DESTINATION MOON: A History of the Lunar Orbiter Program
The Scherer Group's Report
[20] According to the Scherer group, STL's orbiter seemed to have the greatest potential for fulfilling the requirements set by OMSF and OSS. The spacecraft would weigh about 320 kilograms, which placed it well within the Atlas-Agena launch vehicle capabilities. It would be spin-stabilized and its monopropellent propulsion system, capable of multi-starts, would give it the added flexibility of being able to change its orbital parameters around the Moon. This spacecraft could photograph the entire Moon from a polar orbit of 1,600 kilometers above the lunar surface and obtain pictures resolving objects as small as 18 meters across. If ground control placed the spacecraft in an equatorial orbit of 40-kilometer altitude, it could photograph the area along the lunar equator at the amazing resolution of 0.5 meter.19 The Scherer group believed that these positive features of the STL system far outweighed the drawbacks involved in image motion compensation, the need for high-speed film, and for high shutter speeds in the camera.

[21] On the other hand the RCA approach, which the group rejected, consisted of injecting a 3-axis attitude-stabilized payload into lunar orbit from a Ranger-type bus. The photographic system onboard would employ a vidicon television which had two major weaknesses: low sensitivity in the vidicon unit and inadequate horizon scanners. In addition, the capsule that the Ranger bus would inject into orbit would weigh a mere 200 kilograms and this left little allowance for the actual payload hardware. The integration of the capsule and the Ranger bus and their separation before lunar orbit insertion further compounded the problem of weight limits on the payload. Even if this could be resolved with a high degree of reliability, the TV system could not detect objects smaller than 130 meters in wide-area coverage and 30 meters in limited area coverage, at best.20

Scherer's group considered these negative aspects of RCA's proposal, together with the estimated cost of $20.4 million for building and flying only three spacecraft, too expensive and inadequate for the needs of Apollo. The group believed that pictures of the lunar surface of equal resolution could be obtained by far less expensive means, [22] such as balloon-borne telescopes. The RCA proposal would require major research and development of a better visual instrumentation system in order to be capable of satisfying Apollo requirements, and this would be too costly in time and money.

There is irony in the Scherer group's final evaluation. The STL system won recommendation while the RCA system did not, and yet the final Lunar Orbiter spacecraft which NASA flew incorporated more of the concepts supporting the RCA system and less of those of the STL system. This was especially true of the attitude control system, although it did not apply for either of the camera systems.

Scherer's report to Nicks recommended that NASA fund two STL studies in 1963 in order "to better establish the feasibility of the proposed Able 5 lunar photographic spacecraft...." and "to provide more detailed information about the Able 5 spacecraft system and its photographic payload." The rationale for this decision was that it was "necessary to establish the confidence needed for duly considering a flight program of this type, should it be deemed preferable to a Centaur-based orbiter for any reason." 21

Plans for the Centaur-based lunar orbiter began to [23] lose their attractiveness once Scherer's group had shown that an Agena-class orbiter, based upon STL research, would give NASA a more expedient means of data acquisition for Apollo requirements. Moreover, the status of the Centaur Rocket Program, originally managed by the Marshall Space Flight Center and then transferred to the Lewis Research Center, did not make the concept of a Surveyor Orbiter more acceptable. Flaws in the rocket's basic fuel tank configuration and delays in the development tests eventually influenced the schedules of the Surveyor Lander at JPL because the overall capability of the Centaur was reduced from 1,100 to 950 kilograms.22