SpaceX thinks a steel strut holding down a bottle of high-pressure helium inside the Falcon 9 snapped on June 28, leading to a rapid "overpressure event" in the rocket's upper-stage liquid-oxygen tank.
The strut was probably poorly made, since it apparently broke under a load of 2,000 lbs. (900 kilograms) of force, despite being certified to withstand 10,000 lbs. (4,500 kg), Musk said. The company plans to individually test every one of the hundreds of struts that flies on each Falcon 9 and will probably source the struts from a different supplier going forward, he added.
Prior to the June 28 Falcon 9 rocket explosion — which ended the company's seventh robotic cargo mission to the International Space Station less than 3 minutes after it blasted off — SpaceX had enjoyed a string of 20 straight successful launches over a seven-year stretch.
"To some degree, I think the company became maybe a little bit complacent," Musk told reporters Monday (July 20) during a teleconference that discussed the probable cause of the mishap. "I think this is certainly an important lesson, and something we're going to take with us into the future.
SpaceX's Falcon 9 broke apart shortly less than 3 minutes after launching on a cargo mission to the International Space Station on June 28, 2015.
Credit: NASA/JPL-Caltech/MSSS/Texas A and M University
NASA officials also expressed confidence that SpaceX will bounce back from last month's accident. (SpaceX holds a $1.6 billion NASA contract to fly at least 12 unmanned cargo missions to the space station using the Falcon 9 and the company's Dragon capsule.)
"SpaceX has demonstrated extraordinary capabilities in its first six cargo resupply missions to the station, and we know they can replicate that success," NASA Administrator Charles Bolden said in a statement shortly after the mishap. "This is a reminder that spaceflight is an incredible challenge, but we learn from each success and each setback."