Word: orbit
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Dates: during 1960-1969
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...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 revolution-when it is behind the moon and blocked from radio...
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...
...matter how carefully it is planned and executed, however, the December flight of Apollo 8 will involve some chilling perils. Besides anticipating the kinds of problems that could occur in a simple near-earth orbital flight, lunar-mission planners must plan realistically for troubles that would be magnified by sheer distance from earth. Should life-support or power systems begin to fail on earth-orbital flights, astronauts are usually within half an hour to three hours of recovery on land or water; a relatively small thrust from a retrorocket can lower their orbit into the atmosphere, where friction provides...
There are other moon flight worries, most of them centered around the functioning of the Apollo command module's SPS engine. Should the SPS fail to ignite, or should it burn for less than 80 sec. during the attempt to place Apollo in lunar orbit, there would be little difficulty; the spacecraft would simply continue around the moon and be whipped back toward the earth and safety. But if the SPS should fail between the 80-and 110-sec. marks of its scheduled 246-sec. burn, Apollo would enter what NASA euphemistically describes as an "unstable orbit." After rounding...
Another tragedy that could occur during Apollo 8 Flight Director Clifford Charlesworth calls the mission's "longest hour." If, after completion of Apollo's tenth lunar revolution, the SPS engine fails to ignite or burns for too short a time, the astronauts would be stranded in orbit without any chance of rescue; they could live only until their oxygen supply was gone. To minimize the possibility of SPS failure, NASA has made nearly all of the engine's components redundant. If one part were to fail, a duplicate would be on hand to take over...