So. They talk about creating big satellites with tons of photovoltaic cells on them to create power from the sun and beam it to earth on microwaves. The reasoning, I believe, is that there is no atmosphere to attenuate the light, and it can be put in an orbit that leaves it in the sun at all times. (Although at the same time you might want it in a geosynchronous orbit, if you were constantly beaming down energy, and I don't think you can do both of those at the same time. (But whatever. It can just fill up big wicker baskets with energy and parachute them to earth, to be picked up by anyone.)) Regardless, my idea is that we just drag free floating, small asteroids into that same orbit and get them spinning so that one side is always facing the sun (with thrusters to keep them that way). One side of the asteroid would be very hot, and the other would be very cold, as they always tell us about the sides of the moon or whatever in astronaut books. Then fit them with heat transfer type energy production devices, like in geothermal plants, heating up water on one side of the asteroid and transferring it to the other to be cooled and go through turbines or whatever. (Oh wait. On earth the movement of water uses gravity and density differences doesn't it? Well. I am sure there are just dandy alternative ways of using the hot to cold difference to generate energy.) I dunno how expensive each option would be, but that is the not-baked part. Maybe this method would be more efficient than building solar panels and satellites and sending them up. And maybe with the kind of asteroid friendliness we would need in order to pull them near earth, we would be in a position to just mine whatever materials we needed to build the plants out of other asteroids anyway. And if you want geosynchronous orbit, just build a bunch so there are always some in the light. Who needs power at night anyway? :-)
-- Skullhead, Oct 19 2002

Lunar Prospector http://nssdc.gsfc.n...ary/lunarprosp.html
Mission cost estimation [FloridaManatee, Oct 04 2004]

Siemens PV specifications http://www.marksnyd...log/pv_siemens.html
Bang for your buck [FloridaManatee, Oct 04 2004]

//I dunno how expensive each option would be//

Actually, we have a heavenly body orbiting the planet (and I don't mean a Tera Patrick look alike on the international space station) - the moon. It's the size of a large to mid-sized asteroid and is about the right distance away because it hasn't bumped into earth recently.

So, let's say that you plan to install your solar array on the moon. The Apollo missions are an unfair comparison, but the Lunar Prospector mission cost US$63m and the reached the moon (but crashed). The payload weighted 158kg (350lbs) on earth. A Siemens SP75 PV array generates max output of 75 watts and weighs 20 lbs. So a payload of 350lbs would generate upto 26kW. And that's before you figure out how to beam the energy back to earth.

These calculations show you would have to pay US$2.4m per kW of capacity.

You can buy a gas-fired power plant for about US$350/kW. Grid electricity tariffs are about US 5 cents per kWh. It would take about 5,500 years to pay back your infrastructure costs.

The heat ransfer option looks interesting. NASA have some dandy 'heat pipes' that they use in their shuttles and space station, and you could theoretically stick a stirling engine in the middle. I guess these rocket scientists are, well, rocket scientists and have probably considered this when they decided PVs were more cost efficient.
-- FloridaManatee, Jan 23 2003


No no. This would be an alternative to PV panel solar energy stations. And I'm talking small asteroids, not the moon. Things we could tunnel through easily. The heat difference would be from one side of the asteroid to the other, not from the core to the outside. We could just build more geothermal plants down here if we wanted that.

And there are much more efficient ways to build things in space. Asteroids contain a lot of metal, and 'heat pipes' wouldn't need much in the way of advanced materials; silicon and the like. Just a form of stirling engine driving a generator. So we would just need to send up one craft to go get straggler asteroids (not in danger of falling into the moon or any large asteroids), use the metal (refinery? uh oh...) to build the heat engines, and push them into orbit.

We can send the electrical energy to earth in focused electromagnetic beams. There would be a lot of attenuation, but it would be free energy (ignoring the construction, maintenance)

Oh. Except beaming the energy to earth would probably require some advanced electronics, which would need to be sent up. Hmm. Well that's where the teleporters come in...

Basically it was just an improvement on the idea of a space power station. They say they should build a station with PV cells and beam the energy to earth, but PVs would need to be sent into space, not built from space material, they would be fragile, expensive, and not very efficient. Power asteroid heat engines might be better in those regards.
-- Skullhead, Jan 29 2003


Humn... actually saw an engineer's concept of an in-space stirling engine somewhere on a NASA website for providing either beamed power to earth or power in space. If I can ever find the link I'll post it.
-- Troubadour, Feb 01 2003



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