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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.
The moon has not atmosphere silly, so the rays coming from the sun are not deflected by anything so that solar panels will be able to absorb more light than they would just about anywhere on earth.
Does it not seem better to build solar arrays in the deserts near the equator (max sunlight) and have the energy transported through a smaller distance than from the moon?
Of course we have a little thing in the way called an atmosphere.
And why is this news for nerds?
Uh, lasers, space, science (sci-fi-like at that). I'm not sure what could be nerdier.
-Peter
Microwaves are easy to recieve - you simply stretch out a wire between two insulated poles, and the power just flows. That's the big advantage of microwaves over other power transmission possibilities.
Granted, given the spill-over from the "concentrated" beam of microwaves, you'll probably have to use some frequency that's not very popular for communication, but it's probably do-able.
The people who are worried about power-line emissions would probably go insane over this, though - the exposure levels would be MUCH higher.
-Mark
By any number of means. Mirrors, lenses, etc. A maser beam will not spread out too much.
2. How will they keep airplanes from flying across the beams?
They probably won't. If the idea really gets off the ground, it wouldn't be hard to equip airplanes with microwave dissipation grids. It'll heat up the grid but the airplane will cross the beam very quickly.
3. Will they coordinate with satellite operators so they can avoid the beam too?
This is the one major problem. The effects would vary depending on what sort of electronics the satellite is carrying.
The only way for this not to harm you would be for it not to strike you.
The article states the beam would have an areal power of about 20% that of sunlight. This is approx. 270 watts per square meter. Pretty strong, but since the microwave beam will be collected, the only way you could be exposed to it would be to stand at the collector.
If you are going to do this beamed microwave thing, build it in Earth orbit, closer to the target. (distance)*(wavelength)= k*(diameter of transmitter aperture)*(diameter of beam at target), where k is a constant somewhere between 1/3 and 3. I think the moon is about 250,000 miles or 400,000 km away. So to focus a 30GHz (1 centimeter wavelength) microwave beam down to a 10 km spot on Earth takes an antenna about 400m across. Or in units the average American understands, a football-field sized antenna would put most, but not all, of the transmitted energy into a 10 mile wide spot. This whole area would have to be blanketed with receiving antennas (expensive!). And people living 20 miles away would be measuring the leaking energy and suing every time they got a cough. (Birds would be safely building nests on the antennas, but American trial lawyers never let science get in the way of a deep-pockets lawsuit.)
The best place for a solar power satellite is probably geosynchronous orbit (40,000 km). This needs a football-field sized transmitter and a mile-wide receiver; still pretty big, but maybe manageable. And the transmitter and receiver don't move relatively. A lunar array would have to keep switching between different receivers as the Earth turns. An SPS in a lower orbit would also have to keep switching receivers, but at least it would have smaller antennas.
A solar plant in orbit is in sunlight almost all the time (depending on distance from earth and orbital particulars, it might spend a few hours a year in earth-shadow). On the moon, two weeks out of every four is night.
The laser installation would also work better in a medium-height earth orbit, where it's solar panels were powered all the time and it was much closer to the targets. At least, I assume that it isn't meteroids headed for the moon that this is supposed to shoot down?
1. Focus - the beam will most likely be a maser, or microwave laser. Given a reasonable size emitter in geosynch or elliptic earth orbit, the footprint on the surface of the planet is only a few kilometers wide, and has an energy density of perhaps ten to a hundred watts per square meter.
2. Guidance - the same way they keep aircraft away from anything else - tell them not to go there. Note that this isn't really a problem, as the metal skin of an aircraft would deflect the beam.
3. Of course they will coordinate with other satellite operators. Although, if some satellite DID accidentally cross the beam path, it wouldn't necessarily be harmed, for the same reasons as 2.
The proposals I've seen for this (including a gov't study in the Sixties), all addressed the safety question. The REAL question is whether or not this can be done ECONOMICALLY - it's no use if the power so produced is ten times more expensive than fossil fuels (though note that such a scheme becomes more attractive as fossil fuels become more expensive...). The most attractive source of building materials for the solar cells and support hardware is not the Earth, but asteriods that cross or come near the orbit of the Earth - they contain all the necessary elements (silicon, iron, hydrogen, carbon, etc.) to make a solar power satellite in orbit, instead of having to haul every component up from the planet.
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Vpered na Mars!
The orbit above the equator is at a quite significant angle to the shadow cast by the earth, due to the angle of dip of the rotation of the earth. That means that the shadow only intersects the geosynchronous orbit about twice per year.
IRC geosynchronous satellites only see darkness for about 40 minutes per year.
This contrasts rather sharply with nearly all points on the lunar surface which see darkness once per month for half the month.
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"Didn't you ever see/read 2001? The lunar monolith being exposed to sunrise is a critical plot element.
"The question of whether a computer can think is no more interesting than that of whether a submarine can swim" -EWD
Scientists restrict study to entire physical universe; creationist
"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."
Does the phrase "tide locked" mean anything to you? The moon's rotation and revolution match each other, so anything set up on the far side of the moon to target incoming debris will never be able to hit earth-based targets, or at least not any time this eon.
X-rays cause cancer due to a higher energy and shorter wavelength. They have rather powerful penetration depths (duh, otherwise they wouldn't be used in medical research). Microwaves don't have that problem (otherwise they wouldn't use them in cell phones/telephones - what do you think a 1.2GHz phone is?)
Microwaves are perfectly safe, in normal intensities, and since they don't refract, you don't have a worry about it spreading past the area you intend it to hit. They can't affect anything smaller than their wavelength, obviously, so you don't have the danger that X-rays have.
People are bombarded with radiation every day, and this wouldn't change anything, really. You're much more at risk from that giant 4 x 10^26 watt light bulb hovering over your head every day. So if you're really worried about these microwave lasers, go hide in a cave.
Insanity is the last line of defence for the master diplomat. But you have to lay the groundwork early.
>Not to mention the fact that one side of the
;)
;)
>moon faces the sun at all times! Any solar
>collectors on Earth are subject to day/night
>cycles. The moon would rarely be impacted, when
>the lunar eclipses happen.
Doh! One side of the moon always faces the EARTH! (synchronous rotation). We had never seen the far side of the moon until we sent something "back there" to take pictures.
So: that being the case, is it really possible that one side of the moon is always bathed in the light of the sun? If so, then how did we ever get visible pictures of the OTHER SIDE of the moon? Did we use a gigantic flashbulb, or something?
Map of the entire surface including the far side
The Far Side of the Moon Consider how this picture would look if it had been taken during a "full moon:" since during a full moon the entire side of the moon that is facing the Earth is lit up, only the portion of the moon in this photograph that is said to be visible from Earth (see the pic's caption) would have any sunlight on it.
Far Side of the Moon, with animation showing the same side of the moon always toward the Earth. This doesn't show where the sun is in relation to the animation; but figure that the sun is way off the screen from the animation...the darkened part of the moon in the animation is representing the side of the moon we never see from Earth, NOT how the light hits the moon (the Earth does not illuminate the moon, although it does sometimes reflect a little of the sun's light onto the dark portion of the quarter moon...)
So, taking this into account, will it be useful to build these lasers on the moon, especially the power plant?
Apollo 11 Laser Ranging Retroreflector Experiment. "Laser beams are used because they remain tightly focused for large distances. Nevertheless, there is enough dispersion of the beam that it is about 7 kilometers in diameter when it reaches the Moon and 20 kilometers in diameter when it returns to Earth. Because of this very weak signal, observations are made for several hours at a time. By averaging the signal for this period, the distance to the Moon can be measured to an accuracy of about 3 centimeters (the average distance from the Earth to the Moon is about 385,000 kilometers)."
Add to this, the fact that the moon wobbles...
Ah yes, here's a thought...