Part V Previously Published in Moon Miners' Manifesto #31, December 1989
Peter Kokh, Mark Kaehny, Myles Mullikin, Louise Rachel, & Joe Suszynski (Chicago SSS)
A. Super Redundancy.
On Earth, rare power outages serve to relieve newsfare boredom, result in some work stoppages and commuting delays, occasionally spoil frozen foods, and sometimes produce a temporary glitch in the birth rate. While electricity has long since insinuated itself into every aspect of our daily lives to the point that it can hardly be called a luxury, temporary loss is something less than cataclysmic.
On the Moon where the ambient conditions are far more severe, no matter how much attention is paid to self-adjusting thermal flywheels and biospheric ecosystems, loss of all power could quickly introduce conditions from which recovery would be difficult. Any one power system is fallible: nuclear, on site-solar, remote solar, chemical fuel cells. Redundancy is critical.
At the same time, power needs differ between the alternating periods of lunar daylight and darkness, each 14.75 days long. Some industrial operations can be polarized into energy-intensive (diurnal) and labor-intensive (nocturnal) processes. On the other hand, agriculture can thrive on the uninterrupted two-weeks of lunar sunshine, but must also have enough artificial light not to just simply survive the equally long night periods but to go on to produce an eventual harvest. It would seem that for a settlement of the size of Prinzton (3,000 plus), these minimal nocturnal food production needs for electricity will be easily much greater than the demands of industry and all other systems. In planning Prinzton therefore, we set as a design goal that each of the available power systems be sized so that in emergency, i.e. all the other systems down, it could alone meet these minimal nighttime agricultural needs. At present, to our knowledge this minimum need has never been quantified. Nuclear winter scenarios have shown that a loss of 95% of normal sunshine would end in the cessation of photosynthesis. This is not quite to the point as we are talking about minimum hours of normal lighting, and not minimum sustained lighting. Therefore, we did not quantify the power needs for our proposed settlement, but left that open.
[This ultimately led to the creation of LUNAX: Lunar Agricultural Experiment Corp.]
NUCLEAR PLANT (FISSION): Our rille sited just north of the large mare-inundated crater Prinz, contains an uncollapsed section of the original lava-tube. It is likely that the cavity it contains is some hundreds of meters in all dimensions and has a roof on the order of 40 meters thick. We believe this is a doubly handy feature. Not only does it provide a natural bridge across the rille but it is about the best conceivable spot to place a large nuclear pile. Even in the event of a runaway meltdown, there could be no danger to the nearby settlement - the hot pile need simply be left undisturbed.
Not only would such a plant be an everyday mainstay for those power needs that did not vary with the local time of the "sunth" (sunrise to sunrise, 29.5 earth days) but it would be an ideal feed for a Laser Power Tower (see below). We did not also specify a nuclear fusion plant, as it is problematic whether or not we will ever surmount the engineering obstacles to such an elusive long-prophesied power source.
ON-SITE SOLAR POWER: The site plan shows three large solar array areas, feeding both the city and the mass driver export device. We left open whether these arrays would consist of advanced photovoltaic cells made from lunar materials or of solar turbines, mirrored dish/stirling cycle systems. The latter would seem the likelier choice, barring developments unforeseen. We made no attempt to determine the amount of area needed for these solar arrays and what is shown on the site plan is no more than artistic license. The actual collector extent needed would be determined by the efficiencies of the nighttime storage system chosen to supply farming needs. The likeliest candidate would seem to be advanced fuel cells power by oxygen and hydrogen heat-cracked or electrolyzed from water reserves during the long lunar daytime by excess solar power, but also see B. below for a possibly complementary option.
[The reader is also refereed to the multi-contributor discussion "Electric Options" in MMM #14 and the earlier "Powerco" in MMM #7, available as reprints per conditions above.]
REMOVE SITE SOLAR ARRAYS: Given current long-distance power transmission technology and acceptable line losses, similar surface-based solar arrays could be emplaced some 600 km (370 mi.) to the east, near the crater Lambert, which could provide a handy predawn boost in power same two days before the Prinzton sunrise. If superconducting lines manufactured from lunar materials are possible (current pessimism to the contrary), a globe-circling chain of solar power arrays, half of which would always be in the sunshine, would keep the grid powered to the brim regardless of local sun time.
Short of that, it might be feasible to place a suitably sized array 70-some degrees away just over the north pole of the Moon, say 2000 km or 1250 mi. due north-then-south of Prinzton (27oN). Using non-superconducting lines such a distance would involve larger line losses then currently deemed acceptable. However, as such a site would be 180o out of phase with Prinzton, it would enjoy sunlight for the entire Prinzton night stretch.
SOLAR POWER SATELLITES: Earth-feeding Solar Power Satellites, providing raw and processed materials for which is likely to be the economic mainstay for Prinzton, will be concentrated in geosynchronous Earth orbit, now the denizen of communications satellites. Often called the Clarke orbit after the science and science-fiction writer who first realized its strategic advantage, "GEO" allows objects to orbit in lockstep with the Earth's rotation so that they seem to be permanently parked above set points on the equator 37,000 km or 23,000 mi. below.
In contrast, owing both to the Moon's low mass (1/81 Earth's) and to the slow rate of its rotation, once every 27.5 days reckoned by the stars rather than by the Sun, what would be its "Clarke Orbit" if the Earth were not present is some 120,00 km or 75,000 mi. out [B.O.E.]. In fact all points this far out from the Moon in its orbital plane are within the Earth's gravity well, not its own. Instead, any Solar Power Satellites intended to beam power down to the Moon will have to be placed at one of the Lagrange points where the Earth-Moon tug of war lies in precarious balance. Of these, so-called L4 and L5, some 60o ahead and to the rear of the Moon respectively in its orbit about Earth, are the best bets, requiring little or no station keeping effort. L5 would serve the eastern flank of the Moon, L4 the western, wherein lies Prinzton. Now this L4/L5-Moon distance is some ten times the Earth-GEO distance. It is the feeling of J. Suszynski that power beamed in the 1 mm wavelength would be best suited given the much greater distance, and that the greater attenuation of the beam (100 times the footprint for same width beam) could be managed. The rectenna net could either be slung directly over the rille or over a nearby crater if preferred. This is as far as we carried the discussion.
B. A HydroElectric Storage System?
Myles Mullikin and Peter Kokh
Surely, one of the most innovative ideas proposed for the Prinzton Project was Myles A. Mullikin's suggestion that we use the elevation differences within MIDVALE, the central village (whose town plan he had designed to serve as downtown for Prinzton and all this area of the Moon) to circulate water through a modest hydroelectric plant. During the day weeks when abundant solar power will be available, water reserves would be pumped from a valley bottom reservoir to one just below the lower vault, and allowed to fall through a bank of generator turbines during the two night weeks. While appreciative of the much greater power advantage to be had from electrolyzing these reserves by day to run through fuel cells by night, he was leery of the idea of storing these volatiles (hydrogen and oxygen) within the village.
Once on the table, this idea, instead of being dismissed, was quickly enhanced. The upper reservoir could be placed full-square on top of the rille shoulder. It would be no problem to pump the water up that high, and the greater head, some 400 meters, even in 1/6th gravity, would still be effectively half again as high as Niagara Falls! Furthermore, out on the rille-top, the water pumped up from below could circulate under quartz panels transparent to the Sun's ultraviolet fury. This would serve as both germicide and bactericide. And if still desired, water in the upper reservoir could still be electrolyzed to be recombined in fuel cells with the onset of night before beginning its fall down the conduits to the generating station below. There would be no appreciable safety risks involved.
A second set of tubes up the rille slope would carry air rushing counterflow as it is displaced by the water being pumped up or falling down as the case may be. Air pressure in the rille-top reservoir would have to be the same as in the village below. A heat-exchange system could cool hot upper reservoir air before it flowed into the village during the day time, giving up heat to the water. The whole system would act as a thermal flywheel to give Midvale the most equable climate of the three villages.
Meanwhile, the generating station could be placed with little sacrifice in power at the top of the Town terraces, the spent water then free to work its way down a series of ponds and cascades to a central lagoon for all to enjoy. The shallow seven acre lagoon with canoes, fishermen, and pink flamingos would be cantilevered over the final reservoir with depth maintaining overflow tubes leading from one to the other. Some of the water from the Hydro station could also be shunted to pressure-fed fountains, further adding to the Metro-class character of this village. While the extra power to be gained by the hydroelectric scheme as opposed to the straightforward fuel cell system, is probably very modest given the limited volume of water probably available, it might well be proportionate to the extra lighting and energy load the twenty-four hour character of Midvale's Metro District would have, serving not only its own village population, but those in the other two villages whose work and living schedules are to be eight hours advanced or retarded. [See Part III: The Three Village System]
HYDROELECTRIC SYSTEM: For the Central Village of Prinzton (MIDVALE). Plan at RIGHT, diagram ABOVE.
- [A] Upper Reservoir includes quartz pane covered purification pond (Solar Ultraviolet in). Option would include tanks to hold liquid oxygen and liquid hydrogen electrolyzed from water, and fuel cell power plant for recombining them.
- [B] Slope of rille.
- [C] Tubes or conduits carrying water and counterflow displacement air. Day dates: water up, air down. Night dates: water down, air up.
- [D] (Heliostats gather and bring sunshine into)
- [E] The upper Farmfield level.
- [F] Hydroelectric station at uppermost terrace of lower Townfield area.
- [G] Decorative cascades. The spent water is put to landscaping use on way to lover reservoir.
- [H] Pressure-fed fountains.
- [I] Shallow 7 acre lagoon cantilevered over
- [J] Lower reservoir fed by overflow pipes from lagoon above. Reservoir fills during the lunar night, is pumped empty during lunar day.
Such a hydroelectric scheme uses solar power priming in a way surprisingly not so different from that we are familiar with on Earth. Here, sunshine evaporates ocean water to fall as rain and work its way down the drainage system. The Moon may be the last place you would expect to find a niche for hydroelectric power, but it will work, for what it's worth. And not only rille slopes, but lava-tubes and larger crater slopes are potential "dam" sites.
C. The Laser Power Tower.
Myles Mullikin, David Cremer (illustration)
Building Prinzton will require a considerable fleet of construction vehicles. To power these with petrochemical fuels is out of the question. Far less expensive and quite clean would be fuel cells using liquid oxygen processed from the lunar soil and hydrogen imported from Earth or, better, Phobos and Deimos. The emission is water which can flow into Prinzton's reservoirs or be resplit into hydrogen and oxygen to be used again. However, the banks of fuel cells needed would be quiet heavy, though they could be put on the vehicles' roofs to double as shielding against cosmic radiation.
An ingenious alternative would be to use the auxiliary nuclear power plant to broadcast power to the construction fleet via a tall laser power tower equipped with the needed dozens of laser transmitters. These would lock on and swivel to follow the slaved vehicles. A circle of guide beams would keep the power beam on target acting as a fail-safe device. If anything interrupted a guard beam, the power beam would shut off before the eclipsing object could be damaged.
In the Moon's light gravity, seismic quiet, and windless conditions, such a tower, without guy wires, could stand thousands of meters high, to cover the entire site, rille bottom and all. Slaved vehicles would only need minimal backup fuel cell emergency power. Only those intended to range a good distance from Prinzton, require fully autonomous power. (Vehicles built exclusively for use within the pressurized areas of the settlement will be fully electric.)
PART V - Multiple Energy Systems
