In an earlier post I speculated about alternatives to ancillary propellant systems for main propellant ullage (ensuring that fuel and oxidizer are available at the pickups in the main tanks).
Another alternative has been identified by the Aerospace Club of the Vanderbilt School of Engineering. In this article they describe the use of baffles within the tank and “small through-flow bobbins to only allow fuel to keep moving towards the pick-up”. These baffles segment the tank. Principle 1 – Segmentation
This is a simple and ingenious solution. The article also highlighted an issue I hadn’t previously considered. When the main engines are cut, particularly during flight through the atmosphere, the result is a sudden deceleration. This causes the liquid in the tanks to rush forward, with as much as two and half times the force of gravity, making the fuel “hit the roof”. This presumably must be addressed with substantial structural strength in the tank. Spreading this force across a series of baffles may allow for a lighter structure overall.