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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.space
Subject: Re: Another Use for Tethers
Message-ID: <6307@utzoo.UUCP>
Date: Tue, 21-Jan-86 15:49:23 EST
Article-I.D.: utzoo.6307
Posted: Tue Jan 21 15:49:23 1986
Date-Received: Tue, 21-Jan-86 15:49:23 EST
References: <8601161312.AA15050@s1-b.arpa>, <98@dg_rtp.UUCP>
Organization: U of Toronto Zoology
Lines: 30

> The notion is to extend two tether ends (with some small mass or other
> on each) away from the station, one primaryward, the other
> anti-primaryward.  Tidal forces will produce a tension on the string...
> Then merely use a solar powered eletcric motor (with the tension on the
> tether as an "anchor") ...
> 
> In fact, isn't this method used (at least partly) to stabilize the space
> telescope?  I had read where at least some satellites were stabilized
> using this method, but I may be remembering some fictional scenario...

Not the space telescope, but a number of satellites are stabilized this
way.  It's called "gravity gradient" stabilization, because the reason
for the tidal forces is that the primaryward and antiprimaryward masses
are at different distances from the primary and hence feel slightly
different gravitational accelerations from it.  Tethers probably would
not do; you need rigid or semi-rigid structures to transmit torque.  The
distances don't need to be all that long, either:  LDEF (the Long Duration
Exposure Facility satellite), which is maybe 3 times as long as it is
wide, is stabilized this way.

Remember that the tidal forces on your "anchor" mass must be stronger than
those on the mass you are rotating.  Remember also that these forces are
fairly small, so don't expect rapid rotation rates.

The Space Station probably will use gravity-gradient stabilization, if
for no other reason because gravity-gradient effects are unavoidable in
something that big, and it's easier to use them than fight them!
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry