Jupiter Icy Moons Explorer

Jupiter Icy Moons Explorer (Juice)
Company type	Spacecraft mission
Industry	Space exploration
Predecessor	Jupiter Ganymede Orbiter concept
Founded	April 14, 2023; 3 years ago
Founder	European Space Agency (ESA)
Fate	Active (as of 2023)
Headquarters	Toulouse, France
Area served	Jupiter system (Ganymede, Callisto, Europa)
Key people	Airbus Defence and Space (principal contractor)
Products	Interplanetary probe for Jupiter's icy moons exploration
Owner	European Space Agency
Parent	European Space Agency

The Jupiter Icy Moons Explorer (Juice, previously styled as JUICE) is an interplanetary probe created by the European Space Agency (ESA) with the purpose of orbiting and investigating three of Jupiter's frozen moons: Ganymede, Callisto, and Europa. These satellites are prioritized because of their presumed subsurface oceans, marking them as prime locations for studying possible extraterrestrial life.

Juice represents the first mission to the outer Solar System undertaken by a non-American space agency and is also the first spacecraft to orbit a moon other than Earth's. It was launched from the Guiana Space Centre on 14 April 2023, with Airbus Defence and Space serving as the principal contractor. After an eight-year transit involving four gravity assist maneuvers, it is expected to reach Jupiter in July 2031. Beginning in December 2034, Juice will commence its detailed scientific observations by entering orbit around Ganymede. Its operational phase will coincide with NASA's Europa Clipper mission, which launched in October 2024.

Background

The mission evolved from the earlier Jupiter Ganymede Orbiter concept, originally planned as ESA’s contribution to the now-cancelled Europa Jupiter System Mission – Laplace (EJSM-Laplace). Juice was selected as a contender for ESA’s first L-class mission (L1) under the Cosmic Vision Programme, with the official announcement made on 2 May 2012.

In April 2012, Juice was favored over competing proposals such as the Advanced Telescope for High Energy Astrophysics (ATHENA) X-ray observatory and the New Gravitational wave Observatory (NGO).

By July 2015, Airbus Defence and Space had been appointed as the lead contractor responsible for designing and constructing the spacecraft, which would be assembled in Toulouse, France.

As of 2023, ESA’s projected budget for the mission stood at approximately 1.5 billion euros (equivalent to $1.6 billion).

Spacecraft

Design considerations for the spacecraft focus heavily on operating at great distances from the Sun, dependence on solar energy, and surviving Jupiter’s harsh radiation environment. The propulsion system must provide sufficient chemical fuel to accomplish orbital insertions at both Jupiter and Ganymede, complete over 25 gravity assists, and perform two flybys of Europa. The spacecraft’s total delta-V capacity is estimated at about .

Juice is equipped with a fixed high-gain antenna measuring 2.5 meters in diameter and a steerable medium-gain antenna capable of X- and K-band communications. It supports data transmission rates up to 2 Gb per day through Deep Space Network antennas and carries onboard storage capacity of 1.25 terabits.

Its primary propulsion engine is a 425-newton hypergolic bi-propellant thruster using mono-methyl hydrazine fuel combined with mixed nitrogen oxides as oxidizer. Thermal regulation is achieved through approximately 100 kilograms of multilayer insulation material. The spacecraft maintains stability via momentum wheels and includes radiation shielding designed to endure equipment-level doses reaching 50 kilorads within Jupiter’s intense radiation belts.

The scientific payload weighs around , comprising instruments such as the JANUS camera system, MAJIS imaging spectrometer, UVS ultraviolet spectrograph, RIME radar sounder, GALA laser altimeter, SWI submillimeter wave instrument, J-MAG magnetometer, PEP particle detector package, RPWI radio and plasma wave experiment, 3GM radio science instrument, PRIDE radio science device, and RADEM radiation monitor. Deployable booms include a boom dedicated to J-MAG and RPWI instruments measuring , a RIME antenna extending , plus four separate booms each supporting components of RPWI measuring . Additional sensors are mounted directly on or within the spacecraft structure.

Launch

The Juice spacecraft was dispatched on 14 April 2023 from the Guiana Space Centre atop an Ariane 5 launcher. This event represented the concluding ESA scientific mission utilizing Ariane 5, which itself was on its penultimate flight. Initially set for 13 April, the lift-off was postponed due to adverse weather. The rocket launched at 12:14:36 UTC on 14 April, with successful separation and radio communication established by 13:04 UTC. Approximately half an hour later, Juice’s solar panels deployed, confirming the mission’s initial success.

Trajectory

Juice’s path to Jupiter incorporates several planned gravity assist maneuvers designed to enhance fuel economy and shorten travel duration:

Earth–Moon flyby scheduled for August 2024
Venus flyby planned for August 2025
Two additional Earth flybys occurring in September 2026 and January 2029

The spacecraft will cross the asteroid belt twice during its journey. A previously considered encounter with asteroid 223 Rosa in October 2029 was ultimately canceled to preserve fuel reserves essential for the primary Jovian objectives.

Key gravity assist events include:

Interplanetary transfers involving flybys of Earth, Venus, and Earth again
Orbit insertion around Jupiter, supported by multiple gravity assists from Ganymede to decrease apocentre velocity
Velocity reduction through combined Ganymede–Callisto assists
Increasing orbital inclination via 10 to 12 gravity assists from Callisto

Summary of intended Jupiter mission phases

Outlined below are the principal elements of Juice’s reference tour around Jupiter (adapted from Table 5-2 of ESA/SRE(2014)1). This plan assumed a launch in early June 2022, with delta-V values reflecting typical orbital dynamics among Europa, Ganymede, and Callisto.

Event	Duration	Delta-V notes
Jupiter orbit insertion: Upon arrival in July 2031, Juice will execute a close Ganymede flyby at approximately 400 km altitude to reduce velocity by around 300 m/s. This is followed roughly 7.5 hours later by a ~900 m/s burn to insert into Jupiter orbit. Subsequently, a Perijove Raising Manoeuvre (PRM) performed at apoapsis elevates periapsis to align with Ganymede’s orbit at about 15 Rj.	186 days	952 m/s
Second Ganymede flyby leading to initial Callisto encounter: Multiple passes by Ganymede serve to shorten the orbital period and adjust inclination prior to the first Callisto flyby.	193 days	27 m/s
Europa phase: Beginning July 2032, two flybys at roughly 400 km altitude over Europa take place, followed by another Callisto flyby. These brief encounters are timed near perijove and limit low-altitude passes per flyby to reduce radiation exposure.	35 days	30 m/s
Inclined phase: Over approximately four months, about six additional gravity assists from Callisto and Ganymede increase orbital inclination up to 22°, facilitating studies of Jupiter’s polar regions and magnetosphere.	208 days	13 m/s
Transfer to Ganymede: A sequence of gravity assists involving Callisto and Ganymede gradually reduces spacecraft velocity by around 1600 m/s. Distant flybys (~45,000 km) near the Jupiter-Ganymede-L2 Lagrange point further decrease required orbit insertion delta-V by an additional ~500 m/s.	353 days	60 m/s
Ganymede orbital phase: In December 2034, Juice achieves a polar orbit around Ganymede with a period of about twelve hours after a braking burn of approximately 185 m/s. Jupiter’s gravitational influence lowers this orbit gradually to near 500 km altitude over roughly one hundred days. Subsequently, two significant engine firings place Juice into a nearly circular polar orbit at this altitude for six months dedicated to examining Ganymede’s surface composition and magnetosphere. The phase concludes with a final orbital stage at around 200 km altitude. By late 2035, natural perturbations will cause the spacecraft to impact Ganymede as fuel supplies run out.	284 days	614 m/s
Complete tour (from Jupiter orbit insertion until mission conclusion)	1259 days	1696 m/s

Science objectives

The Juice orbiter is set to carry out comprehensive studies of Ganymede to evaluate its capacity to sustain life. Comparative examinations of Europa and Callisto will enhance understanding of these Galilean moons, which are thought to contain subsurface liquid water oceans, a key factor in assessing the potential habitability of icy celestial bodies.

Primary scientific goals for Ganymede and Callisto encompass:

Identifying oceanic layers and locating underground water reservoirs
Creating detailed maps of surface topography, geological features, and chemical composition
Investigating the physical characteristics of the icy crusts
Exploring internal mass distribution, dynamic processes, and evolutionary history
Studying Ganymede’s thin atmosphere
Assessing Ganymede’s inherent magnetic field and its interaction with Jupiter’s magnetosphere

For Europa, investigations concentrate on life-supporting chemistry such as organic compounds, the formation of surface structures, and materials beyond water ice. Juice will also execute the inaugural subsurface sounding to measure the thickness of Europa’s icy shell above active volcanic areas.

Moreover, spatially resolved observations will be conducted on smaller irregular satellites as well as the volcanically active moon Io.

Science instruments

On 21 February 2013, ESA finalized the selection of 11 scientific instruments developed primarily by European teams with collaboration from the United States. Japan contributed components for SWI, RPWI, GALA, PEP, JANUS, and J-MAG instruments and is involved in their testing.

Jovis, Amorum ac Natorum Undique Scrutator (JANUS): A camera system capturing images of Ganymede and Callisto at resolutions finer than 400 meters per pixel. It achieves high-resolution imaging down to 2.4 meters per pixel utilizing 13 filters spanning 0.36–1.1 μm wavelengths along with stereo imaging capabilities. JANUS integrates spectral, laser, and radar data within a geological framework.

Moons and Jupiter Imaging Spectrometer (MAJIS): A visible to infrared imaging spectrograph operating between 0.5 and 5.56 μm with spectral resolution ranging from 3 to 7 nm. It analyzes Jupiter’s cloud structures and minor atmospheric gases while characterizing surface compositions of icy moons with spatial resolution as fine as 75 meters on Ganymede.

UV Imaging Spectrograph (UVS): Functioning over 55–210 nm wavelengths with spectral resolution below 0.6 nm, it examines exospheres and auroral phenomena on icy moons—including searching for plumes on Europa—as well as Jupiter’s upper atmospheric layers.

Sub-millimeter Wave Instrument (SWI): A spectrometer probing Jupiter’s stratosphere and troposphere along with exospheres and surfaces of icy moons across frequencies from 530 to 1275 GHz, offering high spectral resolving capability.

Ganymede Laser Altimeter (GALA): A laser altimeter featuring a 20-meter spot size and vertical accuracy of 10 cm from an altitude of 200 km, designed to map topography and tidal flexing on icy satellites.

Radar for Icy Moons Exploration (RIME): Ice-penetrating radar operating at 9 MHz equipped with a 16-meter antenna capable of investigating subsurface structures up to 9 kilometers deep with vertical resolution reaching 30 meters within ice. Following initial deployment challenges after launch, the antenna successfully deployed on 12 May 2023.

Juice-Magnetometer (J-MAG): This instrument measures magnetic fields to investigate subsurface oceans beneath icy moons and their interaction with Jupiter’s magnetosphere via a highly sensitive magnetometer.

Particle Environment Package (PEP): A collection of six sensors designed to detect ions, electrons, neutral gases, thermal plasma, and energetic neutral atoms throughout Jupiter’s magnetosphere over an energy range from 1 meV up to 1 MeV.

Radio and Plasma Wave Investigation (RPWI): Characterizes plasma environments and radio emissions using Langmuir probes alongside receivers covering frequencies from 80 kHz to 45 MHz. Its logo notably includes Sonic the Hedgehog.

Gravity and Geophysics of Jupiter and Galilean Moons (3GM): A radio science suite featuring a Ka band transponder and ultrastable oscillator aimed at mapping gravity fields up to degree 10 on Ganymede, defining the extent of internal oceans, and studying atmospheric plus ionospheric structures on Jupiter and its moons. It incorporates an atomic clock developed in Israel for precise measurement capabilities.

Planetary Radio Interferometer and Doppler Experiment (PRIDE): Generates signals transmitted by Juice’s antenna that are received through very-long-baseline interferometry techniques for highly accurate gravity field measurements concerning Jupiter and its icy satellites.

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