The effects of solar activity on the orbital evolution of low Earth orbiting satellites

Low altitude satellites (below 1000 km) are under the effect of the upper atmosphere drag. As it is well known, the upper atmosphere is strongly dependent on solar activity. Variations in atmospheric density are primarily influenced by variations in solar activity. Geomagnetic storms driven by solar flares are known to have significant effects on the total density of the upper atmosphere, especially, in the range 250-1000 km. The paper uses some results obtained at the Satellite Tracking Station No. 1132 of Cluj-Napoca Astronomical Observatory in the years elapsed from the launch of the first Earth's artificial satellite. We analyzed orbital evolutions of several satellites (e.g. SAMOS 2, Polyot 1, Explorer 19 and PAGEOS 1). The influence of flares and other short-duration solar events are examined. Flistorical remarks are pointed out.