Data reviews indicate that the SpaceX Crew Dragon explosion occurred approximately 100 milliseconds prior to ignition of Crew Dragon's eight SuperDraco thrusters and during pressurization of the vehicle's propulsion systems. Evidence shows that a leaking component allowed liquid oxidizer [fuel]– nitrogen tetroxide (NTO) – to enter high-pressure helium tubes during ground processing. A slug of this NTO was driven through a helium check valve at high speed during rapid initialization of the launch escape system, resulting in structural failure within the check valve. The failure of the titanium component in a high-pressure NTO environment was sufficient to cause ignition of the check valve and led to an explosion.
SpaceX engineering leader Hans Koenigsmann said it was now increasingly difficult for SpaceX to expect a crewed launch of its new spacecraft in 2019.
SpaceX engineers would isolate the oxidizer from the pressurization system and replace the four titanium valves with a simpler component called a burst disc. The impact on the schedule might be "relatively minor," but said about 20% of the accident investigation remained to be done and that other documented issues needed to be solved as well.