h a l f b a k e r yContrary to popular belief
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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
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-seen
thousands of square miles of the stuff [Vernon, Oct 04 2012]
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Perhaps the SJT will FINALLY find out what happened to Jimmy Hoffa... [+] |
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...or the sudden disappearance of an entire shipment of lepatata Mambu's. [ ] |
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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. |
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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. |
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space is very, VERY big. you'll have to keep sending up
fuel |
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I've been thinking of starting The Black Hole Trash Collection Company... |
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
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[Vernon] - what about aluminium foam? |
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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. |
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// 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. // |
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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. |
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I think a gill net configuration might work better than a drag net in this application. |
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1) A drag net will need something to keep it open. If not, the orbits of the opposite corners will cross. |
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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. |
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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. |
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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. |
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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. |
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// 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. // |
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I addressed that very point in the 2nd-to-last paragraph.
I'm glad you agree. |
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I like the gill net. As for controlling the net, I specified
small thrusters at the corners and along the trailing edge. |
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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. |
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frozen gas pellets: stray pellet pieces sublimate. |
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The physics of this giant space net are wicked complicated, but here are some easy-math only feasibility estimates: |
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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. |
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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. |
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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. |
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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. |
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[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. |
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// I originally read the idea when you first published it
and forgot some of the points (and forgot to re-read it
carefully) // |
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I perpetrate the same crime on a regular basis. |
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Yes, but is this method certified dolphin-safe?
And if you are thinking "there are no dolphins in space," just remember your Douglas Adams. |
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//remember your Douglas Adams//
And your David Brin. |
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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. |
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