Dynamics and control of a full-scale flexible electric solar wind sail spacecraft

Abstract

The dynamics and control strategies of a full-scale flexible electric solar wind sail (E-sail) spacecraft are studied in this work. The configuration of the E-sail is an umbrella shape consisting of 100 main tethers of 20 km long, with a remote unit attached at the free end of each main tether; such remote units are also connected by an auxiliary tether with 100 separated segments; the electric voltages of each main or each segment of the auxiliary tether can be independently prescribed to control the orbit, orientation, and vibrations of the E-sail. Two computationally effective formulations, the reference nodal coordinate formulation (RNCF) and the nonlinear floating frame of reference method (FFRM) in a large deformed configuration, are developed to describe the dynamics of the E-sail spacecraft. The RNCF is accurate and comprehensive, but requires over 10000 degrees of freedom to describe the highly flexible and nonlinear dynamics of the E-sail. The FFRM requires only tens of degrees of freedom, and can be adopted for controller designs. The time scales of the orbit motions, the orientation motions and the structural vibrations of the E-sail are quite different. The modes in FFRM are categorized into three groups, such that the influences of the electric voltages on each category of modes are distinctively different, and the controllable properties of each category of modes are explored for controller designs. Although it is designed from the simplified FFRM approach, the resultant controller is implemented to the full-scale RNCF approach to verify its effectiveness, which validates that the E-sail spacecraft can be adopted for solar system exploration missions.