The Office of Systems under NASA's Office of Manned Space Flight completed a manned lunar landing mode comparison embodying the most recent studies by contractors and NASA Centers. The report was the outgrowth of the decision announced by NASA on July 11 to continue studies on lunar landing modes while basing planning and procurement primarily on the lunar orbit rendezvous (LOR) technique.
The results of the comparison between the LOR technique, a two-man C-5 direct flight, and a two-man earth orbit rendezvous EOR mode were:
- The C-5 direct flight mode required cryogenic fuels and was marginal, even with a two-man spacecraft.
- Both the LOR and EOR modes were feasible.
- The reliability differences between LOR and EOR could not be demonstrated conclusively by analysis at this time. LOR appeared to have a higher probability of mission success at less risk to the astronauts.
- Designing the lunar excursion module specifically for the lunar landing anti performing the mission with a single C-5 launch vehicle were important advantages of the LOR mode, offsetting the problems connected with LOR rendezvous.
- Human factors considerations were not significant in the mode selections; the addition of rendezvous to the requirement for lunar landing and reentry did not add appreciably to crew stress or fatigue or to the overall hazards of the mission.
- Both LOR and EOR provided the basis for projected national space requirements before the development of Nova-class launch vehicles. The C-5 launch vehicle capability met estimated payload requirements. LOR provided experience in personnel transfer between spacecraft as contrasted with fuel transfer in EOR.
- The lunar landing mission could be accomplished at least one year and probably 18 months sooner by using LOR rather than EOR.
- The LOR mode was 10 to 15 percent less expensive than EOR.
- The LOR mode provided the cleanest management structure within the NASA organization.
In conclusion, the LOR mode offered the best opportunity of meeting the goal of an American manned lunar landing within the decade of the sixties.