Spin parameters of High Earth Orbiting satellites Etalon-1 and Etalon-2 determined from kHz Satellite Laser Ranging data

The high repetition rate Satellite Laser Ranging (SLR) system developed in Graz, Austria, measures ranges to the High Earth Orbiting satellites Etalon-1 and Etalon-2 with the millimeter accuracy. The 2 kHz repetition rate of the laser and the relatively high return rates allow to use the SLR data to calculate the spin parameters of the Etalon satellites. The analysis of the 10 years (October 2003 September 2013) of the SLR data gives trends of the spin axes orientation (J2000 Inertial Reference Frame): Etalon-1: RA = -11.39.Y + 432.341 [degrees], Dec = -0.0402979.Y + 10.154 [degrees], Etalon-2: RA = -12.7871.Y + 328.144 [degrees], Dec = 0.0141925.Y + 1.563 [degrees], where Y is in years since launch (Etalon-1: 1989.02489, Etalon-2: 1989.41193). The frequency signal obtained from the SLR data indicates that the satellites rotate counter-clockwise about the spin axes with a period of: Etalon-1: T = 60.843.exp(0.00319710.Y) [s], Etalon-2: T = 58.958.exp(0.00695744.Y) [s], where Y is in years since launch. The spin model built upon the derived trends shows that the Etalons are losing rotational energy with the lowest rate among the geodetic satellites (8 satellites compared). It takes 170.9 years for the spin period of Etalon-1 to double, and 82.24 years for Etalon-2. The complete spin trends presented in this paper can help to model the acceleration pattern of the spacecrafts, and thus improve accuracy of the precise orbit determination of Etalon-1 and Etalon-2. (C) 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.