Re: Threading a moon

"IsaacKuo" <mechdan@xxxxxxxxx> wrote in message
news:1193674323.131681.139770@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Oct 29, 10:24 am, Logan Kearsley <chronosur...@xxxxxxxxx> wrote:
On Oct 29, 8:07 am, IsaacKuo <mech...@xxxxxxxxx> wrote:

As far as I can tell, yes. However, I think you can get much
better performance by putting the tethers in Jupiter orbit.
Put the tethers in Io's L1 or L2 point, to keep outside of
Io's "wake". You're still essentially getting energy from Io
due to the gravitational tugging, but you don't need to do
any tunneling and you can get a lot more exposure to
the ambient plasma.

How would you keep it stable?

Tidal forces do the hard part for you--namely, keeping the
tether stretched taut and oriented perfectly up/down.

The more interesting part is staying in orbit around the L1
or L2 point. As I understand it, there are stable orbits
which circle around an L1 or L2 point. If you stand on the
moon and look at the lagrange point, the satellite appears
to keep the same distance as the lagrange point, but it
slowly circles around it.

Those orbits only work in the plane normal to the line between the
moon and
its primary. Magnetic drag sould cause the satelite to drop further
in
towards the primary (or get pushed farther out, if the magnetic field
is
rotating rapidly enough), after which it loses its orbit and goes
flying off
on its own.

I wonder if you might be able to set up a co-orbital arrangement, with
the
satelite starting out in a slightly lower, faster orbit as a
consequence of
magnetic drag, but then getting pulled up by the moon's gravity when
it
catches up with it from behind; periodic gravitational assists,
essentially,
to transfer KE from the moon to the powersat.

Even if that works, though, I still don't like transmission losses.

-l.
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