ESA’s Juice uses Earth gravity to boost speed and test instruments en route to Jupiter
The Jupiter Icy Moons Explorer spacecraft flew within 8,640 km of Earth on 28 September, using the planet’s gravity to alter its trajectory by 20° and add 3.5 km/s of speed while conserving fuel. The encounter also served as a real-world test of its scientific instruments.
On 28 September, ESA’s Jupiter Icy Moons Explorer (Juice) skimmed the outer atmosphere of Earth at an altitude of 8,640 km above the Indian Ocean, executing a gravity-assist that turned its course by 20° and boosted its speed by 3.5 km/s while using only a small amount of reserved fuel. The maneuver required ultra-precise navigation and only one small correction out of six planned opportunities in the preceding weeks. In addition to reshaping its trajectory, the flyby provided a valuable opportunity to calibrate and validate Juice’s suite of ten scientific instruments, following earlier tests during a lunar-Earth assist in 2024 and comet 3I/ATLAS observations in 2025.
Teams coordinated instrument operations to prioritize activities that would best prepare the payload for the demanding observations of Jupiter’s icy moons. While passing through Earth’s magnetotail, Juice measured magnetic fields and charged particles, data that may be linked with simultaneous observations from the European-Chinese Smile mission. The spacecraft will conduct a third Earth encounter in January 2029 to set its final path for arrival at Jupiter in 2031, where it will perform 35 flybys of Ganymede, Callisto and Europa.
Why it matters
The maneuver saves fuel for Juice’s Jupiter mission and validates its instruments, crucial for studying potentially habitable moons.
In this story
