The Galileo mission utilized a single launch of a combined Orbiter and Probe using the space shuttle Atlantis and an inertial upper stage (IUS) to inject the Galileo spacecraft on its interplanetary trajectory to Jupiter. The launch occurred October 18, 1989. Since the IUS did not have the energy to inject Galileo on a direct trajectory to Jupiter, the spacecraft was launched first towards Venus for the first leg of its Venus-Earth-Earth gravity assist (VEEGA) trajectory.
Target-of-opportunity science observations were made at Venus (closest approach February 10, 1990), the first Earth encounter (closest approach to Earth and Moon December 8 and 9, 1990), the asteroid Gaspra (closest approach October 29, 1991), the second Earth encounter (closest approach to Earth and Moon December 8, 1992), the asteroid Ida (closest approach August 28, 1993), and distant observations of the impact of comet Shoemaker-Levy 9 into Jupiter's atmosphere from July 16-22, 1994.
The Probe separated from the Orbiter on July 13, 1995. After this time, the Probe proceeded on a ballistic trajectory to its entry point (6.54 deg north latitude, 4.46 west longitude) into the atmosphere of Jupiter. The Orbiter used its 400 Newton engine on July 27, 1995 to perform a deflection maneuver to keep from following the Probe into the atmosphere of Jupiter, and to retarget the Orbiter to the proper encounter conditions required for the Jupiter Orbit Insertion phase of the mission.
A close flyby (892 kilometer altitude) of the Jovian satellite Io occurred at 17:45:58 UT on Dec 7, 1995, during the Jupiter Orbit Insertion phase. This flyby allowed fields and particles science observations to be made and slowed the Orbiter down relative to Jupiter by nearly 200 meters/second in order to reduce the propellant required during the Jupiter Orbit Insertion (JOI). Remote sensing observations of Io were not made at this time due to an anomaly with the onboard tape recorder associated with high speed recording that was not well understood at the time of the flyby. Perijove at 4.00 Jupiter radii occurred at 21:53:44 UT on the same day. A few minutes after perijove passage, the Probe entered the Jovian atmosphere and began relaying data back to the Orbiter.
The Probe mission and data relay lasted