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DESTINATION MOON: A History of the Lunar Orbiter Program


CHAPTER X: MISSIONS IV AND V: THE LUNAR SURFACE EXPLORED

The Final Mission



[290] A NASA Boeing Lockheed team launched Lunar Orbiter V successfully from Launch Complex 13 at Cape Kennedy on August 1, 1967, less than one year after the first Orbiter had made its long journey to the Moon. The countdown proceeded smoothly throughout the day with only one anomaly in the Agena, causing a short hold. Then it resumed until mid-afternoon. The launch was scheduled for 4:09 p.m. EDT, [291] but a rain storm delayed it for two and one half hours. The threat of postponing the launch grew serious because the launch window on August 1 lasted only from 4:09 p.m. to 8:00 p.m. EDT. The threat was significant to the mission because, if the weather forced a delay until the launch window of the following day, a partial loss of farside photography would result. Lunar Orbiter V was targeted for a high, elliptical polar orbit so that it could perform photography over the Moon's entire surface. The Moon rotates 13° of arc on its axis per Earth-day. A delayed launch of one day would mean the loss of a 13° portion of the lunar far side to darkness.³⁸
Fortunately the weather improved, and the countdown resumed. Launch control fired the Atlas-Agena carrying Lunar Orbiter V on its way to the Moon at 6:33 p.m. EDT. In the monitoring room program officials sat watching the large display panels as various signals lit up, telling them that the different marks of the launch operation had been achieved. Early telemetry data indicated that all systems were functioning excellently. Fifty minutes into the mission the Deep Space Tracking Network station at Woomeras Australia, acquired radio contact with the spacecraft. It confirmed for [292] ground control that the spacecraft had separated from the Agena and deployed its soar panels and two antennas and that its power system was operating on solar energy. All subsystems continued to perform normally and within acceptable temperature limits.³⁹
Flight controllers at the Jet Propulsion Laboratory, where DSN operations shifted after the launch, executed the first midcourse maneuver at 2 a.m. EDT on August 3. This corrected the spacecraft's trajectory, which was about 7,000 kilometers off the aim point, for the deboosting maneuver into lunar orbit. Lunar Orbiter V carried out a roll maneuver of +42.1°, a pitch maneuver of +29.1° and a burn of its velocity control engine of 26 seconds. The resulting velocity increment of 29.76 meters per second was sufficient to put the spacecraft on course for arrival at the planned aiming point at the specified time. No second midcourse correction was necessary.⁴⁰
During the cislunar transit the spacecraft had no difficulty acquiring Canopus before the midcourse maneuver. [293] The radiation dosimeter at the film supply cassette registered a dose of 0.75 rads as the spacecraft passed through the Van Allen Belt. After transit the dosimeter in the camera storage looper was turned on, and it registered 0.0 rads. The ship recorded no micrometeoroid hits, and all subsystems continued to perform well.
At 12:48 p.m. EDT on August 5, after executing a roll and a pitch maneuver, the spacecraft fired its 100-pound-thrust rocket for 8 minutes and 28 seconds and decelerated by 643 meters per second into the gravitational captivity of the Moon. The initial orbital parameters were: apolune, 6,023 kilometers; perilune, 194.5 kilometers; inclination, 85.01°; period of orbit, 8 hours, 30 minutes. One and a half hours after orbit insertion, ground control commanded Lunar Orbiter V to scan the Goldstone test film, and the subsequent readout showed high-quality data. Following this, flight controllers prepared for the major photographic work of the mission.⁴¹
Photography commenced at 7:22 p.m. EDT on August 6. At this time the spacecraft took its first photograph of the Moon at a distance of about 6,000 kilometers from the lunar surface. The target was a previously unknown area of the far side. Then it executed a maneuver early on August 7 [294] that lowered the perilune to 100 kilometers while maintaining a 6,023-kilometer apolune. The spacecraft continued farside photography, exposing eighteen out of nineteen frames during the first part of the mission. The nineteenth was a "film set" frame, moved through the photo subsystem in an eight hour interval to prevent film from setting and Bimat from drying out. While this was a planned item In the film's budget, the decision which program officials made early on August 7 changed the next scheduled "film set" frame significantly. They decided to use it to take a photograph of the Earth with the 610 mm high-resolution camera lens instead of passing It unexposed through the system.⁴²
Site VA-9, as the Earth photograph was identified, had not been in the original plan. Program officials decided, however, that the position of Lunar Orbiter V relative to the Moon and the Earth and the Earth's position relative to the Sun afforded a very fine opportunity to take such a picture. The Langley program planning staff together with flight controllers implemented a plan to make an Earth photograph when the spacecraft neared apolune between orbits 7 and 8. Since the spacecraft's orbit geometry kept it in view of Earth at all times, the Moon would not appear in [295] the photograph.⁴³
Exactly seven hours twenty-three minutes elapsed between the exposure of the previous photograph of Site VA-8 and the moment when Lunar Orbiter V's camera made the historic picture of the nearly full Earth on August 8 at about 9:05 Greenwich Mean Time. Shutter speed was 1/100 second, but the Earth's high albedo caused some overexposure of the film. This was unavoidable. Later Langley Research Center photography specialists successfully applied image enhancement techniques, using magnetic tape video records of the readout of the photograph, to bring out details which would not have shown up in a negative reconstructed from the raw readout data. (Note that enhancement techniques did not involve any "doctoring" of photographic data in order to "show" something which was not there.)
Approximately 149° of arc of the Earth's surface appeared clearly in the photograph. It illustrated the possible synoptic weather observations that a satellite could conduct in cislunar space or that could be made from the Moon.⁴⁴
[296] Very early on August 9, EDT, Lunar Orbiter V executed a second orbital maneuver which reduced its apolune from 6,023 kilometers to 1,500. The final orbital parameters were: apolune, 1,499.37 kilometers; perilune, 98.93 kilometers; inclination, 84.76°; period of orbit, 3 hours 11 minutes. All spacecraft subsystems continued to perform normally. The micrometeoroid detection experiment had recorded one hit, and the radiation level registered by the dosimeter at the film cassette remained constant at 1.0 rads, up from 0.75 rads.⁴⁵ In the following days the spacecraft continued to perform its mission as planned without experiencing any troubles. By August 14 it had completed 51 orbits and had exposed 107 of 212 film frames. Sixty frames had been read out, of which the picture of Earth showed remarkable detail from such a great distance.⁴⁶
The photographic mission ended on August 18 when the spacecraft made its last photograph and ran out of Bimat at 11:20 p.m. EDT. In all it had successfully covered 5 Apollo sites, 36 science sites, 23 previously unphotographed areas on the lunar far side, and a view of the nearly fully illuminated Earth. The Apollo coverage included 5 sets of [297] convergent stereo photographs, each comprising two 4-frame sequences, and 4 westward-looking oblique views. Lunar Orbiter V had transmitted seventy-eight percent of the high-resolution photography to Earth at a rate of about 4 frames per orbit or 27 frames per day as of August 21, and ground control expected to conclude readout by August 26.⁴⁷