Solar Sail Momentum Management With Mass Translation and Reflectivity Devices Using Predictive Control

TL;DR

The paper addresses momentum management for large solar sails by preventing reaction wheel saturation under solar radiation pressure disturbances. It introduces two MPC-based strategies that explicitly model AMT-driven mass translation and RCD-based reflectivity actuation, employing a mixed FOH/ZOH discretization and PWM-inspired quantization to enable real-time onboard optimization. A backwards-in-time iterative approach further embeds PWM quantization into the prediction, improving performance without resorting to computationally heavy mixed-integer methods. Numerical simulations with Solar Cruiser-like parameters demonstrate reduced actuator usage and preserved attitude control, indicating practical viability and robustness of the proposed framework.

Abstract

Solar sails enable propellant-free space missions by utilizing solar radiation pressure as thrust. However, disturbance torques act on the solar sail and effective attitude control leads to the continuous accumulation of reaction wheel angular momentum, necessitating an efficient momentum management strategy to prevent saturation. This paper presents a novel momentum management controller using model predictive control (MPC) that is tailored for solar sails, accommodating the unique actuation mechanisms of an active mass translator (AMT) and reflectivity control devices (RCDs). A first-order hold discretization and tailored motion costs are applied to the AMT translation, while the RCD actuation is handled using pulse-width modulation (PWM)-inspired quantization to address their on-off inputs. To enhance prediction accuracy, an iterative backwards-in-time MPC approach is introduced, incorporating the effects of PWM-quantized inputs into the optimization process. The dynamic model accounts for the time-dependent center of mass and moment of inertia changes caused by AMT translation, extending its applicability to other spacecraft with mass-shifting actuators. Simulation results demonstrate the effectiveness of the proposed framework in reaction wheel desaturation, attitude control, and momentum management actuation efficiency, highlighting the potential of integrating MPC to manage coupled nonlinear dynamics and discrete actuator constraints for solar sails.

Figures (13)

• Figure 1: Depiction of the active mass translator (AMT). Image Credit: NASA inness2024controls
• Figure 2: (a) A depiction of the reflectivity control devices (RCDs) embedded in a solar sail membrane. (b) A close-up schematic of the tenting setup used for the RCDs. Image Credits: NASA johnson2019solarJohnsonLes2020SCTM
• Figure 3: Conceptualized solar sail model with AMT translation between bus $\mathcal{P}$ and sail $\mathcal{S}$ (not drawn to scale), where the position vector is denoted by ${\underrightarrow{{{r}}}}^{ps}$.
• Figure 4: Quantization of the RCD input using a PWM-inspired approach and thresholding.
• Figure 5: Iterative solving MPC backwards in time with a prediction horizon of $N=5$ and quantized inputs with the PWM-inspired method.