Also of note, in zero-gravity the ullage space must be forced to the opposite end of the tank before ignition so the fuel is at the intakes. Commonly this task

Also of note, in zero-gravity the ullage space must be forced to the opposite end of the tank before ignition so the fuel is at the intakes. Commonly this task is accomplished by "ullage motors" which fire to settle the fuel before primary ignition[1]. [1] https://en.wikipedia.org/wiki/Ullage_motor https://en.wikipedia.org/wiki/Ullage_motor