Lunar Lasers

Two different articles about building lasers (well, lasers and a maser perhaps) on the moon. Reuters has a story about a potential lunar power plant, creating electricity with solar panels and beaming it to Earth with microwaves. Space.com has a piece about building a sort of super-sized Star Wars program on the Moon, giant lasers set up to blast incoming space debris and not, of course, anyone here on Earth.

Comments

20 percent of noontime sunlight

[vlad_petric]

AFAIK 20 percent is roughly the efficiency of a photovoltaic cell. So you'd need a close to 100% efficiency for a rectenna just to break even with photovoltaic cells (from a surface standpoint).
It may be cheaper to build rectennas, however I'm not convinced how it could break even in 5 years with >50 billion spent.

The Raven

I've got an even better idea

[SIGFPE]

Why not spend $50,000,000,000 on solar panels for use on Earth. This proposal has a number of cool features:

1. You don't have to send lots of equipment up to the moon
   
2. You don't have the hassle of building microwave transmitters and receivers to transmit the energy to the Earth
   
3. They couldn't easily be hijacked to make a nasty weapon
   
4. The equipment would be easy to service. You wouldn't need regular flights carrying crews to the moon.
   

So where's the energy density?

[Myself]

The microwave energy beam, which could pass through rain and clouds, would have the intensity of about 20 percent of noontime sunlight...

Okay, so if this thing is so much weaker than sunlight, why wouldn't we just use terrestrial solar cells to receive existing sunlight rather than some receiving station for funky microwave power?

Come on! In order to be even slightly useful, the energy beam coming back would have to be terribly intense, which would make it terribly dangerous. Even noontime sunlight can be nasty, ask a suburban sidewalk ant or any pale-skinned swimwear-clad human.

An Old and Silly Idea That Won't Go Awayt

[Prof_Dagoski]

Gawd, I've seen this idea so many times before. It's something they always bring out as a gee-whiz justification of manned space exploration. Y'know, just to show that space has practical applications. The arguements against are pretty persuasive. Safety, cost, and effectiveness. I don't buy it and didn't even think much of it as a kid. I just with these people would stop insulting our intelligence. A better way to address power consumption through technology is in effeciency. A good example that works is the new compact flourescent light bulbs. I've saved my bill before and compared it to after I swithced my apartment over to them. My power bill went down by a little less than half. Pretty nifty. I figure if we can do more with less, we can satisfy our needs for more people, and we can do it without crazy crap like this. In any case, some of the new home solar products are making this thing a moot point. In the meantime, there's lots of better reasons to explore and develop space.

Catching them is a lot simpler than that

[Spamalamadingdong]

No, they don't boil water and spin turbines. What you do is to take the microwaves, catch them with an antenna (they are radio, after all) and rectify them with a diode (what you get is just very, very high-frequency alternating current which can be converted to DC with that most simple of all semiconductor devices).

Before you go "Bah", please understand that this has actually been tested over an atmospheric path crossing as much air as you'd need to from a typical orbit, and efficiencies around 80% were measured.

Re:Why bother?

[jandrese]

Do you have any idea how big a 200x200 mile area is? For comparison, the State of West Virginia has an area of about 24,087 square miles. You are looking at creating a solar array that is 20,000 square miles in size. Where are you going to put this monster? How are you going to clean it? Who's going to pay for the solar cells. If you are using the normal 12% efficent cells (because they are much cheaper), then this whole array is going to cost $91,929,436,402,366US. For comparison, the current US GDP is around $10,229,700,000,000US. Oh, and those solar cells only last about 20 years, so you'll have to keep replacing them. This alos doesn't touch on the current US silicon production capacity vs. what you would need to build this.

On the other hand, my back of the evelope calculation suggests that on a bright sunny day (1000 watts/m^2 of energy hitting the surface) these solar cells could power pretty much the whole world (ignoring transmission loss of course).