A theoretical alternative to ullage motors is to impart a spin on the vehicle. Then the fuel would pool at either end, or along the tank walls, depending on the

A theoretical alternative to ullage motors is to impart a spin on the vehicle. Then the fuel would pool at either end, or along the tank walls, depending on the type of spin. There's some diagrams and discussion here: https://exrocketman.blogspot.com/2021/08/propellant-ullage-problem-and-solutions.html?m=1 https://exrocketman.blogspot.com/2021/08/propellant-ullage-p...