May 30, 2011
I hate to start debating radio transmission with Steven Den Beste of all people, but I’m not sure there’s an issue. Den Beste says to get the power density low enough to be safe, you need a much-bigger-than 100 square kilometer receiver. That’s not impractically large, as he suggests, when you recognize that it’s a receiver for — as he notes — a godawful lot of power. Indeed, as I recall, and as this Wikipedia entry indicates, the old Solar Power Satellite concept called for receiver arrays that were kilometers square to receive considerably smaller — gigawatt-range rather than terawatt-range — power inputs. And these were to be open dipole arrays that would allow crops to be grown underneath, accepting a small reduction in efficiency for a much lower footprint.
That’s not to say that the Japanese idea is a good one (what do you do about the Earth’s rotation, something that isn’t a problem for geosynchronous satellites), but one of the characteristics of the old SPS idea was design for low-density beams that would ensure that a station couldn’t be turned into a weapon. Obviously, that would have to be the case with any lunar power system, too.
UPDATE: Mark Whittington emails: “Glenn – The Japanese scheme seems to be based on a concept developed by David Criswell some years ago. He has a paper that answers some of the questions being raised. For one thing, the article seems to have made a mistake about the 13,000 TW figure. That is the amount of solar energy the entire lunar surface recieves. Criswell’s scheme would transmit 20 TW which he says would provide sufficient energy for 10 billion people.”