Lunar Orbiter 2
Courtesy of NASA's National Space Science Data Center
Launch Date/Time: 1966-11-06 at 23:21:00 UTC
On-orbit dry mass: 385.60 kg. (850 lb.)
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 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 November 18 to 25, 1966, and readout occurred through December 7, 1966. 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 3.0 degrees N latitude, 119.1 degrees E longitude (selenographic coordinates) on October 11, 1967.
Lunar Photographic Studies
This experiment consisted of a dual-lens camera system designed to
satisfy the primary mission objective of providing photographic
information 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. Automatic sequences of 1, 4, 8, or 16 photos could be obtained. At an altitude of 46 kilometers (29 miles), which was approximately the perilune height, the HR system photographed a 4.15- by 16.6-kilometer (2.58- by 10.32-mile) area of the lunar surface which was centered on a 31.6- by 37.4-kilometer (19.64- by 23.2-mile) area photographed by the MR system.
Resolutions were 1 and 8 meters (3 and 26 feet), respectively. At apolune, on the moon's
farside at about 1850-kilometer (1,143-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 Recontruction
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. Of
the 211 simultaneous exposures, 209 MR and 202 HR were completely read
out. The loss of two frames was due to the failure of the
traveling-wave-tube amplifier during final readout operations. All
recovered photography is considered usable. Experiment performance was
nominal until the final readout on December 7, 1966. 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 (range rate) and propagation times (range). 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 first and second
ellipse, and the extended mission (from end of the 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. Three micrometeoroid hits
were recorded during the photographic portion of the mission.
Cesium Iodide 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 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 1
Lunar Orbiter 3
Views of the Solar System Copyright © 1997 by
Calvin J. Hamilton. All rights reserved.