That is a nice explanation. However, it fails to answer the question posed to the assertion regarding gravity:
>> The gravity of the Earth absolutely changes the speed of the probe.
> Wait! Wouldn't Earth's gravity take away when departing just as much as given when arriving?
As I understand your contribution, it is congruent with Earth's velocity altering the speed of the probe, not Earth's gravity.
The flyby of Earth reduced Juice’s speed by 4.8 km/s relative to the Sun, guiding Juice onto a new trajectory towards Venus. Overall, the lunar-Earth flyby deflected Juice by an angle of 100° compared to its pre-flyby path.
I can see how your characterization of "goes shooting back" doesn't mean 180° change, but a change relative to where Venus will be as the probe interacts with Earth and arrives back to Venus.
I have a hard time understanding how the flyby fits in the overall plan however. This is the first Earth flyby, right? "Flybys en route: August 2024 Lunar-Earth, August 2025 Venus, September 2026 Earth, January 2029 Earth" [0] If so, the probe is not going "back" to Venus, because it hasn't been there yet. It has been on an orbit of a different ellipse than Earth and so this flyby is where it takes a left turn to head towards Venus for the first time.
As JUICE starts its first elliptical solar orbit, its distance to the Sun decreases. This results in an increase in speed—according to Kepler's second law of planetary motion—and the spacecraft overtakes Earth. [1]
Well, it's the gravity that alters the spacecraft's trajectory. If the Earth was massless then the craft would just sail by.
Here's a nice short-ish web page from NASA with nice details [1].
Yeah, "back" seems a little wonky. Maybe somebody got confused by earlier plans? Your second link, to the ESA video, is from 2017 and evidently isn't what they wound up with. According to that video the Vensus flyby was supposed to have been last October, and next encounter would be Mars. Or maybe they're thinking "back down to Venus's orbit."
The flyby of Earth reduced Juice’s speed by 4.8 km/s relative to the Sun, guiding Juice onto a new trajectory towards Venus. Overall, the lunar-Earth flyby deflected Juice by an angle of 100° compared to its pre-flyby path.
I can see how your characterization of "goes shooting back" doesn't mean 180° change, but a change relative to where Venus will be as the probe interacts with Earth and arrives back to Venus.
I have a hard time understanding how the flyby fits in the overall plan however. This is the first Earth flyby, right? "Flybys en route: August 2024 Lunar-Earth, August 2025 Venus, September 2026 Earth, January 2029 Earth" [0] If so, the probe is not going "back" to Venus, because it hasn't been there yet. It has been on an orbit of a different ellipse than Earth and so this flyby is where it takes a left turn to head towards Venus for the first time.
As JUICE starts its first elliptical solar orbit, its distance to the Sun decreases. This results in an increase in speed—according to Kepler's second law of planetary motion—and the spacecraft overtakes Earth. [1]
0. https://www.esa.int/Science_Exploration/Space_Science/Juice
1. https://sci.esa.int/web/juice/-/58815-juices-journey-to-jupi...