Can the location of gas bubbles in a tank in a spacecraft in zero gravity be influenced?

Question

Can the location of gas bubbles in a tank in a spacecraft in zero gravity be influenced? They for sure cannot be determined, then I guess they also cannot be influenced?

Answer 1

It can.

1. ullage - provide a small, maybe even very small acceleration that will provide minuscule amount of "artificial gravity" to bring the bubbles where needed. During launch, this is typically regular (linear) acceleration provided by ullage motors, small thrusters that assure the bubbles float to the surface, away from the fuel intake. In orbit this can be achieved by introducing a spin, which will bring the bubbles to the center.

2. Assuring there are no bubbles - collapsing them. This can be achieved by pressurizing the ullage space (empty volume) of the tank with an inert gas (helium) and e.g. having the fuel separated by a diaphragm from the empty space. Also, keeping the cryofuels cold enough they don't boil off where you don't want the bubbles to form.

3. If the bubbles are small enough and far apart enough that they don't introduce a significant difference in amount of fuel supplied, they can be atomized further through means of porous filters or such into much smaller bubbles which won't impact the pump and engine operation.

By the way, a sonar-like device would easily determine the positions of bubbles and it would work just fine in 0g without even compromising the mass budget or being too expensive. It's just pointless - you don't really need to know the positions of the bubbles, the methods of mitigating their presence simply don't require that.