Spin parameters of LAGEOS-1 and LAGEOS-2 spectrally determined from Satellite Laser Ranging data Original Research Article

The Satellite Laser Ranging (SLR) measures distance to the spacecrafts equipped with Corner Cube Reflectors (CCRs). The range measurements contain information about the spin parameters of the observed satellites. In this paper we present results of the spin rate and the spin axis orientation determination of LAGEOS-1 and LAGEOS-2 by frequency analysis of the SLR data. Analysis of 6734 passes of LAGEOS-1 (L1; January 5, 1984–December 30, 1997) and 12156 passes of LAGEOS-2 (L2; October 24, 1992–June 30, 2008) indicates the exponential slowing down of the satellites. The inertial spin period of the LAGEOS satellites can be expressed by the functions: TL1 = 0.6188667 · exp (0.328951 · Y) (s), TL2 = 0.7673569 · exp (0.455635 · Y) (s), where Y is year since launch (L1: 1976.3415, L2: 1992.8085). The slowing down rate of the satellites is not constant but varies in time by about 50%. Applying the apparent corrections to the observed spin rates allows to identify precession of the spin axes of the satellites around the southern pole of the inertial reference frame. The direction of rotation around the spin axis of LAGEOS-1 is clockwise, and counter-clockwise for LAGEOS-2. The obtained results are compared (and present good agreement) with the predictions given by the LOSSAM model.