After a gravity assist maneuver using Earth and the Moon, JUICE heads toward Venus and beyond

ESA's Juice spacecraft is set to embark on a long journey to the Jupiter system. It will be the first spacecraft to fly between Earth and the Moon to perform a gravity assist maneuver

The first spacecraft to use gravity assist maneuverwas NASA's Mariner 10 in 1974. It used a gravity assist from Venus to reach Mercury. Such a maneuver is now a vital part of modern space travel.

The latest spacecraft to use gravity assist was the European Space Agency's (ESA) JUICE spacecraft.

ESA launched its JUICE spacecraft on 14 April 2023. Its ultimate destination is the Jupiter system and its icy moons Europa, Callisto and Ganymede. But it's a long journey, so the spacecraft has decided to take a shortcut by flying close to Earth and the Moon, using their gravity to gain speed and change its trajectory.

It's the first spacecraft to ever use the Earth and Moon for a gravity slingshot, and it took some pictures to share with us.

JUICE stands for Jupiter Icy Moons Explorer, and its mission is to study three moons with suspected oceans buried under layers of ice. It has a long way to go, and on long missions, fuel economy is critical. This slingshot maneuver between Earth and the moon is aimed at conserving fuel.

“The gravity assist flyby went flawlessly, everything went smoothly, and we were very happy to see JUICE return so close to Earth,” said Ignacio Tanco, spacecraft operations manager.

During its closest approach to Earth, JUICE passed over Southeast Asia and the Pacific Ocean at an altitude of just 6,840 km. It was a risky maneuver, but it saved between 100 and 150 kg of fuel.

This flyby of the Moon and Earth isn’t the only gravity assist JUICE will perform. It will fly by Venus next August, and by Earth on September 26 and in January 2029. All of these gravity assists will give JUICE a boost for its journey to Jupiter. JUICE will reach Jupiter in 2031, and all of these assists will give it more fuel when it gets there.

JUICE has completed its first gravity assist maneuver and will perform another maneuver with Venus in a year.

“Thanks to the very precise navigation performed by the ESA Flight Dynamics team, we were able to use only a small fraction of the fuel reserved for this flyby. This will increase the reserve we will have for a rainy day or to extend the scientific mission after arrival at Jupiter,” said Ignacio Tanco, head of space operations for the JUICE mission.

Modern orbiters are loaded with scientific instruments, antennas, and cameras. JUICE is no exception. Among all its instruments and scientific cameras, it carries two monitoring cameras called JMCs, or JUICE Monitoring Cameras. These are cameras with a resolution of 1024×1024 pixels and different fields of view. Their job is to monitor the spacecraft’s booms and antennas, and their work was especially important when they were deployed after launch.

ESA's Jupiter Icy Moons Explorer has two Juice Monitoring Cameras, or JMCs, which take images with different fields of view. Their main job is to monitor the spacecraft's components, but during their recent flyby they took images of the Earth and the Moon.

During the flyby, JUICE used its JMC to take images of the Earth and the Moon.

JUICE's 2nd camera captured this image of the Moon as it passed by on August 10. “A closer look reveals an accidental 'photobomber' – Earth appears as a dark circle outlined by a light crescent moon in the upper center of the image, peeking out from behind the spacecraft structure (look just above for the fuzzy blue patch, which itself is a ghost image caused by sunlight reflection)”

Eight of the ten instruments were used to collect scientific data from Earth, and all ten were used for the Moon.

“The timing and location of this double flyby allows us to closely study the behavior of the JUICE instruments,” explains Claire Vallat, a Juice operations scientist.

JMC 1 captured this image of the Moon during a lunar flyby.

JUICE's primary science camera is JANUS, the high-resolution optical camera. Its role is to obtain detailed images of the surfaces of Ganymede, Callisto, and Europa. The JUICE team used JANUS to obtain more than 400 early images of the Earth and Moon.

“After more than 12 years of work proposing, building and testing the instrument, this is the first opportunity to see first-hand data similar to those we will obtain in the Jupiter system from 2031 onwards,” says Pasquale Palumbo, a researcher at INAF in Rome and principal investigator of the team that designed, tested and calibrated the Janus camera.

The Moon's surface is spotted, as shown in this image by JANUS.

“Even though the flyby was intended solely to facilitate the interplanetary journey to Jupiter, all of the instruments on board the probe took advantage of the flyby near the Moon and Earth to acquire data, test operations and processing techniques – we had the advantage of already knowing what we were seeing,” Palumbo said.

The image of Earth was taken at dawn on August 20, 2024, by the JANUS optical camera on board JUICE. The image shows the island of Hawaii (dark spot on the left), the largest island of the Hawaiian archipelago in the central Pacific Ocean in the United States. The view is very low, and after a while, Earth left the field of view of JANUS.

These early mission images whet our appetites before the real fun begins in seven years. JUICE will reach the Jupiter system in July 2031, making 35 flybys of the gas giant’s icy moons. Then, in December 2034, it will enter orbit around Ganymede.

There is growing evidence that Europa, Ganymede, and Callisto have warm, salty oceans buried under thick layers of ice. These are prime targets in the search for life. But unfortunately, we don’t know for sure whether they can support life, or whether oceans exist at all.

Hopefully, JUICE will be able to tell us about it. But it couldn't have done so without those risky maneuvers early in the flight.