On April 11, 1970, the goal was to land on the moon. By April 13, the goal was to get astronauts Lovell, Swigert and Haise back to Earth in one piece. Or at all.
Crippled by oxygen-tank explosions and the loss of all but one fuel cell, Apollo 13 found itself stranded in space without full power and water reserves and quickly running out of air and other life-support systems.
Mission Control and the crew had four days to completely rework the processes for navigating and powering up a spaceship. At their disposal were the few working systems onboard and what would turn out to be unmatched ingenuity and resourcefulness.
The crew shut down power in the Command Module, then moved into the undamaged Lunar Landing Module (LM) and sealed it off. What followed was a desperate flurry of brainstorming, action and life-threatening measures implemented over the course of about four days.
To conserve power, they let the temperature inside the spaceship drop to 38 degrees Fahrenheit (3 degrees Celsius). To conserve water, astronauts drank 6 ounces (0.177 liters) each per day (normal consumption is more like 60 ounces or 1.7 liters). To get the Command Module's CO2-removal canisters to fit the LM slots and keep the air breathable, they devised adapters using plastic bags, cardboard and tape.
To get them back onto an Earth-bound course (they had been headed to the moon when the explosion occurred), Mission Control calculated a series of burns that would consume the least amount of power while getting the craft into a homeward trajectory. And with the navigation system down and debris from the explosions making the usual navigation stars invisible, they reworked the entire navigation procedure using the sun.
Freezing, dehydrated, sleep-deprived and with everything, hopefully, in place, the astronauts jettisoned the Service Module, moved into the Command Module and headed home. They splashed down in the Pacific on April 17, 1970, safe and sound.
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