Launched on October 18, 1989, the Galileo spacecraft has used
planetary gravity assists to put itself on a trajectory to Jupiter. This
technique allows the spacecraft to change velocity as it passes close
by a planet. During Galileo's six-year path to Jupiter it has travelled
past Venus once and Earth twice, with two passes through the asteroid
belt that provided flybys of Gaspra and Ida.
Galileo consists of two principal parts: an orbiter and an atmospheric
probe. The probe was released from the orbiter 148 days before arrival
at Jupiter and entered Jupiter's atmosphere to study the temperature,
pressure and composition of the cloud layers and relay its data back
to the orbiter. The Galileo probe arrived at Jupiter on December 7,
1995. Preliminary details about what the Probe discovered is available
from the Galileo Probe home pages.
Now complete with the probe mission, the Galilo is in orbit about
Jupiter. During its two year orbital mission, close flybys are planned
of the Galilean satellites Europa, Ganymede, and Callisto (one each
on ten of eleven orbits). Io, another Galilean moon, was scheduled to
be visited with a close flyby just prior to the probe entry into Jupiter;
however, this activity was cancelled due to a tape recorder problem
. Galileo will also study Jupiter's atmosphere and magnetosphere during
each of its orbits around Jupiter.