Word: orbiters
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Behind the moon again, on their 14th revolution, Eagle's descent engine was fired, slowing the module down and dropping it into the orbit that would take it to within 50,000 ft. of the lunar surface. The crucial word from Houston was relayed by Michael Collins, Columbia pilot, when a burst of static momentarily cut Eagle off from the ground: "You are go for PDI [powered descent insertion]." Again Eagle's descent engine fired, beginning a twelve-minute burn that was scheduled to end only when the craft was within two yards of the lunar surface...
...racking part of the mission. If the ascent engine had failed to start, Eagle would have been stranded on the lunar surface. Too short a burn would have tossed the module into a trajectory that would send it smashing back onto the lunar surface. Had the LM achieved an orbit with an apocynthion (high point) much less than 50,000 ft., Columbia would have been unable to reach it. As it turned out, departure from the moon was triumphantly smooth. Of course, even after lift-off and redocking, there were still the dangers of the homeward trip. Control failures could...
Less than twelve minutes after liftoff, a brief boost from the S-4B third stage placed Apollo into a circular 119-mile orbit at a velocity of 17,427 m.p.h. Over the Pacific for the second time, just 2½ hrs. after launch, the spacecraft was cleared by Houston for "translunar insertion" (TLI). Firing for five minutes, the reliable S-4B engine accelerated the ship to 24,245 m.p.h., fast enough to tear it loose from the earth's gravitational embrace and send it toward the moon. At a point 43,495 miles from the moon, lunar gravity exerted a force...
Continuing their flawless flight, the astronauts zoomed past the western rim of the moon at 5,645 m.p.h. They were whipped behind the far side and into lunar orbit by the moon's gravity and a 5-min. 57-sec. burn of the reliable SPS engine that reduced their speed to 3,736 m.p.h. When they emerged from behind the eastern edge, after 34 minutes during which radio communication was blocked, they had dropped into a 70-by 196-mile-high orbit...
...thing the astronauts did not observe was Apollo's companion in lunar orbit?the Soviet Union's unmanned Luna 15 moon probe (see p. 17). Arriving in the neighborhood two days before the U.S. spacecraft, Luna went into an orbit as close as ten miles from the moon and eventually landed. The chances that Luna would be visible from Apollo 11?much less collide with it?were estimated by Houston's Christopher Columbus Kraft, director of flight operations, as about "one in a billion...