CubeSat orbit and attitude control using reduced sets of continuous low-thrust gimbaled thrusters for libration point missions

This work proposes an innovative AOCS architecture design: a set of 3/4 electric gimbaled thrusters is proposed to control the CubeSat 6-Degrees of Freedom (DOFs) around Libration point orbits. Two thruster configurations are proposed: the thrusters are low-thrust and can perform thrust vectoring through a gimbal mechanism. The first configuration consists of four thrusters located at the opposite faces of the spacecraft. The second configuration uses only three gimbaled thrusters, located on-board similarly to the first architecture. The proposed orbit-attitude control synthesizes a Linear Quadratic Gaussian (LQG)} controller, for Station-Keeping, and a Non-Linear Fast Terminal Sliding Mode (NFTSM) control for attitude control. This combination can reject noise from the sensors and provides robustness in the attitude control to ensure accurate pointing. The second configuration, nevertheless, become critical to be handled by the AOCS proposed. The overall control performance gets significantly degraded once the reference attitude must be evaluated in real-time after that the Station-Keeping control force is computed upstream. The Steady-State-Riccati-Equation (SDRE) control is proposed as an alternative solution to overcome this important shortcoming. The control performance is evaluated in scenarios where injection errors, measurement noise and control execution errors are introduced in the form of Additive-White-Gaussian-Noise (AWGN).

Il progetto propone due innovative architetture per il Sistema AOCS di CubeSats. Queste architetture sfruttano 3-4 attuatori elettrici per fornire controllo continuo a bassa spinta per Station-Keeping e controllo di assetto. Vengono considerati anche dei maccanismi di gimbal per permettere agli attuatori di fornire controllo direzionale di spinta. Il sistema di controllo di orbita e assetto sintetizza un controllore “Linear Quadratic Gaussian (LQG)” per Station-Keeping e un controllore “Non-Linear Fast Terminal Sliding Mode (NFTSM)” per il controllo di assetto. Viene adottato anche il controllore “State-Dependent-Riccati-Equation (SDRE)” agente sul modello a 6 gradi di libertà per sopperire alle limitiazioni che caratterizzano LQG e NFTSM.