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Tethers Will Be Tested To Boost, Deorbit Payloads
Constellation writes: "The IEEE is posting an article on how a tether (a long thin piece of wire) can be used to increase to orbit of, or deorbit, a spacecraft. The article also details NASA's plans to test this technology in December. A further article describes how a similar technology will be applied to Mir later this year, or early next year." Sure -- while you're up there, why not drag a 5km wire around for a while?
The problem with dragging a wire is that the wire is smaller than the size of the hole many pieces of micro-debris would make. This means 1 impact = broken tether. To avoid this, at least one company is working on a "mesh" tether which has multiple redundant load paths and is interconnected at relatively close spacings. If one strand of the mesh is broken, other strands take up the load. This greatly extends the lifespan of the tether even in a hazard-rich environment.
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Time is Nature's way of keeping everything from happening at once... the bitch.
Although space junk is a real and growing problem, this will not contribute to it unless the tether breaks. While you can't rule out that probability, conventional satellite boosters contribute to space junk by their nature, as they spew out flakes of, say, aluminum. So I think we win here.
The SETI comment simply makes no sense. The wire might be long, but it's thin -- according to the article, 1.2 millimeter (=0.12 cm) in diameter. According to SETI@home, the search uses 1.64 GHz, or a wavelength around 20 cm. As elementary wave physics tells you, the wire is much too small to be "seen".
I suppose it might be possible that this could act as an antenna. In that case, it is small and high, and the signal almost certainly will be negligible ... even if it happens to radiate around 20 cm, which requires a cosmic conspiracy to happen.
The Mongrel Dogs Who Teach
NASA has been experimenting for sometime using long strands of wire and the earth's magnetic field to generate large amounts of electricity to power space stations and the like. Now they seem to be using it for a different purpose. Still relies on all the same principles. I suppose physics is just glorified math anyway.
This will actually reduce space junk, not make more of it. Rather than having to send up new satelites when the fuel runs out or sending extra resupply flights with fuel for the space stations, solar panels can collect electricty and provide thrust via these wires. All this and its environmentally friendly, since it doesn't waste millions of pounds of fuel just trying to get fuel into orbit!
science is a religion
Just to clarify a bit. There are a few different things you can do with tethers once you've mastered the art of winding and unwinding them, building tethers resistant to single-point breakage, and so on.
1. Trade off electrical power for orbital altitude. You can do this either way, running as either a motor or a dynamo.
2. Dangle an object in the upper fringes of the atmosphere. This is an area which is normally hard to study, as you can't stay in orbit long, but it's too high to fly a plane or balloon. A big orbitting spacecraft dangling a small instrument package on a tether can be a useful combination.
3. Rotating tethers can be used to tranfer orbital momentum between different satellites in various possibly useful ways. The most extreme case has one end of the tether actually touching the ground (with no horizontal velocity) every rotation. You just grab hold and get lifted up into orbit, or even launched out of Earth orbit -- of course you have to land enough matter to keep the tether spinning.
4. stabilization. Even quite a short (100m) tether will be stabilized by Earth's tidal forces and can be used to keep a satellite pointed in a certain way
AIAA-2000-3615 Design and Simulation of Tether Facilities for the HASTOL Architecture (Hoyt)
AIAA-2000-3866 Design and Sim of a Tether Boost Facility for GEO, Lunar, and Mars Transport (Hoyt, Grant, and Bangham)
AIAA-2000-3865 Computation of Current to a Moving Bare Tether, (Onishi & Martinez, MIT, and Cooke, AFRL)
AIAA-2000-3870 Future Application of Electrodynamic Space Tethers For Propulsion (Santangelo, Michigan Technic and Johnson, Nasa Marshall )
.pdf format on CD-ROM at the conference anyway, and 2) many distribution systems exist which would allow the organizations to distribute them electronically and still get paid. Please complain (nicely) to Webmaster@aiaa.org about this, since my lonely voice is probably not loud enough to cause action.
I apologize for not being able to link to the specific papers or give much additional information, since this panel ran at the same time as one I was more interested in and the papers are copyrighted by AIAA. The fact that technical publications are generally not available upon demand except in bulk or by federal express is increasingly irritating to me, since 1) they are available in
Rev. Neh
propulsion geek
... and there is no doubt, that one day he will be
where the eye of his telescope has already been
you may make light of this development, but it really is quite significant. The earth has a magnetic field, and as we all know from our basic physics class we had to slog through in college, that a conductor passing through a magnetic field generates a current, and from the current a force. If you play the wire down from your position, and let it generate electricity ( IE dont provide a stopping voltage) your speed decreases and your orbit drops, if you play the tether up from yoru position and apply a voltage to the wire, say from some solar panels, you increase your speed and your altitude increases (actually your speed goes down when you go up and up when you go down, just one of the kinks of orbital mechanics) All of this can be done WITHOUT PROPELLANT, which really kicks some major ass, because a huge amount of money is spent on propellant and complicated ion and regular rocket engines, and wire is really really cheap. THis is a major development for the space and satellite industries
So thats whats with all those kids i've seen running around the mall with leashes attached to them... that was just NASA testing the feasability of tethers on high speed objects.