The Evolution of the Ballistic Parameter of the BeppoSAX Satellite (2000-2002)

The knowledge of the ballistic parameter is critical to model the orbital decay due to the air drag. More than three years of BeppoSAX orbital data, kindly provided by the NASA/GSFC Orbital Information Group, were used to obtain monthly average values of the satellite ballistic parameter by fitting, in a least squares sense, the semi-major axis decay observed. In such a way, the evolution of the BeppoSAX ballistic coefficient was recovered, providing insight on its dependence on the attitude control mode and aerodynamic influences. After the BeppoSAX deactivation, the ballistic parameter oscillated around a new average value, with no clear increasing or decreasing trend. Therefore, for residual lifetime estimations, the best strategy seems, at present, that adopting as nominal ballistic parameter the average value observed since the satellite switch off. Concerning the solar activity prediction, the adoption of the updated 27-day forecast issued by NOAA is recommended. For the subsequent months, such 27-day values should be repeated, with a decreasing trend of 4.8 x 10^4 Jy per month. Regarding the definition of the reentry window, a ballistic parameter variation range of +/- 25% is considered reasonable; in fact, based on the analysis carried out and taking into account the intrinsic uncertainties of the solar activity forecasts, such a variation interval should guarantee a confidence level of about 90%.