Word: aquarius
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...Aquarius responded well, but mission planners were still faced with a number of agonizing decisions. How could they best bring the distressed spacecraft home as quickly as possible but with a minimum of risk? A "deep-space abort"?turning the spacecraft around before it reached the moon and sending it back to earth?was obviously beyond the power of the lunar module's small descent engine. Odyssey's big propulsion engine, in the service module, was powerful enough to turn Apollo in midflight, but Houston was reluctant to try using it. Controllers were concerned that the engine might have...
...astronauts could use a small burn of the Aquarius descent engine to jog Apollo 13 back into a "free-return" trajectory, the combination of the spacecraft's velocity and lunar gravity would do the rest, slinging the ship around the moon and hurling it back on a direct course to the earth. Ironically, Apollo had been on a free-return trajectory, but its course was changed in preparation for the lunar landing...
...would splash down in the Atlantic off the coast of Brazil in only 38 hours. Again Mission Control decided not to risk firing a possibly damaged engine. If, on the other hand, the 26-ton service module were jettisoned after rounding the moon, a long burn of the small Aquarius descent engine would impart about the same velocity to the lightened spacecraft, setting it down in the South Atlantic in less than 40 hours. But that strategy too carried unnecessary risks. It would so deplete the LM's fuel supply that later course corrections might not be possible. Also, loss...
Next morning, having weighed the possibilities, the flight planners had a compromise answer. The Aquarius descent engine would fire just long enough to reduce the remaining flight time to 63 hours and drop the astronauts in the South Pacific about 600 miles southeast of Samoa. It was what engineers typically call a "trade-off"?not the fastest possible journey home, but one that would save fuel for later course corrections, not strain the remaining Aquarius oxygen, electricity and fuel supplies aboard, and set Odyssey down within easy range of the prime recovery ship Iwo Jima, already in the area...
...windows that a star sighting?to align Apollo properly for the burn?was impossible ("It looks like we're in the middle of the Milky Way," the astronauts had remarked earlier). But the spacemen neatly improvised by taking rougher fixes on the moon and the sun. Then they fired Aquarius' descent engine, increasing Apollo 13's speed by 600 m.p.h. The 4-minute, 24-second burn was so accurate that only two more small course corrections were subsequently needed...