After their launch in 1984, the identical spacecraft Vega 1 and Vega 2 launched from a Russian Proton Rocket for their double mission of flying through the tail of Halley’s Comet and landing scientific payloads on the surface of Venus. In addition to a regular parachuted lander, the Vega spacecraft each carried a 22-kilogram balloon assembly that detached from the main lander during descent and deployed about 50 km above the surface of Venus. Both of these balloons landed on the night side of Venus. With only 60 hours of battery life on the balloons, and with days on Venus clocking in at a lingering 243 Earth days, it would seem that the Vega balloons would never see the daylight side of Venus. However, over the next 60 hours, the balloons were carried to the daylight side of Venus by the hurricane speed winds found in the middle of the three layers of the Venusian atmosphere. According to NASA, the probes measured “the local atmospheric dynamics, pressure, temperature, lightning, illumination levels, and cloud properties over a period of about 46 hours in both the night- and day-side.”
Pictured above is a formerly proposed mission by the ESA to launch another Venus balloon to follow up the Vega missions, but this project has not yet received funding.