PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM LABEL_REVISION_NOTE = "20090629, L. Gaddis - Initial Version 20101001 C. Isbell - post review" OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = "LO4" INSTRUMENT_ID = {"80MM_FLC","610MM_FLC"} OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = {"80-MM FOCAL LENGTH CAMERA", "610-MM FOCAL LENGTH CAMERA} INSTRUMENT_TYPE = "DUAL LENS CAMERA" INSTRUMENT_DESC = " LUNAR ORBITER IV PHOTOGRAPHIC SYSTEM OVERVIEW ============================================== Much of the information in this document was abstracted from Kosofsky and El- Baz, 1970; Hansen, 1970; and Bowker and Hughes, 1971]. See references cited for more detail. The Lunar Orbiter photographic system included the spacecraft's photographic subsystem; the ground reconstruction electronics (GRE); and the communications system. The five Lunar Orbiter missions used a dual-lens camera system a 610-mm narrow angle high-resolution (HR) lens and an 80-mm wide-angle medium resolution (MR) lens [e.g., Boeing Company, 1967, 1968a, b; Hansen, 1970; Kosofsky and El-Baz, 1970; Bowker and Hughes, 1971; Byers, 1977]. Both lenses placed their frame exposures on a single roll of 70 mm film. The axes of the two cameras were coincident so the areas imaged in the HR frames were centered within the MR frame areas. The telephoto lens provided coverage equivalent to 1 meter from an altitude of 46 kilometers and the wide-angle lens an 8 meter object from the same altitude. Malfunctions plagued the photographic subsystem on Mission IV. The camera thermal door did not respond well to open and close commands and was kept in the open position. As a result, the spacecraft had to be oriented so that the temperature of the camera could be kept within the range needed for successful functioning, reduced condensation and so that light leakage would not degrade the film. Spurious signals from the readout looper caused problems with reading out the photos. Despite the problems, spacecraft maneuvers and re-photographing the region of the moon in which photos were damaged resulted in an extremely successful mission. Scientific Objectives --------------------- The primary objective of the five Lunar Orbiter missions was to locate smooth, level areas on the Moon's nearside and to confirm their suitability as manned landing sites for the Apollo program. This required photographic coverage at a ground resolution of 1 meter within 5o of the equator between longitudes 45oE and 45oW. Lunar Orbiter IV was placed in a very different orbit from the other missions, a high polar orbit with an inclination of 85o. This allowed the mission to achieve its primary objective of a systematic photographic survey of the lunar surface to increase scientific knowledge and for added detail in site selection for subsequent missions. Like the other missions, Lunar Orbiter IV collected selenodetic, radiation intensity, and micrometeoroid impact data. THE LUNAR ORBITER IV PHOTOGRAPHIC SUBSYSTEM ============================================ The photographic subsystem was designed to photograph the lunar surface, process the exposed film, scan the processed film with a flying spot scanner and provide video signals to the communications subsystem for transmission to Earth [e.g., Beeler and Michlovitz, 1969; Boeing Company, 1968a, b; Hansen, 1970; Kosofsky and El-Baz, 1970; Anderson and Miller, 1971].. The system comprised a dual camera, a film processing unit, a readout scanner, and film- handling apparatus. The photo subsystem simultaneously exposes two pictures at a time, processes the film and converts the information to an electrical signal for transmission to Earth. Active photography was initiated on Orbit 6 on 1967-05-11. During the 30 successive orbits, 199 dual-frame exposures were taken. Of these exposures, 86% provided over 99% coverage of the nearside of the Moon. These photos provided the first detailed data on numerous areas of scientific interest in all areas of the visible surface. In addition, the first detailed information on the spectacular Orientale basin on the western limb was obtained. Within the limits of the 6110 km photographic altitude and acceptable illumination, the apolune photography provided additional information of the farside to be added to the data from the first three missions. Examination of the photos obtained showed that coverage of the nearside from the normal perilune and recovery apolune photography provided visibility of the lunar surface at least 10 times better than that obtainable from Earth- based operations. Perilune photography, which provided pole-to pole coverage of the nearside every other orbit, was taken as single-frame exposures from altitudes of approximately 2600 km near the equator to about 3600 km for the polar regions. Dual Cameras ------------ The two cameras, one with a high resolution (HR) lens and one with a medium resolution (MR) lens, operated simultaneously, placing two discrete frame exposures on a common roll of 70-mm film. The high-resolution (H) frame was exposed through a 610-mm narrow-angle lens and a focal plane shutter. The medium-resolution (M) frame was exposed through an 80-mm wide-angle lens and a between-the-lens shutter. The 80-mm focal-length lens provided an angular coverage of 44.4o by 38o; the 610-mm focal-length lens had an angular coverage of 20.4o by 5.16o. The two camera axes were coincident so that coverage of the H-frame was centered within the coverage of the M-frame. Each camera operated at a fixed f/5.6 lens aperture, at shutter speeds of either 1/25, 1/50, or 1/100 second. Exposure times were recorded in digital form on the film alongside the M-frames. V/H (velocity-to-height ratio) was not used on Mission IV due to its high orbit. The photographic mission experienced problems with the camera thermal door early on. The camera thermal door protects the photo subsystem lenses from heat loss and direct sunlight, and was to be opened only prior to each photographic sequence. However, starting with the 3rd set of photos taken in Orbit 6, telemetry data indicated that the door was not responding well to open and close commends. So that the door would not fail in the closed position and terminate the photography mission, flight controllers commanded the door to stay open. To eliminate light leakage and reduce the cold-sink source, an effective procedure of controlling the camera thermal door and the photo subsystem window temperatures was developed. Condensation had completely evaporated by Orbit 13. Spacecraft maneuvers were not entirely successful and damaged photos were retaken later in the mission. Calibration ----------- Tests and calibrations performed on the photographic subsystem included lens- film characteristics, exposure calibration and control, image motion compensation, camera alignment, readout quality, and photogrammetric distortion calibration of the 80-mm camera. Film ---- The Kodak special high definition 70-mm film aerial film, type SO-243 with a recording capability of 450 lines/mm met the resolution requirement of approximately 76 lines/mm and low enough speed to make it relatively insensitive to space environment radiation. Camera Film Advance -------------------- Camera film advance was completely satisfactory and within tolerance, as indicated by telemetry and subsequent readout [e.g., Boeing Company, 1968b, p. 166]. Filters ------- The Mission IV photo subsystem was equipped with a 0.21 neutral-density filter in front of the 80-mm lens to nearly equalize the light transmission characteristics of the two lens systems. Exposure -------- The relatively high altitude and near-polar orbit resulted in each photo covering a wide range of surface and reflective characteristics. Experience gained during the previous three missions was used to refine the selection of photographic parameters needed to determine the required exposure settings. Since many areas were photographed for the first time, changes were made in exposures during the mission. Several photographs were exposed to give detailed information on a feature, sometimes at the expense of the exposure of the surrounding area. Light fogging or flare on the exposed but unprocessed film degraded photographs taken during Orbits 7 through 10 (exposures 27 through 51), although this was not detected until the photos were read out. Resolution ---------- The requirement for resolution for the Lunar Orbiter missions was that the photograph could detect a 1-meter object with the telephoto lens and an 8- meter object with the wide-angle lens from an altitude of 46 kilometers. This required a resolution of 76 lines per millimeter on the spacecraft film or 10 lines per millimeter on the GRE record. The resolution requirement was equivalent to detection of objects with images spanning four scan lines. Resolution capability of the telephoto perilune photography varied from about 60 to 90 meters, depending on the slant range to the surface and the location within the frame format. PATTERNS OF PHOTOGRAPHIC COVERAGE ================================= Perilune photography was taken at four latitude positions: +42.5 and -42.5 at altitudes of 2,880 to 3,000 km, including the surface area from about 26 to 60o latitude with a typical telephoto photograph area of 275 x 1,100 km, and +14 and +14.5 at altitudes of 2,680 to 2,740 km, and covered an area of about 250 x 1,010 km. Perilune photography also included the North and South polar regions from + 72 degrees latitude and from altitudes between 3,340 and 3,610 km with each photo covering a band from 50 to 90 degrees and surface area of 330 x 1,300 km. Apolune photography was from an latitude of 6,102 to 6, 149 km. Apolune photos that were taken to replace the damaged perilune photos and were from nearly twice the altitude were still better than photographs taken by Earth- based systems. At apolune, on the moon's farside, the photographed areas were larger than those taken at perilune. Film Processing --------------- Prior to being placed onboard the spacecraft, the photographic film was soaked in a monobath processing solution to develop the exposed portions to a negative image, with exposed with strip numbers, a nine-level grayscale bar, resolving power chart, and reseau marks. After exposure, film-processing took place on board the spacecraft by the Kodak Bimat diffusion transfer technique. The average processor rate was 2.42 inches per minute, below specified. At least two frames were processed each orbit to minimize Bimat dryout effects. The undeveloped silver ions were transferred to the processing web, where they were reduced to form a positive image. The negative film went through the drying section, and then the film went through the readout scanner to its takeup spool. Seventeen photographs were not developed because 'Bimat cut' was commanded earlier than planned. Film Readout ------------ Film density readout was accomplished by a high-intensity light beam focused to a 6.5-micron-diameter spot from a linescan tube, which converted the photographic images into electrical signals. The flying spot scanner swept 2.67 mm 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 mm scan lines along the film. The special cathode-ray tube whose phosphor layer was coated on a rotating cylindrical metal anode put out a bright spot of light that repetitively traced a line across the phosphor drum. The scanning of a complete dual exposure took 43 minutes. The resulting sections of spacecraft film scanned in this manner, referred to as framelets, are the basic units eventually used for the ground reassembly. The intensity of light reaching the photomultiplier tube was modulated by the density of the image on the film. An electrical signal proportional to the intensity of the transmitted light was generated, amplified, and fed to the spacecraft communications subsystem. The raster signal received at the ground station was recorded on magnetic tape and also fed to ground reconstruction equipment (GRE). 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 1967-06-01. Final readout was terminated when all of the desired photos had been read out by either priority or final mode. Additional problems with the photo subsystem began in Orbit 24 when the readout sequence was terminated by a spurious 'readout looper-full' signal. Flight controllers reset the photo subsystem electronics memory and readout continued. During Orbit 35, a spurious 'readout looper empty' signal kept the looper from emptying. The decision was then made to cut the Bimat and initiate the final readout to be sure that the photos not read in priority readout could be recovered. Final readout was initiated on Orbit 41 and complete on Orbit 48 on 1967-06-01 when all desired photos had been recovered. [Boeing Company, 1968a, b]. To recover the maximum amount of the damaged images where the nearside perilune photography was degraded, the mission plan was revised during Orbit 29 to allow the spacecraft to re-photograph the area from near apolune, even though there was a reduction in resolution. The combination of perilune nearside and apolune nearside (recovery) photographs provided more than 99% coverage of the visible half of the lunar surface [Boeing Company, 1968a, b]. The nearside images were at least 10-times better than Earth-based. After LO IV, 80% of the far side had been successfully photographed during the first four missions. TRANSMISSION AND RECONSTRUCTION OF PHOTOGRAPHS ============================================== The original photograph was transmitted to Earth as analog data. Photographic prints from the film strips were hand mosaicked into sub-frame (for HR data) and full-frame (for MR data) views and widely distributed. The video data coming from the photographic subsystem occupied a frequency spectrum from 0 to 230 kilohertz. This signal was modulated on a 310-kHz subcarrier (single sideband, suppressed carrier). The video signal, telemetry signals, and a 38.75-kHz pilot tone were summed, and the resulting composite signal phase- modulated the S-band (2295-MHz) carrier. A 10-watt traveling-wave tube amplifier and a 92-cm parabolic antenna transmitted the signal to Earth, where it was received at one of the three deep space stations (DSS) [e.g., Bundick et al., 1965]. The 10-MHz intermediate frequency of the DSS receiver, containing the composite signal, was recorded on magnetic tape for permanent storage. At the same time, it was passed to the ground communications equipment which recovered the telemetry and video. The video signal was fed to the GRE where it was converted into an intensity modulated line on the face of a cathode-ray tube. In a continuous motion camera, 35-mm film was pulled past the image of this line, recording each readout framelet at 7.18 times the spacecraft's image size. The recording film was cut up into framelets, which were then reassembled into enlarged replicas of the original spacecraft frames. The MR frames were reassembled in complete form, while the HR frames, which would be about 1.5 meters long if fully reassembled, were reassembled into three component sections." 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