Orbital Motion and Attitude Control of the Spectrum–Röntgen–Gamma Space Observatory

The Spectrum–Röntgen–Gamma (SRG) space observatory was launched from Baikonur on July 13, 2019, and is currently on a flight trajectory in the vicinity of the collinear Sun–Earth libration point L2. The planned service life of the observatory is 7 years and includes an all-sky survey and in-depth studies of individual objects in the X-ray range 0.3–15 keV. We consider the technical limitations of the mission pertaining to the launch scenario, the spacecraft design and system characteristics, including the data and command transmission, orbital motion and attitude control systems, and the peculiarities of the ground segment used to accomplish these tasks. The flywheel offloading strategy for the attitude control system is analyzed within the mentioned limitations. The goal of this analysis is to determine an optimal balance between the flywheel offloading operations while controlling the attitude of the observatory, the orbital maneuvers to keep it on a given trajectory, propellant consumption, and the requirements from the scientific measurements. The proposed method allows the total propellant consumption to be minimized by coordinated control of the operation of the system of attitude control rocket engines while simultaneously using them to maintain the specified orbital parameters.