Asri-unix.750 net.space utcsrgv!utzoo!decvax!ucbvax!ARPAVAX:C70:sri-unix!jef@LBL-UNIX Wed Feb 10 14:32:14 1982 Lunar SPS (Solar Power Station, not satellite) The antenna size and feedback loop problems both go up only linearly with increased distance of transmitter. The moon is ten times as far as GEO. Thus the transmitting and recieving antennas must be sqrt(10) times as big (their PRODUCT must be 10 times as big), and the earthside reference transmitter must lead the recieving array by kilometers instead of 100's of meters. (For those of you who haven't come across the rule-of-thumb for minimum antenna sizes before, it's: d d = l lambda 1 2 where d1 and d2 are the antenna sizes, l is the distance between them, and lambda is the wavelength you want to transmit.) So, the extra distance of a lunar SPS is a disadvantage, but not a big one. As was mentioned before, there are obvious advantages: the materials are available locally, we don't have to cope with the unknowns of zero-G engineering. The day/night problem remains, though. One suggested solution was two SPS's on opposite sides of the moon. I think you would want three, but either way, this either requires relay antennas in orbit (in which case, why not build the SPS there in the first place??!?), or a power transmission grid on the moon's surface. Since the grid would have to cover many thousands of km, it had better be superconducting. So here's my question: what about superconducting cables on the moon? Would simply shielding them with a mirror keep them cool enough, or is refrigeration necessary? --- Jef ----------------------------------------------------------------- gopher://quux.org/ conversion by John Goerzen of http://communication.ucsd.edu/A-News/ This Usenet Oldnews Archive article may be copied and distributed freely, provided: 1. There is no money collected for the text(s) of the articles. 2. The following notice remains appended to each copy: The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996 Bruce Jones, Henry Spencer, David Wiseman.