Powering a rover through the two week lunar night is receiving a bit of attention. Most of the attention seems to be on better batteries and thermal control with some suggesting that nuclear is the only reasonable option for such a long time period of extreme cold and darkness. It may be possible to power a lunar installation through the night without using extreme storage or the dreaded nuclear. It may be time to think about the advantages of a Lunar SPS to bridge the gap between the periods of abundant sunlight energy on the ground.
While Lunar stationary would be restricted to orbits so far out as to make the required rectennas too large for rovers and other small early prospectingÂ missions, a lower Lunar orbiting SPS would be able to service much smaller installations. Required rectenna size is inversely proportionate to distance from the power source. Half the distance being half the required diameter and a quarter of the area required. A rectenna on Earth receiving from GEO needs to be a mile or more in diameter with the beaming distance of 22,300 miles or more if not directly under the SPS . A Lunar SPS at 250 miles or so altitude could efficiently hit a rectenna 1% of that or around 50 feet in diameter. Fifty feet diameter is possibly Â reasonable for a small rover on a world withÂ light gravity and no wind. It is certainly reasonable for a stationary prospector of small size.
The drawbacks are both the intermittent nature of the available power and the variable angleÂ with distance of the rover from the SPS. The intermittent nature of the available power willÂ probably be solved for powerless periods of two to three hours followed by intense charging periods with relatively small battery systems. Â Rectennas can be designed to accept power from multiple angles with relatively minor design work. The variable distance means that much of the low angle power will be wasted unless a much larger rectenna is built into the surface station. That waste could easily be more acceptable than nuclear depending on the political environment during a particular mission or exploration era. Even wasting 90% of power could be more acceptable than ground systems that must shut down for half of their working lives.
Once a Lunar SPS is operating in this manner it can be used for a multiple of ground stations accross a period of decades.