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Space junk is an ever-growing problem, due both to the
increasing quantities of junk and the increasing number of
satellites that have to thread their way through it. Yet
methods to clean up space seem slow and expensive, as they
target only one piece of debris at a time.
Most space junk
is metallic (or partly so), and hence
conductive although little of it is made of ferrous metal. Non-
ferrous metals, passing through a magnetic field, are slowed
by virtue of eddy currents (and hence magnetic fields) induced
in them.
So, how about a magnetic junk decelerator? Simply set up a
huge (but thin) loop of wire, and run enough current through it
to generate a decent field. It would be nice if the wire could
be superconducting, but not essential. Every piece of junk
passing through the loop will experience a very slight
deceleration at each orbit, resulting eventually in orbital
decay and re-entry to burn up in the Earth's atmosphere.
Active satellites could be let through the loop unimpeded by
just turning off the current for a moment.
Birkeland Current Transformer
by [Ian Tindale]. Mentioned in my anno [notexactly, Sep 16 2019]
Wikipedia: Electrodynamic tether
https://en.wikipedi...ectrodynamic_tether
Mentioned in my anno. A device for converting electric energy to orbital energy or vice versa, inside a magnetosphere [notexactly, Sep 16 2019]
Wikipedia: Van Allen radiation belt § Proposed removal
https://en.wikipedi...lt#Proposed_removal
by V. V. Danilov; refined by Robert P. Hoyt and Robert L. Forward. Mentioned in my anno [notexactly, Sep 16 2019]
[link]
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Numbers would have to run for field strength against a laser ablating a surface on the debris. I feel a large, fine power loop in space isn't right somehow. It doesn't feel very green. |
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With a sufficiently large loop, perhaps passing
through the Van Allen belts, could we create a
decent current using the earth's magnetic field?
Would doing so slow down the earth? |
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Super conducting is easy at space temperatures,
you just need a little solar shielding. How will the
system cope with the wife variety of junk orbits? |
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How much would the eddy currents slow down an object moving at miles per second? |
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Space junk is orbiting at 7.5km/s. I'm guessing you need to reduce that to 6.5km/s to deorbit. |
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So you need the space junk to convert kinetic energy to a different form of energy. In this case, the eddy currents will become almost entirely heat energy. So you need to radiate 7MJ/kg in heat. (If you want the eddy currents to form a repulsive magnetic field to repel against the wire, you'll need the wire to be *really* close). |
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If you could raise the temperature of the junk of mass X kg by YºC, it would radiate that amount of heat in Z seconds. Given a value X, calculating the values of Y and Z are left as an exercise for the reader. |
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I don't think you're going to get any noticeable effect from a single loop of wire. |
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Magnetic field strength falls away at 1/r³ so size matters. |
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Maybe if you made coil tubes (rather than a single wire) with radius at a maximum of about 10 meters you might be getting somewhere. |
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On second thought I don't think the losing energy via
heat would work. You also need to transfer
momentum. Although you can transfer momentum
with photons, they would all need to be travelling in
the opposite direction the junk is moving to slow it
down. |
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//How will the system cope with the wife variety of
junk orbits?// |
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Keeping the various and sundry flotsam of hair
products, curling, straightening, and make-up that
encircle our sink from overwhelming us and forming
a small planetoid is indeed problematic. If there is a
solution here to be had, I'm all for it. |
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//How will the system cope with the wife variety of junk
orbits?// Well, they're mainly between work, Tesco and the
local hairdresser so I'm thinking they'll be the easy ones. |
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More generally, though, the loop (or loops) would just
cruise around, slowing the orbits of whatever happened to
pass through. |
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I might also mention that a single pass is not intended to
de-orbit a piece of junk. Rather, this would act over
months or years, with multiple passes of junk through the
loop. |
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The question of who would operate it could become
a bit of an international bother. Could we perhaps
casually
'forget' to turn it off every time certain Russian
'weather satellites' passed by? |
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While you've been away on your hunt, your doorman
left a message with me that there's been some
visitors with random and varied accents calling who
seemed anxious to interview you. The usual NASA
guys with whom you're familiar, some folks from
the newly-formed Trump Space Force, a nice fellow
from the British Space Program, MI6, several seedy-
looking Russian callers wishing to 'escort you' to
parts unknown, a Chinese contingency of Huawei
executives, an Israeli Defense contractor, some
engineers from India, or perhaps it was Pakistan,
several fellows who simply wouldn't identify
themselves except by number and who worked for a
Mr. Blofeld, I presume they were business
associates of yours, and Sturton. Naturally I did not
disclose
to Sturton your whereabouts. |
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I wouldn't have been over there except that I simply
had to
complain about the bad parking habits and noisy
scuffles
raised amongst this motley assortment, which were
disrupting a nice game of croquet I had going on
with Prince Andrew. I recommend hiring a valet. |
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I think the main issue with this idea is that space is just too big for any practically-constructable ring
to be very effective. |
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The ring would take some of the momentum of the deceleratees (?), due to conservation of
momentum. If it's orbiting oppositely to them, which would be best for their deceleration, it would
also itself be maximally decelerated. If it's orbiting in the same direction, but more slowly (which
would be possible at the same altitude if that altitude is the ring's apogee, and the debris has a
higher perigee than the ring does), it would be accelerated and thereby kept in orbit by the debri's*
momentum, but it would also decelerate the debris much less. It may be possible to work around
this by using a "tacking" kind of technique, where it takes debris that's orbiting perpendicular to its
own orbit, effecting a (very small) plane change to itself instead of a raising or lowering of its
orbit. Then the deceleration of the debris is middling, while the ring's orbit is only affected in
direction. That could even be used deliberately, to maneuver into other orbital planes and clean
them up too. |
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// With a sufficiently large loop, perhaps passing through the Van Allen belts, could we create a
decent current using the earth's magnetic field? Would doing so slow down the earth? // |
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For the first question, probably. See related idea "Birkeland Current Transformer" [link]. You could
even, maybe, use that to power an electrodynamic tether [link] to raise the ring's orbit. For the
second question, I doubt it. I don't see how the momentum would be coupled back to the body of
the planet. But it has to come from somewhere, so maybe. |
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Tangentially, as a secondary purpose for this ring, you could also use it, or said electrodynamic
tether, to remove the Van Allen belts: [link] |
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//space is just too big for any practically-constructable ring
to be very effective// You're probably right. But if it
worked, each ring could be very cheap to build, and no
more expensive than a small satellite to launch. So, you
could have a lot of these things up there at any one time,
each of them whittling away at debris in one particular
orbit. |
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Alternatively, you could build a few smaller, very high-field
devices with enough propellant (or maybe ion thrusters) to
move around. Then you pick one piece of orbiting debris,
move a loop to intercept it, and degrade its orbit by a large
amount in one go. This still requires "one-by-one" clearance
of debris, but seems possibly easier and cheaper than other
"one-by-one" proposals like nets. |
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