The Juice spacecraft, a European Space Agency mission to visit the icy moons of Jupiter, has just made a world’s first maneuver. This week, the craft swung back to Earth on its way to Jupiter and used both Earth and the moon’s gravity to slingshot it onward, in the first lunar-Earth flyby.
When you think about spacecraft traveling to distant parts of the solar system, you might imagine them pointing directly toward their targets and traveling in a straight line. But that uses an awful lot of fuel, as the spacecraft needs to overcome the gravity of various bodies. It is much more efficient in terms of fuel usage to travel in a series of circular orbits, gradually adjusting course to move out in a spiral pattern with the sun at the center. This takes more time but less of the precious fuel that is so heavy to carry.
That’s why spacecraft often leave Earth only to arrive back at our planet a few months or years later, performing a flyby maneuver. In Juice’s case, it launched in 2023, and has now swing back around to visit us again. By swinging around Earth, the spacecraft can get a boost to push it farther along its journey.
What makes this flyby unusual is that Juice didn’t only use the gravity of Earth — it also made use of the moon. It first flew past the moon, and then Earth, using the gravity of both to change speed and direction. It is now on course to do a flyby of Venus next year, before swinging by Earth twice more before being shot off toward Jupiter.
“The gravity assist flyby was flawless, everything went without a hitch, and we were thrilled to see Juice coming back so close to Earth,” says Ignacio Tanco, spacecraft operations manager for the mission, in a statement. “Thanks to very precise navigation by ESA’s Flight Dynamics team, we managed to use only a tiny fraction of the propellant reserved for this flyby. This will add to the margins we keep for a rainy day, or to extend the science mission once we get to Jupiter.”
As a bonus, the flyby also gave the scientists on the mission a chance to test out the spacecraft’s instruments. Among other data, the spacecraft snapped a stunning image of Earth as it passed by:
“The timing and location of this double flyby allows us to thoroughly study the behavior of Juice’s instruments,” explained Claire Vallat, Juice operations scientist. “It happens early enough in Juice’s journey that we can use the data to prepare the instruments for arrival at Jupiter. And given how well we know the physical properties of Earth, the Moon, and the surrounding space environment, it’s also the ideal location to understand how the instruments respond to a real target.”
Data from this flyby should be published within the next few weeks, including more high-resolution images of both Earth and the moon taken by the spacecraft’s JANUS camera.
