Juice to fly past Earth for third gravity assist

The European Space Agency's Jupiter Icy Moons Explorer (Juice) will return to Earth on 28 September 2026, with flight controllers guiding it close to the planet to alter its speed and direction en route to Jupiter. Juice began its journey almost 3.5 years earlier, launching in April 2023 from Europe's Spaceport in French Guiana. Since then controllers have guided it through the first ever lunar-Earth flyby—a braking manoeuvre that sent it on a shortcut to Jupiter via Venus—and then a Venus flyby that bent its orbit and added a little speed.

To avoid needing enormous amounts of fuel to reach the right final track, Juice will make two further Earth flybys. On 28 September 2026 it will come within 8640 km of Earth. This interaction will set it up for a final Earth flyby in January 2029, putting Juice onto the optimum path to intercept Jupiter in July 2031. The upcoming flyby will deflect its trajectory by about 20 degrees and increase its velocity by about 3.5 km/s, with closest approach over the Indian Ocean at 13:45 CEST (11:45 UTC).

Between 15 and 30 minutes before closest approach, Juice will pass over Australia from the northeast to the northwest. Amateur astronomers using the right telescope or binocular equipment may be able to track it, and trajectory data are available.

The excerpt explains that flying straight to Jupiter and braking hard there would have been much quicker but would have required an enormous rocket and an unthinkable amount of fuel to build enough speed, plus a huge amount more fuel to stop Juice from flying straight past Jupiter. Instead, flight controllers devised a strategy to use planets and their gravity: Earth, the Moon and Venus are helping Juice pick up speed and adjust its path almost entirely for free. This leaves plenty of fuel in its tanks to enter orbit around Jupiter in 2031 and then around the giant moon Ganymede in 2034.

The flyby's navigation campaign began on 17 August. Six timeslots were set aside—including at four weeks, two weeks, one week, and three days before the flyby—to make tiny corrections to Juice's trajectory, ensuring it arrives with exactly the right angle and velocity for an optimum gravity assist.