Coupling Dynamics of Flexible Spacecraft Filled with Liquid Propellant

Abstract

This paper discusses the coupling dynamics behavior of spacecraft equipped with flexible appendages and liquid propellant tanks. The moving pulsating ball model (MPBM) is used to imitate large-scale liquid propellant motion in a tank. The flexible appendage is modeled as a three-dimensional Bernoulli–Euler beam with a free end and an end fixed to the rigid part of the spacecraft. Governing equations for the beam’s elastic motion, a set of nonlinear partial differential equations, are discretized into an infinite system of nonlinear ordinary differential equations by two different methods: assumed mode method (AMM) and rigid-flexible coupling mode method (RFM). For AMM, the beam mentioned previously is assumed to be a cantilever beam. For RFM, the modal shapes and frequencies of the beam are determined by mutual interaction between spacecraft motion and an appendage’s elastic motion, which is neglected in AMM. The spacecraft’s attitude transition is carried out using a momentum transfer technique, and a feedback controller is designed accordingly. Numerical simulations demonstrate the beam elastic vibration, spacecraft angular rates, liquid propellant motion, liquid-flexible coupling behaviors, and a comparison between AMM and RFM results. The work presented here may provide new insights into the coupling dynamics of liquid-filled flexible spacecraft systems.