#90 November 1995
Section 220.127.116.11.090.of the Artemis Data Book
For sake of best long-shadow lighting conditions as well as heat management, all the Apollo missions landed shortly after local sunrise, and as if subconsciously frightened senseless of nightfall, left well before local noon. We haven't come close to experiencing a whole lunar dayspan/nightspan cycle! Here are the figures for each mission.
|TD 10.93 hrs after local sunrise|
LO after 21.60 hrs after local sunrise
(like 6.22-7:06 am on Earth with 6:00 am sunrise)
|TD 10.12 hrs after local sunrise|
LO after 19.52 after local sunrise
(like 6:21-7:01 am on Earth with 6:00 am sunrise)
|TD 20.75 hrs after local sunrise|
LO after 33.51 after local sunrise
(like 6:42-7:50 am on Earth with 6:00 am sunrise)
|TD 14.04 hrs after local sunrise|
LO after 68.91 after local sunrise
(like 6:29-8:49 am on Earth with 6:00 am sunrise)
| TD 17.82 hrs after local sunrise|
LO after 71.04 after local sunrise
(like 6:36-9:00 am on Earth with 6:00 am sunrise)
| TD 16.8 hrs after local sunrise|
LO after 75.00 after local sunrise
(like 6:34-9:06 am on Earth with 6:00 am sunrise)
Sunrise to Sunset is 354.367 hrs or 14.7653 days
Full Sunth (local day) is 708.734 hrs or 29.5306 days
This is a pattern similar to early sorties to Antarctica. There, we came after the spring pack-ice breakup and left well before the fall freezeup - for the first two decades. It wasn't until Byrd set up Little America in 1929 [a site abandoned 30 years later in '59 as U.S. Antarctic operations concentrated on McMurdo Sound] that we took the plunge and "overwintered." That was quite some hurdle, mentally and emotionally, as well as operationally and logistically. Now we face the same hurdle on the moon. But until we do it, all our talk of "permanent presence" is just so much empty macho bravado.
In the case of Little America, the major hurdles to be overcome were the need to build up during the summer months enough fuel (heat, power, and vehicles) and food reserves to last the long cold winter night months when resupply would be impossible. Rescue would also be impossible, meaning medical supplies and kits had to be more adequate, and medical personnel more fully trained. On the moon the challenge will be similar although the nightspan is only a twelfth as long.
Surface temperatures drop drastically and quickly after lunar sunset. But, these are surface effects only. The powdery soil is a poor conductor, and a poor reservoir, of either heat or cold. A couple of meters down, below the blanket of shielding soil, temperatures remain about -4° F or -20° C all the time.
Most expect a heat buildup within the buried habitat, heat from living, heat from operations, that will not be drawn off by the surrounding soil as fast as it is generated - even at night. If an equation of heat inputs and losses shows a net heat rise even during nightspan, a system of external heat-shedding radiators will be necessary.
If, however, because available power during nightspan means powered down operations, and if that in turn means a thermal deficit during nightspan, then some sort of thermal heat sink accessed by a heat pump might not be a bad idea. We'll have, or should have, the former - in the form of water reserves. A large reserve tank can be buried in the soil not far from the habitat. Heat from the water would be pumped into the habitat by nightspan, the direction reversed for dayspan cooling. A net heat excess over the whole dayspan/nightspan cycle would then be shed by external radiators.
If we don't bring along, find, or generate (i.e. adding hydrogen to locally produced oxygen, probably in fuel cells to produce night power and water both), enough water to make such a heat-pump accessible water reservoir work, then our plans to make our presence "permanent" are in big trouble.
Successful thermal management will depend largely on how much care is taken to isolate major heat-producing activities from the habitat areas. This means automated unpressurized processing and manufacturing plants, saving low temperature aspects of production (finishing, assembly, etc.) for occupied areas.
Many suggest solving the nightspan power problem by bringing along a small nuclear power unit. Even if the legal and political hurdles can be overcome (e.g. by having the Russians contribute this system), the point is missed. No matter how big the nuke, there will still be less power available during nightspan than during dayspan for the simple reason that during the latter, the Sun also shines, its heat ready to do work - simply and cheaply.
The Sun can provide nightspan power in these ways:
Solar heat can be used via several processes to produce oxygen from moon rock by dayspan. During nightspan this oxygen is combined with hydrogen brought from Earth, in fuel cells, to produce power - with pure potable water as the byproduct.
If necessary, solar power can also be used during dayspan to electrolyze a portion of the water reserves back into hydrogen and oxygen for nightspan fuel cell fuel. (In addition, the Sun's raw ultra-violet rays can help purify the remaining water reserves under cover of UV-transparent quartz.)
If there is an early cast basalt industry to provide paving blocks and other low performance items useful to the expanding base, possibly as a sideline to oxygen production through heating the moon rock, this would open another road for Sun and water to work synergistically to provide nightspan power. If during dayspan, when the solar concentrators power these industries, there builds up an excess residual pool of molten rock and this is kept shielded from the heat-sucking night sky in an underground reservoir, the residual heat of this "magma pool" can be tapped to produce steam to run the base's nightspan generators. This is the idea of LUNAX director David Dunlop. A refractory lining of aluminum oxide would make such a magma-pool reservoir more efficient, but might not be absolutely necessary.
Mark Reiff of General Space Corporation suggests another form of lunar heat pump. If vibro-accoustic testing locates a relatively small underground void (cavern) near the surface (less than 100 feet), this can be accessed by drilling. The natural reservoir can then be filled with a thermally conductive material (he suggests smelting regolith into molten aluminum). The thermal properties of the available material should drive the purity requirements. The material would be allowed to reach an equilibrium (cool). Next you would set up a thermal dynamic generator (Sterling cycle would work good) with your heat source on one end and the newly created heat sink connected to the other. You could shade the generator and the top of the heat sink to even provide power by dayspan too. [Smelting aluminum, however, is not likely to be an early outpost technology - Ed.]
The Sun and water, then, seem to be the simple and elegant basic ingredients for a nightspan power system (as well as maintaining thermal equilibrium). Elaborate and expensive plans for providing nightspan power (or maintaining thermal equilibrium) by other higher tech means seem foolish.
The division of labor into hot in-vacuum and cool in-habitat chores (see above) in order to assist in thermal management will also work neatly to separate man-hours into energy-intensive dayspan aspects and labor-intensive nightspan aspects of the total production and operations cycles.
I have suggested that this fortnightly change of pace will become a well-liked feature of lunar life. Some have seen it as a burden to be avoided. Do not forget that on the moon there are no seasons, no daily changes of weather, both of which add spice and interest and renewal to living on Earth. If this nightspan power "deficit" were ever to be effectively eliminated, the biggest source of rhythm and change of pace would be gone with it. Productivity gains would be temporary as morale slowly plummeted from routine, boredom, ennui.
Other nightspan power solutions frequently proposed are well down the road, something for later generation advanced settlements to consider. These include solar power satellites, lunar solar array networks (one over the nearest pole makes the most sense as it would be in sunlight whenever the outpost is experiencing nightspan), helium-3 fusion plants, and, oh yes, lunar hydroelectric.
Overnighting will also require much more capable recycling systems than did missions only intended to spend a couple of days on the morning Sun lit surface. Some water recycling chores can be solar-operated, as suggested above. By nightspan, used water could simply accumulate; or, freezing (by sky exposure) could work to separate out some impurities.
Human solid wastes could be stored out-vac, left to freeze in shaded sanitary containers. Rather than be a problem for eventual disposal, such compostable organics-rich material will become a banked resource of great value for the eventual commencement of regolith-soil based agriculture, once creation of significantly cheaper pressurized expansion volume becomes possible using on-site produced building materials.
Plan as we will to stock up by dayspan for a dayspan-only logistics operation of resupply and manpower relief from Earth, we will be prudent to allow for the possibility of night landings and launches. Once we can land on a dime using signal clues rather than visual ones, this should be no big deal. It does mean, however, that the outpost's "spaceport" be more than a simple designated circle in the sand. It will need to be equipped with beacons and lights and radio.
For this and who knows how many other contingencies, a service vehicle that can operate at night is also a must. This means more than headlights. It means power supplies, motive systems, and lubricants that can withstand temperatures of -200° F or -130° C with no problem.
Any approach to lunar outpost design, NASA/International or commercial, in which every aspect does not reflect the needs of "overnighting" begs to fail. If you are honest, you will realize that some of the above capacities are not self-obvious if you conveniently ignore the fact that some time after your base setup landing, the Sun will set, and stay set for almost fifteen days, over and over again every sunth, forever.
Contents of this issue of Moon Miners' Manifesto