Juice’s Bold Double Flyby Prep

Next month, ESA’s Jupiter Icy Moons Explorer (Juice) will carry out a daring and unprecedented maneuver – the first combined lunar-Earth flyby. This highly precise maneuver will harness the gravitational forces of the Moon and Earth in quick succession, bending Juice’s trajectory and lining it up for the next stage of its journey to Jupiter.

Juice is Europe’s first mission to explore the Jupiter system, and to reach its distant target, the spacecraft will perform a series of gravity assists – flybys that use the gravity of a large object like a planet or moon to change the spacecraft’s speed and trajectory. These gravity assists conserve fuel and allow Juice to be packed with as many scientific instruments as possible for exploring Jupiter’s intriguing icy moons.

The upcoming lunar-Earth flyby is particularly complex, as it involves two flybys back-to-back. On August 19th, Juice will pass just 700 km from the Moon’s surface at 23:16 CEST. Almost exactly 24 hours later, on August 20th at 23:57 CEST, it will perform a second flyby, passing 6807 km from Earth’s surface.

The strategy behind this daring maneuver is to harness the Moon’s gravity first to slightly bend Juice’s trajectory, improving the effectiveness of the much larger gravity assist from Earth. However, this dual flyby requires extraordinarily precise navigation and timing. As Angela Dietz, Juice Spacecraft Operations Engineer, explains, “For a typical gravity assist, spacecraft operations have to be highly precise. For a double flyby, they must be pinpoint.”

At ESA’s mission control center, teams across various departments are hard at work preparing for Juice’s lunar-Earth flyby. The Juice team has been performing a series of trajectory correction maneuvers to fine-tune the spacecraft’s path, ensuring it arrives at the Earth-Moon system with the precise angle and speed required.

During the critical flyby phase, Juice will maintain near-constant communication with mission control via ESA’s network of deep space antennas. The continuous stream of real-time telemetry data will enable the flight control and flight dynamics teams to closely monitor Juice’s position, speed, and trajectory, allowing them to rapidly respond to any anomalies or deviations.

As Juice passes within the altitude of geostationary and medium-Earth orbits during the Earth flyby, ESA’s Space Debris Office will thoroughly scan its trajectory to ensure a safe passage, free from other satellites or space debris.

To prepare for this spaceflight first, the flight control team has been conducting rigorous training campaigns. They have rehearsed recovery procedures to swiftly bring the spacecraft back on track if a “safe mode” is triggered while passing behind the Moon. Additionally, they have practiced planning and executing emergency trajectory correction maneuvers.

During a recent dry run, the team commanded Juice to operate its various cameras and scientific instruments, precisely as it will during the actual flybys. This exercise ensured that all systems behave as expected, while also providing a rare opportunity to test and calibrate the instruments on Earth-like objects, preparing them for their scientific activities at Jupiter.