DESTINATION MOON: A History of the Lunar Orbiter Program
Lunar Orbiter V Mission Objectives
[286] The fifth mission's objectives can be divided into two categories: photographic and non-photographic. The former composed the primary part of the mission, the latter the secondary. The spacecraft would perform five basic photographic tasks. Task 1 entailed additional Apollo landing site photography, employing three modes of photography: near-vertical, convergent telephoto stereo, and oblique. Task 2 would accomplish broad survey photography of unphotographed areas on the Moon's farside. Task 3 was to take photos of additional Surveyor landing sites of [287] high scientific interest to investigators. Task 4 would have the spacecraft concentrate on potential landing sites for later Apollo Program missions, with particular stress on their scientific value. Finally, Task 5 was related to the fourth in that it encompassed photography of a wide range of scientifically interesting sites.31
The second category of mission objectives did not differ markedly from the first four missions. It included the following: 1) acquisition of precision trajectory information for use in improving the definition of the lunar gravitational field; 2) measurement of the micrometeoroid flux and radiation dose in lunar environment, primarily for analysis of the spacecraft's performance; 3) provision to the Manned Space Flight Network tracking stations of a spacecraft which they could track for purposes of evaluating the network and the Apollo Orbit Determination Program.32
Lunar Orbiter V would fly a nearly polar orbit inclined 85° to the Moon's equator. The spacecraft would deboost into an initial orbit with an apolune of 6,000 [288] kilometers and a perilune of 200 kilometers. In this orbit it would take photographs of the lunar far side. Finally, the spacecraft would maneuver to a new orbit with an apolune of 1,500 kilometers and a perilune of 100 kilometers to execute the remainder of the photographic tasks.33
As approved the mission plan called for a total of 212 film frames to be exposed. Of these it had allocated 44 frames to Apollo tasks and 168 frames to scientific areas, including those thought suitable for the later Apollo missions and for Surveyor landing sites. Five Apollo sites along the equatorial zone, ranging from 42°56´ east longitude to 36° 11´ west longitude and from 0°45´ north latitude to 3°30´ south latitude, would be photographed. Potential Apollo Program sites which Lunar Orbiter V would photograph included: the Littrow rilles; the Sulpicius Gallus rilles; the Imbrium flows; the craters Copernicus, Dionysus, Alphonsus, Dawes, and Fra Mauro; Copernicus secondary craters; the domes near Gruithuisen and Gruithuisen K; the Tobias Mayer dome; the Marius hills; the Aristrachus plateau; the area of Copernicus CD; and the areas south of the crater Alexander on the northern edge of Mare Serenitatis.34
What did mission planners use as criteria for selecting science sites? Donald E. Wilhelms of the United [289] States Geological Survey, working with the Lunar Orbiter Program Office, described one of the major criteria:
The primary criterion for selection of Mission V sites was freshness of the features in the site. Earlier Orbiter missions have shown emphatically that most lunar terrain has a subdued appearance at all Orbiter scales so that little new is learned from high resolution photography. Fresh young craters (mostly light) and fresh young rock units (mostly dark) that are not yet much modified by repeated cratering and wasting potentially reveal the most about rock type and origin, both in photographs and when sampled on the ground. Old terrains show effects of the processes that waste lunar slopes, and though these are of interest, they seem to be sufficiently sampled in high resolution photography by earlier Orbiter missions, except for very high and steep slopes. A few high and steep slopes and other non-fresh targets have been selected for the purpose of rounding out terrain sampling.35
The fifth Orbiter mission would perform the most exacting, precision photography of all five missions. It also had the experience of the previous four flights to call upon in establishing greater confidence in mission controllers concerning operational procedures. As a result they could demand more of Lunar Orbiter V. Nevertheless the spacecraft exhibited several problems during preflight tests and check-out at Cape Kennedy. The most serious problem [290] developed when the bladders of the oxidizer tanks began to leak. The leaks forced NASA to return Spacecraft 3 (the fifth flight spacecraft) to Boeing in Seattle on May 12. It arrived there on May 17 and the oxidizer bladders were replaced by June 6. It was then returned to Hangar S at Cape Kennedy on June 16 for retesting. Integration and checkout with the launch vehicle took place on July 12, with final mating on July 19.36
By July 27 Lunar Orbiter V had successfully completed pre-launch tests and had been mated with the launch vehicle in preparation for an August 1 launch.37 Program officials subsequently conducted a simulated launch exercise on July 28. The fifth mission was about to begin.