Passivity-Based Robust Shape Control of a Cable-Driven Solar Sail Boom for the CABLESSail Concept

TL;DR

The paper tackles robust attitude-control challenges for flexible solar sail booms by developing a passivity-based PD controller that actuates boom shape via cables. It builds a nonlinear single-boom model, derives forced equilibria, and proves linearized passivity to justify a stable PD scheme with time-varying feedforward for nonzero setpoints. Validation includes both nonlinear simulations and a small-scale TRAC boom prototype, with experimental mapping of torque to tip deflection significantly enhancing tracking. The results show that time-varying feedforward and an experimentally informed tip-deflection mapping markedly improve stability and tracking, supporting scalable deployment for the Solar Cruiser concept and other large flexible space structures.

Abstract

Solar sails provide a means of propulsion using solar radiation pressure, which offers the possibility of exciting new spacecraft capabilities. However, solar sails have attitude control challenges because of the significant disturbance torques that they encounter due to imperfections in the sail and its supporting structure, as well as limited actuation capabilities. The Cable-Actuated Bio-inspired Lightweight Elastic Solar Sail (CABLESSail) concept was previously proposed to overcome these challenges by controlling the shape of the sail through cable actuation. The structural flexibility of CABLESSail introduces control challenges, which necessitate the design of a robust feedback controller for this system. The purpose of the proposed research here is to design a robust controller to ensure precise and reliable control of CABLESSail's boom. Taking into account the system dynamics and the dynamic properties of the CABLESSail concept, a passivity-based proportional-derivative (PD) controller for a single boom on the CABLESSail system is designed. To reach the nonzero desired setpoints, a feedforward input is additionally applied to the control law and a time-varying feedforward input is used instead of the constant one to effectively track a time-varying desired boom tip deflection. This control law is assessed by numerical simulations and by tests using a smaller-scale prototype of Solar Cruiser. Both the simulation and the test results show that this PD control with the time-varying feedforward input robustly controls the flexible cable-actuated solar sail.

Figures (12)

• Figure 1: An illustration of the CABLESSail concept, where actuating cables are routed down the length of the solar sail's structural booms.
• Figure 2: A single boom with a single cable of CABLESSail.
• Figure 3: Equilibrium boom tip deflection as a function of equilibrium tension.
• Figure 4: Bode plots of the uncertain linearized system remaining passive with the transverse deflection rate of the boom tip as an output when (a) $T_{eq}=0$ N and (b) $T_{eq}=1$ N.
• Figure 5: Bode plots of the linearized system with a varying number of assumed modes, $n$, remaining passive with the transverse deflection rate of the boom tip as an output when (a) $T_{eq}=0$ N and (b) $T_{eq}=1$ N.