Richard Lawrence - The Mammoth Book of Space Exploration and Disaster

At Houston the shift changed. Glynn Lunney’s “Black” team took over from Kranz’s “White” team which began working on Apollo 13’s problems: how to bring them back before their resources ran out.

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.”

Two rows down and one console over, Chuck Deiterich, an off-duty retrofire officer, or RETRO standing behind his accustomed console, and Jerry Bostick, an off-duty flight dynamics officer, or FIDO, could not hear Kranz and Kraft’s discussion, but they knew the options as well as their bosses. Though it was Kraft and Kranz and Lunney who would ultimately decide the ship’s route home, it was Deiterich and Bostick and the other flight dynamics specialists who would have to come up with the protocols to pull the plan off. At the FIDO station, Bostick pushed his microphone out of range of his mouth, and leaned toward Deiterich.

“Chuck,” he said quietly, “How do we all want to do this thing?”

“Jerry,” Deiterich answered, “I don’t know.”

“I assume we’re ruling out Odyssey’s engine.”

“Absolutely.”

“I assume we’re going around the moon.”

“Absolutely.”

“And I assume we want to get them on free return as quick as possible.”

“Definitely.”

After a moment Bostick said, “Then I suggest we get our shit together fast.”

Close to a quarter of a million miles away, in the crowded cockpit of Aquarius, the men on whose behalf Bostick and Deiterich would be working had more elemental things on their minds than a return-to-Earth engine burn. Settling into his two-man spacecraft with his three-man crew, Jim Lovell had the chance to look around at the hand circumstance had dealt him. He did not like what he saw.

It was 58 degrees and falling inside the LEM but there was plenty of food because they had enough for a 10-day trip. Lovell:

Lovell tried a pitch-changing maneuvre from the LEM but the centre of gravity of the combined spacecraft made such maneuvres very awkward.

Capcom told Aquarius what they had decided. Lovell:

“Also Aquarius,” the Capcom now said, “we’d like to brief you on what our burn plan is. We’re going to make a free-return maneuver of 16feet per second at 61 hours. Then we’re going to power down to conserve consumables, and at 79 hours we’ll make a PC + 2 burn to kick what we’ve got. We want to get you on the free-return course and powered down as soon as possible, so how do you feel about making a 164 foot-per-second burn in 37 minutes?”

Lovell released the controller, allowed his ships to drift, and turned to his crewmates with a questioning look. Swigert, still at sea in the alien LEM, once again shrugged. Haise, who knew the LEM better than any man on board, responded similarly. Lovell turned his palms upward.

“It’s not like we have any better ideas up here,” he said.

“Do you think 37 minutes is enough?” Haise asked.

“Actually, no,” Lovell answered. “Jack,” he now said back to the Capcom, “we’ll give it a try if that’s all we’ve got, but could you give us a little more time?”

“OK, Jim, we can figure out a maneuver for any time you want. You give us the time, we’ll shoot for it.”

“Then let’s shoot for an hour if we can.”

“OK how about 61 hours and 30 minutes?”

“Roger,” Lovell said. “But let’s talk back and forth till then and make sure we get this burn off right.”

“Roger,” Lousma said.

The hour until the free-return burn would be a frantic one for the crew. In a nominal mission, the flight plan allowed at least two hours for the so-called descent activation procedure, the ritual of configuring switches and setting circuit breakers that preceded any burn of the LEM’s lower-stage engine. The crew would now have barely half that time to do the same job, and do it without sacrificing the necessary precision. On top of that, there was still the elusive fine alignment to establish, something that, with all the space-craft’s wild movements, Lovell was not yet close to accomplishing. But while the hour would be a breathless one aboard the ship, on the ground it would provide a chance to draw a breath.