Lunar Orbiter 2 Mission

Alternate Names: Lunar Orbiter-B, 02534
Launch Date: 1966-11-06
Launch Vehicle: Atlas-Agena D
Launch Site: Cape Canaveral, United States
Mass: 385.6 kg
Nominal Power: 375.0 W
Launch/Orbital information for Lunar Orbiter 2
Experiments on Lunar Orbiter 2
Data collections from Lunar Orbiter 2


The Lunar Orbiter 2 spacecraft 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 a cislunar trajectory and injected into an elliptical near-equatorial lunar orbit for data acquisition after 92.5 hours flight time. The initial orbit was 196 km x 1850 km at an inclination of 11.8 degrees. The perilune was lowered to 49.7 km five days later after 33 orbits. A failure of the amplifier on the final day of readout, 7 December, resulted in the loss of six photographs. On 8 December 1966 the inclination was altered to 17.5 degrees to provide new data on lunar gravity.

The spacecraft acquired photographic data from November 18 to 25, 1966, and readout occurred through December 7, 1966. A total of 609 high resolution and 208 medium resolution frames were returned, most of excellent quality with resolutions down to 1 meter. These included a spectacular oblique picture of Copernicus crater which was dubbed by the news media as one of the great pictures of the century. Accurate data were acquired from all other experiments throughout the mission. Three micrometeorite impacts were recorded. The spacecraft was used for tracking purposes until it impacted the lunar surface on command at 3.0 degrees N latitude, 119.1 degrees E longitude (selenographic coordinates) on October 11, 1967.

Spacecraft and Subsystems

The main bus of the Lunar Orbiter had the general shape of a truncated cone, 1.65 meters tall and 1.5 meters in diameter at the base. The spacecraft was comprised of three decks supported by trusses and an arch. The equipment deck at the base of the craft held the battery, transponder, flight progammer, inertial reference unit (IRU), Canopus star tracker, command decoder, multiplex encoder, traveling wave tube amplifier (TWTA), and the photographic system. Four solar panels were mounted to extend out from this deck with a total span across of 3.72 meters. Also extending out from the base of the spacecraft were a high gain antenna on a 1.32 meter boom and a low gain antenna on a 2.08 meter boom. Above the equipment deck, the middle deck held the velocity control engine, propellant, oxidizer and pressurization tanks, Sun sensors, and micrometeoroid detectors. The third deck consisted of a heat shield to protect the spacecraft from the firing of the velocity control engine. The nozzle of the engine protruded through the center of the shield. Mounted on the perimeter of the top deck were four attitude control thrusters.

Power of 375 W was provided by the four solar arrays containing 10,856 n/p solar cells which would directly run the spacecraft and also charge the 12 amp-hr nickel-cadmium battery. The batteries were used during brief periods of occultation when no solar power was available. Propulsion for major maneuvers was provided by the gimballed velocity control engine, a hypergolic 100-pound-thrust Marquardt rocket motor. Three-axis stabilization and attitude control were provided by four one-lb nitrogen gas jets. Navigational knowledge was provided by five Sun sensors, Canopus star sensor, and the IRU equipped with internal gyros. Communications were via a 10 W transmitter and the directional 1 meter diameter high gain antenna for transmission of photographs and a 0.5 W transmitter and omnidirectional low gain antenna for other communications. Both antennas operated in S-band at 2295 MHz. Thermal control was maintained by a multilayer aluminized mylar and dacron thermal blanket which enshrouded the main bus, special paint, insulation, and small heaters.

Results of the Lunar Orbiter Program

The Lunar Orbiter program consisted of 5 Lunar Orbiters which returned photography of 99% of the surface of the Moon (near and far side) with resolution down to 1 meter. Altogether the Orbiters returned 2180 high resolution and 882 medium resolution frames. The micrometeoroid experiments recorded 22 impacts showing the average micrometeoroid flux near the Moon was about two orders of magnitude greater than in interplanetary space but slightly less than the near Earth environment. The radiation experiments confirmed that the design of Apollo hardware would protect the astronauts from average and greater-than-average short term exposure to solar particle events. The use of Lunar Orbiters for tracking to evaluate the Manned Space Flight Network tracking stations and Apollo Orbit Determination Program was successful, with three Lunar Orbiters (2, 3, and 5) being tracked simultaneously from August to October 1967. The Lunar Orbiters were all eventually commanded to crash on the Moon before their attitude control gas ran out so they would not present navigational or communications hazards to later Apollo flights. The Lunar Orbiter program was managed by NASA Langley Research Center and involved building and launching 5 spacecraft to the Moon at a total cost of $163 million.

Original source: NASA - NSSDC

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