Jed Rothwell wrote:
Um -- I can't comment on the _latest_ incarnation, but I can say that the earliest version of space-based energy systems I'm aware of was indeed solar-to-microwave. The trouble with that is the antenna farms at the receptor end, and the downlink energy density. That's always been the trouble with it: with very low energy density in the downlink, it's safe, but you need enormous antenna farms to collect it (think solar energy: at low power densities the beam energy density will be comparable to sunlight). At high beam power densities you have a problem finding a spot for the beam that won't affect people or animals. From what I've read, hazards of stray microwaves seem more significant now than they did back in 1976 and opposition to high-intensity downlinks would probably be even stronger now than it would have been then. 30 years ago nobody had a clue how microwaves could possibly cause damage to living creatures, save by cooking them, so they were generally considered completely safe. As I recall, some time in the last decade it was finally determined that non-ionizing radiation _can_ affect chemical processes about which living things care, and the idea of a microwave downlink in somebody's back yard no longer seems so jolly.The only conventional energy source that offers the same kind of unlimited power and incredible capablities that BLP or CF offer is spaced-based solar. I guess that would be solar-to-microwave, in the latest incarnation. (Right?)
Or an L-5 colony, which, I seem to recall, was the original planned platform for putting the SSPS units in place :-) But then, how do you get the colony in place without an elevator? Uh....And as I see it, the only way to get that is with a space elevator.
Some of the ideas for collecting solar power from that era were kind of cool, actually. For a cheap mirror, for instance, you take a big blob of liquid plastic (melted or not polymerized yet, whatever) and blow a bubble in it. If you do it right, you can make the bubble re-e-e-a-lly big -- like a kilometer or so across (vacuum and microgravity are supposed to make this easy). Then after it hardens, you cut a small hole in the bubble, zip to the middle, drop a thermite bomb there, and leave before it goes off. The bomb goes off, aluminum and iron vapor go whizzing off in all directions only to be stopped by the plastic film, and Shazam, you have an aluminized (or iron-ized?) plastic sphere a kilometer across. Now carefully cut it in half, and separate the two hemispheres. Now you have the mirrors to build two solar furnaces, each a kilometer in diameter, and the material cost was almost nothing. Granted the mirrors aren't very good -- wicked spherical abberation -- but for solar concentration they're just fine.
I wish the people in Washington would take that seriously, instead of chasing off after expeditions to Mars. I wish they would ditch the International Space Station and get on with elevators instead.I dunno if an elevator will ever work, but I agree about the ISS -- a cash sink of that magnitude without an obvious purpose isn't doing anyone any good. It was scaled back so much that NASA itself said it should be scrapped rather than pursued at the current level, but it didn't happen (this was ~10 years ago; wish I could remember the quote).
If we can't have an elevator, then even a sensible space plane would be better than what we've got now.
Mars won't happen, anyway -- it's another of those wonderful unfunded projects of the current administration. All the big expenses are pushed to the future and little or no actual cash is disbursed in the present. But it sounds good in a speech.
- Jed
