Remember how, while figuring out lunar module lifeboat procedures after the Apollo 10 simulation, Legler had worked out a way to run power from the lunar module to the command module back along the electrical umbilicals that connected the spacecraft? That was about to come in handy now, because that power could be used to recharge the Odyssey's batteries.

"The biggest problem was that initially the lunar module guys didn't know how much power they were going to need" for the Aquarius to serve its role as a lifeboat, remembers Aaron. For the first 30 hours, Aaron's power-up team didn't think the lunar module guys were going to have any power to spare for the Odyssey: about twelve hours after the explosion, "we talked to them about getting some power," says Aaron. "They threw us out of the room."

But the PC+2 burn had shortened Apollo 13's return flight sufficiently that the Aquarius would be able to supply the power needed to charge the batteries. Working with North American Aviation and Grumman, through lunar module gurus Hannigan and Mel Brooks in the SPAN room, to refine the procedure, Legler and Bill Peters wrote up the needed instructions. The charging process was "only 20 to 25 percent efficient," remembers Legler, but it was enough.

But even with fully charged batteries, the Odyssey risked running out of electricity before it splashed down. Batteries are rated using a term called ampere-hours. If you start with a 40 amp-hour re-entry battery, and then turn on a piece of equipment that uses 1 amp-hour, and it takes 8 hours to finish the re-entry and splashdown, you have only 32 amp-hours left to power everything else. But if you can delay turning on that piece of equipment until 2 hours before splashdown, now you have 38 amp-hours to go around. "It's not only a matter of how large a load is, but how long that load is on for," says Aaron. Once a system had been turned on in the Odyssey, it had to stay on, so "the only variable was how few systems could we turn on and how late could we wait?" he explains.

Aaron had an inspiration. Normally in a spaceship power-up sequence, one of the first things turned on is the instrumentation system so everyone can be sure that the rest of the sequence is progressing normally. But for Apollo 13, the instrumentation would be turned on last for a final check of the Odyssey just before re-entry began.

It Was A Gutsy Move. It required the crew—in particular the command module pilot, Swigert—to perform the entire power-up procedure in the blind. If he made a mistake, by the time the instrumentation was turned on and the error was detected, it could be too late to fix. But, as a good flight controller should, Aaron was confident his sequence was the right thing to do.

"I still wake up at nights in a cold sweat and wonder about that," an older and wiser Aaron told Spectrum, "because the one thing I wasn't conscious of, and I prided myself on being conscious of everything, was the condition of the crew." Despite the cold, and the fatigue, and the stress, the crew had voiced few complaints. "You couldn't tell from listening to their voices how bad conditions had got. When they got back I realized, 'Oh my goodness, I built this incredible procedure that had to be executed perfectly, and I handed it off to a crew that hadn't had any sleep for three days,' " shudders Aaron, "I've thought about that a lot, ever since."

But Swigert and the rest of the crew powered up the Odyssey, seemingly effortlessly. "Therein lies the reason we chose test pilots" to be astronauts, says Kraft. "They were used to putting their lives on the line, used to making decisions, used to putting themselves in critical situations. You wanted people who would not panic under those circumstances. These three guys, having been test pilots, were the personification of that theory," explains Kraft.

Accident's Aftermath:: After being jettisoned from the command module, the Apollo 13 service module shows extensive damage, with an entire panel of its outer skin blown away.

As part of the re-entry procedure, the crew jettisoned the damaged service module, snapping pictures and beaming down video of the huge gash in the side of the module as it tumbled into the distance [see photo, Accident's Aftermath]"There's one whole side of the spacecraft missing," radioed Lovell. "It looks like it got to the [main engine] bell, too," added Haise, validating Kranz's gut decision, four days earlier, to rule out using the main engine and go around the moon.