The Apollo 11 lunar module landed with an estimated 2 ft/sec lateral motion. Photographic evidence and astronaut observations indicate that only a fraction of an inch of material was eroded from the surface during the descent. These indications agree with a computed maximum depth of eroded material using an empirically derived erosion law. The onset of erosion was determined from descent motion pictures and astronaut comments during the landing approach. The first noticeable erosion occurred when the lunar module was at 65 ft, followed by thin steady erosion at 55 ft and strong steady erosion at 45 ft. These observations compare with a predicted onset of erosion at greater than 40 ft and fully developed erosion between 20 and 40 ft.

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