Lunar Polar Greenhouse
A Lunar Polar Greenhouse
In economically rational development of lunar resources, remotely controlled devices would be used to establish some industrial infrastructure before people would be sent to Luna in person. Then the first employees would eat all imported food for some time. Air and water would be recycled to a considerable extent with the loss of some locally produced oxygen being tolerated. Human waste would be incinerated to recover water, carbon as carbon dioxide and other volatiles for industrial use. Hydrogen and perhaps some other volatiles would be mined from the lunar poles if practical but hydrogen and therefore water would still be rare and expensive on Luna.
When the extent of development permits, this underground greenhouse could be built in a polar region. It would require that the vast majority of materials be locally obtained. The greenhouse would be built as a 100 meter diameter ring around a hill. Then the top of the hill would be flattened enough to provide fill to bury the greenhouse 3 meters deep. Mirrors would be used to concentrate sunlight and send it to the greenhouse through periscopes. Sunlight would be dispersed in the greenhouse to the proper strength for plants. Radiation composed of subatomic particles would not be reflected by the mirrors so the greenhouse would be protected. Most ultraviolet light requires a special coating to be well reflected.  So the periscopes would protect against ultraviolet also. A glass window would provide further protection against ultraviolet. Light would not shine on the intake mirrors of all periscopes at the same time, so crops would be grown on flat top rail road cars to shuffle them around to get eight hours of light every day for each rail road car during the growing season, which would be the local summer at the pole. Since light enters the greenhouse in concentrated form through a minority of the area of the walls and ceiling, it would provide sufficient heat for the greenhouse and the problem would be controlled cooling. Radiators on top of the flat hill would cool the greenhouse as other industrial installations on Luna will be cooled. Radiation of infrared can be indirect by reflection to protect the radiator from micrometeoroids. With the start of gardening human waste would no longer be incinerated but used to produce sewage sludge which would fertilize the greenhouse crops. Humidity would be reduced by air conditioning and the condensate would be recycled to water the crops.
The High Cost of Food
The many considerations beyond what is required on Earth that must taken into account to start operating a lunar greenhouse will result in expensive food. It only needs to be cheap enough to compete against food imported from Earth, and that is worth its weight in gold.
If a sunlight collection mirror at the pole is 10 meters high, then on the day when the shadow of that mirror is the shortest, it will be 370 meters long. So greenhouses could shade each other if they are spaced too closely. Considering that and shading from landscape features, there would be limited area available for agriculture on the moon's surface that can take advantage of sunlight every day of the local summer. When population growth requires additional agriculture, options for additional acreage include orbiting space habitats, lunar surface agriculture that is adapted to 14 day periods of darkness, and artificially illuminated crops.
- McGraw-Hill Encyclopedia of Science and Technology (c) 1997 article on "Telescope, Ultra Violet Telescope"