This article is from the Space FAQ, by Jon Leech leech@cs.unc.edu and Mark Bradford tla@surly.org with numerous contributions by others.
LUNAR ORBITER 1 through 5 were designed to orbit the Moon and image
various sites being studied as landing areas for the manned APOLLO
missions of 1969-1972. The probes also contributed greatly to our
understanding of lunar surface features, particularly the lunar farside.
All five probes of the series, launched from 1966 to 1967, were
essentially successful in their missions. They were the first U.S.
probes to orbit the Moon. All LOs were eventually crashed into the lunar
surface to avoid interference with the manned APOLLO missions.
 
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