Almost three years after an explosion that destroyed a Falcon 9 destined for the International Space Station, NASA has released the findings of their independent review team. The public summary report details the 2015 explosion pointing to a “design error” as the cause of the explosion that destroyed the vehicle.
The nineteenth Falcon 9 mission lifted off from Cape Canaveral on June 28, 2015, at 14:23 GMT (09:23 EST). The rocket performed as expected for over two minutes until a white vapour cloud was spotted emanating from the Falcon 9’s second stage at T+140. Ten seconds later at T+150, the vehicle began to break up and the Dragon capsule was ejected from the wreckage of the Falcon 9.
Although the Dragon capsule was pushed clear of the blast, software that controlled the capsule did not include provisions to deploy parachutes under those conditions. The result was a total loss of the capsule.
Following the incident, SpaceX formed an Accident Investigation Team (AIT) to determine the cause of the vehicle’s failure. Officials from NASA, the US Air Force and the FAA were all assigned to work with the AIT.
According to the report, investigators discovered that the white vapour and accompanying drop in LOX tank pressure pointed to a failure of the Stage 2 composite overwrapped pressure vessel (COPV). It was also found that the failure was caused when an axial strut supporting the tank broke free. The investigation further concluded that the struct had broken free as a result of the failure of a single cast stainless steel eye bolt.
Once the COPV had broken free, its buoyancy caused it to accelerate and impact the LOC dome. The force from the impact caused structural damage which quickly caused the vehicle to break up under load.
These findings detailed in the NASA public summary are, however not new. A report released by SpaceX detailed the same events that lead up to the destruction of the Falcon 9. The SpaceX report also identified the failure of the cast stainless steel eye bolt. Where the two reports differ is why the bolt failed.
SpaceX officials had blamed a third-party manufacturing fault resulting in the bolt being below acceptable thresholds. However, the NASA report identifies the launch provider’s insistence on using industrial instead of aerospace grade parts in their pursuit of lower costs as a “design fault”. Additionally, the report cites inadequate “load testing of the part under predicted flight conditions” as a contributing factor.
Following the 2015 failure, the Falcon 9 was redesigned to negate the deficiencies identified by both SpaceX and NASA.
Image Credit: SpaceX | Video Credit: NASA