The Starship SN4 prototype was planned to perform a "hop" flight test after the crewed Dragon mission, but after today's static test, that's not an option anymore. The test itself appears to have worked well, but before it got completely detanked, something happened.
https://www.space.com/spacex-starship-sn4-prototype-explodes.html
The current group of new launch vehicles in development all share a common propellant combination, methane and LOX. Liquid methane and LOX are miscible. The end result is liquid explosive that is about twice as energetic as TNT and much more sensitive. So theoretically a rocket weighing in the kilotons, with most of that being propellant, can approach mushroom cloud territory (e.g. after a common bulkhead separating the tanks fails).
For comparison, other propellant combinations like LH2/LOX or RP1/LOX can also create big explosions, but to a lesser degree. Because the liquid temperature range of both propellants doesn't overlap, they can't be mixed well. This limits how much of the total available energy can be released in the form of a detonation.
Those are all theoretical worst case scenarios, but I still wonder what kind of safety distances we will be seeing when these rockets become operational.
EDIT:
@Marc_G was faster:
https://www.rocketryforum.com/threads/spacex-sn4-goes-boom.159757/
Reinhard
. The forces on those bulkheads must be enormous. Hopefully they will release what the problem was sometime.
