Lunar Orbiter 1

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Lunar Orbiter 1
Lunar orbiter 1 (large).jpg
Operator NASA
COSPAR ID 1966-073A
SATCAT № 2394
Mission duration 80 days
Spacecraft properties
Manufacturer Langley Research Center
Launch mass 385.6 kilograms (850 lb)
Start of mission
Launch date August 10, 1966, 19:31 (1966-08-10UTC19:31Z) UTC[1]
Rocket Atlas SLV-3 Agena-D
Launch site Cape Canaveral LC-13
End of mission
Disposal Deorbited
Decay date October 29, 1966 (1966-10-30)
Orbital parameters
Reference system Selenocentric
Semi-major axis 2,694 kilometers (1,674 mi)
Eccentricity 0.33
Periselene 40.5 kilometers (25.2 mi)
Aposelene 1,866.8 kilometers (1,160.0 mi)
Inclination 12 degrees
Period 208.1 minutes
Lunar orbiter
Orbital insertion August 14, 1966
Impact site 6°21′N 160°43′E / 6.35°N 160.72°E / 6.35; 160.72
Orbits 577

The Lunar Orbiter 1 robotic (unmanned) spacecraft, part of the Lunar Orbiter Program, was the first American spacecraft to orbit the Moon. It was designed primarily to photograph smooth areas of the lunar 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 August 10, 1966 at 19:31 (UTC). The Trans lunar injection burn occurred at 20:04 (UTC). 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 by 1,866.8 kilometres (117.5 mi × 1,160.0 mi) and had a period of 3 hours 37 minutes and an inclination of 12.2 degrees. On August 21, perilune was dropped to 58 kilometres (36 mi) and on August 25 to 40.5 kilometres (25.2 mi). The spacecraft acquired photographic data from August 18–29, 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.

Instruments
Lunar Photographic Studies Evaluation of Apollo and Surveyor landing sites
Meteoroid Detectors Detection of micrometeoroids in the lunar environment
Caesium Iodide Dosimeters Radiation environment en route to and near the Moon
Selenodesy Gravitational field and physical properties of the Moon

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