Jupiter has been visited four times: by Pioneers 10 and 11 in 1973 and 1974 and Voyagers 1 and 2 in 1979. Data from those missions will be expanded by the Galileo mission in 1985, which will be the first entry probe into Jupiter's atmosphere. Galileo will also include an orbiting observatory that will provide long-term detailed studies of the entire Jupiter system.

Components for the Galileo spacecraft, which consists of the orbiter and the entry probe, are nearing completion. The development model for the heat shield on the probe recently passed tests at the NASA Ames Research Center, Mountain View, Calif. NASA says that approximately 95% of the flight parts have been delivered, and the design for the two parts of the spacecraft and the mission are nearing completion.