Attitude perturbations induced by free-molecular flow interactions in perigee region

A theoretical model for the spin axis attitude changes induced by free-molecular torques during the perigee region passage in a geostationary transfer orbit is developed. It is shown that the direction of the attitude change is essentially normal to the plane formed by the attitude orientation and perigee velocity vectors. A verification of the model is performed using actual MARECS-A solar aspect angle measurements before and after the three perigee passages. A consistency of better than 16 percent is achieved between predicted and reconstituted attitude changes. The discrepancies between the results for the three perigee passages are expected to be due to deficiencies in local air density modelling.