Zubrin citisism

> Yes, but by the time we've depleted all the various resources
you've
> mentioned, I think we'll be several millenniums into the future.

Centuries, anyway. Exponential growth and all. But yes, long
enough that what we imagine now about the technology then is more
speculation or guess than prediction.

> My viewpoint is that advances of technology will never change the
> fact that obtaining resources from shallow gravity wells will
> require less energy than from steep ones. That will always make a
> difference, economically speaking.

It will indeed take more energy, and that will make a difference,
but if fusion works well, the additional energy well may be cheaper
than the time value of money to have your equipment moving from
asteroid to asteroid, for example. Then there's the recoil issue,
as with the moon: if you fling payloads from a colony or asteroid,
you've changed the orbit of the rest, whereas if you fling them from
mars or the moon you virtually haven't.

> The problem with mass drivers for Mars is that while Mars doesn't
> have much of an atmosphere, it's still enough to make horizontal
> EM launch off the surface more difficult and problematic than
> launch through a vacuum. Such launch from the Martian surface
> might be easier than from the Earth's surface, but that's not
> saying much; it's fairly impractical from the Earth's surface.

I recall reading some allegation that you would only lose about half
the energy of a telephone-pole-shaped payload launched from earth.
No idea whether that's accurate, though.

--- In spacesettlers@yahoogroups.com, "Combs, Mike"
>
> From: spacesettlers@...m
> [mailto:spacesettlers@yahoogroups.com] On Behalf Of Dan Wylie-Sears
>
> > > Mars is a waste. Too much gravity to make any mining
affordable.
> >
> > That depends on the value of the materials, and the technology
> > available to mine and launch them. By the time we deplete the
> > main belt, the Kuiper Belt, and various moons (assuming we don't
> > kill ourselves off first), mining Mars will definitely be
feasible.
>
> Yes, but by the time we've depleted all the various resources
you've
> mentioned, I think we'll be several millenniums into the future.
In
> which case technology will be so different that most any
prediction we
> make today will be wrong.
>
> My viewpoint is that advances of technology will never change the
fact
> that obtaining resources from shallow gravity wells will require
less
> energy than from steep ones. That will always make a difference,
> economically speaking. Marvelous technological advances may
reduce the
> magnitude of that difference, but will never eliminate it.
>
> > Possibly even before, depending on the technology. If mass
> > drivers, catchers, and energy sources all fulfill all our
fondest
> > hopes, then it might be simpler, for many materials anyway, to
> > throw stuff from Mars than to go chasing down asteroids.
>
> The problem with mass drivers for Mars is that while Mars doesn't
have
> much of an atmosphere, it's still enough to make horizontal EM
launch
> off the surface more difficult and problematic than launch through
a
> vacuum. Such launch from the Martian surface might be easier than
from
> the Earth's surface, but that's not saying much; it's fairly
impractical