DESTINATION MOON: A History of the Lunar Orbiter Program
The Plan for Mission II
[248] While Boeing reworked the camera thermal door, the Lunar Orbiter Project Office at Langley continued to formulate plans for the second mission. Original planning for Mission B had only photographic data from Earth-based telescopes and Ranger spacecraft to rely upon because Lunar Orbiter I had not yet flown. On May 6, 1966, representatives [249] from Bellcomm and the Apollo, Surveyor, and Lunar Orbiter Program offices convened at Langley for the Mission B Planning Meeting. The information and requests which they provided enabled Langley mission planners to set up the following guidelines for Lunar Orbiter Mission B:
1. Distributed sampling with a string of sites in the northern part of the Apollo zone.
2. Sampling of both mare and highland with greatest number of samples in the mare.
3. Sites spaced consistent with the lighting of LEM landing constraints. (Present value of sun elevation of 7 to 20 degrees would be used, resulting in optimum spacing equaling 11 degrees, plus or minus 2 degrees.)
4. One of the mare sites to be the Ranger VIII impact point.
5. The availability of a landed Surveyor or any new data to necessitate a review of any mission design.
6. Mission B sites to be selected whose terrain to the east appeared to be consistent with the Apollo landing approach constraints, where possible.39
The members of the several organizations at the meeting aided Langley officials in producing a Mission B plan which the Lunar Orbiter Program Office in Washington presented to the Surveyor/Orbiter Utilization Committee on June 1. The plan had three primary goals based upon Ranger and [250] Earth-telescope data and performance evaluations of the Lunar Orbiter spacecraft subsystems:
A. Photographic-To obtain detailed lunar topographic and geologic information of various lunar areas to assess their suitability for use as Apollo landing sites.
B. Selenodetic-To provide trajectory information which will improve the definition of the lunar gravitational field.
C. Environmental-To provide measurements of micrometeoroid and radiation flux in the lunar environment for spacecraft performance analysis.40
Apollo requirements had priority as on the first mission. The area to be covered was a swath along the front side of the Moon ranging from +5° to -5° latitude and +45° to -45° longitude. Topographic considerations affecting the mission plan dictated that Lunar Orbiter B (Lunar Orbiter II) look for areas smooth enough for the Apollo Lunar Module to land on. The approaches to these areas had to be free of obstacles over a certain height to allow satisfactory performance of the Lunar Module landing radar.41 Because the Apollo missions would operate in a retrograde lunar orbit instead of the posigrade orbit of the Lunar Orbiter missions, the landing approach zone would be east of the [251] landing site.42
The Lunar Orbiter Project Office at Langley selected eleven sites pertaining to Apollo missions to be photographed on the second Orbiter mission. In order to keep the mission simple the spacecraft would execute a minimum number of attitude maneuvers. There would be one photographic pass per site, and high orbit photography would be eliminated. Lunar Orbiter II would carry out contiguous high-resolution vertical photographic coverage between adjacent orbits. This called for an inclination of 11° to 12° to the lunar equator. Surface lighting conditions had to be such that photography could detect cones of two-meter diameter and one-half meter height and slopes of 7° in an area of seven meters square.43
On September 29 the tentative Mission B plan was amended. The photography and spacecraft performance evaluations of Lunar Orbiter I-in addition to further inputs from Bellcomm, the U.S.. Geological Survey, the Army Map Service, the Manned Spacecraft Center (Houston), NASA Headquarters Office of Manned Space Flight, and the Surveyor Project Office-confirmed tentative mission objectives for the second Lunar Orbiter flight more than they altered them. As of October [252] 26 these objectives were:
Primary - To obtain, from lunar orbit, detailed photographic information of various lunar areas, to assess their suitability as landing sites for Apollo and Surveyor spacecraft, and to improve our knowledge of the Moon.
Secondary - To provide precision trajectory information for use in improving the definition of the lunar gravitational field.44
To provide measurements of micrometeoroid flux and radiation dose in the lunar environment, primarily for spacecraft performance analysis.
During the process of site selection for the second Orbiter mission a hypothesis based upon Earth-telescope photography and the very useful Ranger VII pictures exerted a particular influence on the choice of sites. Data from these two earlier sources tended to show that bright rays extending from younger craters were actually heavily cratered, making landings very hazardous or impossible in such areas. To test this, Lunar Orbiter I had photographed sections in lightly rayed areas. Specifically, photographs of Site A-3 in Mare Tranquillitatis revealed smooth areas where a Lunar Module could land. Orbiter I Frame M-100 of Site A-3 showed an area in a light ray where cratering was insufficient to rule it out as a landing site. The ray in this photograph was faint and probably had its origins in [253] the crater Theophilus but had subsequently been filled in.45
Planners concluded from Orbiter I photography that some ray areas were possibly smooth. Moreover, photography from the first Orbiter had actually previewed certain targets in the second mission. Thus planners decided to change several sites in Mission B and to have Lunar Orbiter II look at the ray areas between the lunar craters Copernicus and Kepler, extending north of the western Apollo zone. The Mission B plan was thus substantially revised as a result of the divergences between Ranger VII and Lunar Orbiter I photographs of crater rays.46