The influence of taking into account atmosphere density variations, caused by solar activity, on accuracy of definition of ISS motion

We investigated the influence of taking into account variations of the solar activity index on accuracy of approximation of measured values of the International Space Station phase vector by solutions of its motion equations. Those equations were written taking into account higher harmonics of the Earth gravitational potential and the atmospher drag. The investigation was carried out using the atmosphere density model of GOST 25645.115-84. Time intervals up to 10 days in March – April 1999 were considered when the station made uncontroled flight in the gravitational orientation mode. Its ballistic factor was practically constant that time, and the station did not undergo the action of any control force and torque. Taking into account of actual variations of the solar activity index allowed to increase essentially theaccuracy of approximation of values of the phase vector on time intervals more than 5 days. At approximation of these values on time intervals less than 3 days, the prize in accuracy was absent practically.