>"Kranz was there at the right time to make the decisions that had to be made rapidly, and then, when Lunney took over he brought a calmness to the control center to do the right things once they had gotten stabilized...They turned out to be a wonderful pair," says their boss at the time, Kraft.

So Bostick speaking to the perfect audience when he voiced his concerns. "We need to get this thing back to a free-return trajectory," Bostick told Lunney. Lunney instantly agreed, but this left Bostick with a problem. Getting Apollo 13 onto a free-return trajectory required a solid push from a big engine. With the Odyssey and Aquarius docked together and the main service module engine out, that left only the engine attached to the lunar module's descent stage, designed to be used only for the relatively short period of time needed to land the Aquarius on the moon. "It was a problem, because we didn't have capability in the control center to calculate the result of a docked maneuver" using the descent engine, remembers Bostick.

During a mission, controllers called on a bank of mainframe computers in a Manned Spacecraft Center facility set up and maintained by IBM, known as the Real Time Computer Complex (RTCC), to calculate the length and direction of engine burns needed to produce a given trajectory. To do these calculations, the mainframes were programmed with information about the spacecraft, such as their mass, center of gravity, how much thrust the engine produced, and so on. Unfortunately for Apollo 13, the program to calculate how the conjoined command and lunar module could be maneuvered using just the descent engine simply didn't exist.

"So the first thing we did was call our computer guys and say 'Hey, call all the IBM guys in and start writing some software!" says Bostick with a laugh. As a backup, the mission planners who originally put together the Apollo 13 mission were called in to double-check the RTCC's results. "In 2 or 3 hours we were able to come up with a free-return maneuver. I think it made everybody feel a lot better—including the astronauts." Bostick remembers talking to the crew after the mission. "When we executed the free-return burn it made them feel that they might get out of this thing alive," he says.

Kranz's Team Hadn't gone home after its shift. The White Team now formed the nucleus of a new Tiger Team, dedicated to figuring out the fastest way possible to get the crew home, given that the spacecraft was going around the moon. They also had to work out how to stretch the lunar module's consumables to last the entire trip and how to get the command module reactivated and configured to survive a re-entry—the astronauts' only way to get home alive.

Arnie Aldrich, the CSM branch chief, had joined the Tiger Team, along with another EECOM, John Aaron. An hour before, Aaron had been at home, standing in front of the mirror shaving, preparing to come in for his shift, when his wife brought him the phone, saying his boss, Aldrich, was on the line. Recalls Aaron, "He said 'John, I need to ask you some questions. There's something significant that's happened out here and these guys can't quite figure it out. It's not going well.' "

Aldrich called Aaron for a couple of reasons. One was that Aaron was an expert on the command and service module's instrumentation system. The other was that Aaron was one of the best mission controllers in NASA.

Four months earlier, Aaron had saved the Apollo 12 mission when, during launch, the rocket was struck by lightning—twice. The second strike knocked the CSM's fuel cells off line, sent the guidance system spinning, and scrambled telemetry to the ground. With warning lights blazing and alarms sounding, it looked like the crew would have to abort the mission, scant seconds after liftoff.

Aaron was in the EECOM's seat for the launch, and as he watched the scrambled data ripple across his console, he was suddenly reminded of a ground test he had seen a year earlier where an electrical malfunction had caused a similar problem. The crazy pattern of the data on his console "was a pattern that I remembered," says Aaron. And, thanks to hours of research he'd put in after the ground test, he knew how to fix it. He uttered the terse command, "Set S.C.E. to Aux," to his flight director, Jerry Griffin. Griffin, like everyone else in mission control, had no clue what that meant. Nevertheless, trusting in his EECOM, Griffin ordered the command to be passed up to the crew immediately. The corresponding switch was flipped onboard and valid telemetry was restored. With valid data, Aaron could see that the fuel cells were off line, and with a second command to reset the cells, Apollo 12 was on its way to moon. The incident cemented Aaron's reputation as a "steely-eyed missile man."

So, when Apollo 13 ran into trouble, Aaron was Aldrich's go-to guy. "I had a very good group of people working for me at the time of the explosion, but we were scratching our heads, and the very best person I had was John Aaron," says Aldrich.

After the explosion, Aldrich had moved into the spacecraft analysis, or SPAN, room, located across from mission control. The SPAN room was fitted out with more consoles and acted as a bridge between the flight controllers and the army of engineers who had actually designed and built the spacecraft. "In there were supervisors like me and executives from the engineering organizations in NASA and the manufacturers, and this group would sit together and monitor the flights," says Aldrich. The SPAN room had come into being because "we learned during Mercury that we wanted immediate access to the manufacturers, that we needed clear and unfiltered data very rapidly," says Kranz.

Over the phone, Aaron asked Aldrich to walk around behind the consoles in the SPAN room and describe what he saw. "I started asking him: tell me what this measurement says, tell me what that measurement says. And that went on for about ten minutes," says Aaron.

In the data Aldrich read to Aaron, Aaron was looking for a pattern that would map to failures in the instrumentation system onboard the Odyssey, but he was coming up empty. "I told Arnie, 'Well, I'll be right there. In the meantime tell those guys they've got a real problem on their hands,' " says Aaron.

As the lunar module controllers raced to power up the Aquarius, Aaron had made it in to mission control. "When I walked in the room, I intentionally did not put a headset on because I could see each of the flight controllers had zoomed in and were trying to sort the problem out from the perspective of their individual subsystem," he says. He walked behind the controllers, looked at their data, and listened to what they were saying to the back rooms. Finally he sat down beside the embattled command and service module controller Liebergot and plugged his headset in. "I said, "Sy, we've got to power the command module down," recalls Aaron.

Aaron didn't just want the command module powered down to minimal systems only. He meant powered down as in off. No guidance system, no heaters to keep back the cold of space, no telemetry to help controllers diagnose the problem. Nothing. Aaron was concerned that even a minimal power draw from the batteries would leave them with nothing for re-entry.