Venus exploration with the Venera 9 and Venera 10 spacecraft

In October 1975 the Venera 9 and 10 space vehicles reached Venus. Two landers separated from the spacecraft and soft-landed on the illuminated side of the planet while their remaining orbiters were inserted into highly elliptical orbits, with pericenters at about 7600 km. These flights became a very important step in the Soviet program of Venus exploration. For the first time two panoramas of the Venus surface were returned to the Earth. Both landers and orbiters were equipped with various scientific instruments for studying the structure and dynamics of the atmosphere, physical properties and structure of the clouds, light attenuation in the atmosphere and illumination properties of the surface at the landing sites, and the composition, structure, and interaction processes in the Venus upper atmosphere and environment. The experiments were of complex character due to the simultaneous measurements from landers and orbiters, while the orbiters delivered very important information provided by systematic observations of the planet with great time and space coverage. In this report the principal characteristics of the flights, construction of the spacecraft, instrumentation, and scheme of landing on the surface are described. The preliminary results of the measurements obtained and their tentative interpretation are discussed.