Analysis of Envisat’s rotation state using epoch method

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Analysis of Envisat’s rotation state using epoch method

Song, Chen / Lin, Hou-Yuan / Zhao, Chang-Yin

Abstract Envisat has been identified as a candidate target for active debris removal. The research on its rotation state is of great significance. The specular glint times in optical observation data can be used in fitting the rotation state of Envisat by the epoch method. Using well-observed variations in synodic frequencies, and minimizing the goodness-of-fit indicator by a grid-search, complete spin state solutions can be derived. By this method, Envisat’s spin axis longitude $α$ and latitude $δ$ in the orbital coordinate system can be calculated. The latitude $δ$ oscillates widely with time between $- 55 °$ and $- 85 °$ with a mean value of $δ_{mean} = - 67.08 °$ . Its distribution has peaks in two areas around $- 60 °$ and $- 80 °$ , which is similar to the results through laser ranging measurements from a single pass. In addition, the precession fit of the spin axis longitude $α$ shows that the spin axis may not precess regularly around the negative normal of the orbital plane. Besides, Envisat’s sidereal period from 2013 to 2015 increases exponentially with the expression: $P_{sid} (\sec) = 121.1 \cdot \exp (4.462 \times 10^{- 4} \cdot t)$ , where t is measured in days from the beginning of 2013, RMS of the fit residuals = 1.8586 s.