Atmosphere of Venus
In 1761, Russian polymath Mikhail Lomonosov observed an arc of light surrounding the part of Venus off the Sun's disc at the beginning of the egress phase of the transit and concluded that Venus has an atmosphere. In 1940, Rupert Wildt calculated that the amount of CO in the Venusian atmosphere would raise surface temperature above the boiling point for water. This was confirmed when Mariner 2 made radiometer measurements of the temperature in 1962. In 1967, Venera 4 confirmed that the atmosphere consisted primarily of carbon dioxide.
High Altitude Venus Operational Concept
Venus is a planet with a runaway greenhouse effect, with surface temperatures and pressure of and respectively. Conventional rocket engines will not work at those pressures. Hence, human missions to Venus have historically been thought impractical, if not impossible. However, Venus has advantages for crewed travel, such as Earth-like gravity (.90 Earth gravity), an atmosphere that provides a level of protection from solar and interstellar radiation, and a much greater proximity compared to Mars.