Electrostatic modelling of the Groza-2 discharge sensor on the Venera missions to Venus

The Soviet Venera 13 and 14 missions landed on the surface of Venus five days apart in 1982. An instrument called Groza-2, designed to search for thunderstorms, carried an electrode that recorded discharge currents in the lower atmosphere. In this paper a possible location and likely geometry of the electrode are deduced using the limited information available on Groza-2, combined with electrostatic modelling. The spacecraft's geometry significantly screens the electrode potential, which helps to constrain the sensor's size, shape and location. Due to its high atmospheric pressure, Venus is anticipated to have a high breakdown field, approximately 300 MV/m near the surface if linear scaling with pressure is assumed. The existence of a signal in the discharge sensor combined with the electrostatic screening of the spacecraft geometry implies there is a substantial potential difference between the atmosphere and the electrode.