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ToSeek
2003-Jun-18, 05:31 PM
Tether Technology: A New Spin on Space Propulsion (http://www.space.com/businesstechnology/technology/tether_tech_030618-1.html)

Not quite the space elevator we've talked about, but maybe it's a first step.

Nicholas_Bostaph
2003-Jun-18, 06:08 PM
I'm not sure if I understand this completely. When the tether grabs the payload and "pulls" it to give it a boost, that object will also pull on the tether which will either slow its spinning down (eventually stopping it) or pull the system out of a stable orbit, right? They could place some kind of propulsion system to maintain the speed and orbit, but getting the fuel up there for that would offset the whole tether system's benefits...wouldn't it? Sorry...a bit confused.

eburacum45
2003-Jun-18, 07:17 PM
Yes, when the tether is lifting mass out of the earth's gravity it does lose energy and therefore finds itself in a lower orbit;
however when it is lowering mass into the earth's orbit it actually lifts itself up.
I presume that more mass will be going up than coming down (at least at first).
you will notice that the tether has solar panels, which can make up part of the shortfall and inefficiencies; the tether itself can generate electricity by cutting through the Earth's magnetic field, although this too takes energy out of the orbit.
Eventually tether systems could become self supporting in energy, assuming a lot of asteroid material is imported from near earth orbit;
these systems would work well at Jupiter or Saturn where there are lots of ring material which could be converted into tether generated electricity.
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Nicholas_Bostaph
2003-Jun-18, 07:30 PM
Of course, I hadn't considered the return trip. I did notice the solar panels but didn't think we had any efficient means of converting solar energy to propulsion. Thanks for the explanation, that helped a lot. :)

daver
2003-Jun-18, 07:51 PM
Y the tether itself can generate electricity by cutting through the Earth's magnetic field, although this too takes energy out of the orbit.
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This is reversible--you can pump electricity into the tether and have it boost itself into a higher orbit (ths ends up looking a bit like an ion drive).

Rotating tethers can be put in a resonant orbit, so that the ends of the tether always descend over the same spots on earth (say, the tether turns four times every orbit, so that one end can pick up at, say, 0, 90E, 180, 90W and the other at 45E, 135E, 135W, 45W). If you size your tether correctly and pick your orbit well, you could make some money on long distance terrestrial travel.

Glom
2003-Jun-18, 09:14 PM
Cool.