Saving energy is silly; the bottom line is money (was Forklifts tip

I partly agree with Mike and partly disagree.

>
>> Therefore, energy differences are not directly relevant. Only 3%
>> of the Saturn 5 launch costs covered fuel (ref.: LEO on the Cheap).
>> Launch costs have virtually nothing to do with energy costs.
>
> Yes, granted, fuel costs are not the primary costs for spaceflight (at least in the current era). But we're not primarily talking about fuel costs. All other things being equal, higher delta-V destinations are more challenging than lower delta-V ones. Higher delta-V's require larger systems which are more expensive to build and operate. If we had been able to wave a magic wand and reduce the delta-V to land 2 astronauts on the moon to 1/20 its value, the Saturn 5 could have been a much smaller rocket and Apollo missions would have been less expensive.

Put another way, the fuel isn't a major cost, but the rocket structure
wrapped around the fuel is.

> The 1/20 delta-V advantage of the lunar surface over the Earth's surface is a significant advantage, and one which will easily outweigh any operational difficulties relating to the moon's lower gravity. If engaged in a program to build 30 or more SPS, the costs savings associated with this energy difference will pay for development of the lunar mine and mass driver, the mass catcher, and the orbital ore refineries and manufacturing facilities.

I have not gone over his figures, but in conversation with Dr. Peter
Schubert he mentioned that the crossover between building up lunar
industry to supply parts for power satellites was around $450/kg.
I.e., below that figure it was less expensive to build them with parts
from the earth. He also mentioned that the capital investment for
lunar industry was around $1.2 trillion and that the time frame was
around two decades to build up the capacity to produce ~300 GW per
year of power satellites. (Not certain I remember the time
correctly.)

By splitting the delta V to GEO between a low mass ratio chemical
stage that provides 4 km/sec and a low mass ratio laser stage that
provides 10 km/sec, I make a case for reducing the cost to GEO to well
under $100/kg. (see http://www.theoildrum.com/node/5485 for more
detail.)

Does that drop the moon out of consideration? Maybe not. One quarter
to one third of the mass of a high efficiency thermal power satellite
is radiator heat transfer fluid (2 km^2/GW of waste heat). Back in
the late 70s Eric Drexler and I wrote a paper for the Princeton Space
Manufacturing Conference on using finely ground lunar rock and a
little gas as a pseudo fluid for this purpose. (Heterodensity heat
transfer apparatus and method U.S. Patent Office: #4,759,404)

The velocity from lunar surface to EML1 is 2.5 km/sec, to GEO from
earth surface is 14.3 km/sec. The energy required to lift is
(2.5)^2/(14.3)^2 * 14.75 kWh/kg or ~0.45 kWh/kg. 100 t/hr from earth
surface to GEO takes 1.5 GW. 100 t/hr from LEO surface to L1 would
need 45 MW, 33 t/hr would require ~15 MW.

In the context of 500 MW/day power satellite construction this is a
nit. The question is efficient application. Space elevators in the
earth to GEO context are not possible at present because we lack
strong enough cable. An elevator from the moon to L1 is well within
existing materials, it need not even be tapered. As an endless loop,
driven from the L1 end it could even provide a few MW of mechanically
transmitted power to a moon base.

If the elevator delivered 2% per day of its mass (1650 tons) and
giving some margin for materials handling on the lunar surface, it
would take the the transport system up from earth less than a day to
lift it. Moving lunar rock from L1 to GEO is only 400 m/second. This
would be about 1.3% of the laser capacity being used to move 100 t/hr
to GEO.

I don't know if it would be less trouble to screen out fine materials
on the lunar surface or to send up unsorted regolith and grind it to
dust in a vibratory ball mill in space.

Best wishes,

Keith

PS, for station keeping reasons, you want a power satellite to be as
efficient as possible (to reduce the area). And the more mass the
better. Lots of mass averages the light pressure acceleration over a
year. Really light power sats require many tons every year of station
keeping reaction mass to prevent light pressure from blowing them away
like dandelion fluff.