During a test of SpaceX’s Starship Super Heavy booster 7 with liquid oxygen and methane propellants on board, an explosion occurred beneath the base of the booster. The explosion did not look like the “rapid unscheduled disassembly” of an engine (no debris flying away, for example), but rather the detonation of a fuel-air mixture in the open. Shortly after the event, Elon Musk confirmed this in a tweet.
Shortly afterward, he added:
So this appears to have been a failure related to the complex start sequence of the Raptor as described here earlier in the post “Tour of SpaceX Starbase with Elon Musk (4)—The Raptor Engine”. It looks like there might have been a large release of unreacted gaseous or liquid methane from an engine which mixed with ambient air and vented oxygen and then exploded upon encountering an ignition source.
There were two subsequent fires in the vicinity of the launch pad. These might have been ignited in the initial explosion and then burned in the oxygen-rich environment as the booster tanks were vented.
Several hours later, Elon Musk reported:
Elon Musk: “I was just out there about an hour ago.”
Leadership! The guy in charge is right there, even knowing the personal risks if something else goes wrong. We have to admire that man – and wish there were a lot more like him in positions of responsiblity.
Here is Scott Manley’s analysis of the Super Heavy “Baby Boom".
Today, 2022-07-18, SpaceX conducted a spin prime test of the Raptor engines on Starship 24. This is the same kind of test which resulted in the explosion below Booster 7 described in the original post. This time, everything went normally, with what looked like clouds of liquid oxygen vapour released from below the ship during the brief test. It was said that this was a test of all six Raptor engines on Starship, but there was no independent confirmation that this was the case.
I have cued the video of the live stream replay to start shortly before the test.
In a spin prime test, the engines’ turbopumps are spun up through the first part of the start sequence, but there is no ignition of the main combustion chamber. This is a test of the “powerhead” of an engine sometimes done to verify its correct operation before proceeding to a static firing.