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Common stillwells attenuate slosh effects in two ways: a decrease in pressure variations with depth and the damping caused by orifices. Often the slosh frequency is near the resonance frequency of the stillwell. Addition of an “inertia tube” can lower the stillwell natural frequency sufficiently to detune the system without seriously increasing the head loss due to propellant outflow. Even in a very short stillwell, where the depth effect is negligible, the “inertia tube” can greatly attenuate sloshing. This paper treats the stillwell as a vibrating system and presents equations for simple stillwells, orifice stillwells, and inertia-tube stillwells.

No pressurizing gas is introduced into the propellant tanks of the Centaur vehicle during engine firing. The consequent pressure decay causes the propellants to boil, and the resulting gas bubbles change the effective density of the propellants. For liquid hydrogen in the Centaur, this change is 1.4% and would show up as an error in any level sensing propellant utilization system. A perforated capacitance probe shows a net 1/2% error because the bubble population is not the same inside and outside the probe. However, a manometer type capacitance probe senses propellant mass without a bubble induced error. This paper outlines the theoretical background for this effect, and presents the results from medium-scale tests in a general form applicable to vehicles other than Centaur.

This paper describes theoretical analyses performed on cylindrical and spherical propellant tanks to establish the basis for selection of the proper mode (electric and magnetic field configurations) of operation of the cavity. Extensive experimental investigations were then conducted. Scale models were constructed and loaded under conditions simulating zero gravity and applied accelerations with typical fuels such as hydrazine and unsymmetrical dimethyl hydrazine. The results of these measurements have verified the theoretical predications and have established the basic feasibility of this radio frequency technique.