Measured states of Sloshsat FLEVO

Abstract

Sloshsat FLEVO is a spacecraft for the experimental study of liquid dynamics and liquid management problems in space. It was launched in GTO as part of the test payload of Ariane 5 ECA on 12 February 2005. Of the total 129 kg mass of Sloshsat, 33.5 kg is liquid water in a smooth 87 litre tank. The operation of Sloshsat is controlled with an orthogonal set of 12 nitrogen gas thrusters of 0.785 N each. The response of Sloshsat to the control thrusts is predicted from the Sloshsat Motion Simulator (SMS). Sloshsat FLEVO is instrumented with six linear accelerometers and three gyroscopes. The data from these sensors allow to determine the motion of the tank. Since the inertial properties of the empty Sloshsat are known, the force and torque on the tank can be calculated. Over a period of 8 days, Sloshsat has been operated during about 57 hours. Thruster activations have been performed ranging from perturbation pulses to manoeuvres under closed-loop control, from initial conditions at rest or spinning. Discussed now is the behaviour of Sloshsat FLEVO from measured states limited to Weber numbers larger than about 2. Special attention is given to the liquid centre of mass location and the liquid response to control actions. Conclusions on the observed motions and damping behaviour have been formulated, supported by predictions from SMS, in particular for a flat-spin manoeuvre. The friction mechanisms may need to be supplied with others. The Sloshsat Investigators' Working Group is introduced, and the near real-time communication link by internet (FACT).