Would anyone be willing to clarify some points for me on SPS? Here's
my thinking so far.

Power can be generated on an SPS from a few technologies.
Traditional PV made from lunar silicon crystal growth. Can be made
completely with in situ resources, but this technology is not very
effective in power conversion. Also, radiation damage over a 30 year
period would neccesitate PV replacement.

A variation of the PV silicon process is Rare Earh PV technology
which yields higher efficiencies, but requires importation of
critical raw materials from earth.

We could use Thin Film technology which has lowest efficiency, but
quickest manufactuirng time.

Or we could use Solar Thermal which has the highest efficiency, but
introduces mechanical complexity and liquid transportation into our
scenario.

After considering these options, I tend to favor the Solar Thermal
route.

So my questions on how to construct a SPS follow.

Considering that whether the SPS is in GEO or at lunar L1 (for
servicing the lunar facility power requirements) the SPS will
require an occasional orbit maintaining burn, this leads me to
conclude that the structure of the SPS will have to be designed to
take these forces into account. It can't be a pure zero-g
construction.

So, what should the infrastructure of the SPS be constructed of?
Steel Pipe? Steel girder? Aluminum? What dimensions for the beams?
Straight beams or triangular trusses? I'd love to hear peoples
thoughts on these issues.

My operating assumption is that the SPS has an infrastructure on
which to lay the Solar collecting apparatus. For the moment I'm
working on the assumption that the SPS would be comprised of row
after row of parabolic troughs, where each trough concentrates the
solar energy on a liquid coursing through a pipe centered on the
focal point of the parabolic trough. The liguid would be taken to a
series of Stirling engines located behind the solar facing surface
(on the dark side) and the electricity generated from these engines
would be sent to a central microwave transmitter.

OK, open fire and let's fix this scenario.

One other assumption I'm working with is that once the microwave
transmitter and at least one engine are in place, power can be
generated and transmitted while construction on the infrastructure
continues and additional power is brought on line. Is this feasible?

Well I'm no engineer to be getting into the specifics, but is there any
reason for the Stirling engines to be on the shadow side? If some of the
collected thermal energy has to be used just to keep the equipment above
-200 Kelvin, that's a needless inefficiency, one that can be easily
corrected. Thermal energy from the sun is abundant out there, and free for
the taking if you just consider the geometry of your craft.

As for operating as you build, the only problem I can see, and it's
solveable, is that any time you do need to use the thrusters, the
center-of-balance equation changes as more pieces are added to the
satellite. As long as you don't use your thruster, it doesn't matter what
the configuration is.

dADdy ASTRA