The first lunar weather stations, matchbox-sized, 270 g Apollo Dust Detector Experiments about 100 cm above the surface of the Moon near Apollo 12, 14, and 15 landing sites, measured dust accretion, charged particle radiation, and temperature changes—three environmental factors proved during Apollo to affect technical systems deployed on the Moon. Degradation of seven horizontal solar cells was measured every lunar daytime from 1969 to 1976. The anomalously intense August 1972 solar particle event (SPE) degraded three covered cells by less than 1%, while two cells desensitized by intense preirradiation showed no measurable effects. Although independent studies estimated the long-term fluence bombarding the cells was less than half that of the August SPE, long-term gradual degradation of five covered cells (normalized to 2000 days) was an order of magnitude greater, between 4% and 10%. If the long-term effects were totally caused by dust, with articulated caveats including simulated (maria) Minnesota Lunar Simulant-1 dust particles with diameters 20 to 38 µm, this provides the first direct measured long-term net accretion of dust with an upper limit of order 100 µg cm−2 yr−1, equivalent to a layer 1 mm thick in 1000 years, but it may be significantly less. Two bare cells were abruptly degraded by 7% during the August SPE, however long-term they measured additional damage of 29% and 24%, indicating a long-neglected suite of low-energy radiation, posing risks for bare materials exposed on the surface of the Moon.
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