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As the earth recedes behind them, the astronauts will separate their spacecraft from the S-4B, move about 50 ft. ahead of it, and then turn to face it. During this maneuver, protective panels will be jettisoned from the S-4B, exposing the dummy lunar module (LM) carried in its nose. The astronauts will then simulate docking with the LMan operation that will be particularly important on the lunar-landing mission next year, when an Apollo spacecraft will dock nose-to-nose with a real LM before taking it into orbit around the moon. Finally, after the astronauts have jockeyed their craft some 8,000 ft. away, the S-4B will dump its remaining fuel into space. That action will generate just enough thrust to shove the S-4B out of the way and into orbit around the sun. Alone in space, the Apollo craft will continue coasting in powerless flight through the final leg of the moon trip, its velocity gradually decreasing as the earth's gravity attempts to pull it back.
Some 30,000 miles from the lunar surface, Apollo will have slowed to a space-age snail's pace2,170 m.p.h. At this point, lunar gravity will overcome the earth's diminishing pull, and the spacecraft will begin accelerating once more. Ahead, the moon will loom ever larger in the spacecraft windows. By the time Apollo curves around the western edge of the moon, its speed will have risen to 5,720 m.p.h.
Without any additional thrust, Apollo's own momentum and the weak lunar gravity would combine to carry it around the moon and fling it back toward earth in a spatial version of crack-the-whip. Indeed, if a recheck of systems and equipment convinces ground controllers and the astronauts that serious problems have developed, the crew will merely continue in this new course and travel back to earth. But if everything seems all right, Apollo's powerful SPS (service propulsion system) engine will be fired for 246 sec. to slow the spacecraft and allow it to be pulled by the moon into a 70-by 196-mile elliptical lunar orbit. Two revolutions later, a brief 10-sec. burn will change the path to a 70-mi.-high circular orbit. Traveling at 3,640 m.p.h., Apollo will circle the moon once every two hours. For 45 nerve-racking minutes during every revolutionwhen it is behind the moon and blocked from radio communication with the earthit will be out of touch with ground controllers.
During their lunar orbiting, the astronauts will take turns shooting still, motion and stereo pictures in color and black-and-white. They will study craters and ridges to see how easily they can be recognized as landmarks. They will plot their position for navigational fixes that will be useful for lunar-landing crews on later missions. On the seventh revolution, they will be able to survey a prime LM landing site at a time when illumination is ideal for observation: the sun will be 6.6° above the horizon, casting the long shadows that best bring out distinctive surface features. During lunar orbit, and on both the outgoing and return legs of the mission, the astronauts will shoot television pictures of the moon and the earth and transmit them back to ground stations as Christmastime TV spectaculars.