Control of Librational Motion on Tethered Space-Tug System Based on Wave Equation

This paper investigates the librational motion control problem of the tethered space-tug (TST) system in the process of deorbiting space debris. By analyzing the dynamic equations of the TST system, the librational motion control problem of the system in 3-dimensional space can be transcribed to librational motion control problems inside and outside the orbital plane. The motion of the TST system inside or outside the orbital plane can be properly characterized through a highly simplified ring-string (R-S) model, which can be properly analyzed using the finite time-domain wave equation. An absorbing excitation method is proposed to suppress the librational motion of the R-S model, where the librational motion suppression control is achieved by offsetting the equivalent excitation obtained through motion analysis. Different from wave-based controls which ignore the mass of execution structure, the effect of the mass of the tug and target on the control rate is compared through numerical simulations of four control rates based on the absorbing excitation method.