This is the 25th in an exclusive series of 50 articles, one published each day until July 20, exploring the 50th anniversary of the first-ever Moon landing. You can check out 50 Days to the Moon here every day.
The phone rang at 1 p.m. at the University of Toronto’s Institute for Aerospace Studies. It was a Thursday—April 16, 1970—and the world was consumed with the story of Apollo 13, the American moon ship that had been crippled by the explosion of an oxygen tank.
The three astronauts—Jim Lovell, Fred Haise, and Jack Swigert—had taken refuge in their lunar module, a cramped spaceship even with two people living in it. They had looped around the Moon and come flying back to Earth, all the while wrestling for five days with the problems of flying in space with a badly damaged spaceship. On Thursday at 1 p.m. ET, they were just 24 hours from splashdown, if their improvised return to Earth continued to work well.
There was one final problem: How to get rid of the lunar module.
The 1995 Tom Hanks film Apollo 13, directed by Ron Howard, depicts the events of the near-calamitous flight, but it leaves out this crucial scene: how NASA solved this last-minute conundrum.
In a typical Apollo spaceflight, the astronauts jettisoned the lunar module while they were all still in Moon orbit. But in the case of Apollo 13, the lunar module Aquarius had been the lifeboat for the astronauts, providing shelter, oxygen, and supplies, because the service module, which usually supported the command module, had a hole blown in its side, rendering the command module ineffective during space flight. The astronauts had powered down the command module Odyssey, preserving its resources for re-entry. So as the spaceships approached Earth, the lunar module that had been indispensable to Apollo 13 in space had outlived its utility and had to go.
But it had to be cut loose in such a way that as Odyssey and Aquarius re-entered the Earth’s atmosphere, the lighter, discarded lunar module would not crash down onto the command module and damage or endanger it.
The usual procedures did not apply here. There was no maneuvering fuel left, which would have helped separate the command module and lunar module in a typical spaceflight.
The docking tunnel connecting the two ships was pressurized, though, so the idea was to use that pressure as a kind of “air spring” to push the two spaceships apart.
But there was a complication. The docking tunnel was typically released using an explosive charge. Normally, that posed no hazard, because the tunnel was depressurized before separation. But if the tunnel was still pressurized, shock waves from the explosives could imperil the Odyssey’s hatch and put the astronauts in harm’s way upon re-entry.
And so the phone rang at the University of Toronto’s Institute for Aerospace Studies (UTIAS), home to a professor and scientist named Barry French, an expert on pressure waves in space.
A secretary burst into a staff meeting with the news that NASA needed their help to get the Apollo 13 astronauts safely back to Earth.
NASA wanted just one number: What should the pressure in the docking tunnel be at separation?
Too much, and the astronauts’ hatch might be fatally damaged.
Too little, and the lunar module wouldn’t be pushed far enough away, and could also endanger the astronauts.
NASA needed an answer by 4 p.m.
Philip Sullivan, then a young faculty member, remembers everyone scrambling to get some basic tools—their slide rules, texts on shockwave propagation—and then gathering in a lecture hall with plenty of blackboard space. They divided into two groups and worked the problem separately, to see what each group would come up with. “We did hours of math to figure it out,” Professor Sullivan says.
By the appointed time, they had agreed on a number: 2 psi in the tunnel, a level the astronauts would set. That was much lower than the standard 5 psi, but enough to push the lunar module away, as Sullivan recalls it, at 2 feet a second, about 1.5 mph.
It worked perfectly. One of the great moments in Apollo’s history is the wild unleashing of joy in Mission Control as Apollo 13’s command module Odyssey appears on its screens underneath its three parachutes (seen here at 9:50 on the video from CBS News).
A potential space disaster turned into a triumph of grit and ingenuity.
Years later, Sullivan says, the University of Toronto crew discovered two things. They re-ran their slide-rule-and-chalkboard calculations using computers, and the graphs came out virtually identically.
Sullivan says they had always assumed that their group, a little removed from the normal army of NASA support folks, had been some kind of backup. Someone else—at Grumman’s lunar module factory on Long Island, or at Mission Control in Houston—was running their own version of the University of Toronto calculations.
In 2010, on the 40th anniversary of Apollo 13’s safe return, Fred Haise, the mission’s lunar module pilot, traveled to the University of Toronto to thank the engineers who’d done the math that Thursday afternoon.
“He told us there was no one else working on our calculations,” Sullivan recalls. “They were relying on us.”
Charles Fishman, who has written for Fast Company since its inception, has spent the past four years researching and writing One Giant Leap, his New York Times best-selling book about how it took 400,000 people, 20,000 companies, and one federal government to get 27 people to the Moon. (You can order it here.)
For each of the next 50 days, we’ll be posting a new story from Fishman—one you’ve likely never heard before—about the first effort to get to the Moon that illuminates both the historical effort and the current ones. New posts will appear here daily as well as be distributed via Fast Company’s social media. (Follow along at #50DaysToTheMoon).