According to most people who pay attention to these things, there are currently over 500,000 pieces of space junk larger than 1cm^2 in orbit around the earth. The estimates concerning smaller debris run into the tens of millions.
There are a number of aerospace companies coming up with methods for clearing the skies, but to be perfectly frank, I think they're approaching this problem from the wrong direction. All of the methods I've read about involve grapples, harpoons, lasers, projectiles, andor explosives. These techniques share some major flaws:
1) They're tackling rogue objects one at a time, using a lot of fuel chasing the target down and attacking it in some manner that drops it to Earth, where it burns to cinders in the upper atmosphere. This seems incredibly inefficient, time-consuming, and wasteful.
D) These so-called 'chaser sattelites' are only tackling the big stuff, yet a chunk of metal no bigger than my thumbnail, orbiting the earth at 17,000 mph, can pose the same or even greater risk to operative equipment and spacecraft as does a derelict 6-ton Soviet spy sattelite.
¿) Some folks* are worried that these chaser sattelites, with their various implements that to the willfully ignorant resemble offensive weapons, could be secretly converted into 'hunter-killers' that would prey on operative sattelites and even manned orbital facilities of rival governments or corporations.
4) Not a single one of them is rhinoceros-compatible.
There are vast segments of the sky that are occupied only by rogue objects. Instead of knocking them out one by one, why not gather them up by the thousands?
The Space Junk Trawler is a large, slow unmanned vehicle which meanders along a predetermined route that keeps it well clear of operative sattelites. This course is constantly updated from tracking stations on the ground, but if communications fail, the SJT has basic object avoidance capabilities and a number of emergency actions it can undertake should the need arise.
When in operational mode, the SJT deploys a giant dragnet that at full extention could be thirty or forty miles wide. An array of small thrusters at the corners and along the trailing edge of the net help adjust its elevation and attitude. The net is composed thusly:
- In 10m weave, the structural matrix of the net is made of 3mm braided carbon fiber cords with a protective polymer sleeve. These provide most of the net's tensile strength and durability.
- In 2m weave, 1mm braided carbon fiber, both to catch and hold large objects and to support the finer weaves.
- In 10cm weave, 48k-tow unbraided carbon fiber filament captures and entangles large- and medium-sized objects.
- In 1cm weave, smaller 12k-tow carbon filament captures ballistic thumbnails.
- Finally, a 20-mill mesh made of goat-silk picks up the smallest debris.
With the dragnet deployed, the SJT just moseys around, seeking out the highest concentration debris fields in its locale. As the net fills up with junk, the SJT's oversized thrusters compensate for the added mass and shifting velocity. The alignment and shape of the net can be altered by the net thrusters and by simply winching it in, reducing the overall width.
When the net has collected a full load of junk (determined by a pre-set limit), slip-lines along its edges are reeled in, closing it at the sides. Then it is cut loose and allowed to fall into the atmosphere. The SJT then deploys a new net from its removable magazine.
Obviously, some rogue objects that are quite large andor moving very fast will blow right through the net. This is okay! The net is disposable, so it doesn't really matter how much damage it sustains, and impact with the net will have significantly slowed the rogue object and possibly even knocked it out of orbit, reducing the hazard it poses and making it easier to capture the next time around. A shock-mounted chassis and a sharp-prowed armored deflection shield protect the vehicle itself from unavoidable collisions.
Getting the Space Junk Trawler itself into space will be a complex, multi-stage operation, with modular components sent up separately and assembled in orbit. Once it's up there, however, it's virtually autonomous. The net magazines and fuel cells are filled on the ground and sent up to an orbital service sattelite, or they can intercept the vehicle is its consumables run low when it has wandered too far from home. The reloading is done automatically by onboard mechanisms. Empty magazines and fuel canisters are returned to Earth in a controlled descent and are reconditioned for continued use. Even the Trawler itself can be repaired or have entire modules replaced at the service sattelite, with tricky work carried out by a technician on the ground, operating the articulated tool-arms via remote control. Best of all, the ponderous, easily-avoided, and weaponless SJT cannot possibly be turned to nefarious purposes, which should calm protest against much-needed development in this increasingly important field.
*probably the same people who insist that a missile fired by an Argentinian Nazi flying saucer was actually responsible for the damage to the Pentagon on 09-11-01-- Alterother, Oct 02 2012 These guys would just roll it up and sell it... Near_20Earth_20Orbi...ation_20Corporation [normzone, Oct 03 2012] Free pumice http://www.npr.org/...dest-thing-ive-seenthousands of square miles of the stuff [Vernon, Oct 04 2012] Perhaps the SJT will FINALLY find out what happened to Jimmy Hoffa... [+]-- Grogster, Oct 02 2012 ...or the sudden disappearance of an entire shipment of lepatata Mambu's. [ ]-- Grogster, Oct 02 2012 couldn't you just hook a bunch of your nets to that 6 ton derelict satellite? Because I think it would appreciate the work. And it has already got all the nefariousness out of its system - those days are behind it now.-- bungston, Oct 03 2012 Why not? If the orbital traffic patterns allowed for it, the SJT could set up a giant junk-trap, go off and do some trawling, then come back when the trap is full and pitch it.-- Alterother, Oct 03 2012 space is very, VERY big. you'll have to keep sending up fuel-- Voice, Oct 03 2012 I've been thinking of starting The Black Hole Trash Collection Company...-- xandram, Oct 03 2012 (link)-- normzone, Oct 03 2012 I'm not sure how to work out how much stretch is in the structure that you propose, but I suspect that that sort of net might be quite a rigid structure - at least as far as a //chunk of metal... at 17,000mph// is concerned. This would probably make your net, or sieve, rather more like a colander, and would be rendered useless quite quickly. Sattellites that are in use needn't have any fear since they would pass right through.
I think you will have to incorporate some sort of mechanism that allows the net to whizz backwards when hit by something and slow it down a bit more gradually, either that or make it vastly more stretchy.-- TomP, Oct 03 2012 Sorry, I mistakenly left out the part about braided carbon fiber being quite 'stretchy'--the strands themselves are not all that elastic, but the braid is loose enough to allow for quite a bit of expansion. Enough? Probably not. That one feature (which I forgot to mention, natch) was the only thought I put into the issue of elasticity. In retrospect, I believe you are far more correct than I am.
A spring-loaded reel on the winch seems like a good idea. It should probably work with electromagnets, because springs are just too low-tech.-- Alterother, Oct 03 2012 Sorry, it still won't work if the velocity difference is too great. What you really need is a kind of bulldozer blade made of something like pumice (evacuated, not air-holding). A pretty large quantity of the stuff was in the news recently (link). It might be nice it if was rubbery as well as full of holes. Fast-moving stuff will impact and be absorbed, without causing much splatter, if the "blade" of this bulldozer was thick enough.-- Vernon, Oct 04 2012 Perhaps a 'blade' fronted with or made entirely of some type of high-viscosity foam that hardens as it expands so that the gas pockets don't rupture in the vacuum. Escaping gas upon impact might even negate a bit of the impact forces.
I guess the real idea, which I'm only fully realizing now, was to start collecting the 500,000+ objects ranging between 1-10cm and let the chasers deal with most of the big stuff. Looking back, I should have focused the emphasis on that. Maybe the chasers could operate from the same orbital service stations and even hitch rides on the Trawlers.
And yes, orbital space is a very big place; this is a slow, set-and-forget type of approach. One unit might not make headway, but properly halfbaked it could prove its worth and justify the funding of dozens more, which could operate in small fleets to clear spacelanes and set up extensive traps based on tracking predictions.-- Alterother, Oct 04 2012 You don't necessarily have to catch them; you could try and just knock 'em around enough so that the orbits become destabilized, and they burn up.-- RayfordSteele, Oct 04 2012 [Vernon] - what about aluminium foam?
My next thought was "custard", but then again, my fluid mechanics lecturer was talking about non-Newtonian fluids today and mentioned that if you throw custard at a wall it will shatter, so this might not be such a good solution (or suspension). Either that or it might just bounce the junk in the other direction at nearly double the speed, which wouldn't be much good.-- TomP, Oct 05 2012 // You don't necessarily have to catch them; you could try and just knock 'em around enough so that the orbits become destabilized, and they burn up. //
True, but that goes back to my issues of how to catch the small stuff and other people's strange conspiracy theories about the potential for weaponization. One key feature of the Space Junk Trawler concept is that it just kind of tools around and skeins up whatever's coming in its direction. If it were targeted maliciously, whatever it was aimed at would have a long time to get out of the way, or at the very least everyone would know who to blame.-- Alterother, Oct 05 2012 I think a gill net configuration might work better than a drag net in this application.
1) A drag net will need something to keep it open. If not, the orbits of the opposite corners will cross.
2) A large percentage of objects hitting the drag net will be in an orbit opposite of the trawler's orbit, so they will have to be accelerated by ~2x orbital velocity.
A gill net (vertical sheet trailing straight behind the trawler) would only have to accelerate the objects it catches by sqrt(2) times orbital velocity, and half of that acceleration is provided by the space junk hitting the other side of the net. (assuming the net is massive enough that the momentum from an object hitting one side won't make it swing too far before an object hits from the other side and straightens it out). In the ideal case the net wouldn't catch the objects at all. If an object traveling perpendicular to the trawler hit the net but slid/rolled off of the net (probably not too likely at that speed), it would loose it's forward momentum, and not be accelerated sideways enough to get into the trawler's orbit, so then it would fall almost straight down. The net would end up being swung back and forth by variaous objects from each side, but the trawler itself wouldn't loose as much momentum.
That brings up another point: The net doesn't necessarily have to be strong enough to prevent objects from punching through. As long as it slows the junk down, the orbit will be degraded and it will fall to earth sooner than it would have. Is that basically what [RayfordSteele] meant? The one issue with that approach is to make sure that when junk punches through the net, if any bits break away from the net, they either stay attached to the space junk or vaporize so they don't contribute to the space junk problem. Once the net starts to get tatterd and risk large pieces being broken off, either a maintenace robot would go back and cut off loose bits, or else the whole net could be reeled in and disposed of properly.
One problem with a gill net will be that since there is no drag on the back end of the net, as things hit the net, it will want to fold up, so there will probably need a thruster at each corner, just like hte drag net. I thought about using an electrodynamic teather in the back for drag to keep the net straight, but I don't think you'd get enough drag that way.-- scad mientist, Oct 05 2012 // The net doesn't necessarily have to be strong enough to prevent objects from punching through. As long as it slows the junk down, the orbit will be degraded and it will fall to earth sooner than it would have. //
I addressed that very point in the 2nd-to-last paragraph. I'm glad you agree.
I like the gill net. As for controlling the net, I specified small thrusters at the corners and along the trailing edge.-- Alterother, Oct 05 2012 Sorry I originally read the idea when you first published it and forgot some of the points (and forgot to re-read it carefully). What I had in mind though wasn't just letting the occasional large object damage the net, but design the net so that all but the lightest or slowest moving objects break a hole in the net. Eventually the net will have too many holes to be useful, but it might be a lot easier to find a material that will break nicely and absorb a bunch of the energy than it will be to find something that can be strong and stretchy enough to stop an object moving at orbital velocity.-- scad mientist, Oct 06 2012 frozen gas pellets: stray pellet pieces sublimate.-- FlyingToaster, Oct 06 2012 The physics of this giant space net are wicked complicated, but here are some easy-math only feasibility estimates:
Accounting for the 3 and 1mm strands and an area of 2500 km^2, the net masses about 4,123,340 kg. Lifting that much into LEO would take 30 Saturn V, 78 Falcon 78, or 395 Falcon 9 launches. At projected prices for the Falcons, the launch cost would be roughly $10,000,000,000 – less than 10% the cost of the ISS program. So it’s cost feasible.
Any structures other than the net aren’t really significant. Unlike a fishing trawler, which is much more ship than net by mass, this space trawler is pretty much all net. Since the net could be conductive, and have lots of solar-generated electricity, it could use electrodynamic propulsion, eliminating the need for conventional rockets and fuel, further reducing its cost. This decentralized design means the net need not be a single structure, but rather can be many smaller ones, flying in formation.
The volume of the spherical shell constituting LEOs – 200 to 2000 km altitude – is about 1.3e21 m^3. Assuming optimum maneuvering, and average orbital speed of about 7000 m/s, the net would fully sweep this volume in about 860 days – about 2 years 4 months. So it’s time feasible.
Next step, the real feasibility maker/breaker: calculating if the net would actually work to deorbit space junk, either by catching or slowing it. This is beyond the easy-math realm, or anything I want to undertake tonight.-- CraigD, Oct 06 2012 [CraigD], thanks for the rundown. I'm always grateful when a 'baker with an actual education drops in to justify my insane ramblings with scientific scrutiny.
// I originally read the idea when you first published it and forgot some of the points (and forgot to re-read it carefully) //
I perpetrate the same crime on a regular basis.-- Alterother, Oct 06 2012 Yes, but is this method certified dolphin-safe? And if you are thinking "there are no dolphins in space," just remember your Douglas Adams.-- sqeaketh the wheel, Apr 19 2013 //remember your Douglas Adams// And your David Brin.-- AusCan531, Apr 19 2013 Although the SJT is a very slow and easily outmanuevered orbital craft, there is in fact a system already in place that provides early warning to space dolphins via text messages from the rhinoceros.-- Alterother, Apr 24 2013 random, halfbakery