A Failed Strut Caused the SpaceX Rocket Explosion

Stages of a SpaceX Falcon 9 rocket being assembled.

As reported by The Verge: The SpaceX explosion on June 28th was caused by a failed strut in the rocket's upper stage liquid oxygen tank, SpaceX chief executive officer Elon Musk said today. The strut was one of several hundred used to hold together the helium pressure vessels in the tank, which help to pressurize and maintain the buoyancy of the rocket. According to Musk, the strut was designed to handle 10,000 pounds of force, but failed at just 2,000 pounds of force.

"THIS IS THE BEST OF WHAT WE KNOW THUS FAR."

"This is the best of what we know thus far," said Musk during a press conference. "We emphasize this is an initial assessment, and further investigation may reveal more over time."

The strut was a steel rod that’s about two feet long and one inch thick. Struts like the one that failed have flown on several previous Falcon 9 flights before. Musk says SpaceX still doesn’t know why the steel rod snapped, but it’s possible that its material was faulty. Musk didn’t name the strut's supplier, but did say it may be that one strut of thousands wasn’t up to code.

When the strut snapped, the helium tanks released a lot of helium into the upper-stage liquid oxygen tank, Musk said. That put too much pressure on the tank and caused it to explode.

The Dragon capsule, filled with supplies for the International Space Station, survived the explosion and continued to communicate data to ground control for a while afterward. If the Dragon had been equipped with different software, the capsule what have been able to deploy its parachutes and save its contents. Future versions of the Dragon cargo capsule will have this capability, Musk said.

"It's the first time we've had a failure in seven years so, to some degree, the company as a whole got a little complacent," said Musk. "Especially with all the successes in a row, I think this is an important lesson and something we'll take with us into the future."

"THIS IS AN IMPORTANT LESSON AND SOMETHING WE'LL TAKE WITH US INTO THE FUTURE."

Nearly a month ago, SpaceX's Falcon 9 disintegrated during its ascent to the International Space Station. SpaceX has a contract with NASA to launch commercial resupply missions to the station; that rocket launch was the seventh of 12 planned missions. The Falcon 9 was carrying 4,000 pounds of supplies, including food and water for the station's crew and a new International Docking Adaptor. The IDA, meant to be mounted on the outside of the station, will allow future US crewed spacecrafts from commercial spaceflight companies to dock with the ISS. SpaceX and Boeing have contracts to ferry astronauts to the ISS beginning in 2017.

At the 2015 ISS Research and Development Conference, Musk described the failure as a "huge blow for SpaceX." Up until the June incident, SpaceX has had an impeccable launch record. This recent rocket loss was the first major failure out of 19 total Falcon 9 launches. As a result of the accident, SpaceX postponed its next scheduled launch of the Falcon 9, which was originally slated for August 9th. The mission, which doesn't have a definitive launch date yet, will carry the National Oceanic and Atmospheric Administration's Jason-3 Earth observation satellite to orbit.