Apollo 13 was on the way home, but could it survive the re-entry?
As Apollo 13 sped toward Earth, mission control was beginning to worry about a new problem. While the lunar module had enough oxygen to accommodate Swigert in addition to the intended lunar module crew of Lovell and Haise, carbon dioxide was beginning to build up. Normally lithium hydroxide (LiOH) canisters absorbed the poisonous gas from the air and prevented it from reaching dangerous levels, but the canisters onboard the Aquarius were being overwhelmed. The Odyssey had more than enough spare LiOH canisters onboard, but those canisters were square and couldn't fit into the holes intended for the lunar modules' round canisters.
Mission control needed a way to put a square peg into a round hole. Fortunately, as with the lunar module activation sequence, somebody was ahead of the game.
As reported in Lost Moon, Lovell's book about the Apollo 13 mission (cowritten by Jeffery Kluger; republished as Apollo 13), Ed Smylie, one of the engineers who developed and tested life support systems for NASA, had recognized that carbon dioxide was going to be a problem as soon as he heard the lunar module was being pressed into service after the explosion.
For two days straight since then, his team had worked on how to jury-rig the Odyssey's canisters to the Aquarius's life support system. Now, using materials known to be available onboard the spacecraft—a sock, a plastic bag, the cover of a flight manual, lots of duct tape, and so on—the crew assembled Smylie's strange contraption and taped it into place. Carbon dioxide levels immediately began to fall into the safe range. Mission control had served up another miracle.
Breathing Easy: To prevent carbon dioxide poisoning, the crew jury-rigged a filter in the lunar module. Astronaut Jack Swigert is on the right.
Although the PC+2 burn had been right on the money, the Trench was increasingly unhappy about the Odyssey and Aquarius's trajectory. Something was pushing the spacecraft off course (afterwards it would be determined that a water vent on the Aquarius had been acting like a little rocket jet, gently pushing Apollo 13 in the wrong direction) and they needed another burn to correct the trajectory. But the Trench had given up the navigation system after the PC+2 burn. “We had to come up with some way to align the spacecraft" properly for the corrective burn, Bostick explained to Spectrum.
One of Bostick's controllers, Charles (“Chuck") Dietrich, remembered an alignment technique that had been developed for earlier NASA missions in Earth orbit. A spacecraft could be pointed in the right direction by using a portion of the surface of the Earth as a reference marker—in this case the terminator between night and day.
“All during the Mercury, Gemini and Apollo Earth-orbit programs, that was a technique we had used, but never on a return from the Moon. It was a little more dicey there." In Earth orbit, a small alignment inaccuracy prior to a re-entry would result in the spacecraft landing miles off target, but it usually wasn't life threatening. But if Apollo 13 missed the trajectory it needed to take to re-enter safely—known as the entry corridor—the results would be disastrous as the command module skipped into space or burned up in the atmosphere. “If you missed the entry corridor by a degree, that's a real bad day," says Bostick.
The crew was cold and exhausted by this point—temperatures on board had dropped almost to freezing point. The astronauts had gotten very little sleep since the explosion, and yet they pulled off the course-correction maneuver—and a second one a day later—perfectly.
This second burn was called for by the Atomic Energy Commission, which was worried about the radiothermal isotope generator (RTG) that was stored in the Aquarius. An RTG uses the heat produced by the slow natural decay of a radioctive isotope, typically Pu-238, to generate electricity. The intent was to leave the Apollo 13's SNAP-27 RTG on the Moon to power surface experiments long after the crew had left. Now it was destined to re-enter the Earth's atmosphere, along with the rest of the LM.
The SNAP-27 was designed to survive re-entry without releasing its contents, but the AEC wanted to make sure it landed as far away from anyone as possible, just in case. Around eight to ten hours before Apollo 13 was due to re-enter, Lunney called Bostick up to his console and told Bostick about the AEC worries about the RTG. “I had been eyewitness to all these tests done on the RTG—it was indestructible… I reminded Glynn of that and he said 'I know, I know, but we've got to put it in a safe place.' I said, 'Glynn, I will do the best I can do but the number one thing is getting the guys back home.' So we did move the landing point a little bit… to put the RTG in the deepest part of the Pacific we could find," says Bostick. Whatever was left of the Aquarius, after its descent through the Earth's atmosphere, would find its resting place about 10 kilometers beneath the waves in the Tonga Trench. Ultimately, no released radioactivity was ever detected, despite a helicopter survey of the area.
It was now over three days since the explosion in oxygen tank two. It was time to get ready for re-entry. The first step was to recharge the batteries in the command module, which had been significantly depleted before the lunar module came on line.
Remember how, while figuring out lunar module lifeboat procedures after the Apollo 10 simulation, Legler had worked out a way to run power back along the electrical umbilicals from the lunar module to the command module? 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 to refine the procedure, through lunar module gurus Hannigan and Mel Brooks in the SPAN room, 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 to be turned on is the instrumentation system so that everyone can be sure 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.
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. “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.
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.
Then it was time to abandon the Aquarius and strap into the command module. For the lunar module controllers it was a bittersweet moment. “We were proud of the Aquarius and very thankful—it had really performed, did everything we asked it to do" remembers Legler. “It's hard to describe that feeling," says Hannigan, “thank God that we made it but..."
“Farewell, Aquarius, and we thank you," radioed Lovell back in 1970 as the astronauts jettisoned the lunar module and watched it slowly drift away. Hannigan remembers hearing Lovell's unbidden requiem for the spacecraft. “He did a good job," says Hannigan.
It was about another hour before the command module, headed for the Pacific, met the first tenuous wisps of Earth's atmosphere. Soon, as the Odyssey plunged into the atmosphere, those wisps would become a tremendous fireball of ionized air. The ionization would block radio communications for several minutes. In the meantime, the heat shield would be subjected to incredible temperatures and pressures, and if it had been cracked during the explosion four days earlier, the crew would burn up without ever being heard from again. Assuming the heat shield was okay, then the parachutes would deploy, slowing the Odyssey to a gentle splashdown—if the parachutes hadn't been turned into blocks of ice and the pyrotechnic charges intended to release them still worked. In a few more minutes Lovell, Haise, and Swigert would either be home free, or dead.
But some of the astronaut's last words before re-entry were not for themselves. They were for mission control. “I know all of us here want to thank all of you guys down there for the very fine job you did," Swigert transmitted. “That's affirm," chimed in Lovell.
A few moments later, the Odyssey disappeared into a sea of radio static.
By Apollo 13, NASA had a pretty good handle on radio blackouts during re-entry, and for a given trajectory, it could work out how long—almost to the second—a spacecraft would be out of touch. In the Odyssey's case, it was about 3 minutes.
The appointed time came and went, and as the seconds turned into minutes without any sign of the Odyssey, the tension dragged out like a blade through mission control.
“It was the worst time of the whole mission," agrees Kranz. “The blackout was a very difficult time for every controller. You ask yourself 'did I give the crew everything I needed to and was my data right?'...It was just a difficult time."
Bostick, the trajectory specialist, was in hell. “It was probably the worst I ever felt in my life," he told Spectrum. “My feeling was 'oh my god, we have done the impossible: we got them all the way home...and now something goes wrong in entry?'...It was one of the most depressing [times] of my life..." Bostick's voice wavers for a moment, the memory still emotionally charged after thirty-five years. Then his voice strengthens into triumph, “but then, when we heard from them, it was the happiest moment of my life," he declares.
An antenna-laden plane, circling in the air as part of the recovery effort, had picked up the command module's signal: the crew had survived blackout! But even after radio contact was re-established, the astronaut's lives were still in danger. The main parachutes still had to be deployed. Kranz and the controllers stood rooted to their consoles, watching the main display on the front wall of mission control. The Odyssey was going to splash down, for good or ill, within sight of the live TV camera onboard the aircraft carrier leading the recovery effort, the USS Iwo Jima.
Suddenly, the parachutes—three red and white canopies—blossomed into view on the screen.
Splashdown: After an agonizing communications blackout, the command module finally splashed down almost on top of its recovery vessel, the USS Iwo Jima. Photo: NASA
Pandemonium broke out in mission control. “I cried," says Kranz simply. “I think many of the controllers did. The emotional release at that instant was so intense many of us were unable to control our emotions. There were an awful lot of wet eyes that day."
Kraft was one of the few not swept away by the sight of the Odyssey gently descending into the Pacific, suspending his celebration until the crew was safely onboard the Iwo Jima. On seeing the deployed parachutes, “I felt fine," he remembers, “but I felt a lot better when I saw them walking on the deck of the carrier. That's the way I always was. Too many things could happen between the parachutes and the deck." Thirty-five years later, Kraft ponders the memory of the crew walking in the open air on the Iwo Jima. “That was one of the most excellent things I've ever seen," he finally says.
When the crew and the flight controllers were finally reunited in Houston, there was, naturally, a raucous celebration, the highlight of which was the playing of an audio tape made by splicing together various mission control voice loop recordings. The creator was merciless, lampooning almost everyone involved, and got a great deal of mileage from Liebergot's “We may have had an instrumentation problem, Flight," and Kranz's later “I don't understand that," sound bites.
Despite President Nixon's award of the Presidential Medal of Freedom to those involved in saving Apollo 13, few dwelt on its significance at the time. They were busy building on the lessons learned from Apollo 13, and nine months later, Apollo 14 would blaze into the skies above Florida as it left for the moon. Indeed for years, although many in mission control viewed it as the highlight of their careers, they detected a sense of embarrassment in NASA about the mission—they had failed to go the moon after all—a taint that wouldn't fully be dispelled until the release of Ron Howard's movie in 1995.
Over the years that followed, the controllers left NASA one by one, leaving mission control to a new crop of flight controllers. But a chain of excellence had been forged—to this day every flight director in NASA has come up through the ranks. Each one studies the trade from flight directors who have also come up through the ranks—right back to the prototype flight director, Chris Kraft, learning the values of discipline, competence, confidence, shouldering responsibility, toughness, and teamwork, that form the foundation of mission control's culture, demonstrated so abley during the Apollo 13 crisis.
Kraft still sees the culture he helped forge in evidence today at mission control. “I think that's the one place in the space program that still has it," he says bluntly. “The people who are running the control center today are just as good as we ever had, and I can't praise them too highly."
While agreeing that today's flight controllers are top-notch, some of the other Apollo 13 veterans worry their authority is being slowly undermined. “Over the years I've seen that authority deteriorate badly," sighs Bostick, pointing to the management structure displayed during the Columbia tragedy as a worrying example. There was a “team of program managers who would meet every day and do flight planning: 'here's what we're going to do today,' and they would pass that on to the flight directors, making the flight directors just executors" of other people's decisions, Bostick says.
Aaron believes the problem stems from a lack of leadership from Capitol Hill on down. Without an urgent and agreed upon goal—such as beating the Soviets to the surface of the moon—NASA started being subjected to the conflicting demands of different individuals and political camps in Congress, says Aaron, who worked at NASA Headquarters in Washington, D.C., in the 1980s. NASA's marching orders have become “diffused and muddled....That then affects NASA management, who instead of being technical gurus, have to become amateur politicians." But—in what can only be good news for an agency now planning to return to the moon after forty years absence—Aaron, who retired from NASA in 2000, is convinced that the space program's engineers are still the best in the business. At the grass roots level at least, we “still got the Right Stuff," he says.
This article is presented in three parts. For the first installment, click here.
To Probe Further
There is a wealth of information, online and off, about the Apollo 13 mission. Some of the best material is listed below. Although many of these books have gone out of print since this article was originally written, but they may often still be found courtesy of online resellers:
Apollo, by Charles Murray and Catherine Bly Cox (South Mountain Books, 2004). This book gives an excellent account of what NASA's engineers and mission control did throughout the Apollo Program.
Lost Moon (republished as Apollo 13; Houghton Mifflin Co., 2000), by Jim Lovell and Jeffrey Kluger. Cowritten by one of the Apollo 13 astronauts, the book details what happened in space as well as the efforts of mission control.
Apollo 13: The NASA Mission Reports, edited by Robert Godwin (Apogee Books, 2000). Reprinted selections from NASA's official documentation, the book features prelaunch press kits, the transcripts of the crew debriefing after the mission, and extracts from the official investigation into the crisis.
The full text of the official investigation into the Apollo 13 accident, with a host of engineering details about the Apollo spacecraft and mission control, is available online at https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19700076776.pdf.
Flight, by Chris Kraft (Dutton, 2001). Kraft's autobiography details the founding of mission control in the Mercury era and continues through the end of the Apollo Program.
Failure Is Not an Option, by Gene Kranz (Simon and Schuster, 2000). The White Team flight director's autobiography gives the flight director's view of the events of Apollo 13.
Apollo EECOM, by Sy Liebergot with David M. Harland (Apogee Books, 2003). Liebergot's autobiography puts the reader in the hot seat during the Apollo 13 crisis and has many anecdotes from mission control. An accompanying CD features more than 3 hours of recordings from mission control's voice loops.
Virtual Apollo and Virtual LM, by Scott P. Sullivan (Apogee Books, 2002 and 2004, respectively). Two books with detailed three-dimensional reconstructions and cutaways of the lunar module and command and service module.