Courtesy of NASA's National Space Science Data Center
Launch Date: 1967-02-05 On-orbit dry mass: 385.60 kg. (850 lb.)
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.
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.
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.