Lunar Orbiter 1

The Lunar Orbiter 1 spacecraft was designed primarily to photograph smooth areas of the moonlunar surface for selection and verification of safe landing sites for the Surveyor and Apollo missions. It was also equipped to collect selenodetic, radiation intensity, and micrometeoroid impact data. The spacecraft was placed in an Earth parking orbit on 10 August 1966 at 19:31 UT and injected into a cislunar trajectory at 20:04 UT. The spacecraft experienced a temporary failure of the Canopus star tracker (probably due to stray sunlight) and overheating during its cruise to the Moon. The star tracker problem was resolved by navigating using the Moon as a reference and the overheating was abated by orienting the spacecraft 36 degrees off-Sun to lower the temperature. Lunar Orbiter 1 was injected into an elliptical near-equatorial lunar orbit 92.1 hours after launch. The initial orbit was 189.1 km x 1866.8 km and had a period of 3 hours 37 minutes and an inclination of 12.2 degrees. On 21 August perilune was dropped to 58 km and on 25 August to 40.5 km. The spacecraft acquired photographic data from August 18 to 29, 1966, and readout occurred through September 14, 1966. A total of 42 high resolution and 187 medium resolution frames were taken and transmitted to Earth covering over 5 million square km of the Moon's surface, accomplishing about 75% of the intended mission, although a number of the early high-res photos showed severe smearing. It also took the first two pictures of the Earth ever from the distance of the Moon. Accurate data were acquired from all other experiments throughout the mission. Orbit tracking showed a slight "pear-shape" to the Moon based on the gravity field and no micrometeorite impacts were detected. The spacecraft was tracked until it impacted the lunar surface on command at 7 degrees N latitude, 161 degrees E longitude (selenographic coordinates) on the Moon's far side on October 29, 1966 on its 577th orbit. The early end to the nominal one year mission was due to the small amount of remaining attitude control gas and other deteriorating conditions and was planned to avoid transmission interference with Lunar Orbiter 2.