State estimation of a three-inline space tethered system with geometric constraints

Space tethered system (STS) has attracted wide attention recently because of its promising application potential. Accurate state estimation of the STS with topology reconfiguration is challenging because of the rigid-flexible coupling dynamics and large-amplitude tether librations. This paper proposes a novel state estimation scheme for the three-inline STS using only two low-cost GPS sensors. The proposed scheme is built on a new dynamics model, two low-cost GPS sensors, and the time-varying tether length constraints using pseudo measurements (PM). The use of geometric constraints helps enhance the filter performance and reduces the number of the needed sensors. Furthermore, the observability of the system is proved based on Lie derivatives and the feasibility of the proposed scheme is verified through the numerical simulations.