A few of my friends got into a discussion a few nights ago about the feasibility of having a space based power plant fueled by the temerature difference between sunlight and dark in space. Put simply, it would be a fairly flat station facing the sun, heating water on the sun side and cooling it on the space side, turning thrusters in between. How the energy generated was to be sent to earth was never fully kinked out.
We ended deciding that much of the cost effectiveness would be determined by how fast the space side could cool off. If it would be fairly cold, then efficiency and power output would be high. If not, it may not be worth it. I’m posting this to get people’s opinions on the idea and get advice on how effective the cooling would be.
Of course, right now it’s not feasible anyway for two reasons: lack of a distribution method and no practical way to get that much mass into orbit around the sun. Go highlift systems!
The idea has been around for some time. Google “L5 Society” for the full story. It was proposed that you could have solar power satellites in geosynchronous orbit, using either solar panels or mirror-focused solar thermal generators. The power would be beamed to Earth by microwaves, which could be converted to electricity with fair effciency. To minimize construction costs, proponents suggested investing in an extensive infrastructure in space of lunar mining and self-sufficient rotating colonies in high Earth orbit. In theory it sounded great but sadly little actual followup beyond concept studies was ever done.
One the biggest problems with this ever getting built is that any so-called ‘power system’ which beams energy down to Earth via microwaves would be identical to a ‘death-ray’ type weapon.
You could probably build something like that, but you’d have problems.
Thermal Efficiency:
This is where you’re lost. Radiation is the worst possible method for transferring heat. Yes, you probably could build a satellite with a “source side” and a “sink side,” but it would have to be enormous to generate anything useful, and how are you going to keep it oriented properly? Gas jets? Which leads me to:
Working Fluid:
What are you going to use? Water? Propane? Hydrogen? How much, and how are you going to contain it? Which leads me to:
Pumps, manuevering, and telemetry:
You have to power all this stuff somehow. (I know, I already asked about the jets.)
Transmission:
You’ve tapped all this power, so how do you get it down here? More equipment, I suppose, but that sort of flux is dangerous for people in airplanes who happen to pass under it. Which leads me to:
Orbital mechanics:
How are you going to get all this stuff up there and keep it there? (I know, jets again.)
The trouble you have is that you have multiple insouluble and interrelated techinical difficulties and a complete inability to lift it in the first place.
You’re on the right track with the heat engine, though.
I don’t have my college physics books handy, otherwise I’d try to find out the radiant properties of a black panel and outer space. Still, I suspect that you’ll gather heat much faster than you can radiate it away on the “cold” side
The collection of solar power will be achieved, but not soon. It probably wouldn’t be a water exhange system, although simplest is best, of course.
**Diceman[b/] the dark side of the collector would radiate until the whole thing reached thermal equilibrium, and this will determine the thermal efficiency.
I expect it would be more likely be solar power cells in gigantic self repairing arrays- most of the materials collected from the Moon and not from Earth.
First you need to cover the Moon in solar collectors to power the linear accelerators to launch the power swarm into orbit-
where shall we put them?
How about the various Lagrange points?
How should we manouever the solar collcting units?
Try He[sup]3[/sup] from the Moon’s regolith.
As you say this whole program will be very expensive, and might take a hundred years to break even (by which time there may be commercially viable fusion, and the power won’t be needed on Earth for a while.).
But once started, the solar collection swarm will continue to grow and could power space craft, industry and orbital habitats around the Earth.
Let’s not overdo the pessimism- with luck every problem can be overcome when the prize is a trillon times the energy budget of the Earth-
it will not happen overnight, is all.
A hundred years to break even is way to long for potential investors in something like this. If we wind up with space power as a secondary result of colonization, cool. If not well you’d better get launch costs down to about a buck a kilo.
Internal gyroscopes can be used as fixed points of orientation to adjust the array. A stirling engine would work quite well as a generator under those conditions.