Shouldn Galileos speed be increasing as it nears Jupiter, not decreasing?
The speed that is posted daily is the speed of the orbiter with respect to the Sun. The Galileo orbiter is currently in an orbit around the Sun and is just past aphelion (the furthest point from the Sun) where the orbiter’s speed is the slowest in its orbit. However, if we look at a Sun-centered coordinate system, the orbiter is actually ahead of Jupiter (i.e. Jupiter is coming up from behind the orbiter). As Jupiter “catches up” to the orbiter, its gravitational attraction is actually slowing the orbiter down with respect to the Sun. Between one and two days prior to arrival the orbiter’s “forward” motion around the Sun will actually stop. Then, moving in the opposite direction (backwards), the orbiter speeds up again as it moves around the back side of Jupiter. While all of this is happening, the orbiter speed with respect to Jupiter is continuously increasing due to Jupiter’s gravitational attraction. The JOI maneuver (which involved firing the main engine for 45 minutes) slowed it
