This experiment consisted of a pair of cylindrical Langmuir probes of the type used on the Atmospheric Explorer (AE) series. Two probes were required, so that one was always out of the wake of the spacecraft. In flight, 56 measurements taken at a rate of one per second provided high spatial resolution for the measurements of electron density and temperature. The results of these high-resolution measurements were used both to study the upper atmosphere and the ionosphere and to investigate the interaction of the solar wind with the Venusian ionosphere. This experiment provided measurements over the whole region traversed by the orbiter, covering a large range of solar aspect angles, to yield a more complete configuration of the physical properties of the ionopause region.