How solar radiation pressure acts on RSAT and VSAT with a small evolving tip-off in SELENE

The solar radiation pressure model for the sub-satellites RSAT and VSAT in the SELENE project is improved to correct the mean acceleration due to an e volving tip-off of the spin during the life time of satellites. The shape o f the satellites is assumed to be a regular octagonal pillar. Solar radiati on pressure force components acting on each surface element of the satellit e are calculated independently and summed vectorially during a total period of Euler's free nutation of the satellite to obtain the mean acceleration of the satellite center of mass. The Doppler tracking data reduction proces s for the RSAT is simulated after incorporating the modified model into the orbit analysis software. Comparing with two other types of solar radiation pressure models, the standard cannonball model and a non tip-off model, it is found that when the tip-off becomes larger than 5 degrees /s, the orbit determination result of using the modified model is better than the result s of using other ones.