The Galileo mission to Jupiter was formally approved by the United States Congress in 1977, several years before the space shuttle Columbia made its maiden flight into Earth orbit. The mission was a cooperative project involving scientists and engineers from the United States, Germany, Canada, Great Britain, France, Sweden, Spain, and Australia. Even though the Voyager 1 and Voyager 2 spacecraft had performed flybys of planet Jupiter and its sixteen moons in 1979, the Galileo mission was envisioned to initiate several novel observations of Jupiter, the most massive gas planet of the solar system, and its principal moons, and conduct exclusive, often in situ, experiments on their fascinating environments.