Venera 10, or 4V-1 No. 661, was a Soviet uncrewed space mission to Venus. It consisted of an orbiter and a lander. It was launched on June 14, 1975, 03:00:31 UTC and had a mass of 5033 kg (11096 lb). When the mission launched, the Soviet Union only disclosed that the mission's objective was to explore Venus and the surrounding space. Western sources speculated that the spacecraft contained a lander. The orbiter entered Venus orbit on October 23, 1975. Its mission was to serve as a communications relay for the lander and to explore cloud layers and atmospheric parameters with several instruments and experiments: The orbiter consisted of a cylinder with two solar panel wings and a high gain parabolic antenna attached to the curved surface.

Wikipedia: https://en.wikipedia.org/wiki/Venera_10. Related NASA reference: https://nssdc.gsfc.nasa.gov/planetary/chronology.html#1975. Description adapted from Wikipedia contributors (CC BY-SA 4.0; https://creativecommons.org/licenses/by-sa/4.0/).