Material trapped in L-points, LSP vs. L-SPS

Material trapped in L-points, LSP vs. L-SPS
Dr. Valentine has provided some responses:
> Someone on the SSI Maillist mentioned the possibility of useful
> resources being trapped at Lagrange points. I had responded with the
> below comment, and they then asked a good question. I know that SSI
> helped somebody with a doctorial dissertation on this topic quite a
> while back, but what kind of observations might have resulted?
That was SSI's first doctoral student, Scott Dunbar. To my knowledge, no one has yet done a systematic search.
> (Ah, but now I've consulted ssi.org and see that it was Sun-Earth
> L-4/L-5, not Earth-moon. But we'd be interested in info on either.)
> Since I never heard any more about it, I had kind of concluded that it
> was a bust.
There are now two known asteroids, each of considerable size, but
unknown composition, trapped in the orbits that Scott Dunbar discovered
nearly thirty years ago. The first is Cruithne. Ed Belbruno and Richard
Gott are formulating plans to visit the second one. Interestingly, an
asteroid was discovered in orbit about the analogous Mars Sun Lagrange
point before the discovery of those of interest to us. There should be
many more. These objects are difficult to see since the Sun is in the
sky most of the time, and they're not particularly close at any time.
The ideal solution to their detection would be a small telescope in
circumsolar orbit at less than 1 A.U. looking outward.
> To what minimum size can we rule out trapped bodies at either L-4 or
> L-5? Since a few years ago they said they had detected a Saturn 5
> upper-stage slipping back into a high Earth orbit, I'd assume anything
> that size or larger at L-4/L-5, we'd have already heard about it. I
> also remember someone telling me that navigation around L-4/L-5 might
> be a problem because clouds of dust had been spotted there, but I
> never saw confirmation of that anywhere else, so I question this. Can
> you let us know what you know on this topic?
I wouldn't worry. Escape speed from orbits around the Earth Moon
Lagrange points is on the order of meters per second IIRC. Even at tens
of meters per second, sunlight pressure would sweep them clean on very
short time scales. On a related note, though, Dave Criswell believes
that if we were to establish a large number of powersats in GEO that
micrometeroid impacts on them would generate a long lived cloud of
secondary debris that would really interfere with transportation.
>
> I might also take the opportunity to let you know that I'm having an
> E-mail exchange with Dr. David Criswell on the subject of Lunar Solar
> Power stations. He had taken note of my article about planetary
> chauvinism (http://members.aol.com/howiecombs/somewhere_else.htm) and
> saw where I implied that this might be the cause of someone supposing
> LSP to be competitive with lunar-material-derived GEO SPS. He
> insisted that his research had indicated that the cost of LSP power
> would be 1/50 that of L-SPS. I still just don't see how that could
> be. Interestingly, lunar lift costs does not seem to be the central
> point of his argument (unless I'm still misunderstanding him). Have
> you ever debated Criswell? What do you think of this comparison?

It is a complicated question. There are too many unknowns to be
confident now. He may very well be right. George Friedman, who has some
expertise in the area of microwave power transmission believes that LPS
could well be the more economic solution. And George does not think the
transmission issue is a problem. I don't worry about it, since the
economic success of either would imply cheap enough space transportation
and mature enough ISRU that we'd be all set for space settlement.
Feel free to post this as you see fit. Best regards, Lee

Regards,
Mike Combs