Editor’s note: To commemorate the 50th anniversary of NASA’s Apollo 11 launch, Field Service Digital interviewed former NASA engineer Stephen Coester, who directed a crucial repair mission hours before the launch that carried astronauts Neil Armstrong, Buzz Aldrin, and Michael Collins to the moon.

At roughly 2:30 a.m. on July 16, 1969—four and a half hours until the scheduled launch of Apollo 11—NASA encountered a problem. The Saturn V rocket was being filled with fuel when a leak detector went off.

A white vapor cloud suddenly billowed around the rocket perched on the Cape Canaveral launch pad.

Three and a half miles away in NASA’s launch control center, the team at the consoles in Firing Room One watched the closed-circuit TV footage as the vapor cloud grew. In less than two hours, three astronauts were supposed to climb into the rocket. This was the mission that would take Americans to the moon.

Engineer Stephen Coester was in charge of the hydrogen propellant loading team—and that leaking valve. Standing at his console in a starched white shirt and tie, Coester still looked like an eager kid at 28. But even with so much on the line, he kept a clear head.

Stephen Coester, pictured second from right.

Despite his youth, Coester was already accustomed to remaining calm in the face of setbacks. He’d graduated six years earlier from the U.S. Naval Academy, but the onset of a serious heart condition had cut short his naval career as an engineering officer for the Civil Engineer Corps. Not one to let a dramatic turn shake his resolve, Coester had sent his resume to Boeing, where he soon became a contractor on Project Apollo.

That personal setback was nothing compared to a hydrogen gas leak waiting to blow.

Up until then, the NASA computer had been running the show. “One of the big IBM mainframes that took up a whole room,” as Coester describes it, the machine had been preprogrammed with the propellant loading sequence. Now Coester and his colleagues would have to override that programming, fix the leak, and manually finish fuelling the rocket from their consoles.

A lot was riding on the launch—for NASA; for the country’s sense of national pride; and for Neil Armstrong, Michael Collins, and Buzz Aldrin scheduled to blast into space atop 260,000 gallons of liquid hydrogen fuel. But Coester put that out of his mind. The worst that could happen, he reasoned, was that they’d scrub the launch.

“We had a job to do. I didn’t really worry about any of the political or geopolitical problems of it,” Coester says. “We were professionals. We stopped the flow [of hydrogen], and we said, ‘Okay, what can we do to fix this thing?’”  

Transcript: NASA Apollo Saturn Launch Control: “This is Apollo Saturn Launch Control; T minus 2 hours, 45 minutes, 55 seconds and counting. As the prime crew for Apollo 11, astronauts Neil Armstrong, Michael Collins, and Edwin Aldrin, are on the terminal part of their trip to the launch pad in the transfer van, it’s now making the curve toward pad. We have discovered a problem at the launch pad itself as the crew is about to arrive. We have a leak in a valve located in a system associated with replenishing liquid hydrogen for the third stage of the Saturn V launch vehicle.” Source: NASA

With Coester’s team huddled, the astronauts sat suited up in the transfer van that would drive them to the launch pad. Despite the paused countdown clock, NASA hadn’t aborted the mission. All eyes were on Coester and his crew to find a solution. Failure was not an option.

Launch Control decided to send a red crew—three technicians and a safety person—to the launch pad to fix the leak. It was a dangerous mission; even an incompletely fueled rocket is like a bomb. The minimum safe distance from a loaded Saturn V was three and a half miles.

As the crew approached the launch pad, Coester watched them on the Firing Room screen, headset on and ready to coach them. The vapor cloud had cleared, but the problem had not. In fact, there wasn’t much the crew could do. The leaking valve was a simple piece of machinery on the red tower adjacent to the Saturn V rocket, just two main pieces and bolts holding them together.

Apollo 11 Saturn V during rollout.

Coester instructed the crew’s mechanics retorque the valve bonnet and the packing gland bolts, according to the official NASA flight report. Then he told them to clear the area.

“They followed my directions,” says Coester. “But there’s not a whole lot you can do.” He knew that if this wouldn’t fix the problem, he and the red crew would have to get creative. Meanwhile, all he could do was wait for the crew to get back. The Firing Room was tense.

Transcript: NASA Apollo Saturn Launch Control: “We have sent a team of three technicians and a safety man to the pad and these technicians are now tightening bolts around the valve. Once the technicians depart, we will send hydrogen again through the system to assure that the leak has been corrected. The astronauts now coming up toward the pad itself as the crew of several technicians at the 200-foot level proceed to tighten some bolts around a leaking valve. The astronaut team which has just arrived at the pad, the transfer van now backing up toward the elevator. In a matter of 5 minutes or so, we’ll be ready for the spacecraft commander, Neil Armstrong, to come across the sill at the 320-foot level. That is our status at 2 hours, 43 minutes, 47 seconds and counting. This is Launch Control.” Source: NASA

When the red crew had returned, the lead engineer, Jack Kramer, pressed the button to restart the flow. A white cloud issued from the valve. They hadn’t patched the leak. Dawn was just around the corner.

Coester had exhausted the predictable fixes. Now he and the crew would have to use their imaginations.


When Coester was being honest with himself, he knew his work for NASA wasn’t just a job. He was good at what he did—the best. But he was also making history. 

Just before NASA had closed the launch pad the night before, Coester took his final walk of the Saturn V. He rode the shaky elevator all the way to the top. He could smell the Atlantic Ocean to the east, but when he looked beyond the lights of the launch pad, the coast was a vast stretch of darkness. 

Coester went about his work, touching every joint in every line on the hydrogen system, out across the swing arms to the vehicle. Then he returned to the elevator, rode down a level, and did it all again—checking all the valves, just looking at everything. He couldn’t stop thinking how “neat” it all was.

When he returned to the ground, he took a moment to stand at the foot of the massive rocket and look up. He thought about what it meant to be alone up on that tower. 

“The neat part about it was, at the time, the Saturn V and the Apollo [space capsule] were sitting out there in all their glory with all the beautiful spotlights shining on them,” Coester says, “and I would be up there.” That was the moment he realized that they were doing something extraordinary. 

But all of the emotions he had about the rocket couldn’t fix the valve. The astronauts had arrived at the base of the tower. Someone had to pull out a genius idea, and fast. Clear, calm thinking was vital. It was at these moments, when everything was riding on well-thought-out decisions, that Coester remembered that his team were professionals. Their sharp, analytical minds worked best in high-pressure situations like this.

NASA Launch Control’s update on the Saturn V hydrogen leak.

The red crew hurried back to the launch pad. Lacking other options, they decided to warm the valve by pouring water on it. The valve didn’t leak while warm. They removed their hard hats, filled each one at the emergency shower, and tossed the water onto the valve. That took care of the leak, but the team couldn’t risk reopening the valve and causing another leak, so they kept it closed. 

Coester’s team wouldn’t be able to pump the rest of the liquid hydrogen fuel into the rocket. And if they couldn’t finish replenishment, they wouldn’t be able to fill the propellant tank with enough fuel. The rocket would never reach the moon.

Coester thought hard. He went back to the previous night when he’d run his hand over every valve in the hydrogen system. Suddenly it was clear: There were other valves. Why couldn’t they use another one?

The red crew technicians decide to bypass the original replenish valve. 

With the original replenish valve out of commission, Coester and his team decided instead to use the main fill valve at a slower flow rate. With only two hours left until launch, the hydrogen team worked at their consoles—filling, releasing, and leveling off propellant until the rocket was ready. 

At 9:32 a.m. the employees in Firing Room One turned away from their consoles to look out through the wall of windows. “Six—five—four—three—two—one—zero. All engine running. Liftoff! We have a liftoff!” 

Coester’s console was the farthest from the windows. But he could still see it. The rocket blazed up from the pad, away from the tower, and out into that blue Florida sky.

Apollo 11 liftoff.

Audio clips and transcripts courtesy of NASA and John Stroll, senior technician, NASA Johnson Space Center. Click here to listen to more audio recordings or to read the full transcripts. Images courtesy of NASA Project Apollo Archive.