Preliminary Characterizations of Altair Lunar Lander Slosh Dynamics and Some Implications for TVC Design

During thrust maneuvers, the sloshing of fuel in partially filled tanks could interact with the controlled system in such a way as to cause the overall system to be unstable. This failure mode could be a result of poor coordination between systems engineers of Structures, Propulsion, GN&C, Mission Operations, and other subsystems. Attentions to the following is a minimum: Placements of fuel tanks, Tank shapes and baffle designs, Separation of TVC BW from slosh mode frequencies, Adequacy of excursion range of engine gimbal actuators in all engine burns, BW of sensors (e.g., gyroscopes) and actuators (e.g., engine gimbal), Structural frequencies of spacecraft and engine mounts, Prediction of S/C's c.m. location, canting of gimbal null axis, others. Check overall TVC performance via validated simulation test bed. Modeling fuel slosh during spacecraft thrusting maneuvers
• Placement of fuel tanks to guarantee stable interactions
between fuel slosh mode and the S/C rigid-body mode
• Estimation of slosh frequencies (as a function of mission
phases):
– Estimation of slosh mode damping
• Some implications for Thrust Vector Control design:
– Selection of TVC controller bandwidth
– Adequacy of the excursion range of engine gimbal actuator
• TVC system design: Complex Interactions between GN&C,
Propulsion, Structure, and Other Subsystems