Juice's Historic Lunar-Earth Flyby: Key Details

Juice's Historic Lunar-Earth Flyby: Key Details
by Simon Mansfield
Sydney, Australia (SPX) Jul 16, 2024

Juice is set to achieve a remarkable milestone with its unprecedented lunar-Earth flyby, the first of its kind. This double gravity assist maneuver is critical for adjusting the spacecraft's trajectory, but it is a complex and high-risk operation.

Since Juice's launch in April 2023, this flyby marks the beginning of its intricate journey towards Jupiter. Earth's gravity will redirect Juice, slowing it down to prepare for a Venus flyby in August 2025. These sequential gravity assists, including two from Earth, will significantly enhance Juice's velocity, akin to the effect of consuming three espressos in quick succession.

Why This Maneuver Is Essential
Jupiter is roughly 800 million kilometers from Earth. Direct travel to the giant planet would require an impractical 60,000 kg of propellant. Moreover, Juice would need additional fuel to slow down upon arrival to avoid overshooting into space.

To address these challenges, Juice is navigating a meticulously planned route, using planetary gravity to adjust its speed and direction. This strategy, developed over 20 years, ensures Juice arrives at Jupiter with the necessary trajectory.

Counterintuitively, this lunar-Earth flyby aims to decelerate rather than accelerate Juice. Utilizing this maneuver to slow down allows for a more efficient route through the inner Solar System. An alternative acceleration towards Mars would have delayed the next planetary flyby.

Execution of the Flyby
Mission operators have fine-tuned Juice's trajectory for optimal arrival first at the Moon, then Earth, ensuring precise timing, speed, and direction. Although confident, the team acknowledges the unprecedented nature of this challenge.

Ignacio Tanco, Juice's Spacecraft Operations Manager, likens the task to "passing through a very narrow corridor, very, very quickly: pushing the accelerator to the maximum when the margin at the side of the road is just millimetres."

Juice will make a close approach to both celestial bodies, requiring real-time, precise navigation. From August 17-22, continuous communication with global ground stations will allow operators to monitor and adjust Juice's course meticulously.

Bonus Scientific Opportunities
In addition to its navigational objectives, Juice will activate its ten science instruments during the flyby, offering a unique chance to gather data from the Moon and Earth.

This flyby serves as a valuable testing ground for instrument calibration and problem resolution, particularly for the Radar for Icy Moon Exploration (RIME) instrument, which is currently affected by electronic noise. The close approach to the Moon on August 19 provides a critical opportunity for the RIME team to assess and address this issue. During the eight-minute closest approach, RIME will operate solo, gathering data to refine noise-correction algorithms.

For enthusiasts, Juice will be visible passing over Southeast Asia and the Pacific Ocean. Observers with powerful binoculars or telescopes might catch a glimpse of the spacecraft. Trajectory data is available for those interested in tracking the flyby.