Lunar Orbiter 4
Courtesy of NASA's National Space Science Data Center
Launch Date: 1967-05-04
On-orbit dry mass: 385.60 kg. (850 lb.)
The Lunar Orbiter 4 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 May 11 to 26, 1967.
Lunar Photographic Studies
This experiment consisted of a dual-lens camera system designed to
satisfy the primary mission objective of providing photogaphic
information for mapping and for the evaluation of Apollo and Surveyor
landing sites. An 80-millimeter lens system was used to obtain
medium-resolution (MR) photos, and a 610-millimeter lens system was used for
high-resolution (HR) photos. The two separate lens, shutter, and platen
systems utilized the same film supply and recorded imagery
simultaneously in adjacent areas on 70-millimeter film. Continual automatic
sequences of photos were obtained. At an altitude of 2,700 kilometers (1,670 miles), which was
approximately the perilune height, the system photographed over 85
percent of the lunar surface. At apolune, on the moon's farside at about
6,110-kilometer (3,800-mile) altitude, the areas photographed were correspondingly larger.
The film was bimat processed on board and optically scanned, and the
resulting video signal was telemetered to ground stations. Film density
readout was accomplished by a high-intensity light beam focused to a
6.5-micron-diameter spot on the spacecraft film. The spot scanner swept
2.67 millimeters in the long dimension of the spacecraft film. This process was
repeated 286 times for each millimeter of film scanned. The raster was
composed of 2.67- by 65-millimeter scan lines along the film. The video signal
received at the ground station was recorded on magnetic tape and also fed
to ground reconstruction equipment (GRE), which reproduced the portion of
the image contained in one raster on a 35-millimeter film positive framelet. Over
26 framelets were required for a complete MR photograph and 86 for a
complete HR image. Fogging of the window rendered some photographs
unusable. Otherwise, experiment performance was nominal until the final
readout on June 1, 1967. A detailed description of the experiment, a
bibliography, and indexes of all the available Lunar Orbiter 1 through 5
photos are contained in the report, 'Lunar Orbiter photographic data,'
NSSDC 69-05, June 1969.
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. The telemetry data were processed in real time
on 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
photo ellipse, and the extended mission (from end of the photographic
mission to July 11, 1967) phases. 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. Two micrometeoroid hits
were recorded during the photographic mission phase of the flight.
Cesium Iodioe 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. The shielding of the loopers and the
looper dosimeter was 0.17 gm/sq centimeters aluminum. These shielding
thicknesses also corresponded approximately to the thickness of the
Apollo module wall and of a space suit. In the case of protons at verticle
incidence, particles with energy greater than 40 and 11 MeV penetrated 2
and 0.17 gm/sq centimeters, respectively.
Lunar Orbiter 3
Lunar Orbiter 5
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