If the probe had to be released before Galileo was in orbit around Jupiter, why not wait until Galileo was quite close to Jupiter?
Galileo’s approach trajectory to Jupiter had the spacecraft flying by Jupiter, much like Voyager. The spacecraft could only enter orbit by performing a braking maneuver known as Jupiter Orbit Insertion, or JOI. JOI was a huge maneuver that, unlike any other maneuver, required the use of Galileo’s 400 Newton thrusters (the Orbit Deflection Maneuver, discussed below, used the 400N thrusters as a “practice run” for JOI). Since the Probe was attached to the Orbiter right below the 400N engine (see illustration), the 400N engine could not be fired until the Probe was released, and, therefore, the Orbiter and Probe could not possibly enter orbit around Jupiter linked together. Even if entering orbit together were possible, keep in mind that the combined Orbiter/Probe would have been much more massive than the Orbiter alone. This means that it would have taken much more propellant to perform JOI successfully. Assuming the Probe would be released before Jupiter arrival, there were two factors
