HAWTHORNE, Calif., July 20 (UPI) -- SpaceX CEO Elon Musk is blaming the company's last rocket failure on a faulty steel strut. The collapsing steel strut, which holds up a helium bottle inside the Falcon 9 rocket, set off a chain reaction that ended in a violent explosion.
"One of those struts failed and was unable to hold the helium bottle down, and the helium bottle would have shot to the top of the tank at high speed," Musk told reporters in a teleconference call on Tuesday.
Musk called his explanation an "initial assessment" -- one that was most likely, but not certain.
The June 28 explosion was one of three consecutive failed attempts to land a reuseable rocket. It was also a letdown for those who had high hopes for the successful demonstration of reusable rocket technology.
After two close calls, the third attempt never happened. The Falcon 9 rocket was destroyed just a couple minutes into flight. SpaceX's last complete rocket failure occurred seven years ago.
Between then and now, Musk and his team had successfully launched 20 rockets in a row. Musk -- who pointed out that his company has grown from 500 to 4,000 employees over that time period -- acknowledged that his team may have gotten complacent.
But such an excuse was unacceptable, Musk insisted.
"It's just the fundamental nature of rocketry: A passing grade is 100 percent all the time," said Musk, the company's lead rocket designer.
SpaceX isn't scheduled to launch another ISS resupply rocket until September, giving the company time to order and test a new strut from a different supplier.