A hybrid approach for observing the skiprope motion of a tethered satellite system

Under the influence of Earth´s magnetic field the tethered satellite system (TSS) exhibits a special motion which resembles the motion of a child´s skiprope. This motion known as skiprope, only develops if the core of the tether is metallic. Active damping must be introduced to control the magnitude of this motion. Unfortunately, direct measurement of this motion is not technically feasible. Therefore, indirect measurements are needed to estimate the magnitude of this phenomenon. The paper presents a hybrid scheme in determining the magnitude and the phase of this motion for the STS075 mission. An adaptive notch prefilter was augmented with an extended Kalman filter operating at a sampling rate of 1 Hz. The resulting observer was successfully used during the actual mission, until an unexpected fault broke the tether causing the observer to diverge