In-Flight Characterization of the Cassini Spacecraft Propellant Slosh Modes

Abstract

Telemetry data from three 445 N engine burns of the Cassini spacecraft are used to characterize the high- slosh characteristics of bipropellants in cylindrical tanks with spherical end domes. Comparisons between flight data and theoretical results indicate that high- clean tank slosh frequency and high- sector mode frequency could be predicted with errors of 3–5%. However, at lower tanks’ fill fractions of , when most of the propellants reside in the spherical end domes of the tanks, the prediction errors deteriorated to . Also, high- full-tank slosh mode in a tank with an eight-panel propellant management device could be modeled using an annular cylindrical tank. Again, prediction error of full-tank slosh frequency degraded with decreasing fill fractions. Based on these results, the high- sector and full-tank propellant slosh frequencies could be well predicted using simple analytical techniques before these predictions are refined by liquid slosh computer modeling tools. A set of small-amplitude oscillatory motions of the spacecraft attitude was detected during 13 science observations conducted in 2007–2008. Their frequencies matched well the low- slosh frequency predicted analytically for uncompartmented tank. The root cause and analytical prediction of the observed spacecraft oscillatory motion in low- condition is an interesting topic for future research.