# Jupiter Icy Moons Explorer

The Jupiter Icy Moons Explorer (Juice, formerly JUICE) is an interplanetary spacecraft on its way to orbit and study three icy moons of Jupiter: Ganymede, Callisto, and Europa. These planetary-mass moons are planned to be studied because they are thought to have significant bodies of liquid water beneath their frozen surfaces, which would make them potentially habitable for extraterrestrial life.
Juice is the first interplanetary spacecraft to the outer Solar System planets not launched by the United States and the first set to orbit a moon other than Earth's Moon. Launched by the European Space Agency (ESA), from Guiana Space Centre in French Guiana on 14 April 2023, with Airbus Defence and Space as the main contractor, it is expected to reach Jupiter in July 2031 after four gravity assists and eight years of travel. In December 2034, the spacecraft will enter orbit around Ganymede for its close-up science mission. Its period of operations will overlap with NASA's Europa Clipper mission, which was launched in October 2024.

## Background

The mission started as a reformulation of the Jupiter Ganymede Orbiter proposal, which was to be ESA's component of the cancelled Europa Jupiter System Mission – Laplace (EJSM-Laplace). It became a candidate for the first L-class mission (L1) of the ESA Cosmic Vision Programme, and its selection was announced on 2 May 2012.
In April 2012, Juice was recommended over the proposed Advanced Telescope for High Energy Astrophysics (ATHENA) X-ray telescope and a gravitational wave observatory (New Gravitational wave Observatory (NGO)).
In July 2015, Airbus Defence and Space was selected as the prime contractor to design and build the probe, to be assembled in Toulouse, France.
By 2023, the mission was estimated to cost ESA 1.5 billion euros ($1.6 billion).

## Spacecraft

The main spacecraft design drivers are related to the large distance to the Sun, the use of solar power, and Jupiter's harsh radiation environment. The orbit insertions at Jupiter and Ganymede and the large number of flyby manoeuvres (more than 25 gravity assists, and two Europa flybys) require the spacecraft to carry about 3,000 kg (6,600 lb) of chemical propellant. The total delta-V capability of the spacecraft is about 2,700 m/s (6,000 mph).
Juice has a fixed 2.5 meter diameter high-gain antenna and a steerable medium-gain antenna; both X- and K-band will be used. Downlink rates of 2 Gb/day are possible with ground-based Deep Space Antennas. On-board data storage capability is 1.25 Tb.
The Juice main engine is a hypergolic bi-propellant (mono-methyl hydrazine and mixed oxides of nitrogen) 425 N thruster. A 100 kg multilayer insulation provides thermal control. The spacecraft is 3-axis stabilized using momentum wheels. Radiation shielding is used to protect onboard electronics from the Jovian environment (the required radiation tolerance is 50 kilorad at equipment level).
The Juice science payload has a mass of 280 kilograms (620 lb) and includes the JANUS camera system, the MAJIS visible and infrared imaging spectrometer, the UVS ultraviolet imaging spectrograph, RIME radar sounder, GALA laser altimeter, SWI submillimetre wave instrument, J-MAG magnetometer, PEP particle and plasma package, RPWI radio and plasma wave investigation, 3GM radio science package, the PRIDE radio science instrument, and the RADEM radiation monitor. A 10.6 meters (35 ft) deployable boom will hold J-MAG and RPWI, a 16 meters (52 ft) long deployable antenna will be used for RIME. Four 3 meters (9.8 ft) booms carry parts of the RPWI instrument. The other instruments are mounted on the spacecraft body, or for 3GM, within the spacecraft bus.

## Timeline
### Launch

Juice was launched into space on 14 April 2023 from the Guiana Space Centre on an Ariane 5 rocket. This was the final launch of an ESA science mission using the Ariane 5 vehicle, and was the second to last launch of the rocket overall.
The launch was originally scheduled for 13 April 2023, but due to poor weather the launch was postponed. The next day a second launch attempt succeeded, with liftoff occurring at 12:14:36 UTC. After the spacecraft separated from the rocket, it established a successful radio signal connection with the ground at 13:04 UTC. Juice's solar arrays were deployed about half an hour later, prompting ESA to deem the launch a success.

### Trajectory

Following the launch, there will be multiple planned gravity assists to put Juice on a trajectory to Jupiter:
* A flyby of the Earth–Moon system in August 2024
* Venus flyby in August 2025
* Second flyby of Earth in September 2026
* A third and final flyby of Earth in January 2029
Juice will pass through the asteroid belt twice. A flyby of the asteroid 223 Rosa was proposed to occur in October 2029, but was abandoned to save fuel for the primary Jovian mission.
Gravity assists include:
* Interplanetary transfer (Earth, Venus, Earth, Earth)
* Jupiter orbit insertion and apocentre reduction with multiple Ganymede gravity assists
* Reduction of velocity with Ganymede–Callisto assists
* Increase inclination with 10–12 Callisto gravity assists

### Summary of intended Jupiter mission phases

The main characteristics of the Jupiter reference tour are summarised below (source: Table 5-2 of ESA/SRE(2014)1). This scenario assumed an early June 2022 launch, however, the delta-V requirements are representative due to the rather short, repetitive orbital configurations of Europa, Ganymede and Callisto.
| Event | Duration | Delta-V notes |
| Jupiter orbit insertion: When it arrives in the Jovian system in July 2031, Juice will first perform a 400 km (250 mi) Ganymede gravity assist flyby to reduce spacecraft velocity by ~300 m/s (670 mph), followed by ~900 m/s (2,000 mph) Jupiter orbit insertion engine burn ~7.5 hours later. Finally, a Perijove Raising Manoeuvre (PRM) burn at apoapsis will raise the periapsis of Juice's initial 13x243 Jovian radii elongated orbit to match that of Ganymede (15 Rj). | 186 days | 952 m/s (2,130 mph). |
| 2nd Ganymede flyby to initial encounter with Callisto: 2nd, 3rd and 4th Ganymede flyby to reduce the orbital period and inclination of Juice's orbit, followed by 1st flyby of Callisto. | 193 days | 27 m/s (60 mph). |
| Europa phase: Starting in July 2032, there will be two <400 km (250 mi) flybys of Europa followed by another Callisto flyby. The brief Europa encounters (during which the probe is expected to sustain a third of its lifetime radiation exposure) are planned such that the radiation exposure is as low as possible, first by encountering Europa at perijove (i.e. the spacecraft's perijove is equal to Europa’s orbital radius), and second by having only one low perijove passage per Europa flyby. | 35 days | 30 m/s (67 mph). |
| Inclined phase: ~6 further flybys of Callisto and Ganymede to temporarily increase the orbital inclination to 22 degrees. This will allow an investigation of Jupiter's polar regions and Jupiter's magnetosphere at the maximum inclination over a four-month period. | 208 days | 13 m/s (29 mph). |
| Transfer to Ganymede: A series of Callisto and Ganymede gravity assists will be performed to gradually reduce Juice's speed by 1,600 m/s (3,600 mph). Finally, a series of distant ~45,000 km (28,000 mi) flybys of the far side of Ganymede (near the Jupiter-Ganymede-L2 Lagrange point) will further reduce the required orbital insertion delta-V by 500 m/s (1,100 mph). | 353 days | 60 m/s (130 mph). |
| Ganymede orbital phase: In December 2034, Juice will enter an initial 12-hour polar orbit around Ganymede after performing a 185 m/s (410 mph) delta-V braking burn. Jupiter gravitational perturbations will gradually reduce the minimum orbital altitude to 500 km (310 mi) after ~100 days. The spacecraft will then perform two major engine firings to enter a nearly circular 500 km (310 mi) polar orbit, for a further six months of observations (e.g. Ganymede's composition and magnetosphere). The orbital phase includes a final stage at 200 km altitude. At the end of 2035, Jupiter perturbations will cause Juice to impact onto Ganymede within weeks as the spacecraft runs out of propellant. | 284 days | 614 m/s (1,370 mph). |
| Full tour (Jupiter orbit insertion to end of mission) | 1259 days | 1,696 m/s (3,790 mph). |

## Science objectives

The Juice orbiter will perform detailed investigations on Ganymede and evaluate its potential to support life. Investigations of Europa and Callisto will complete a comparative picture of these Galilean moons. The three moons are thought to harbour internal liquid water oceans, and so are central to understanding the habitability of icy worlds.
The main science objectives for Ganymede, and to a lesser extent for Callisto, are:
* Characterisation of the ocean layers and detection of putative subsurface water reservoirs
* Topographical, geological and compositional mapping of the surface
* Study of the physical properties of the icy crusts
* Characterisation of the internal mass distribution, dynamics and evolution of the interiors
* Investigation of Ganymede's tenuous atmosphere
* Study of Ganymede's intrinsic magnetic field and its interactions with the Jovian magnetosphere.
For Europa, the focus is on the chemistry essential to life, including organic molecules, and on understanding the formation of surface features and the composition of the non-water-ice material. Furthermore, Juice will provide the first subsurface sounding of the moon, including the first determination of the minimal thickness of the icy crust over the most recently volcanically-active regions.
More distant spatially resolved observations will also be carried out for several minor irregular satellites and the volcanically active moon Io.

## Science instruments

On 21 February 2013, after a competition, 11 science instruments were selected by ESA, which were developed by science and engineering teams from all over Europe, with participation from the US. Japan also contributed several components for SWI, RPWI, GALA, PEP, JANUS and J-MAG instruments, and will facilitate testing.

### Jovis, Amorum ac Natorum Undique Scrutator (JANUS)

    The name is Latin for "comprehensive observation of Jupiter, his love affairs and descendants." It is a camera system to image Ganymede and interesting parts of the surface of Callisto at better than 400 m/pixel (resolution limited by mission data volume). Selected targets will be investigated in high-resolution with a spatial resolution from 25 m/pixel down to 2.4 m/pixel with a 1.3° field of view. The camera system has 13 panchromatic, broad and narrow-band filters in the 0.36 μm to 1.1 μm range, and provides stereo imaging capabilities. JANUS will also allow relating spectral, laser and radar measurements to geomorphology and thus will provide the overall geological context.

### Moons and Jupiter Imaging Spectrometer (MAJIS)

    A visible and infrared imaging spectrograph operating from 0.5 μm to 5.56 μm, with spectral resolution of 3–7 nm, that will observe tropospheric cloud features and minor gas species on Jupiter and will investigate the composition of ices and minerals on the surfaces of the icy moons. The spatial resolution will be down to 75 m (246 ft) on Ganymede and about 100 km (62 mi) on Jupiter.

### UV Imaging Spectrograph (UVS)

    An imaging spectrograph operating in the wavelength range 55–210 nm with spectral resolution of <0.6 nm that will characterise exospheres and aurorae of the icy moons, including plume searches on Europa, and study the Jovian upper atmosphere and aurorae. Resolution up to 500 m (1,600 ft) observing Ganymede and up to 250 km (160 mi) observing Jupiter.

### Sub-millimeter Wave Instrument (SWI)

    A spectrometer using a 30 cm (12 in) antenna and working in 1080–1275 GHz and 530–601 GHz with spectral resolving power of ~10$^7$ that will study Jupiter's stratosphere and troposphere, and the exospheres and surfaces of the icy moons.

### Ganymede Laser Altimeter (GALA)

    A laser altimeter with a 20 m (66 ft) spot size and 10 cm (3.9 in) vertical resolution at 200 km (120 mi) intended for studying topography of icy moons and tidal deformations of Ganymede.

### Radar for Icy Moons Exploration (RIME)

    The RIME antenna in stowed configuration. A "selfie" photograph, shortly after launch by the Juice monitoring camera 2 (JMC2), with Earth in the background
    An ice-penetrating radar working at frequency of 9 MHz (1 and 3 MHz bandwidth) emitted by a 16 m (52 ft) antenna; will be used to study the subsurface structure of Jovian moons down to 9 km (5.6 mi) depth with vertical resolution up to 30 m (98 ft) in ice.
    During post-launch commissioning of the spacecraft, the RIME antenna failed to properly deploy from its mounting bracket. After several weeks of attempts to free the instrument, it was successfully deployed on 12 May of the same year.

### Juice-Magnetometer (J-MAG)

    The scalar sub-instrument (MAGSCA), an optical magnetometer with low absolute error, is part of J-MAG
    Juice will study the subsurface oceans of the icy moons and the interaction of Jovian magnetic field with the magnetic field of Ganymede using a sensitive magnetometer.

### Particle Environment Package (PEP)

    A suite of six sensors to study the magnetosphere of Jupiter and its interactions with the Jovian moons. PEP will measure positive and negative ions, electrons, exospheric neutral gas, thermal plasma and energetic neutral atoms present in all domains of the Jupiter system from 1 meV to 1 MeV energy.

### Radio and Plasma Wave Investigation (RPWI)

    RPWI will characterise the plasma environment and radio emissions around the spacecraft, it is composed of four experiments: GANDALF, MIME, FRODO and JENRAGE. RPWI will use four Langmuir probes, each one mounted at the end of its own dedicated boom and sensitive up to 1.6 MHz, to characterize plasma, and receivers in the frequency range 80 kHz to 45 MHz to measure radio emissions. This scientific instrument is somewhat notable for using Sonic the Hedgehog as part of its logo.

### Gravity and Geophysics of Jupiter and Galilean Moons (3GM)

    3GM is a radio science package comprising a Ka transponder and an ultrastable oscillator. 3GM will be used to study the gravity field – up to degree 10 – at Ganymede and the extent of internal oceans on the icy moons, and to investigate the structure of the neutral atmospheres and ionospheres of Jupiter (0.1 – 800 mbar) and its moons. 3GM carries Israeli-built atomic clock "that will measure tiny vacillations in a radio beam".

### Planetary Radio Interferometer and Doppler Experiment (PRIDE)

    The experiment will generate specific signals transmitted by Juice's antenna and received by very-long-baseline interferometry to perform precision measurements of the gravity fields of Jupiter and its icy moons.