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The European Space Agency’s Juice mission is making two historic firsts on its long journey to study the potential habitability of Jupiter’s icy moons.
The Juice, or Jupiter Icy Moons Explorer, spacecraft — launched in April 2023 — is conducting the first flyby of the moon and Earth in succession, and the first double gravity assist maneuver, this week. This process will serve as a slingshot, allowing Earth’s gravity to put the brakes on Juice’s current trajectory and redirect it for a flyby of Venus in August 2025.
Then, Juice can take a shortcut through the solar system and be on track to arrive at Jupiter and its moons in July 2031.
Juice flew by Earth’s moon on August 19 at 5:16 p.m. ET. Next, it will zip by Earth nearly 25 hours later at 5:57 p.m. ET on August 20. The space agency is providing animated tracking of the spacecraft, and some people with binoculars or telescopes in Southeast Asia may be able to see Juice as it flies directly overhead.
All the while, Juice’s two cameras are taking photos during the flyby and sending them back to Earth, where they are appearing on the agency’s blog.
An image captured by one of Juice’s cameras on Monday shows color differences in large-scale features on the lunar surface.
But the pioneering maneuvers are also incredibly daring and challenging, and one small mistake could knock Juice off course and end the mission.
“It’s like passing through a very narrow corridor, very, very quickly: pushing the accelerator to the maximum when the margin at the side of the road is just millimetres,” said Ignacio Tanco, Juice’s Spacecraft Operations Manager, in a statement.
High-risk, high reward
On average, Jupiter is located 497 million miles (800 million kilometers) from Earth, so reaching it without an enormously powerful rocket or thousands of pounds of onboard propellant requires some careful strategizing by mission planners. And the plan for Juice’s journey has been in the works for 20 years.
Using the gravity of planets like Earth and Venus can make just the right adjustments to Juice’s trajectory to put it in the proper direction and at the optimal speed to reach Jupiter and go into orbit without whizzing right by the planet.
Gravity assists can speed up or slow down spacecraft, depending on how they are used, and they conserve fuel and allow spacecraft to be outfitted with a multitude of scientific instruments.
The double flyby of Earth and the moon will slow down Juice just enough so it can fly by Venus for an energy boost next year before looping around our planet twice for more boosts, according to the agency.
Minor adjustments to Juice’s flight pattern put the spacecraft on track to arrive at the moon and Earth at the right time and speed while coming extremely close to both. Juice first passed 434 miles (700 kilometers) from the moon’s surface and then it will fly 4,229 miles (6,807 kilometers) from Earth’s surface.
The moon’s gravity slightly bent Juice’s path so it receives a much larger gravity assist from Earth. But every detail of the dual flyby has to go perfectly.
“For a typical gravity assist, spacecraft operations have to be highly precise,” said Angela Dietz, Juice Spacecraft Operations Engineer, in a statement. “For a double flyby, they must be pinpoint.”
Operators using ground stations around the world will closely track Juice’s data before, during and after the flyby to make any necessary adjustments at a moment’s notice.
The flight control team has trained and rehearsed for the flyby in case any anomalies occur so they can quickly get Juice back on track.
“A lunar-Earth flyby has never been attempted before,” Dietz said. “There are risks, but all of Juice’s onboard systems have been rigorously tested, and we are well prepared.”
Although Juice was designed to explore the cold, dim reaches of the solar system near Jupiter, it will be closer to the sun during the flyby and must tilt its solar arrays to prevent overheating. The spacecraft will also aim its high-gain antenna at the sun to act as a heat shield, while its low-gain antenna will remain pointed at Earth to relay communications during the flyby.
A chance opportunity
Telescopes and observatories have been tracking Juice’s close approach throughout of the summer.
On July 6, an object triggered the automated NASA and ESA warning systems that monitor for potentially hazardous asteroids. The object was estimated to be 164 feet (50 meters) in diameter and on track to pass very close to Earth and the moon.
But it was just Juice, and given that it has large, reflective solar arrays, the spacecraft appeared much larger and brighter, like an asteroid. And the agencies have confirmed that Juice poses no risk to Earth or the moon during its flyby.
Juice will also activate all 10 of its scientific instruments during the double flyby to calibrate them before arriving at Jupiter. In addition to testing the instruments, the mission team could also make some discoveries about Earth and the moon while the instruments operate.
The RIME team, in charge of the Radar for Icy Moon Exploration instrument, is eager to gather data on electronic noise within the spacecraft that seems to disturb the instrument. This could be one of only a few chances to measure any impacts to the instrument before it arrives at Jupiter.
During the flyby, RIME will take eight minutes to make observations while the other instruments shut off or go into quiet mode, and that data could help the mission team fix the noise problem.
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