The spacecraft made its closest approach to the Moon at 23:15 CEST (21:15 UTC) on August 19, followed by a near-Earth flyby just over a day later at 23:56 CEST (21:56 UTC) on August 20. During its passage 6,840 km above Southeast Asia and the Pacific Ocean, Juice captured images with its onboard monitoring cameras and gathered scientific data using eight of its ten instruments.
"The gravity assist flyby was flawless, everything went without a hitch, and we were thrilled to see Juice coming back so close to Earth," said Ignacio Tanco, Spacecraft Operations Manager for the mission.
This dual flyby maneuver was designed to alter Juice's trajectory by using the gravitational forces of the Moon and Earth. The Moon flyby increased the spacecraft's speed by 0.9 km/s relative to the Sun, while the Earth flyby reduced its speed by 4.8 km/s, steering Juice towards Venus. The overall effect of the flyby changed Juice's path by 100 degrees compared to its pre-flyby direction.
Despite the complexity and inherent risks of the operation, the flyby was executed with precision, saving the mission an estimated 100-150 kg of fuel. In the month leading up to the flyby, spacecraft operators made small adjustments to ensure Juice was on the correct trajectory, followed by continuous tracking from August 17 to 22.
Thanks to the successful launch on an Ariane 5 rocket in April 2023, Juice has some extra propellant reserves. This success during the lunar-Earth flyby ensures that the spacecraft can approach Jupiter's moon Ganymede more closely than initially planned, allowing for additional scientific observations.
"Thanks to very precise navigation by ESA's Flight Dynamics team, we managed to use only a tiny fraction of the propellant reserved for this flyby. This will add to the margins we keep for a rainy day, or to extend the science mission once we get to Jupiter," added Ignacio.
First Spaceborne Science Operations
While the primary objective was to adjust Juice's trajectory, the flyby also served as an opportunity to test the spacecraft's scientific instruments. All ten instruments were activated during the Moon flyby, with eight continuing to operate during the Earth flyby.
ESA plans to release images and spectral data gathered by Juice's instruments in the coming weeks, once the data has been transmitted back to Earth and analyzed. This will include high-resolution images of the Moon and Earth captured by Juice's scientific camera, JANUS.
"The timing and location of this double flyby allows us to thoroughly study the behaviour of Juice's instruments," explained Claire Vallat, Juice Operations Scientist. "It happens early enough in Juice's journey that we can use the data to prepare the instruments for arrival at Jupiter. And given how well we know the physical properties of Earth, the Moon, and the surrounding space environment, it's also the ideal location to understand how the instruments respond to a real target."
Next Destination: Venus
The lunar-Earth flyby redirected Juice's trajectory towards Venus, where it is scheduled for a flyby in August 2025. This encounter with Venus will propel the spacecraft back towards Earth, enabling two additional gravity assists in September 2026 and January 2029 before its eventual arrival at Jupiter in July 2031.
ESA's Jupiter Icy Moons Explorer, Juice, represents humanity's next significant venture into the outer Solar System. The mission aims to conduct detailed studies of Jupiter and its three major ocean-bearing moons-Ganymede, Callisto, and Europa. Juice will utilize a comprehensive array of remote sensing, geophysical, and in situ instruments to explore these moons as potential habitats for life.
The mission will also investigate Jupiter's complex magnetic, radiation, and plasma environment, studying its interactions with the moons and contributing to our understanding of gas giant systems across the Universe.
Launched aboard an Ariane 5 from Europe's Spaceport in Kourou in April 2023, Juice is currently on an eight-year cruise involving multiple flybys of Earth and Venus to slingshot it towards Jupiter. Once there, Juice will conduct 35 flybys of the three large moons before entering orbit around Ganymede.
Related Links
Juice at ESA
The million outer planets of a star called Sol
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