Late on 13 April 1970, the night shift had started in Houston’s Manned Spaceflight Center. Engineers tried to sift through reams of odd data coming about the Apollo 13 spacecraft, from instrument readings to the confused reports from three astronauts. It looked like they were rapidly losing their oxygen supply. “First of all, we thought we’d boil it down to something simple and obvious,” engineer Arnold Aldridge recalled later. He made a phone call to an especially insightful young engineer, John Aaron.
Aaron recalled being at home, winding down after a long shift at Mission Control. Aldridge told him they were facing an instrument problem or “flaky readouts”—there was no way data this extreme could be real – they couldn’t lose the mission’s stored oxygen so quickly. Aaron asked to hear the numbers from various instruments, one at a time, over the phone. “That’s not an instrumentation problem,” he told them. Thinking back on it, he saw his distance from the Control Center as good fortune – he could see the entire forest of information. “You guys are wasting your time,” he said. “You really need to understand that the [spacecraft] is dying.”
As word spread through the ranks, everyone who could possibly help swarmed to the center. Aldo Bordano, in his early twenties, remembers the commute. “All of a sudden, it was about midnight, it was just a line of cars with their lights on. … We’d all gotten called in—all three shifts.” They efficiently filled the parking lot outside Mission Control. “It was a real eerie moment,” he said. “There might have been two hundred of us turning our cars off and walking in at the same pace. Nobody said a word to the guy on the left or the guy on the right. We just went to our stations.”
Scores of engineers started their calculations. With the spacecraft’s fuel cells mostly useless now – just like astronauts, they required oxygen to run – the engineers had to conserve every bit of electrical power. They knew how much they would need, with luck, in the mission’s last minutes. They would need enough juice to safely guide the crew capsule into Earth’s atmosphere. Working backward from that goal, to every minute of the return path, they ruthlessly budgeted the mission’s electricity. “We had to cut our energy consumption in half in order to make it back home,” engineer Henry Pohl recalled. “To do that, you’ve got to turn every heater off that you don’t absolutely have to have.” The spacecraft was going to get very cold, and shivering astronauts were just one of many worries.
Pohl oversaw the command module’s little thruster rockets. “I calculated . . . how cold the [thrusters] were going to get, and I gave myself four degrees above freezing on it,” he said, recalling his small margin for error. If the propellants froze, it wouldn’t matter how much electrical power the astronauts had at their disposal. They would be close enough to see the welcoming Pacific Ocean from space but unable to maneuver for re-entry, either burning up or bouncing off the atmosphere and sailing helplessly away. In the end, Pohl says his propellant almost froze— only 2˚ Fahrenheit from disaster. “We cut those margins pretty dad-gum close.”
NASA had the astronauts move from the crippled command module into the lunar lander for most of the journey back to Earth, since the lander had working batteries and a separate oxygen supply. While the lander’s emergency role is sometimes portrayed as a desperate, last-minute idea, the engineers had game-planned it in advance. It was simply one of thousands of unlikely yet carefully scripted horror stories. Engineer Cynthia Wells recalled one of her earlier NASA assignments, a “lifeboat” study for the lunar lander. “Everybody laughed at it,” she said of this unlikely work, years before the Apollo 13 mission. But just in case, her group ran the numbers.
In the wake of the miraculous survival of the mission, there was surprisingly little finger pointing. A stack of small errors had caused an oxygen tank to explode in flight. (Centrally, a miscommunication between the Apollo launch facilities and the tank manufacturer meant a little heating wire inside the tank had received way more voltage than it could handle prior to launch.) Mainly, everyone involved felt fortunate. The tank could have easily blown two days later than it did, with the lander and two astronauts on the Moon and a lone astronaut left in an expiring, powerless ship in lunar orbit. The astronauts would have expired a quarter million miles from Earth.
As it was, the engineers had just enough time to work the myriad, entangled problems and get them home. The triumph of Apollo 13 highlighted the work of engineers for the general public like no other mission. With the astronauts mainly just shivering for a few days, broadcasts had to at least attempt covering technical challenges, clever emergency fixes, and the years of careful planning that had paid off.
Yet, a few of the engineers, like Marlowe Cassetti, have always wondered if it hurt the space program. “I think there was a whole mood that changed in Washington,” Cassetti said. “Apollo 13 scared the management and they thought it was way too risky.” The public too was getting the idea that space was less romantic and less full of wonder than they’d assumed in 1958, at the inception of NASA. Space seemed dangerous, and spaceships were not sleek and sexy; they were claustrophobic and uncomfortable. Life in space was razor stubble, messy hair, urine bags, and nausea. And even in a nail-biter like Apollo 13, journalists and audiences had to wade through drifts of technical terms and acronyms.
As we once again plot courses to the moon and beyond, Apollo 13 serves as a good reminder: Space is hard. It comes with hiccups. And even our best-computed plans will, sooner or later, require nimble, fresh-eyed problem-solving and pre-planned alternate routes.
Featured image: (16 April 1970) Feverish activity in the Mission Control Center during the final 24 hours of the problem-plagued Apollo 13 mission. Image courtesy of NASA.