by Bernard Foing, European Space Agency's SMART-1 spacecraft principal scientist
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So a peak of eternal light would be a good central base from which to begin our lunar activities. It could provide a source of solar power for exploration, astronomical observations, life science experiments, and the investigation of possible water in the dark craters.
To extend beyond a few hundred kilometers from the peaks, however, we would need to develop nuclear power systems. That would provide enough energy to allow us to grow from a little refuge to a global village on the moon.
As exciting as it may be, I am a bit skeptical about the utility of the mountain in perpetual sunlight. O.K., it's in perpetual sunlight, but what does it take to utilize it? The solar flux will be coming in almost horizontally. This will require a large, tracking photovoltaic array, oriented vertically. This necessitates more structural supports, the complication of some kind of clockwork tracking mechanism. Also, there is the necessity of hauling everything up to the top of a mountain, whos geology must be necessarily characterized in order to safely engineer foundations for this equipment.
The real utility of such a base is in its relative close proximity to the ice deposits thought to be there.
I suspect that it may be ultimately more useful to build a more conventional base near the lunar equator, probably just about smack dab in the middle of side facing the Earth. The moon is tidally locked with Earth, so this base would always be pointed at Earth. Communications should not be a problem.
Using a large array of photovoltaic panels, surplus electric power could be used to split water into hydrogen and ozygen, storing them as cryogenic fluids. A large fuel cell plant can be used to power the base during the two weeks of lunar night time. However, a small nuclear plant can do much the same. If a mass driver will be in operation, then a nuclear plant will be a necessity, as a large mass driver may consume 100 MWe or more.
Water could be brought to the base via a 'road train,' a lunar analogy of the old 60 ox borax trains of Southern California in the 1880's. A nuclear powered overland vehicle could transport hundreds or thousands of tons of water and other volatiles extracted from the ices burried beneath the lunar surface. These materials would be essential for starting sustaining any kind of lunar colony.
Anyways, the mountain of perpetual light is great, but it is not in an area where a mass driver could be set up. Also, a vertically oriented tracking solar panel is no small engineering feat--it must be positioned on a towaer above the base at the very peak of the mountain. While there is no air and no weather to blow over or damage the panel by lightning strikes, the construction of such a system is compounded by the complexity of transporting construction materials up a very steep slope.
Not to say a 2500 km overland pack train of vehicles is no small feat either--there is the necessity of scouting out, plotting, and then building (and maintaining) a lunar road through vast ranges of mountains taller than Mount Everest. Such a road on earth would have many unique challenges and is itself no small feat, but such a road built on the moon may be a vast challenge requiring even more infrastructure. It would be ironic that for all the billions of tons of ices thought to be at the lunar poles, that they may still be unreachable!
But I'm more optimistic about the peaks of eternal light.
I think that the image of sharp lunar mountain peaks belongs to the quaint depictions from the nineteen-thirties (or earlier ?). The peaks of eternal light are much more likely to be the gently rounded or table-top mountains seen in Apollo-era imagery. The locations are certainly very high up compared to the surrounding geography. I guess its comparable to the sprawling astronomical installations on the top of Hawaii's volcano -- except that instead of having to haul things up the side of the mountain, we'll be coming down to the peak from orbit. My concern is that the spot not be too far from the deep-down ice deposits, so that the power cables aren't dozens of miles long. At some point, it may be more advantageous to microwave the power down into the crater basins. But that's when the geography may get in the way - particularly if its gently rounded or table-top mountains.
Anyway, a self-contained, portable little defrosting unit with nuclear power seems much more practical for this sort of application. At least initially, at a modest plant scale.
As for the solar panel tracking, I can hardly imagine a simpler place to do it than at the poles, with one-sixth earth gravity : just put the things on rotating vertical poles. End of story.
I would avoid the equatorial regions -- too much temperature extremes. Unless of course there happens to be a conveniently located underground lava tube
I was wondering, since there ARE eternal points of light, why not set up a battery recharging system of sorts, and skip the risky nuclear launching required to live out the village on the moon scheme?
But lemme ask you astro guy's something you might have a good answer for... Why does the earth spin on it's axis, but not the moon, while in their orbits?
Why does the earth spin on it's axis, but not the moon, while in their orbits?
The moon does spin -- at exactly the same rotational period as it's 30-day orbit around the earth. Hence it always faces with the same hemisphere to the earth. It is tidally locked into this motion, just as many other moons of other (particularly the jovian) planets.
Just to get an idea of what we're talking about. Let's suppose we have a base that uses on average about 2 MW of electrical power. Now if we use some kind of power storage system to supply power during the 2 week lunar night, then we would need a PV panel with more than twice this capacity. Suppose we use hydrogen and oxygen in a fuel cell, and then during lunar daylight, re electrolyze this water back to hydrogen and oxygen. An electrolyzer plant can operate at about 45% efficiency, that is only about 45% of the elctrical energy delivered to the elelctrodes actually ends up making hydrogen and oxygen. Further, let's suppose that a crygoenic liquification plant is used to liquify the hydrogen and oxygen--this takes up a lot of energy too (almost 1/3 of the total amount of energy released by combustion of the hydrogen alone!) And if we want to allow for extra storage (a contingency storage) of electrical energy, in case of future electrolyzer failure let's say, then we'd better bump up our PV array some more, say 33% for a good safety factor. 50% would be better.
So how big is our panel now?
Obviously, the panel must generate atleast 2 MW to satisfy base load demand, and it must also generate an additional (2MW/(0.45))*1.5=6.7 MW for a total of 8.7 MW. Doesn't sound like much?
Well, insolation is the actual solar energy streaming in from the sun and has a vacuum value at Earth's orbit of 1373 W/m^2 (page 14-2 from the 85th edition of the CRC Handbook of Chemistry and Physics.) Using space rated solar photovoltaic cells with an overall efficiency of 17% then the size of a panel needed to supply 8.7MW of power is:
8.7*10^6W/(1373*W/m^2*0.17)=37270 m^2 or if it is a square array, it will be 194 m on a side. This is approximately a square 600 ft on a side! This is a substantial, non-trivial structure, even in lunar gravity. The bending moments alone will require substantial reinforcement of the structure to support suspended solar panels, and the thrust bearings at the swivel joint will still have a substantial load. Without doing a full on structural analysis of likely construction materials such as lightweight aluminum, or steel (or even titatnium,) the support structure will mass many, many tons. If this is to be the only power source available, then ALL of this construction material must be transported all the way from Earth.
The reason why I point out that nuclear power is necessary is that it allows for the construction of an ultimately larger and more capable base, because it allows for local resources to be used. Only nuclear power can supply enough initial power to initiate base startup. Eventually a base can grow to utilize all solar energy, but the required infrastructure really demands the use of local resources (aluminum, silicon, titanium, and iron or steel.) The only other alternative is to transport everything from the earth to the moon, which is not trivial, I assure you. Looking at the mathematics of the rocket equation V=c*ln(mi/mf) and with the choices of available fuel/oxider combinations (overall Isp about 350 seconds,) and the effectiveness of staging to achieve 4.4 times exhaust velocity, then to land a single kilogram on the moon requires between 70 and 100 kilograms of rocket at launch on earth. To transport 100 tons to the moon requires 7000 to 10000 tons of rocket(s) launching. Just as a ball park, the Lunar Excursion Module and the Command and Service Modules, together massed almost 50 tons--which roughly breaks down to a launch vehicle massing 3500 tons, which is pretty close to the Apollo Saturn 5 vehicle at take off. For a rough figure I think that's a good estimate.
Also, I think it should be possible to engineer a semi-man rated vehicle, an armored capsule than can carry the fissile fuel for the reactor core (or even possibly the whole reactor.) Such a capsule is extremely robust, would have its own reentry heat shield, floatation, and parachute systems, as well as recovery beacons and of course launch/abort/escape rockets, just like the manned capsules of the Apollo era. A machine such as this need not carry a life support system (you're not launching a crew with it,) so it need not carry oxygen, water, and food. Infact, it could be stripped down to being just an airtight (and water tight) can with a heatshield and parachutes. An inflight emergency, all the way up to orbit can be delt with by simply allowing the capsule to come back down and parachute easily to the ground or water (water preferably as the package could be recovered by ship.) Once the reactor or reactor core was installed in the lunar descent lander, while safely en route to the moon, then the 'fissile shipping' container could simply be jettisoned.
For an energy storage "battery", what about using a gravity system? It won't have the losses of electrolysis. If your main "industry" is harvesting lunar water, then you'd use two water tanks--one at/above ground and one buried deep underneath.
But then, I'm a fan of nuclear power...it seems to me that one possibly good way to do the water harvesting AND give you power might be to simply drill a hole and set off a nuke underground. You get steam back up the pipe (along with crud, which has to be dealt with). This depends on the location of the water (if any), of course. For this scheme to work, there needs to be a lot of water deep enough for the ceiling of an underground nuke to seal off the cavern--leaving just one escape outlet for the steam.
if it is a square array, it will be 194 m on a side. This is approximately a square 600 ft on a side! This is a substantial, non-trivial structure, even in lunar gravity. The bending moments alone will require substantial reinforcement of the structure to support suspended solar panels, and the thrust bearings at the swivel joint will still have a substantial load.
Yes, well, I think there's really no need to put everything into one gigantic monolithic structure.
I was thinking more along the lines of many smaller ones -- the simplest structure being just a stick with a "T" bar at the top, from which you hang a thin-sheet solar panel, and then slowly rotate the support pole to constantly point at the sun throughout the month. If each of these rotating drapes were 100 x 100 ft, then you'd need 36 of them. Seems quite doable. Moreover, you can start small - with one or two units - and gradually add more as your lunar base grows.
