When it started doing cartwheels and the announcer said "beginning the flip for stage separation" I was like "WTF does that mean? That can't be nominal!"
Nah it's the nominal KSP launch trajectory. You forget to add first stage fins, launch up to the gravity turn, do the cartwheel, separate and continue to orbit. Seems like they forgot to check their staging though.
Imagine how magnificent it would have been if they managed stage separation after doing a 360 cartwheel, via some sick on-the-fly manual intervention. I was half hoping for it.
This isn't what the commentators are referring to when they talk about "the flip".
Rockets traditionally have some type of separation mechanism to separate stage 1 and stage 2. This is usually some type of pyro charge or an actual pneumatic pusher. SpaceX wants to avoid this complexity with Starship and instead "throw" off stage 2 (Starship) by doing a flip with the booster. I don't believe it's been done before for stage separation, but this is also how they deploy Starlink satellites. [0]
Obviously, something went wrong in stage separation today so Booster+Starship just continually flipped. We don't know exactly what the true flip will look like.
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.
