Analyzing deviations of returning load from targeted landing point when space tether system is used

When tether system is used, we analyze the deviations, which are due to the errors of the deployment process of returning load from targeted landing point. We first give the mathematical model and calculation procedure of the whole processing, including: deployment of the tether line, free-swinging, cutting the tether line, entry into the atmosphere and eventually falling into zone surrounding the targeted landing point; next, in the absence of any error condition, we calculate the appropriate track position for beginning the release of tether line, so that the returning load can land on the targeted landing point; finally, when there is an error of orbital altitude, orbital eccentricity or the timing of tether line cutting, we calculate the range of deviation from the targeted landing point.