Wednesday, December 04, 2013

Glowing Wind Blows In Lunar Solar Power?

     Vast amounts of (electrical) power and a Moon colony by 2030?  Count me in!

     It's an ill wind that blows no good and the "hot" wind for Fukushima has left Japanese engineers and futurists wondering how they'll keep the lights on.  One idea reboots an old notion: solar power from orbit, beaming down microwaves or lasers.  Inefficient?  Sure, but with the Sun on the other end of the line, who care?  Atmospheric losses are low and you let the beams spread and pick them up on huge "rectennas" or broad, floating solar collectors.

     But where the original concept called for solar power satellites in orbit, Shimizu takes another approach: "paving" the Moon in solar cells and transmission facilities in a broad ring around its equator.  Crazy?  Maybe; but it does avoid the tricky parts of trying to build really big structures in orbit, and keep techs around to work on 'em.  Mind you, it's on a scale that makes damming the Strait of Gibraltar and lowering the Mediterranean Sea look like a Science Fair project, but the payoff would be even bigger.

     ...Look for it to get shouted down by the same idiots who don't understand RF field strength that doomed the original SPS, but if Japan gets cold enough, they'll try something and I sure hope this is still on the table.


Ygolonac said...

I thought it was "Pave the Earth" and "Chrome the Moon"? Is my ancient Usenet lurking failing me?

Bear said...

Call me one of those idiots...

...and being an idiot, maybe I screwed up the math but it looks like free space path loss alone is going to be in the neighborhood of -230dB. (This is just looking at the RF system, not the proposed laser transmission.) Well, with 13,000 TW on the transmit end, and 20 kilometer parabolic antennas (never mind the RX rectenna fields which should amount to arrays of unity gain antennas), I guess that's OK.

Of course, to gather the 13 PW in the first place is a neat trick. But then, you'll have that 400 KM wide belt of PVCs clear around the Moon... um, with only half illuminated at a time. Probably only about 20% at optimum angle... So you've already got some impressive inefficiency. Just in collection/conversion.

Now you've got to get that electricity to the transmitters. Not a huge problem (relatively speaking) at full moon, when the PVCs near the Earth-facing transmitters are illuminated. It's not clear what the transmitter spacing is, so I'm not sure sure how much transmission line loss to figure between PVC and transmitter (the rule of thumb number for Earthly power transmission is 30% loss, so I supoose you'd need to convert some 18-19 PW of power to start). Oh well, let's just throw some magically inexpensive superconductors at the prob. We don' need no steenkin' line loss. And that takes care of the would-be-greater losses at other times of the month when the power has to be moved even greater distances to the transmitters.

I do hope they'll be inventing something more efficient than magnetrons for this project. I figure at 65% efficiency, those 7,000 teraWatts of waste heat would also require magical cooling syst... I know, we'll assume room temperature superconductors and just use that to pipe the waste heat to the lunar dark side. No prob!

All in all, if we really want to go solar, I can't help but wonder if we'd be better off applying that remarkable assumed technology to an Earth-based system where we don't have to ship hydrogen to make water to build transmitters to send power 384,000 kilometers just to send it to where we actually want it on Earth.

On the other hand, that would make a hell of a pirate radio station.

Old NFO said...

And you 'know' the environmentalists will have 'kittens' over all the birds you're going to kill...

Bear said...

Old NFO: Nah. It's solar, so it's green. Therefore, dead birds don't count.

(Of course, if I had entire deserts or oceans to use as targets, I'd spread my beams out to keep power density below the "microwave popcorn" level. Air travel might be more problematical; I'd need a lot more data to figure if the power level could be low enough to not screw with avionics yet still be useful.)

Roberta X said...

Carl: the idiots were the ones who assumed very low field densities were going to cook birds. (The very same idiots who hate radio towers that they claim take out huge numbers of birds, but love windpower towers....that take out at least a many birds per tower and are usually planted in groups of a dozen-plus.)

Efficiency, smeficciancy -- *if* initial and operating cost are low enough and you can get rid of the heat well enough. They can run the whole Lunar enterprise on thermocouples....

Building it, unless somebody dopes out how to start a jillion von Neumann machines making solar cells (etc.) and more of themselves out of readily-available Lunar materials, the Pyramids will look like a garden shed in comparison.

Be some damn thing to leave for the future, though, and it would kind of fulfill one of Philip K. Dick's nightmares: a huge mask-like face in the sky with "slotted eyes." We'd have the Man in the Moon wearing wraparound sunglasses!

Bear said...

Roberta: "the idiots were the ones who assumed very low field densities were going to cook birds."
I've seen that happen. In fact, we'd occasionally sit at the edge of the antenna field (with cases of beer) to watch it happen. Of course, we were running 10KW and above, with 60 foot parabolic dishes. Um... around 2.5GHz at the location I'm recalling. And the birds still had to fly pretty close to the feedhorn. Yeah, we were bored. Isolated mountaintop in the middle of desert (different location, but similar setup)

I'll also confess to using the irrational fears of RF to discourage unwanted visits (any other kind?) from brass hats.

Stranger said...

I have done the math a few times for sync orbit. A sun facing platform the size of the Mojave would be enough to power Spaceship Earth even with path losses. RX antenna the same size to keep FS down to a level that will not cause flying aircraft to start spitting sparks.

Keeping the radiators pointed in the right directions so you do not cook the cactus in Phoenix and the spuds in Pocatello would be a pain but doable. And the heating tends to serve as aversion therapy for flyers.

Building a similar station on the moon? How tight a beam can you hold? Otherwise, doable, but anyone trying that had better have some heavy lifters on the drawing board.

And there is one thing about the sync orbit and the moon. Really hard vacuum is cheap.

But comparatively speaking, so would 4,000 or so "neighborhood capacity" pebble bed plants. At a price of a billion US mini-bux each.


Bear said...

Hmm... I feel compelled to point out that I don't actaully object to something like this in principle (you might note that SPS short story I linked previously, and I even made some prize money doing a science fair project on SPSs back in the '70s). I just think that claiming they can do this... even start to do this in 20 years is a little ambitious (remember they plan full-scale SPSs as an early step before the Lunar Ring is constructed).

Another concept I always thought was cool was -- I think Forward dreamed it up; correct me if I'm wrong -- a Moon-girdling solar-power (similar to the Shimizu PVC array) particle accelerator to produce antimatter. No idea how serious he was; I think he just needed to explain where got all that antimatter for ships in his novels.

Roberta X said...

I didn't think you objected to it, Carl, but it sounded as if you thought I'd classed you with the "don't cook the birds" idiots, and I already knew you knew better.

Roberta X said...

(Bird-cooking in re the SPS proposals, that is; the trick is very, very low field density. High-power RF will cook 'em dead, as you have observed; when one of the religious shortwave outfits had a transmitter site here, a regular duty of the transmitter techs was to go sweep dead birds from under the matching section between a huge antenna and the open-wire line that fed it: the birds would fly down it until they were cooked on the wing.)

DJ said...

If you capture energy from the sun that normally doesn't hit the planet and then, in effect, redirect it so it does hit the planet, why, that would heat up the planet.

No, I haven't run the numbers. They won't matter to AGW proponents any more than any other numbers do. It's the concept that'll scare the crap out of 'em. If anyone makes serious noise about such a scheme and someone tells 'em the planet will get fried, it'll be damned entertaining, won't it?

Larry said...

Bear, what kind of site was that? The antennas reminded me of the White Alice installation at Adak, Alaska. That had 120' antennas and 50 kW transmitters to link with other garden sites in the Aleutians such as Shemya. Birds certainly got fried there, including numbers of bald eagles every year. Not that they were rare on Adak. They were almost as common as sparrows and ravens.