Analysis of Low-Gravity Sloshing in a Spherical Tank

Uncontrolled sloshing in spacecraft tanks can significantly impact the vehicle attitude and dynamics, posing serious threats to the success of fundamental maneuvers such as docking, proximity operations, pointing, rendezvous, and in-orbit refueling. Despite decades of research, low-gravity and microgravity sloshing dynamics are yet to be fully understood and reliably modeled, mostly because of the lack of experimental data. Simplified spherical pendulum mechanical analogies are widely adopted in GNC algorithms and in spacecraft dynamics analyses to enable real-time modeling of propellant sloshing in coupled systems. In this context, the SILA (Sloshing Imaging and Load Analysis) parabolic flight experiment is designed to analyze sloshing in a spherical tank partially filled with water under low-gravity (Bo < 50) conditions. Video, force, and acceleration data are collected over 28 parabolas. The free-surface is tracked and reconstructed, and the experimental results are compared to those obtained with a CFD setup and a spherical pendulum mechanical analogy, respectively, in ANSYS Fluent and MATLAB. For the low-gravity regimes under study, the contact angle hysteresis is revealed as a fundamental physical factor in fluid motion modeling that simplified pendulum analogies fail to simulate, thereby invalidating their use in widespread spacecraft GNC algorithms.