SOLAR POWER FROM SPACE (again)

[madd0ct0r]

Tiptoeing closer:

http://www.guardian.co.uk/environment/2 ... arms-space


Though I can't see how they plan to keep a contiuons stream of energy going to one earth based reciever.

Bit of a fusion idea i suspect.

[Ford Prefect]

Though I can't see how they plan to keep a contiuons stream of energy going to one earth based reciever.

Microwave transmission of power is, as I recall, plausible or at the very least possible.

[madd0ct0r]

almost constant but not quite.

thinking it over though, the lost time would be in the middle of the night when consumption's low anyway.


They were talking about radio waves not micowaves.
That may be to avoid bad associations, or they may be intending to use radio. not certain.

[GrandMasterTerwynn]

almost constant but not quite.

thinking it over though, the lost time would be in the middle of the night when consumption's low anyway.


They were talking about radio waves not micowaves.
That may be to avoid bad associations, or they may be intending to use radio. not certain.

Err . . . microwaves are radio waves. They're just radio waves in a certain portion of the frequency spectrum. If you've got a cellular phone, you've got a source of microwaves. Think about that the next time you make a call. Putting that aside, microwaves are ideal for use with space-based solar systems as you can pick a frequency that the atmosphere is transparent to, which can be picked up with relatively small and inexpensive rectenna design.

[Sky Captain]

What kind of rocket are they going to use? Building an orbital solar power station would require some serious heavy lift capacity since you`d need many square kilometers of solar panels and associated support structure to put any dent in worlds energy production. Such a project may only become practical when NASA develops Ares V heavy lift rocket.

[Karrick]

This is something my roommate and I are constantly arguing about. He claims that putting what amounts to a microwave gun on a satellite violates some (unspecified) treaty the U.S. is a signatory of. I've tried digging through treaties that sounded relevant, but couldn't find anything. Does anyone have any info on that? Could you even use this sort of satellite to fry people from space? What would the effects be of constantly transmitting that much energy through the atmosphere?

[Samuel]

Weather control. I like it already. How wide can we make the beam? Is it possible to make it city sized?

[Commander 598]

What kind of rocket are they going to use? Building an orbital solar power station would require some serious heavy lift capacity since you`d need many square kilometers of solar panels and associated support structure to put any dent in worlds energy production. Such a project may only become practical when NASA develops Ares V heavy lift rocket.

Time to tell NASA to dust off the data for Sea Dragon?

[Jeremy]

Project Orion?

[GrandMasterTerwynn]

This is something my roommate and I are constantly arguing about. He claims that putting what amounts to a microwave gun on a satellite violates some (unspecified) treaty the U.S. is a signatory of. I've tried digging through treaties that sounded relevant, but couldn't find anything. Does anyone have any info on that? Could you even use this sort of satellite to fry people from space? What would the effects be of constantly transmitting that much energy through the atmosphere?

As has been mentioned, a SPS would be pushing this energy through at a density lower than that of sunlight, and they'd select a frequency to which the atmosphere is transparent and one which is poorly absorbed by water molecules (as having an SPS beam be blocked by clouds, and serve as an enormous death-ray for anything unlucky enough to venture into it, would be eminently undesirable.)

[kinnison]

One would also be intercepting energy that isn't otherwise going to hit Earth anyway, but keep going into interstellar space. As for the argument about lifting the powersats into orbit; well, O'Neill covered this one in the 1970s. Basically, the materials for the powersats (at least the bulk components - to start with) come from asteroids or the Moon; in both cases the energy input is much less than for an Earth ground launch. In any case, the numbers appear to tell us that to get SPS to work we have to have a major presence in cislunar space - at least. Which has other benefits that I hope I don't have to spell out, especially on this forum.

[Darth Wong]

http://bbs.stardestroyer.net/viewtopic. ... 5#p3080535

Kinnison, I'd rather not have to hound you, but you have been delivered an ultimatum in a HOS thread. You seem bound and determined to ignore it. Five hours left.

[Sea Skimmer]

I had an idea for reducing the mass needed for the solar collectors. How about a giant mirror, which for the surface area should be far lighter then solar cells wired together to microwave transmitters, that reflects light onto a much smaller solar cell array that can operate at a higher energy density? As an added advantage, the giant space mirror could also be used on the side as a means of creating artificial moonlight to light up disaster areas or war zones.

For heavy space lift the best thing to do is just take a design, any design, and mass produce 100 of the things in one long production run. That’d drive down costs enormously, compared to the current methodology of buying 1-2 of a rocket per year, and shutting down production after perhaps 10-20 of the things. Problem is it requires a BIG commitment up front to gear up for that kind of production. Mass investment in solar would could be that kind of commitment. Orbiting more communications satellites isn’t so it doesn’t happen.

[Starglider]

I had an idea for reducing the mass needed for the solar collectors. How about a giant mirror, which for the surface area should be far lighter then solar cells wired together to microwave transmitters, that reflects light onto a much smaller solar cell array that can operate at a higher energy density?

The obvious problem with that is that if you put too much energy onto the solar cells, you will exceed the limits of passive cooling, and active cooling is heavy. Solar cell efficiency will be about 30% (maybe 40% if the best current lab demonstrators can be mass produced), so waste heat is already about 890 W / sqm without concentration. For comparison, the rated heat rejection capability of the ISS radiators is only 480 W/sqm, though that is total system capability and probably with a lower working temperature. I assume that's with the radiators illuminated but oriented away from the sun. Temperatures above 100 degrees C dramatically shorten cell life, so I would be surprised if you could get away with light multiplication of more than two. I doubt that's worth the extra complexity of having a mirror system.

[Surlethe]

almost constant but not quite.

thinking it over though, the lost time would be in the middle of the night when consumption's low anyway.

No. This is only the case if the geocentric orbit goes through the Earth's shadow, which I do not think is a given.

[Starglider]

No. This is only the case if the geocentric orbit goes through the Earth's shadow, which I do not think is a given.

Most of the time it doesn't, because of the earth's axial tilt, but for about six weeks a year (around the equinoxes) geostationary satellites are shadowed, for up to 70 minutes per day (the maximum shadow period occurs on the day of the equinox).

[Starglider]

I think such a thing sort of exists - a thin solar cell with a large focusing mirror built into the cover. Not quite the same, but it does use the idea of focusing the light onto a smaller cell to reduce mass.

Concentrator solar cells normally use plastic lenses to focus the light. Note that these are not used on spacecraft, which are exposed to at least 50% brighter light, can't use convective cooling and are more concerned about mass than cost. Solar thermal stations do use huge mirror arrays to concentrate sunlight on the boiler, but that requires a large condensing plant to recover the water.

[Sky Captain]

Are there any estimates available how much say 1 GW solar power satellite would weigh thus allowing to estimate how much it would cost to put the whole thing in orbit?

[Starglider]

Are there any estimates available how much say 1 GW solar power satellite would weigh thus allowing to estimate how much it would cost to put the whole thing in orbit?

Lots. This study makes a reasonable case for ~10,000 tonnes, using careful design to maximise the useful output of a monolithic stationary solar/transmitter array, instead of a separate tracking solar and transmitter arrays. For comparison, the ISS solar wing/truss assembly has a maximum output of 131 kW and masses about 103 tonnes.

[Commander 598]

Are there any estimates available how much say 1 GW solar power satellite would weigh thus allowing to estimate how much it would cost to put the whole thing in orbit?

http://www.projectrho.com/rocket/rocket3ay.html

1 gW Solar Power Satellite 1,900 metric tons
10 gW Solar Power Satellite 19,000 metric tons
1 tW Solar Power Satellite 1,900,000 metric tons
1.5 tW Solar Power Satellite 2,800,000 metric tons

Disclaimer: May not be accurate.

[Sky Captain]

Are there any estimates available how much say 1 GW solar power satellite would weigh thus allowing to estimate how much it would cost to put the whole thing in orbit?

Lots. This study makes a reasonable case for ~10,000 tonnes, using careful design to maximise the useful output of a monolithic stationary solar/transmitter array, instead of a separate tracking solar and transmitter arrays. For comparison, the ISS solar wing/truss assembly has a maximum output of 131 kW and masses about 103 tonnes.

Now that is some serious mass to lift to geostationary orbit. So I think it`s safe to say without a huge cheap rocket like Sea Dragon to lift all that stuff space based solar power is likely to be too expensive to be competitive.

[Kwizard]

As an alternative to hauling every ton of power satellite equipment up into geosynchronous orbit atop heavy lift vehicles, what about launching a much smaller mass of semi-autonomous mining/construction systems to extract metals from near-Earth asteroids and assemble the power satellites out in space?

[Beowulf]

There's an idea of using holographic film to concentrate the sunlight. It allows better sun tracking than the plastic lens or mirror ideas, which reduces complexity. In addition, there's the possibility of directing sunlight that doesn't meet the minimum frequency threshold away from the cell, reducing heating.

[Hawkwings]

As an alternative to hauling every ton of power satellite equipment up into geosynchronous orbit atop heavy lift vehicles, what about launching a much smaller mass of semi-autonomous mining/construction systems to extract metals from near-Earth asteroids and assemble the power satellites out in space?

You'd have to mine, refine, manufacture, and assemble in space, starting with raw materials and ending with a quite precise finished product. Not impossible, but certainly very hard, much harder than simply launching everything.

[Stormin]

<snip>

You'd have to mine, refine, manufacture, and assemble in space, starting with raw materials and ending with a quite precise finished product. Not impossible, but certainly very hard, much harder than simply launching everything.

And there isn't any equipment up there to do ANY of that so all that would have to be sent up too after being designed built tested etc. It would cost a lot more and take years/decades longer to do than simply sending up finished product or components ready for assembly.