lunar poles, orbits, trajectories

From: spacesettlers@yahoogroups.com
[mailto:spacesettlers@yahoogroups.com] On Behalf Of Dan Wylie-Sears

> The situation I'm talking about is that there's no point in
> mining the moon where the hydrogen is, because the only place
> you can have it caught isn't accessible from there.

Other possibilities include building a rail line from a pole to a
launcher near the equator, although this would be a very expensive
proposition. But there may yet be a solution which still involves
mass-drivers.

I had to work this out for a short sf story I wrote a few years back
(http://members.aol.com/howiecombs/tnbttbt.htm).

You have a launcher near the pole which is pointed toward the equator.
You launch not just the ice, but the bucket that the ice resides in.
The bucket travels 1/4 of the way around the moon, skimming the surface
and just barely clearing mountains. Near the equator, a sort of
"reverse mass-driver" decelerates the bucket and its payload to a stop.
The ice in the bucket is then launched to L-2 in the usual manner. You
alternate between sending buckets of ice to the equator, and launching
empty buckets back to the pole.

I was attracted to this scenario because, unlike with a rail line, there
was no need for infrastructure every mile of the way.

An interesting aspect of this is that if the equatorial
mass-driver/catcher is decelerating full buckets, but only accelerating
back empty buckets, it will be generating more electrical power than it
will consume. So this mass stream would provide a conduit for energy
generated at the poles to be sent to a place which must endure the 2
week long night.

A few years after I wrote this story, an SSI associate spoke of the need
for what he called an "anti-mass driver". I took encouragement from
this since it seemed at least somewhat similar to what I had
hypothesized.

> If you could launch with an arbitrary amount of excess speed
> to an orbiting catcher,

Unfortunately that won't work. Excess amounts of speed would only raise
the apogee (apolune) of the catcher's orbit. The problem we face is
that catching payloads launched from the surface will depress the
perigee (perilune) of the catcher's orbit. I don't think anything will
raise the low point of the orbit save a reaction engine on the launcher,
which means we're talking loss of reaction mass.

The lunar-surface-to-L-2 scenario was only judged economically viable
because it could involve small dumb payloads (sintered balls of soil,
actually) and because at L-2 there was no need for the catcher to
overcome the action/reaction of the incoming payloads.

> Of course the attached mass driver would be a motor, but why
> shouldn't it also be a delivery system?

Because action/reaction forces would propel the catcher away from us,
and it would be lost. Someone on the list said it best: The big
advantage of the moon is that its enormous mass means we can launch and
launch from it without changing the orbit of the launcher.

Regards,

Mike Combs