Research on Estimating the Rotation State of the Upper Stage of Falcon 9 Rocket by Using Lightcurve

Lightcurve measurement is one of the main methods for ground-based space-target observation, as the photometric information of the targets can be used to estimate their relevant characteristics. Aiming at better understanding of the rotational state of the space target, a representative upper stage of the Falcon-9 rocket is selected as the object to analyze its rotational state through light curve study. Firstly, the photometric data of the upper stage of the Falcon-9 rocket is obtained with the 1.2-m optical telescope of the Yunnan Observatories. Then the target's magnitude is processed with slant-range normalization. The photometric changing information is obtained, and the time-dependent light curve of the target magnitude is analyzed. Accordingly, the approximate rotation period of the target is estimated, and then the accurate synodic period is calculated by the phase discrete minimization method. Based on the position relationship between the Sun, the target and the observatory, the main inertial axis pointing, the rotation axis pointing, the initial phase and other factors, the theoretical magnitude is calculated using the attitude rotation matrix. The main inertial axis direction, the initial phase angle and the rotation axis pointing direction are determined as well. Finally, the parameters such as the rotational period, the synodic period and the pointing direction of the rotational axis of the upper stage of the Falcon 9 rocket are given, which can serve as a reference for following studies on the photometric information of other space targets.