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Lunar Orbiter 3

Courtesy of NASA's National Space Science Data Center

Launch Date: 1967-02-05
On-orbit dry mass: 385.60 kg. (850 lb.)


Description

The Lunar Orbiter 3 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 lunar orbit for data acquisition. It was stabilized in a three-axis orientation by using the sun and the star Canopus as primary angular references. A three-axis inertial system provided stabilization during maneuvers and when the sun and Canopus were occulted by the Moon. Communications were maintained by an S-band system which utilized a directional and an omnidirectional antenna. The spacecraft acquired photographic data from February 15 to 23, 1967, and readout occurred through March 2, 1967. Accurate data were acquired from all other experiments throughout the mission. The spacecraft was used for tracking purposes until it impacted the lunar surface on command at 14.3 degrees N latitude, 97.7 degrees W longitude (selenographic coordinates) on October 9, 1967.

Selenodesy Experiment

The instrumentation for this experiment included a power source, an omnidirectional antenna, and a transponder to obtain information for determining the gravitational field and physical properties of the moon. High-frequency radio signals were received by the spacecraft from earth tracking stations and retransmitted to the stations to provide doppler frequency measurements (range rate) and propagation times (range). The telemetry data were processed in real time by an IBM 7044 computer in conjunction with an IBM 7094 computer. They were then displayed on 100-wpm teletype machines, x-y plotters, and bulk printers for analysis. Data coverage was continuous while the spacecraft was visible from earth. Information was acquired during the cislunar, the first and second ellipse, and the extended mission (from end of photographic mission to lunar impact) phases of the mission. Doppler, ranging, hour angle points, and declination angle points data were accumulated during tracking. The quality of recorded data ranged from good to excellent.

Meteoroid Detectors

Twenty 0.025-millimeter beryllium copper pressurized cell detectors were used to provide direct measurements in the near-lunar environment of the rate of penetration by micrometeoroids. The detectors were arranged on the periphery of the tank deck. Each cell was a helium pressurized semicylinder with a pressure sensitive switch that remained closed until pressure was released by puncture of the cell's surface. Meteoroid hits were recorded by discrete telemetry channel state changes. The total exposed area of the detectors was 0.282 square meters, and the effective area after shielding by other components was 0.186 square meters. One micrometeoroid hit was recorded during the photographic mission and four hits were recorded during the extended mission.

Cesium Iodine Dosimeters

The principal purpose of the Lunar Orbiter radiation measuring systems was to monitor, in real time, particle fluxes that would damage processed film in case of major solar cosmic ray events. This would make it possible for the mission control to minimize darkening of the film by operational maneuvers. A secondary purpose was to acquire a maximum amount of information on radiations on the way to the moon and near the moon. The sensor system consisted of two separately monitored thin cesium iodide scintillators (2-Pi solid angle acceptance) that were positioned and shielded in the same way as the film in the cassette and in the loopers. The shielding thickness of the cassette and cassette dosimeter was 2 gm/sq centimeters aluminum. These shielding thickness also corresponded approximately to the thickness of the Apollo module wall and of a space suit. In the case of protons at vertical incidence, particles with energy greater than 40 and 11 MeV penetrated 2 and 0.17 gm/sq centimeters, respectively.

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