Juice's 2024 Moon-Earth assist

The 2024 encounter

On 19-20 August 2024, Juice completed the first lunar-Earth gravity assist. It passed the Moon, then Earth about a day later, and emerged on a path toward Venus.[2]

Gravity bends a route

Gravity assists use a planet's or moon's gravity to redirect a spacecraft and alter its speed relative to the Sun. ESA planned the Moon pass as a small adjustment before the much larger Earth encounter, so the first body could make the second more effective. A carefully chosen approach lets gravity do part of the route-shaping work without a major onboard burn; these manoeuvres conserve fuel and leave more propellant for later stages. The navigation had to be precise because even a small error could send Juice onto the wrong trajectory.[1]

Speed is not direction

The Moon encounter increased Juice's speed relative to the Sun by 0.9 kilometres per second. Earth's flyby then reduced it by 4.8 kilometres per second and deflected the trajectory by about 100 degrees, placing the spacecraft on its Venus leg. ESA estimated that the combined manoeuvre would save 100-150 kilograms of fuel.[2]

Venus before Jupiter

Venus was the next encounter, not an immediate outward leg: ESA's 2024 plan said that flyby would send Juice back toward Earth.[2]

Juice has since passed Venus and completed another Earth flyby on 28 September 2026. ESA describes that encounter as the third of four planned assists; one more Earth flyby is planned for 2029, before Jupiter arrival in 2031. The 2024 double pass was one link in a deliberately staged route, not a direct launch toward the giant planet.[3]