A spacecraft used Earth as a slingshot and bent its own path 20 degrees

Juice, the European Space Agency’s Jupiter Icy Moons Explorer, passed 8,640 kilometers above the Indian Ocean at 11:45 UTC on September 28, 2026, and left the encounter pointed 20 degrees away from where it had been heading and moving 3.5 kilometers per second faster. No engine burn produced that change. The spacecraft borrowed it from Earth’s gravity, in the third gravity assist of a journey that ends at Jupiter in July 2031.

The maneuver cost the mission almost nothing in fuel, which is the whole point. Propellant spent now is propellant missing later, when Juice has to brake into orbit around the giant planet and then around its largest moon. The route to Jupiter is stitched together from planetary encounters for exactly that reason.

The geometry of an Earth swing-by

A gravity assist swaps a small amount of motion with a planet. As Juice fell toward Earth and swung around it, the planet’s pull bent the spacecraft’s trajectory and, in the frame of the Sun, added speed. ESA’s own flyby release reports the closest approach at 13:45 Central European Summer Time, 8,640 kilometers over the Indian Ocean, with the 20-degree deflection and 3.5 kilometers per second gain as the result.

Space.com converted the speed gain into roughly 7,830 miles per hour and the distance into 5,370 miles in its report on the flyby. By ESA’s account this was the third gravity assist of the cruise, following the lunar-Earth assist of August 2024 and a Venus assist in August 2025, so the spacecraft has now used three different bodies as steering posts, and a fourth encounter, with Earth again, is still scheduled.

The navigation crew at ESA

Angela Dietz, Juice’s spacecraft operations manager, summed up the work in ESA’s release: the flyby required ultra-precise navigation in real time, and thanks to very careful planning the team used only a small amount of the propellant reserved for it. The navigation campaign had opened on August 17, according to ESA, and the team had six slots for course corrections in the four weeks before the encounter. Only one minor correction was needed.

Claire Vallat, the mission’s project scientist, had been blunt about the stakes in the lead-up. As quoted in a preview of the flyby, she said all flybys are risky and require very careful planning, though this Earth pass was operationally simpler than the lunar-Earth flyby of 2024 because the spacecraft’s instruments could be aimed at different targets.

Juice was due to cross over Australia 15 to 30 minutes before closest approach, within reach of amateur observers. The navigation camera also tested optical navigation techniques on images of the Moon.

Ten instruments, one test target

With Earth and the Moon as targets, Juice’s ten science instruments ran calibrations, with priority on those that matter at Jupiter. The JANUS camera returned high-resolution images of both bodies, and ESA says this was the third instrument-testing opportunity of the cruise, after lunar observations in 2024 and comet observations in 2025. Calibration windows ran from September 23 through October 3, according to the preview.

The route also took the spacecraft through Earth’s magnetotail, the stretched-out tail of the planet’s magnetic field. Magnetic field and charged-particle instruments measured it while the European-Chinese Smile mission, which watches auroras near the poles, observed from its own vantage, giving scientists a paired dataset that links conditions far from Earth with activity near the poles.

Remaining legs to Jupiter

The reason for all this care is what waits at the end. ESA describes the mission as a set of detailed observations of Jupiter and its three large ocean-bearing moons, Ganymede, Callisto and Europa, studied both as planetary objects and as possible habitats, with the wider Jupiter system treated as a prototype for gas giants elsewhere. Every kilogram of propellant saved at Earth becomes margin for the 2031 orbit insertion and the years of moon flybys that follow, which is why the operations team measured its success partly by how little fuel the encounter consumed.

This was not the last time Juice will use the planet. ESA’s mission overview lists a further Earth gravity assist in January 2029, after the lunar-Earth assist of August 2024 and a Venus assist in August 2025. The probe launched on April 14, 2023, aboard an Ariane 5 from French Guiana, carries 85 square meters of solar wings, and is due at Jupiter in July 2031.

Once there, Juice is planned to make 35 flybys of the moons Ganymede, Callisto and Europa, with Ganymede the mission’s main focus and the orbit around it set to begin in 2034, per the preview. A summary of the agency’s announcement repeats the January 2029 date for the final Earth pass. That 2029 pass is the next scheduled chance for the team to reshape the trajectory before the final approach to Jupiter.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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