But doesn't that result in Starship pointing in the wrong direction after separation? I get that it's the right direction for the booster. Also a flip seems much more risky than the well-understood current separation mechanisms.
I don’t know the reasons for it, all I know is that the first part of the flip is intentional and the rest happened because stage separation failed.
I have heard some theories on why they do this. One is that it gets around the need for “ullage thrusters”, independent thrusters that fire early to provide initial momentum forcing the fuel to gather at one end of the tank to provide full uninterrupted flow to main thrusters. Another theory I’ve heard is that it’s an attempt to develop a stage separation mechanism that doesn’t require consumables like explosive bolts or heavy special-purpose equipment like hydraulic pushers. Both seem plausible to me given the goal of a truly re-usable rocket; the vision seems to be that you literally just fill up the gas tank and go again, you don’t have to refuel independent thrusters or install a new explosive decoupler.
