Talk:Lunar Radiator

It is still to be determined the efficiency of the system. Vacuum on the moon will not allow a proper cooling. The only output of the system is infrared radiation. The point is how the infrared radiation will scape properly the radiator given the fact that the radiator is practically covered.

A solution would be to uncover the radiator during the night.

Another solution would be to cover the radiator with cold and compact regolith and replacing it once it reaches more than the needed temperature.

The average temperature underneath the surface is -23 degrees Celsius. During the nigth the regolith can reach -153 degrees Celsius.

(There is no actual data about how cold is the interior of the moon below 20 meters and volcanic activity is still something unknown yet).

During the day the radiator could be covered with cold regolith from the night. And during the night the heated regolith could be removed and replaced with cold regolith again.

Yesterday I was reading the microfiches of the handbook of lunar materials. It is really unknown the termodynamic behavior of the regolith underneath the surface.

I can be wrong...

--Jotagiraldez 20:00, 6 November 2010 (UTC)

It is true that the only output of a lunar radiator is infrared radiation. That is the main point. That is the difficulty of lunar industrial operations. It requires a large radiating area to get rid of a large amount of heat. In particular the amount of heat radiated is 5.67 times ten to the minus 8 watts per square meter times the emissivity of the radiator times the fourth power of the temperature in kelvin. So if the radiator is maintained at 46.85 C (116 degrees F) the absolute temperature is 320 K. If the emissivity of the radiator is 0.80 then it will radiate 476 watts per square meter. To radiate 40 kilowatts at that temperature a radiator of 84 square meters is needed. If you have a radiator as I described and the ditch is 84 meters long, the ditch would need to be scaled to have the radiator 1 meter high.

There is a reason for almost covering the radiator. If micrometeoroids strike it at any time day or night, it could start to leak expensive coolant. If it is exposed to sunlight it will not get very cool. The surrounding ground gets hotter than the boiling point of water in the day so the radiator must be protected from the infrared radiation of the surroundings. The day time is when there is solar power to use so the daytime is when the heat must be radiated. A process of storing big piles of cold regolith during the night and using them during the day for coolant would be a big material handling problem. I do not expect it would be part of an efficient industry.

Now the drawing you provided for a lunar radiator is neatly done but it differs in a few particulars from the radiator I intended. The focus is shown on a line on the top of the micrometeoroid shield. It should be raised above the shield somewhat. The sun rays are shown projected into the image plane as vertical lines as they would be at the equator. The point is that the radiator must be able to work at any latitude. So the plane of symmetry of the parabolic ditch must tilt from vertical at an angle equal to the latitude at which the radiator is installed, leaning toward the equator. I depicted an installation at latitude 13 degrees North. As I drew the installation the ground on each side of the ditch is at the same level, your drawing shows the ground level higher on the south side of the ditch.

There are other types of radiators that are possible, I showed just one concept. It is good to have a classy looking drawing, but it is more important to have the concept portrayed correctly. So I will restore my crude but correct image.

It is possible to have a radiator not shielded from the infrared of the surroundings and just have the low temperature for a heat engine at a higher temperature than the surroundings. This causes some thermal inefficiency, but a smaller radiator installation is needed. Also if any part of the lunar base needs to be cooler than the surroundings, a heat pump would need to pump the heat out at the temperature of the radiator even if that is more than 100 C. Engineers will finally decide what is actually done. --Farred 00:10, 7 November 2010 (UTC)

One possibility for storing cold during the lunar night is having coolant pipes run through an emplacement of bricks. The radiator could operate more efficiently during the night because of not needing shielding from the sun and from hot surroundings but it would still need micrometeoroid shielding. Building up a large thermal mass of bricks would be a considerable task. --Farred 04:09, 7 November 2010 (UTC)

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