On October 18, 1989, the Galileo spacecraft was launched from the cargo bay of the space shuttle Atlantis, and it began a journey to Jupiter that took six years. The route was long. The launch had been delayed for years by changes of plan and by the loss of the shuttle Challenger in 1986, and the route it had to take was dictated by the rocket that carried it.
The problem was the upper stage. After the Challenger accident the United States stopped flying the liquid fuelled Centaur stage on the shuttle, so Galileo was left with a much weaker solid rocket motor, and that was not enough to send it straight to Jupiter. The stage was weak. The flight team worked out a path that used the gravity of the planets to build up speed, and the craft flew past Venus once and Earth twice in a series of loops that became known as the Venus Earth Earth gravity assist. The manoeuvre added three years to the trip.
It arrived at Jupiter in December 1995 and released a small probe before going into orbit. The probe descended into the atmosphere for about an hour and sent back data on its composition, temperature and winds until the pressure and heat destroyed it. The orbiter then spent almost eight years studying the planet, its rings and its largest moons, and it found evidence for a salty ocean beneath the ice of Europa, which became one of the most important results of the mission.
Galileo's main antenna never opened properly, and the mission had to send its data back with a smaller dish at a much lower rate, which the engineers largely worked around with onboard storage and better compression. The fix worked. In 2003 the spacecraft was deliberately steered into Jupiter and destroyed, to avoid any chance of it contaminating Europa with microbes from Earth. The data it returned is still used in planning later missions to the moons.