Fuel-displacing bladders keeps the fuel towards the back. The ullage motors help, but what if there's a misfire due to excessive splashing - now you're out of ullage motors.

I'd opt for both options!

I think I've also seen a design for a bladder which is anchored at both ends and the space between the bladder and the insides of the fuel tank are displaced with nitrogen. Sort of like a toothpast tube, but with less liklihood that the bladder wouldn't be injested into the fuel pump.

That would be bad. Probably fatal, even if it's at the very end of the burn.

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I am Mugs, of the Alien clan of Usa, Nordamerica, a Terran, of Sol.

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