Awatmath.1678
net.space
utcsrgv!utzoo!decvax!watmath!pcmcgeer
Tue Feb  9 20:35:00 1982
Mooning Around
	The Lunar SPS would, of course, deliver power only for half the time.
Of course, this could be said about a geostationary SPS, since it would be
in the shadow of the earth for 12 hours out of 24.
	The Lunar SPS proposal has some merits, though :
1) We could keep it stable.  Precisely how would we keep a free-floating SPS,
several square kilometers, from tumbling about a planar axis?  And if we could,
precisely how do we stress something like that?  These really are mundane
questions, but do we know how to do these things?
	A lunar SPS, on the other hand, has no such problems.  It's merely
a large, flat plain of collectors.  We transmit from the surface (probably
Mare Crisium) to a sattelite in Geosynch orbit above the moon, which transmits
to a buddy in High Earth Orbit.  The principal advantage is no large,
freestanding structure;
2)	The materials are there, or at least we hope they are.  Siliates are,
for sure.
3)	(A cheap advantage, certainly) There would probably be much more
public support for a Lunar base than for one in High Earth Orbit.  The Moon
has always had an emotional appeal that HEO doesn't share.  The space program,
like all government programs, depend in the long run on their public support;
therefore, the chances are better that we will be able to build the Lunar
SPS, if it's technically feasible;
	Which it might not be.  The power-half-the-time problem can be
solved by putting another SPS over on Farside.  Another, better question,
which I haven't got the foggiest idea about, is how we transmit the power -
even a laser spreads somewhat over 400,000 KM, and the satellites orbiting moon
and the earth, the ends of this game of celestial pitch - and - catch, will
have a velocity difference between them.
	This is further complicated by the 3-sec feedback loop.
	To another question - yes, the Moon does orbit in the plane of
the ecliptic, or near enough as to make no difference.  This fact, plus
the low tug-of-war ratio for the moon (about .46, as against an empirical
minimum of 30.00 for a true satellite, led Asimov to speculate that the
Earth-Moon system is in fact a binary planet system..
                                    Cheers,
                                          Rick.

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