As JUICE struggles with antenna deployment, program manager highlights status of the mission

by Bella Richards

The European Space Agency’s (ESA) latest interplanetary mission that is set to explore Jupiter and its three largest Moons, the Jupiter Icy Moons Explorer (JUICE), successfully launched on Friday, April 14, has been touted as a near-perfect feat. JUICE had little-to-no issues during the launch sequence, right from blasting off atop an Ariane 5 rocket from the Centre Spatial Guyanais (CSG) in Kourou, French Guiana within a one-second launch window, to deploying its massive solar arrays.

Now it has been a few weeks since JUICE launched and began its voyage to the outer Solar System, and over the next few weeks, the spacecraft will begin deploying a 16-meter-long radar antenna, 10.6-meter-long magnetometer boom, and various other instruments to aid its study of the Jovian planet and its largest Moons – Ganymede, Callisto, and Europa. While the spacecraft’s mission up to this point has been pretty smooth-sailing, ESA announced on April 28 that JUICE’s radar antenna was having trouble with releasing from its mounting bracket — which, in turn, is preventing the antenna from fully deploying as expected.

To learn more about the spacecraft’s launch, the current status of the mission, and what’s next for JUICE teams, NSF sat down with JUICE program manager Giuseppe Sarri of ESA.

JUICE’s launch was “perfect”

The spacecraft, developed by Airbus Defence and Space, arrived in French Guiana on Feb. 9, 2023, with the launch date set for months later on Thursday, April. 13. However, lightning warnings pushed back the attempt by one day, with JUICE finally lifting off on Friday, April 14 from pad ELA-3 at 12:14 UTC (9:14 AM local), marking the Ariane 5’s 116th launch, and Arianespace’s first for the year.

At the moment of liftoff, Ariane 5’s twin solid rocket boosters ignited, followed shortly before by the ignition of its Vulcain 2 main engine, which produces 140 T of thrust, seven seconds before launch. Then, two minutes and 16 seconds after launching, the 31-meter-tall solid rocket boosters were jettisoned.

“The launch was really perfect,” Sarri said. In fact, as JUICE was placed into an escape trajectory to outrun the Sun’s gravitational pull, ground teams were planning for an Orbital Correction Manoeuvre, also dubbed the launcher injection correction. However, due to the Ariane 5’s perfect precision and the accuracy of the launch time, the teams were able to avoid the maneuver altogether, saving the spacecraft some fuel for future use at Jupiter.

To add to the complexity of its launch and trajectory to Jupiter, JUICE had the added burden of an extremely tight launch window of one second to achieve its future flybys. “To get to Jupiter, you have to have a super powerful rocket, but it has to be two or three times more powerful than the Ariane 5”, Sarri said. While the soon-to-be-retired Ariane 5 boasts almost 30 years of reliability, it doesn’t have enough power to fly JUICE straight to Jupiter. “Therefore, we needed to increase the speed and we will do this with a gravity assist maneuver” – which utilizes the gravity of other planets to increase its velocity.

JUICE will complete a first-of-its-kind flyby of the Earth-Moon system called a Lunar-Earth Gravity Assist (LEGA) in 2024, a Venus flyby in 2025, and an Earth flyby in both 2026 and 2029 before arriving at Jupiter in 2031.

To ensure JUICE will be able to achieve these flybys, it needed to launch when both Earth and Jupiter were in perfect alignment, which allows the spacecraft to be placed on the fastest trajectory out to the Jovian system. However, this perfect alignment doesn’t happen every day, Sarri explained. JUICE was given a launch opportunity at a precise time each day from April 13 to the end of April, and if none were successful, the spacecraft would have to re-attempt a launch in August. If August were to also be unsuccessful, JUICE would then have to try again next year, with Sarri adding a launch in 2024 would have added “a lot of financial implications” to the already $1.7 billion mission.

After escaping the Earth-Moon system, spacecraft separation occurred at T+27:45, with the acquisition of signal (AOS) scheduled shortly after, at around T+32 minutes. However, AOS occurred at 10:05 AM local time (T+51 minutes), with JUICE’s first signal (from space) reaching the New Norcia Ground Station in Australia.

While the broadcast teams at the European Space Operations Centre (ESOC) in Germany explained that the AOS was slightly late, Sarri claimed it was right on time. He explained that there is a range of about 15 minutes in which the AOS is expected to occur, which is typically right after the spacecraft stabilizes in orbit.

“This stabilization depends on the way the spacecraft is released,” Sarri said. “The stabilization is done by the attitude control system in the spacecraft, and it takes some time, which is impossible to predict precisely. If the spacecraft is released and has a little bit of rotation, it takes a little bit more time to stabilize.”

While the AOS didn’t occur immediately as some predicted it would, Sarri said: “We acquired the signal in the middle of the signal acquisition period, so it was okay, but people did not know that”.

The last key milestone on launch day was the deployment of the largest solar arrays to ever be flown into interplanetary space – measuring 27 meters from tip to tip. During launch, the arrays were neatly folded against the sides of the spacecraft, with the two wings successfully extending away from JUICE at 10:34 AM local time on Friday (T+ 80 minutes). Sarri said that milestone was the biggest relief as the arrays are paramount to the operation of the spacecraft.

Challenges ahead for JUICE

Jupiter is just over 890 million kilometers away from Earth, and JUICE will have to navigate beyond the asteroid belt and complete several gravity-assist flybys to maintain speed and reach the planet.

“The first big challenge is to have a spacecraft that is fully functional, and in the next three months we should know [that],” Sarri said. “We have to go through the asteroid belt which is tied between Mars and Jupiter. Normally, there is no particular issue because the rest of the space is empty but still, we have to go to a place in which there is more than just one asteroid.”

While the eight-year journey toward Jupiter should mostly be smooth-sailing, Sarri said the biggest challenge will be when JUICE arrives at the Jovian planet. “When we arrive at Jupiter, we [JUICE] are going so fast”, Sarri said, as the spacecraft’s speed will be extraordinarily fast after escaping the gravitational pull of the Sun. “When we [JUICE] arrive at Jupiter, it may pass by but not be captured by its gravity, so we have to brake and therefore have an engine which we will use not to accelerate, but to brake,” he said.

“The Jupiter insertion maneuver is a very critical maneuver, because it’s life-threatening to the mission – if we don’t do it right, we will either pass by or crash into Jupiter, and that’s one of the big challenges.” JUICE is equipped with two titanium propellant tanks and a 425-Newton main engine, and 20 additional small thrusters, which will be used for the spacecraft’s orbital insertion at Jupiter. The chemical propulsion system was integrated into the spacecraft in April 2020.

Jupiter’s largest Moon, Ganymede, is also the only moon known to generate its own magnetic field and, therefore, will pose risks to the spacecraft as it enters into its orbit. Furthermore, any electromagnetic fields generated by the spacecraft itself must not interfere with JUICE’s sensitive scientific instruments. As such, the spacecraft is designed with quiet motors to make them magnetically clean. Furthermore, JUCE is equipped with shields and special protective vaults to protect it from the extreme temperature differences it will experience during its mission, namely at Venus and Jupiter.

However, Sarri said that scientists’ knowledge of the radiation around Jupiter is “not very precise”, so they may find that the radiation levels around Jupiter are worse or better than expected. “Jupiter is a new world full of the unknown”, the program manager said. “We will just have to see how to deal with it, but I do not expect any major trouble before we get to Jupiter”.

A few of the many complex and hazardous environments JUICE will endure while in orbit around Jupiter. (Credit: ESA)

What’s next for JUICE

JUICE is carrying a suite of ten instruments onboard, all developed by ESA and NASA with contributions from the Japanese Aerospace Exploration Agency (JAXA) and the Israel Space Agency.JUICE has already started the commissioning of its instruments, which is expected to last about three months. “So far, things are going well”, Sarri said. “Our plan is by the middle of July to have the spacecraft ready, and we are starting now to deploy the first antenna.”

However, as aforementioned, ESA announced on April 28 that teams were having issues with deploying the spacecraft’s 16-meter-long radar antenna from its mounting rack.

JUICE teams at ESA’s mission control center in Darmstadt, Germany are working diligently to free the antenna from its mount. Teams have managed to deploy the antenna to about a third of the expected fully extended length, with the antenna showing more signs of movement every day. Teams currently believe that a tiny pin near the antenna deployment system is stuck, and has yet to release itself from the area surrounding the antenna and the deployment mechanism. Given the size of the pin, just millimeters of movement could fully release the antenna.

In an effort to try and force the release of the antenna, JUICE teams are planning to burn the spacecraft’s engine, which would shake the spacecraft and hopefully free the antenna, followed by several rotations of the spacecraft itself. These rotations would heat up the antenna and its mount, which are currently hiding in the cold shadow of the spacecraft.

It should be noted, though, that the antenna is the only major issue on the spacecraft that teams are tracking. JUICE has performed excellently up to this point and teams are anticipating a smooth commissioning process.

While JUICE has an eight-year journey ahead, its arrival at Jupiter will be jam-packed. Between July 2031 and November 2034, JUICE is expected to complete 35 icy moon flybys. The spacecraft will complete two 400 km approaches at Europa to search for biosignatures, pockets of water, and to understand its geology, surface, and subsurface. After Europa, JUICE will make several approaches at Callisto, which has one of the oldest surfaces in the solar system, to learn about the environment around Jupiter during its early years as a planet.

Lastly, in 2034, JUICE will enter orbit around Ganymede, becoming the first spacecraft to enter the orbit of a moon other than our own. JUICE will study the vast ocean that may be hidden under its icy surface and will determine if the Moon possesses the necessary conditions to sustain life. While it will make a 500-kilometer approach at Ganymede when it is in orbit, JUICE may aim for a 200-kilometer approach if it has extra fuel.

To conclude its mission, JUICE will deorbit and crash into Ganymede, since there is no risk the spacecraft will contaminate the potential liquid ocean under its icy crust.

JUICE’s mission up until launch day was an 11-year culmination of work from ESA, Airbus Defence and Space, Arianespace, and the other contributing member states involved. It was selected in 2012 as an L-class mission as part of ESA’s Cosmic Vision Programme, which is focused on developing European-led space science missions that launch at least once a decade.

NASA’s upcoming Europa Clipper mission, which is set to launch in 2024 and study Europa, will complement JUICE and its scientific study of the Jovian icy moons. In a pre-launch briefing on April 6th, Olivier Witasse, JUICE’s project scientist, said the two agencies are already discussing joint science opportunities for the two spacecraft when they are both at Jupiter.

(Lead image: artist’s illustration of JUICE fully deployed in space. Credit: ESA)

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