Space Elevators

> And mars has very little that would justify a space elevator.

Depends on the time frame. In the near to merely long term, yes.
But exponential growth could deplete asteroid resources in a matter
of centuries, at which point the greater amount of matter in planets
would be of interest.

> Even settlement wouldn't do it, since settlers would want to
> spread out, and a elevator that just sits in one spot (or at best
> slowly orbits the equator) wouldn't be much use to them.

Surface transport seems likely to be fairly easy between all parts
of a settlement.

> Current 'low cost' plans for an earth SE mean 90% of its mass
> is 'launched' by cheep climbing robots that thicken the cable and
> act as a counterweight. All that carbon would have to be launched
> from Earth or harvested from an asteroid for a lunar SE - both of
> which would probably invalidate any savings in cost or simplicity.

Basalt fiber should work at least for the middle part that's nearly
in free-fall. This page
http://www.albarrie.com/presentations/basaltinfo.pdf
gives its tensile strength as 4.8 GPa and density as 2.8 g/cm3. I
don't know what the requirements are for a lunar space elevator, but
Wikipedia mentions a proposal to launch only a seed elevator and
make the rest out of lunar materials.

Even if a larger amount of earth-launched material has to be used,
at least it only has to get launched to L1 rather than needing the
additional delta-vee to fight the lunar gravity on the way down. So
it may fare better in comparison to other lunar plans than might be
expected.

--- In spacesettlers@yahoogroups.com, "ANTIcarrot"
wrote:
>
> > From: Brad Walsh
> >One thing I've gleaned, though--the engineering
> > challenges are so much less in a luner space
> > elevator, even a Mars one, that these will
> > probably be the proving grounds for the concepts.
>
> A lunar elevator would consist of a ribbon that points towards
Earth, and is
> long enough that its tip passes through the L1 point and is
affected by
> Earth's gravity, and hence self stabilising. I think
this 'stationary'
> construction might be too different to a 'moving' earth-style
space elevator
> to validate it. Current 'low cost' plans for an earth SE mean 90%
of its
> mass is 'launched' by cheep climbing robots that thicken the cable
and act
> as a counterweight. All that carbon would have to be launched from
Earth or
> harvested from an asteroid for a unar SE - both of which would
probably
> invalidate any savings in cost or simplicity.
>
> And mars has very little that would justify a space elevator. Even
> settlement wouldn't do it, since settlers would want to spread
out, and a
> elevator that just sits in one spot (or at best slowly orbits the
equator)