It is understood that one of the test objectives of the May 29 static fire was to test disconnecting the umbilicals ahead of a planned 150-meter test flight scheduled for the following week. The umbilicals must be able to quickly detach when the launch vehicle leaves the pad.

During the testing of the quick disconnects, the system malfunctioned – spilling large amounts of propellant. This could be seen during NASASpaceflight’s live stream of the test.

The propellant eventually ignited, leading to a large explosion. It is not entirely clear what the ignition source was, but a still frame from the NASASpaceflight broadcast shows that the ignition occurred near the base of the vehicle.

Notably, the structural integrity of Starship is not believed to be the cause of the accident. SpaceX has had issues with the prototypes collapsing under high pressure in the past. All of the previous full-scale prototypes failed cryogenic pressurization testing.

Including the May 29 test, SpaceX completed five static fires with Starship SN4. No previous Starship had even gotten far enough to have an engine installed. The Raptor engines performed well throughout testing, and the vehicle’s primary structure held strong.