CURRENT-VOLTAGE CHARACTERISTICS OF THE TETHERED SATELLITE SYSTEM - MEASUREMENTS AND UNCERTAINTIES DUE TO TEMPERATURE-VARIATIONS

One of the primary goals of the Tethered Satellite System reflight mis sion (TSS-1R) is to determine the current-voltage characteristics of t he TSS satellite orbiting in the ionosphere. While the collected curre nt was measured directly with high reliability, the satellite potentia l could only be deduced from a circuit model or from interpretation of measurement data below satellite potentials of 500 Volts. The greates t uncertainty in the circuit model is the value of tether resistance R . We have provided quantitative calibration of the resistance based on instrument data for Vs < 100 Volts. We have reached the important con clusion that the R value in the TSS circuit model is correlated to tem perature changes associated with the diurnal cycles along the TSS flig ht path. We have also applied the calibrated R value in the TSS circui t equation to construct the I-V curves that extend to high voltages. T he resulting I-V characteristics are presented with error bounds on sa tellite potential to indicate the uncertainty associated with the teth er resistance determination. The I-V relation exhibits different scali ngs in the high (> 100 Volts) and low (< 10 Volts) voltage regimes, wh ich indicates a fundamental transition for the current collection phys ics in the ionospheric plasma surrounding the satellite.