Maneuvering Control of a Spacecraft with Propellant Sloshing

Propellant slosh has been a problem studied in spacecraft designs since the early days of large, liquid-fuel rockets. The conventional design solution involves physical structures inside the fuel tanks that limit propellant motion. Although effective, baffles and bladders add to spacecraft mass and structural complexity. In this research, the sloshing fuel mass is treated as an unactuated degree of freedom within a rigid body. Specifically, the propellant is modeled as a pendulum mass anchored at the center of a spherical tank. After obtaining the coupled equations of motion, several linear controllers are developed to achieve planar spacecraft pitch-maneuvers while suppressing the slosh mode. The performance of these linear controllers will be compared to that of a nonlinear controller developed using Lyapunov’s Second Method. It is shown that the linear controllers are ill-equipped to achieve the desired spacecraft attitude and transverse velocity simultaneously, especially during aggressive pitch-maneuvers; while the Lyapunov controller is superior in this regard