster. For "normal" objects, you can't prolong the life of a satellite by cutting it into pieces. If you increase the mass to cross-sectional area ratio by cutting the thing you didn't do it by increasing the mass, so you have to do it by reducing the cross-sectional area. Normally, you don't reduce the cross-sectional area by cutting something up, unless you can somehow stack the pieces. That could happen for some objects for instance if you have an umbrella which is open but spring loaded to close, if you cut of a piece that lets it close, you can reduce the cross-sectional area. Alain Fournier |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
space junk?? comet? what is it ? | MasterMind | Astronomy Misc | 0 | December 2nd 07 12:49 AM |
How bad will the Space Junk problem get? | [email protected] | Policy | 12 | February 8th 07 02:21 AM |
Jettisoned space junk -- how big? | Jim Oberg | Space Station | 48 | June 29th 06 06:56 PM |
Jettisoned space junk -- how big? | Jim Oberg | History | 59 | June 29th 06 06:56 PM |
sci.space.news junk | Brian Gaff | Space Shuttle | 4 | February 21st 06 06:57 AM |