THE LUNAR ORBITER 4 MISSION

Mission Description

Launch:  4 May 1967
Imaged Moon:  11-26 May 1967
Lunar mapping mission

Mission 4 differed greatly from the previous missions in both concept and conduct. Because the Lunar Orbiter program tasks had been completed during the first three missions, project objectives were extended to increasing the understanding of the Moon as a whole. Surveying the entire lunar surface and examining in detail various surface geological processes became the new objectives. The secondary objectives of obtaining gravitational field and environmental information remained the same. Active photography was initiated on May 11, 1967. During 30 successive orbits over 15 days, 199 dual-frame exposures were taken. Despite some operational problems during the mission, Orbiter 4 was highly successful in fulfilling its purpose. The photographs obtained provided information and detail at least 10 times better than Earth-based observations.

Selection of the Target Sites

This mission did not involve photography of particular sites in the sense of the preceding missions. Except for the first orbit, photographs were taken as individual, single-frame exposures. For this reason, each frame was considered as a site. For operational purposes, nine photographic zones were designated. However, by the end of the mission, nearly the entire nearside surface and an appreciable amount of the farside had been photographed.