||Originally known as Jupiter Orbiter with Probe, the Galileo mission was approved in 1978. Its target was the gas giant Jupiter, which the Voyagers were about to fly past. Galileo was scheduled to launch in 1986, but due to the tragic explosion of Space Shuttle Challenger, it did not fly until 1989. Without the more favorable arrangements of the planets that had occurred in 1986, Galileo had to use gravity assists from Venus and from Earth (twice) to gain enough velocity to reach Jupiter.
Galileo was a very complex spacecraft. It carried an atmosphere entry probe designed by NASA's Ames Research Center, and in addition had two major sections: a spinning piece that allowed some of its instruments to sweep through space at a specific rate, and a "despun" section that allowed accurate pointing of other instruments. It also had a novel inflatable high-data rate antenna; this unfortunately failed to deploy early in the mission. Clever workarounds by the mission's engineers enabled the spacecraft to complete the mission anyway.
During its six-year voyage to Jupiter, Galileo carried out flybys of Venus, Earth, and two large asteroids, Gaspra and Ida, becoming the first spacecraft to visit an asteroid. In July 1994, while still a year from Jupiter, it provided the only direct observations of the spectacular disintegration and impact of comet Shoemaker-Levy 9 with Jupiter.