FLUID FORCE ACTIVATED SPACECRAFT DYNAMICS DRIVEN BY GRAVITY GRADIENT AND JITTER ACCELERATIONS

Using as an example the liquid helium dewar of the Gravity Probe-B spa cecraft, the dynamics of liquid motions in a slowly rotating, partiall y liquid fill tank are investigated under the combined action of gravi ty gradients and g-jitter accelerations. The equilibrium configuration of the liquid interface, which is controlled by centripetal accelerat ion and surface tension, is a torus. Three different cases of liquid r esponses are examined: 1) when gravity gradient is the dominant drivin g acceleration, 2) when g jitter is the dominant acceleration, and 3) when g-jitter and gravity gradient accelerations are comparable. For c ase 1, the vapor bubble responds in an asymmetric oscillation in which the part of the bubble on one side of the centerline rises while the other side sinks (one-up, one-down oscillation). For case 2, the bubbl e responds in a combined up-and-down and side-to-side oscillation. The response for case 3 is a combination of the responses for cases 1 and 2. The motion-induced forces and torques are also computed for these cases to quantify the effects on spacecraft control.