NASA’s finest hour: The engineers who saved Apollo 13
In this excerpt from The Apollo Chronicles: Engineering America’s First Moon Missions, Brandon Brown tells the story of Apollo 13 and the engineers who worked tirelessly to bring the astronauts home.
In preparing for Apollo 13 in early 1970, technicians had assembled the service module which, among other supplies, carried two tanks of liquid oxygen. These provided astronauts their breathing sustenance and fed the fuel cells to generate electricity for the mission. After running various tests to make sure the tanks were leakproof, a technician’s grip slipped and one medicine-ball-sized tank dropped to the floor with a loud plunk. It fell just two inches and looked fine, so they continued their work.
Once snug in the service module at Cape Canaveral, the tank showed itself to be stubborn. Technicians filled it and then emptied it as part of routine preparations. But the tank refused to lose its last few gallons of liquid oxygen. Wasn’t this a bad sign? NASA officials had to make a devil’s choice — one of many. If they started tearing apart the oxygen system, that could delay their launch. But more importantly, extra tinkering with the service module could damage other equipment, including the second oxygen tank. Engineers thought the tank’s problem was probably a slightly loose interior tube, and on its own, that shouldn’t jeopardize a mission. NASA decided to keep this oxygen tank and march onward. To fully empty it, the engineers used an interior heater to simply boil any residual liquid oxygen away.
None the wiser, engineers refilled the empty tank before launch, and Apollo 13 carried a broken tank, with newly bared wires immersed in liquid oxygen, into space.
But now an insidious detail, lurking in deep technical weeds, bit the agency. The Cape had upgraded launch pad electrical lines to triple their original voltage. And while NASA had sent this detail along to the tank manufacturer, the numbers were buried with countless other myopic specs. In short (electrical pun regretted) engineers force-fed the tank’s heater three times the voltage it expected. As technicians warmed the tank, they let the heater run about eight hours. The tank’s little thermostat couldn’t handle the new excess voltage, and it fused into a permanently “on” position. Without alerting anyone, the tank rose to a temperature of about 800 ̊ Fahrenheit, melting some of the wires’ insulation. None the wiser, engineers refilled the empty tank before launch, and Apollo 13 carried a broken tank, with newly bared wires immersed in liquid oxygen, into space.
The astronauts completed their first manoeuvres without incident. They pointed themselves on a path to the Moon and twirled barbecue style for the next two days. Eventually, with the Moon growing larger in the capsule windows, an astronaut marched through his checklist and hit a switch to stir the oxygen tank: routine business in the realm of zero gravity. But this jolt of current through the tank’s damaged wires cooked up a small fire. Nearly two hundred thousand miles away from Earth, the astronauts heard a loud bang, like nothing they’d heard before from control thrusters or simulations or anything else. They’d actually heard the oxygen tank explode.
The engineers on the ground immediately started thinking through the problems. They’d already lost most of the stored oxygen in the service module. Senior Engineer Chris Kraft had moved into more of a managerial role in Apollo, but he returned to the trenches now. He realized that those tanks were connected to the three smaller oxygen tanks in the astronauts’ command module. In happier times, those tanks kept a nice supply of oxygen near the crew, but now it meant the awful opposite: they were surely draining backward through their ruptured sibling. He called out, “Seal ’em off,” and saved precious gallons of oxygen. But the prospects remained grim. In the words of one engineer, if they had seen such a scenario during a practice mission, “we’d have said, ‘Well, you can kiss those guys goodbye.’ ”
NASA had the astronauts move into the lander for most of the journey, since it had working batteries and its own oxygen supply. While it was designed for all things lunar, this time it drove the whole bus home. Its main engine (designed for landing) and its various thrusters (used for docking and fine adjustments) were fully functional. Even though it wasn’t designed to move around with the rest of Apollo attached — like an acrobat balancing a stack of plates on his head — it worked well enough. And while this is sometimes portrayed as a brilliant last- minute idea, the engineers had game- planned it in advance. It was one of hundreds of practiced horror stories. The lander’s designers had thought about using it as a “lifeboat” from their first musings in 1961. Allowing such a mode required more fuel and oxygen for the lander. But in turn, that provided a fringe benefit: A healthy mission could linger longer on the Moon. And in 1963, the company building the other modules asked if the lander’s thrusters might be able to maneuver all the modules together, in a worst- case scenario where the command and service modules lost power.
Engineer Cynthia Wells recalled a 1967 NASA assignment: a lifeboat study. In an emergency, how could the lander basically run an entire mission? “Everybody laughed at it,” she said. “Because everyone thought it was so stupid. . . .The flight controllers thought you’d never need to do that.” But just in case, her group calculated, for instance, how long the lander could fully pressurize air in the command module. The unlikely had become the only option, and now little details — some helpful, others alarming — came home to roost like never before.
The discomfort of their cold confines, with floating urine bags, combined with prioritizing water for equipment, meant the astronauts slowly became dehydrated as well. One developed a kidney infection.
With the clock ticking in the lander, mission planners looked for options to hasten the return journey. They decided to burn the lander’s main engine, speeding the whole Apollo chain on the far side of the Moon. Authors Murray and Cox describe having the lander trying to push the other modules as “using a small car to push a limousine, but in three dimensions.” (The weight of the combined command and service modules was about twice that of the lander.) On the back side of the Moon, out of communication with Earth, the astronauts started the requested extra burn of the engine, running it for about four long minutes. Once the mission emerged, engineers felt their hopes rising — the burn looked like it had worked perfectly and the astronauts just might make it home. They’d be miserable and cold, to be sure, but they could have just enough air to breathe.
With no power to spare for cabin comfort, astronauts, with no blankets, suffered plunging temperatures in the lander. Records show a low of 43 ̊ Fahrenheit, while the abandoned command module sunk below 40 ̊ Fahrenheit. In addition, to avoid any nudge off their homeward path, engineers asked the astronauts not to make any waste dumps. So, they struggled to find new ways to contain their urine, filling every spare plastic bag from either module. The discomfort of their cold confines, with floating urine bags, combined with prioritizing water for equipment, meant the astronauts slowly became dehydrated as well. One developed a kidney infection.
The entire planet followed the journey home. A dozen or more foreign governments offered their assistance with the coming ocean recovery. In Mission Control, and at Grumman headquarters, engineers took catnaps on top of desks and conference tables, ignoring their managers’ appeals to please go home. Approaching Earth, the astronauts crawled from the lander to the command module, where they had to wake every system from a chilly and unplanned sleep. Would Henry Pohl’s thrusters work correctly? Would the computer start up? Were the parachutes frozen stuck? Preparing for re-entry, they jettisoned their plucky lifeboat, the lunar module. The astronauts’ last call to Houston before entering the atmosphere thanked the engineers for their incredible work in getting them this far. After tense minutes of radio silence and the incredible (probably welcome) heat of re-entry, Apollo 13 gently splashed down. When all three astronauts emerged, the delirious engineers shouted in celebration.
Brandon R. Brown is a Professor of Physics at the University of San Francisco. His research includes work on superconductivity and sensory biophysics. He enjoys writing about science for general audiences, including articles and essays in New Scientist, SEED, and the Huffington Post, as well as a biography, Planck, that won the 2016 Housatonic Award for Nonfiction.
