[ExI] Why no space colonies or lunar bases? was Moo

Keith Henson hkeithhenson at gmail.com
Mon Jul 25 15:27:38 UTC 2011


On Mon, Jul 25, 2011 at 5:00 AM,  "spike" <spike66 at att.net> wrote:

> The challenge with a space elevator on the moon is that Luna's synchronous
> orbit is so far away because of the slow rotation rate.  Earth is in lunar
> synchronous orbit.  So we have materials theoretically capable of doing
> that, but we need one that is over a quarter of a million miles long.

Lunar elevator as envisioned by Jerome Pearson is a different kind of beast.

The counter tension is not from rotation, but from hanging down into
the earth's gravity well.

L1 is only 55,000 km off the lunar surface.  The cable goes through L1
and far down into the earth's gravity.  It needs a counterweight, and
the shorter the cable, the larger the weight needs to be.  I worked
one out with a small counterweight and then realized that there was an
ideal length if the point of a lunar mine and elevator was to get mass
to GEO.  190,000 off the lunar surface happens to be where just
releasing something puts it in an Hohmann transfer orbit to GEO.
(Plane changes have to be considered.)

So an elevator made of Spectra massing 0.1 ton per km would take
19,000 tons of cable and 65,000 tons of counterweight.  Built as a
loop and powered with 15 MW, it could deliver 1000 tons per day for a
mass return on investment of around 100 days.  Totally silly at
present, but where 500,000 tons per year of power satellite parts was
being lifted from earth, you could borrow power sat parts for the
counterweight and replace them with lunar rock 65 days after start up.

Some of the mass for power satellites, gravity gradient "space
anchors," can be made out of unprocessed lunar rock, the solid part of
heat sink pseudo fluid can be made out of regolith ground to dust.

> Given the relatively modest escape velocity and very low surface atmospheric
> density, an electromagnetic rail launcher is a more attractive means of
> getting out of that gravity well.

That's so 70s.  Lunar elevator is a much better solution than
electromagnetic launch.  You don't have to soft land a kg on the moon,
just lower the cable with a 65 ton crawler/miner on the end.

A flat version of Keith Lofstrom's launch loop would also work on the moon.

Keith




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