The failed launch this June of SpaceX’s Falcon 9 rocket (Defense Daily, June 29) was likely caused by a strut in the second stage liquid oxygen tank, which broke free during flight, said the company’s CEO and chief rocket designer Elon Musk. After the strut failed, the highly-pressurized helium bottle it was securing shot to the top of the tank at high speed, leading to the rocket explosion just two minutes after launch.
The stainless steel strut was designed to handle 10,000 pounds, but failed after just 2,000, he told reporters during a conference call held today. It was about one inch thick and two feet long.
During its investigations — which Musk stressed are still in their preliminary stages—the company found that the strut “failed five times below its normal strength, which is pretty crazy,” he said.
Musk declined to name the supplier.
SpaceX will switch to a different strut design and material—most likely from a different supplier—and will individually test every one, he said. It will replace the struts in both the second and first stage tanks.
The process will add some time and cost, but not a “significant amount” that would affect the price paid by SpaceX customers.
The June 28 explosion occurred as Falcon 9 started its seventh Cargo Resupply Services (CRS-7) mission to the International Space Station. It was the first failure for SpaceX over 19 Falcon 9 flights. After that many successful launches, Musk said that the company may have become too complacent.
“I think this was an important lesson and something we’ll take with us into the future,” he told reporters.
A SpaceX Dragon 1 spacecraft, which was loaded with cargo meant for the ISS, was also destroyed during the failed June launch. Although all such spacecraft are equipped with a parachute that can help it save itself in case of a failure, only Dragon 2 craft have the software necessary to deploy it, Musk said. In the future, the company will ensure that both versions have the software onboard.
The explosion will delay further flights of Falcon 9 until at least September, Musk said. Because the company is focusing attention on that rocket, the first launch of Falcon Heavy will be pushed from this year until next spring. “Maybe April,” he added.
The company has been sharing data with NASA, the Air Force and the Federal Aviation Administration and briefed its government customers last week, he said. “They agree with our conclusions thus far.”