The Galileo mission, named in honour of Italian astronomer Galileo Galilei who in 1610 discovered the four large moons orbiting Jupiter, received Congressional approval for flight in 1977, targeting a Space Shuttle launch in late 1981.
It fired its main engine on Dec. 7, 1995, becoming the first artificial satellite of Jupiter
By that time, Pioneer 10 and 11 had completed the first exploratory flybys of Jupiter and the more sophisticated Voyager 1 and 2 had just set out for their respective flybys.
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The new project, first known as Jupiter Orbiter/Probe (JOP), intended to place a sophisticated spacecraft into orbit around the largest planet in the solar system for in-depth observations over two years. In addition, prior to orbital insertion, the spacecraft would release a probe to make in-situ observations during its plunge through Jupiter’s upper atmosphere, relaying the data to Earth via the orbiter, before succumbing to extreme environmental conditions.
The orbiter fired its main engine on Dec. 7, 1995, becoming the first artificial satellite of Jupiter with an initial orbital period of 198 days. Galileo soon began its nominal two-year science mission during which it completed 11 orbits around Jupiter.
Mission planners designed these trajectories to optimize studies of Jupiter’s magnetosphere and to enable encounters with Jupiter’s largest moons Callisto, Europa, and Ganymede.
Galileo also studied Jupiter’s ring system, composed largely of dust derived from impacts with the planet’s four small inner moons Thebe, Amalthea, Adrastea, and Metis, as well as the Great Red Spot and other atmospheric phenomena.
On Dec. 7, 1997, NASA managers approved the two-year Galileo Europa Mission (GEM) extension that included eight consecutive encounters with Europa to study that moon’s frozen surface in great detail.