On June 28, 2015, hundreds of rocket-watchers along the Atlantic coast of Florida gazed into the clear skies over Cape Canaveral, puzzled by what they had just seen. They’d gathered to watch the launch of SpaceX’s Falcon 9 rocket carry an un-crewed spacecraft with supplies to the International Space Station. As the rocket soared through the blue sky, the flames behind it shrank into a pinprick as it approached the atmosphere’s upper limit. Two minutes and 19 seconds after liftoff, a burst of white smoke appeared, lingering in the sky like a cloud.

Most people watching the launch from the Canaveral National Seashore assumed the rocket had simply separated from the Dragon capsule bound for the ISS, much like the missions before. Theodor Kim, an amateur videographer who had parked among the piers where Florida’s cruise ships docked tells Inverse that he, like everyone around him, had assumed the launch had gone as planned.

“We didn’t know at the time that it exploded,” he said.

Squinting into the sky, it was hard to determine what had happened. Fire and smoke, after all, are part and parcel of any rocket launch. But somewhere along the same coastline, Jim Ramsay, a visiting software engineer from the U.K., was watching the launch through the lens of his powerful camera. As he zoomed in, he knew something had gone wrong; up close, the nine engines of the rocket appeared to explode like sputtering white fireworks.

“That blew up,” he exclaims on his recording, which he posted to YouTube. “That disintegrated. 100 percent sure of that. That’s a failure.”

Surrounded by whispers about the rocket’s would-be landing on Of Course I Still Love You, SpaceX’s barge 200 miles into the Atlantic Ocean, Ramsay broke the bad news. He told the other onlookers in his strong Scottish accent: ”That’s going nowhere.

Meanwhile, the experts at SpaceX headquarters knew exactly what was going on. Not long after the crowds had driven back to their homes along Florida’s State Road 401, SpaceX founder Elon Musk — who was celebrating a disappointing 44th birthday — posted this tweet confirming Ramsay’s hunch: “There was an overpressure event in the upper stage liquid oxygen tank. Data suggests counterintuitive cause,” Musk noted. In a follow-up tweet, he added, “That’s all we can say with confidence right now.”

Almost a month after the explosion, after SpaceX had conducted a thorough “fault tree analysis” with input from the FAA, NASA, and the U.S. Air Force, Musk discussed the explosion in a press teleconference: The “overpressure event” he had alluded to in his tweets had been triggered by a hardware malfunction.

There have been other, far more fiery explosions closer to Earth in recent history: The Orbital Sciences rocket explosions in October 2014 springs to mind. But for SpaceX, this was a setback, nonetheless.

The catastrophe came down to a single, faulty steel strut. The metal fixture in question — a standard-issue ,two-foot-long bar — had one very crucial function: Holding down a tank of high-pressure helium. When this particular strut snapped during the rocket’s ascent, the tank it was holding down shot to the top of the rocket booster’s upper-stage liquid-oxygen tank like a bullet, triggering the “overpressure event” that destroyed the rocket.

Hundreds of these struts — which are certified to withstand about 10,000 pounds of force — are used in the construction of the Falcon 9 vehicles. They’re used in both the upper and lower stages of the two-stage spacecraft, where they strap down bottles of cryogenically cooled helium, like the one that triggered the blast. While the rocket is in flight, the helium is warmed as it’s routed toward the engines, and once it reaches higher temperatures, it’s used to equalize the pressure within the booster’s oxygen and fuel tanks after their contents are used up during flight.

Musk never did name the supplier that sold SpaceX the faulty struts during the teleconference, but he made it clear it was never going to sell his company “incorrectly made” parts again. “It’s not something that should have ever failed at this force level,” he said. But much like the onlookers on the Florida shore, there’s no way his engineers could have been able to foresee what was going on from the outside.

In addition to Musk’s tweets, word of the explosion spread rapidly online, fueled by viewers who had watched NASA’s official coverage. The news quickly filtered down to the crowds who’d stuck it out under the blazing Florida sun, still craning their necks toward the sky.

Onlookers like Aaron Crabtree, a vacationing mechanical engineer from Ohio who’d brought his family to see the launch, learned what happened after posting his homemade video on Facebook. “Some people who had watched on TV had made a comment about it exploding,” he told Inverse. “I didn’t even realize what I saw.”

Kim, who had been following the SpaceX missions, was unable to hide his disappointment after realizing what had happened. “All the stuff on board basically vaporized,” he said. “I believe there were a lot of experiments for schools that were on board. All of that went to waste.”

Despite a postponement of its later missions — the launch of the climate satellite Jason-3 via a Falcon 9 rocket had to be pushed to January — SpaceX shrugged off its June failure, successfully launching (and landing back on earth) the upgraded Falcon 9 on December 21.

A remote camera photo from "Of Course I Still Love You" droneship on April 8, 2015 as the first-stage of the Falcon 9 lands.

SpaceX reached a milestone on April 8, when the Falcon 9 successfully landed on the droneship for the first time.

So where does SpaceX place the crash in its history?

“The lessons learned from the mishap have helped us to develop an even safer and more reliable launch vehicle,” Dex Torricke-Barton, Head of Communications at SpaceX, tells Inverse. “We’ve launched Falcon 9 seven times in a row successfully since CRS-7 and are continuing to focus on achieving the highest levels of mission assurance for all our customers.”

In the 365 days since the Falcon 9 explosion, SpaceX has launched seven successful missions. Three of those missions have seen the Falcon 9 land successfully on its droneship in the middle of the Atlantic, a feat that, at this time last year, hadn’t been accomplished even once. Since then, none of them have blown up in mid-air, although the Falcon 9’s failure to successfully land earlier this month ended a streak that had seen three successful droneship landings in a row.

The next Falcon 9 launch — one of a dozen or so this year — is planned for July 18. Once again, the rocket will attempt to bring cargo up to the ISS. There’s no doubt that onlookers, like Kim, Crabtree, and Ramsay, will once again line the Canaveral shores.

In the minds of certain SpaceX fans, the memory of the June 28 explosion has not faded, but it hasn’t discouraged them from keeping up with the missions, either. Kim, for one, continues to show up to SpaceX launches when he can, his camera in tow. Crabtree looks back on the experience as an altogether “interesting” family vacation.

Ramsay, now back in the U.K., admits that the memory of the rocket crash has only deepened his fascination.

“It was a view I’ll certainly remember for the rest of my life. Very memorable,” Ramsay said. “It’s not every day you see a space rocket blown up.”

Photos via SpaceX