Word: orbiter
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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...
There is one final, crucial phase or Apollo 8's mission: reentry. As it plunges back to earth, traveling some 7,000 m.p.h. faster than a returning earth-orbit mission, Apollo will have to re-enter the atmosphere at an angle no greater than 7.4° nor less than 5.4°. Reentry at too steep an angle would cause too sudden a deceleration. The force on Apollo and its occupants could then exceed 20 g's, and friction with the atmosphere would heat the spacecraft far above its design limits. Says Lieut. General Samuel Phillips, Apollo program director...
...equally dreadful fate would befall Apollo if it hit the atmosphere at too shallow an angle. Like a flat stone skipping on water, it would bounce off the atmosphere and sail into a large elliptical orbit around the earth. Having shed Apollo's service module before reentry, the astronauts would have insufficient oxygen and electrical power to survive the several hours it might take to return to the atmosphere and land. In Phillips' laconic words, "It's a crew-loss kind of situation...
...contingencies as the failure of a backup system, an inadvertent early cutoff of the S-4B rocket while it is blasting Apollo toward the moon or unusually intense radiation from the sun, NASA has devised a number of alternative flight plans. Thus, Apollo 8 might merely remain in earth orbit, duplicating Apollo 7's eleven-day flight. It could also loop out as far as 25,000 miles from the earth and then descend into a low earth orbit for several days-or it could re-enter the atmosphere after traveling as far as 69,000 miles into space...