A friend recently leant me a copy of the Spacecraft Films production of "The Mighty Saturns." It contains lots of footage of Saturn rocket launchs from many angles, including inside the fuel tanks. With a camera mounted at the top of the tank, you can see the fuel drop very quickly as it is consumed by the engine(s). Once the engine shuts off, there is a sudden "whiplash effect" as the fuel is exposed to no acceleration forces. Blobs of fuel begin to float all around the inside the tank.

I know that the lower stages of the Saturn were one-time fire stages, but the third stage of the Saturn 5 had to be restarted. How was the engine restarted with the fuel flopping around inside the tank as blobs? I would imagine that unless the unused fuel was forced to the drain opening of the tank, the engine would get a mixture of liquid and gaseous fuel, which would probably be a bad thing.

I guess this question applies to any liquid-fueled engine that has to be started in "weightlessness." How do rocket engineers keep the fuel near the drain of the tank?

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"All natural, huh? So is lightning." - Mike Rowe