Spherical satellites: from the dawn of the space age to modern experiments (for the 60th anniversary of the launch of the first Earth satellite)

60 years ago, on October 4, 1957 the R-7 rocket developed at the Special Design Bureau No.1 led by the Chief Designer S.P. Korolev put into orbit the first ever artificial Earth satellite. To speed up the development work on the first satellite in order to make sure that our country was to be the first to launch it, it was decided that the satellite would be very simple and still have a distinctive shape. It should be noted that satellites of spherical shape, just as it was in the case of the simplest satellite Sputnik launched 60 years ago, are still of interest from the standpoint of conducting a number of scientific studies even today. Through observing the motion of a satellite of a perfect spherical shape, which has precisely known mass and dimensions, it is possible to determine the atmospheric density and update atmospheric model parameters. For this purpose, within the framework of space experiment Vector-T, test satellites of spherical shape are periodically launched from the International Space Station. The latest in the series of such satellites was launched on August 17, 2017 by cosmonauts S.N. Ryazansky and F.N. Yurchikhin. The paper describes methods for updating atmospheric model parameters from the motion of the test satellite and provides some examples of the calculations.