Re: Why Planetary Bias in SF? Was: Terraforming Mars by crashing comets into it

On Mar 11, 11:43 pm, jdnic...@xxxxxxxxx (James Nicoll) wrote:
In article <be572550-fd06-400d-97df-1e9ea21f4...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
<CharlesRCap...@xxxxxxxxx> wrote:
On Mar 11, 12:29 pm, jdnic...@xxxxxxxxx (James Nicoll) wrote:
In article <01a4d523-253b-4b87-9d7a-c1ad01626...@xxxxxxxxxxxxxxxxxxxxxxxxxxx>,
<CharlesRCap...@xxxxxxxxx> wrote:

If I haven't screwed up my figures, the Earth's crust is
about 8% aluminum, a slighly fraction than the fraction of regolith
that is aluminum. Why do we need to go to the Moon to acquire an
element that is so common on Earth?

It's not the commonality of the element itself that's really at issue;
the problem is that aluminum is really energy intensive to produce.
Ever wonder why steel is still used for automobile frames while
aluminum would be lighter and thus more fuel efficient? It's because
aluminum is so much more costly to produce and form due to the vast
electrical requirements. In addition to costing more in a dollar
format it is also more costly in heat pollution. (Which is not a
problem just yet on Earth, but it's not hard to see it becoming so in
the future. My foray into "stealth in spaaaace" has taught me (if
nothing else) that no matter how efficient you become in generating,
transmitting, and using electricity, the waste heat is always there.)
(There has been some discussion of using the new electrothermal
technology that is coming out recently to recapture some of the heat
wasted in the aluminum process to make it more efficient, perhaps
enough to supplant steel for automobile frames.) If you can move the
waste heat and the energy requirements of production off of Earth you
get three major advantages. One is you no longer need those unsightly
strip mines on earth (or that army of lawyers your company uses to
keep the greens off your back), two is you no longer need to spend
that electricity on producing aluminum so you can use it on other
things, and third is that waste heat no longer needs to be dumped into
a handy river. There is some question of whether it would be cheaper,
and I don't think we have enough data to answer that yet (though I
remember seeing figures purporting that it would be), but it is
certainly cheaper to produce it there for space applications than
launching it from the surface of the Earth.

It could also beam power to Earth while the sun is shining at
least.

And why would I expect this to be cheaper than applying similar
technology on Earth?

Well for one, since the moon is airless and the sunlight is stronger
you can get a much higher thermal gradient on the moon (as well as
higher total input), making the process more efficient. (373K to 126K
is a mighty fine gradient to work with, and the top end is much higher
if you use mirrors to concentrate the light.) Finally the higher
temperatures and steep gradient allows for the use of turbine
generation instead of photovoltaic cells. Solar cells would be a good
choice starting out, once you really get going the turbine types
ultimately would be more efficient.

Aside from the cost of manufacturing these things on the moon, it
would be cheaper, but that's not the point. It would mean less surface
space cluttered with opaque photovoltaic cells and less heat
pollution. (No matter how efficient you make the solar cells or other
types of devices being discussed they are still going to produce some
waste heat.) The receiving end of microwave transmission is something
like 80+% efficient, and could be polished to reject the solar
radiation or pass it through to solar cells or pastureland underneath.
Also you can put a higher density of energy into a rectenna than a
solar cell, so you don't need forests of them to get the electricity
into the system.

So it's not really about being cheaper, but practicality. I'm all for
green energy, but the one thing that does bother me about solar is
that not everywhere is as good a place to do it as my old stomping
grounds as a child. I used to live in the high desert north of Los
Angeles. The place is nearly the perfect place to do solar: Its
average cloud cover is negligible, the altitude is high so the solar
intensity is about as good as it gets in the US, and finally there is
just miles and miles and miles of absolutely nothing there. In short,
a perfect place to do solar. It also happens to be one of the best
places in the US to do wind power also since the winds are constant,
strong, and predictable. So California has a great green energy
resource in the high desert. However I currently live in South
Carolina. The situation couldn't be more different: there is little or
no wind, it's cloudy all the time and the altitude is low. There is
tidal power at the beaches, but it's not nearly as strong as on the
west coast and I think that the tourism people would pitch a fit if
someone tried to put up a series of tidal generating stations. South
Carolina does not have much in the way of green energy resources.
There is hydro, but I think most people know that's not as green as it
looks (and they already have all the best spots dammed as it is),
there is also biomass, but that is still burning stuff to make heat.
Not exactly the wave of the future. So it's no surprise that the
southeast is looking into building more nuclear plants. It's really
the only good solution to the problem. Even though solar will work it
would just not be reliable enough to produce the baseload power that
we need, and the literal forest of solar cells that would need to be
erected to provide the juice would be staggering. (Considering the
average amount of energy that reaches the ground and the current 10%
efficiency rate.)

So aside from Fission power, beamed microwave power seems like the
best option. It's not stopped by clouds and you could put the
rectennas up over farmland (which there is plenty of here). So if
there were to be solar power from space (most likely on free floating
satellites in geosync orbit rather than the moon) there would
definitely be a market for it. So if you are on the moon producing
aluminum anyway you might as well get into the solar power game as
well. But since the best option for such power are those free floating
geosync satellites, the moon would be a handy place to build and
launch them.
.

Relevant Pages

  • Re: The future of Lunar exploration?
    ... explorers will be robotnauts:) CMU is working on giving them AI ... Lets look at a system that has been used to power high-altitude solar ... So, for the moon; ...
    (sci.space.policy)
  • Re: The future of Lunar exploration?
    ... explorers will be robotnauts:) CMU is working on giving them AI ... Lets look at a system that has been used to power high-altitude solar ... So, for the moon; ...
    (sci.space.policy)
  • Re: A Moon base is too far; an asteroid ship better alternative:)
    ... >> comes from solar panels on the other side of the moon or from a great big ... >> nuclear pile a couple of miles away... ... >Running power lines all the way around the Moon is itself a daunting ...
    (sci.space.tech)
  • Microwave power transmission on the lunar surface
    ... Assuming a lunar settlement uses solar power for all their energy ... moon, total power production would be relatively constant. ...
    (sci.space.tech)
  • Re: The Cold Equations
    ... > All that aluminum stuff was just myself being in jest, ... >>for 1 year at our current rate of energy consumption. ... > The low estimate of a million tonnes worth of available He3 is being ... > highly conservative about what the moon has to offer. ...
    (sci.space.shuttle)