The Mammoth Book of Space Exploration and Disasters

A spacecraft heading for the moon from Earth could take a “free return” trajectory which would take it around the moon and bring it back like a slingshot. But Apollo 13’s current flight path had been altered to allow it to go into lunar orbit so it would need to fire its engines to get onto the free return trajectory. An additional “burn” at PC + 2 would shorten its journey home. PC meant Pericynthion, the closest point to the far side of the moon; PC + 2 was two hours after this point. Lovell:

Of all of the problems Lunney faced, the most complex was the burn. In the hour or so since the astronauts had moved over to Aquarius, no definite decisions had yet been made about how to propel the docked ships toward home, and with the spacecraft moving closer to the moon, at a speed climbing back up to 5,000 miles per hour, the options were quickly fading. A direct abort, if one could even be attempted, got harder and harder the farther the ships got from Earth. A PC + 2 burn, if one was going to be attempted, would take a lot of planning, and the time for pericynthion was closing in fast. It would always be possible to fire the engine after the PC + 2 point, but the earlier in the earthward transit a burn was attempted, the less fuel it would take to affect the trajectory; the longer the burn was delayed, the longer the engine would have to be fired.

Chris Kraft was the former flight director. The control team had been expanded to four teams working in shifts, each team with its own flight director. Kraft was then deputy director of the Space Center. He had just returned to Mission Control from a press conference.

Pacing behind Kranz, who was also pacing, Kraft knew which return route he’d choose. The service propulsion engine, he was certain, was useless. Even if there was some way of mustering enough electricity to get the engine going, Kraft was not convinced that the crippled Odyssey would be able to take the strain. No one knew the condition of the service module, but if the force of the bang had been any indication, it was possible that the sudden application of 22,500 pounds of thrust would collapse the entire back end of the spacecraft, causing both docked ships to tumble ass over tea kettle, sending the crew not back toward Earth but barrel-rolling down to the surface of the moon.

The only way home, Kraft figured, was to use the LEM’s engine – and more important, to use it right away. It would be tomorrow evening before the docked ships first passed behind the shadow of the moon, and it would be close to three hours beyond that before they reached the PC + 2 milestone. Waiting the better part of a day to get the crew on its homeward trajectory seemed nonchalant at best and downright reckless at worst. What Kraft wanted to do was fire the descent engine now, get the ship back on its free-return slingshot course, and when it emerged from behind the moon and reached the PC + 2 point, execute any maneuvers that might be required to refine the trajectory or increase its speed.

In the past, when Chris Kraft had an idea like this, that idea got implemented. Nowadays, though, things were different. It was Gene Kranz who dictated the direction of things, Gene Kranz who was the true capo di tutti capi of the control room. If Chris Kraft wanted something done, he was free to suggest it to Kranz, but he could no longer decree it. In the aisle behind the flight director’s console, Kraft was about to stop Kranz’s pacing and discuss his two-step burn idea when Kranz turned to him.

“Chris,” he said, “I sure as hell don’t trust that service module engine.”

“I don’t either, Gene,” said Kraft.

“I’m not sure we could fire it even if we wanted to.”

“I’m not either.”

“No matter what else we do, I think we’re going to have to go around the moon.”

“Concur,” Kraft said. “When do you want to burn?”

“Well, I don’t want to wait till tomorrow evening,” Kranz said. “How about we try a quick burn for a free return now, get that squared away, and then figure out if we want to speed them up with a PC + 2 tomorrow.”

Kraft nodded. “Gene,” he said after a considerable pause, “I think that’s a good idea.”