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 possible; in effect, continue the philosophy in the test program of capitalizing on success. If everything continues to operate properly, the first lunar mission would be a landing mission. If there are problems of any significance along the way, depending on what the problem is and where it occurs, the mission will be changed or brought back.

2. The various limitations and constraints imposed on a lunar landing mission limit launch to roughly three days in any given month. Due to recycle time associated with the launch vehicle there must be an intervening day between each of these three days.

3. A major launch date constraint is that of lighting at the moon at the time of arrival. Lighting conditions are limited to the sun being in the region of 7° to 20° above the horizon and behind the astronaut as he approaches the site.

4. Due to the considerations for recycle time and the lighting con­straints the mission will have to be prepared to go to any of three selected sites.

5. Data on the landing sites will come from three major sources: earth­ based information, Orbiter A information, and Orbiter B information. Surveyor will be used to confirm this information and to tell in general what the lunar surface is like rather than to certify an individual site. We are not proposing to land, for the first mission, at an actual Surveyor site.

6. The spacecraft will be loaded with the maximum propellant and con­ sumables that are consistent with the launch vehicle capability at the time of the mission.

7. Attitude variations will be used to control the spacecraft thermal extremes. This has resulted from design trade-offs which ease hard­ ware design problems and save weight.

8. The Manned Space Flight Network will be used as the prime navigation source; however, onboard navigation capability is provided. 'lhe normal mission will be designed to conserve RCS consumables so that attitude maneuvers are to be minimized.

9. The LM descent engine will be used as a valid backup to the SM engine through lunar orbit insertion.

10. A free return trajectory will be used through lunar orbit insertion.