Estimation of Attitude Thruster Activity of Spacecraft on Sun Acquisition Mode

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Estimation of Attitude Thruster Activity of Spacecraft on Sun Acquisition Mode

O. Montenbruck / E. Gill

In the course of positioning the phase of Eutelsat 2 F1 and F2, notable orbit perturbations were observed when the satellites were in Sun Acquisition Mode (SAM). Analysis of the tracking data residuals indicated a type of perturbation similar to the effect of the solar radiation pressure. Investigating various possible explanations it became clear that the effect could be attributed to the attitude thruster activity in SAM. In this mode, thrusters facing the Sun are used to control the pitch axis, while thrusters in the opposite side are used for yaw axis control. Since the acceleration due to each thruster has a considerable component along the rotation axis, a continuous attitude control results in an effect similar to the solar radiation pressure. A detailed analysis of the thruster on time telemetry together with information on expected thruster performance was used to model the observed perturbations for different types of orbits.