SpaceX: Strut went kaput and possibly led to Falcon 9 explosion

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SpaceX has revealed that the explosion of its Falcon 9 rocket on June 28 was caused by an overpressure event in the upper stage liquid oxygen tank initiated by a flawed piece of support hardware (a ‘strut’) inside the second stage.

The private spaceflight company revealed that its investigators with oversight from the FAA and participation from NASA and the U.S. Air Force carried out extensive investigation of over 3,000 telemetry channels as well as video and physical debris in a bid to find out what exactly went on before, during and after the explosion events.

SpaceX revealed that the sequence of events was so fast that the first indication of an issue to loss of all telemetry took just 0.893 seconds. The company added that because of the pace at which the events happened, its investigators had to spend thousands of hours going through the painstaking process of matching up data across rocket systems down to the millisecond to understand that final 0.893 seconds prior to loss of telemetry.

The company said that several hundred struts are used on every Falcon 9 vehicle, with a cumulative flight history of several thousand. The strut that we believe failed was designed and material certified to handle 10,000 lbs of force, but failed at 2,000 lbs, a five-fold difference. Detailed close-out photos of stage construction show no visible flaws or damage of any kind.

In this particular mission, SpaceX said, it appears that one of these supporting pieces inside the second stage failed approximately 138 seconds into flight. The pressurization system was performing normally, but with the failure of this strut, the helium system integrity was breached which caused a high pressure event inside the second stage within less than one second and the stage was no longer able to maintain its structural integrity.

Despite the fact that these struts have been used on all previous Falcon 9 flights and are certified to withstand well beyond the expected loads during flight, SpaceX will no longer use these particular struts for flight applications. In addition, SpaceX will implement additional hardware quality audits throughout the vehicle to further ensure all parts received perform as expected per their certification documentation.

SpaceX stressed that the conclusions are preliminary and that it will continue investigating until all aspects of the vehicle are not exonerated. The company added that it expects to resume flight operations as early as this autumn.