Three years on the way to Jupiter: LIP’s contribution to the JUICE mission
"Due to arrive at Jupiter in 2031, JUICE carries RADEM, a radiation monitor developed with LIP’s involvement and already active in collecting and transmitting data throughout the journey."
Top - Representation of the JUICE spacecraft orbiting Jupiter. Credit: ESA
Bottom left - Launch of the Ariane 5 rocket for the JUICE mission. Credit: ESA
Bottom right - RADiation-hard Electron Monitor (RADEM) for ESA’s JUICE mission, developed by LIP, Paul Scherrer Institute (Switzerland), EFACEC S.A. (Portugal) and IDEAS (Norway). Credit: LIP
It is now three years since ESA’s JUICE mission (Jupiter Icy Moons Explorer) was launched towards Jupiter and three of its icy moons: Europa, Ganymede and Callisto. Launched in April 2023, the spacecraft is expected to reach the Jovian system in July 2031, where it will explore an extreme planetary environment and investigate moons believed to harbour subsurface oceans.
On board is RADEM (RADiation-hard Electron Monitor), a radiation monitor designed and developed by LIP and Efacec, in collaboration with the Norwegian company IDEAS and the Paul Scherrer Institute in Switzerland.
LIP took part in all beam tests of the instrument — controlled trials designed to verify that it responds as expected to the radiation environment it will encounter in space. LIP is also responsible for operating the instrument.
“In very simple terms, RADEM uses several silicon detectors, almost like small particle ‘antennas’, to register the passage of protons, electrons or ions. Depending on the type of particle and its energy, a different electrical signal is produced. Because it has remained switched on throughout these three years of travel, the instrument has already measured radiation in interplanetary space, detected more than 30 solar events, and observed Earth’s radiation belts during the Earth–Moon flyby. The fact that it is always on means it can gather valuable data,” explains Luísa Arruda.
Left - The Cebreros station, DSA 2 (Deep Space Antenna 2), located 77 km west of Madrid, Spain. Credit: ESA
Top right - Cebreros antenna: Terminal MER remote control console. Credit: ESA
Bottom right - View of Earth captured by JUICE. Credit: ESA
These data are sent back to Earth via JUICE’s antenna through ESA’s network of ground stations, ESTRACK. Because the spacecraft is so far away, communication is not instantaneous: delays can reach several tens of minutes, and transmission capacity is limited, meaning not all information can be sent continuously.
The signals are received on Earth by antennas such as the one at Cebreros, in Spain, and are first routed to ESA’s operations centre, ESOC, in Darmstadt, Germany, where the telemetry is decoded, the spacecraft’s status is checked, and the successful receipt of the data is confirmed. They are then passed on to ESAC, near Madrid, where scientific processing begins. This is also where LIP’s role comes in: the laboratory is responsible for the quality control and archiving of the instrument’s scientific data, an essential step in ensuring that this information can be used reliably by the scientific community.
But the most demanding phase is still to come.
What RADEM will encounter at Jupiter
“When JUICE reaches the Jupiter system, RADEM will finally enter the environment it was actually designed for,” says Luísa Arruda.
One of its main goals will be to measure the extreme intensity of electron and proton fluxes in the radiation belts of Jupiter and Ganymede, the only moon in the Solar System with its own magnetosphere — a kind of magnetic shield that affects the motion of charged particles around it. Scientists want to understand how these energetic particles are distributed, identify rapid variations, and map the most hazardous regions for the spacecraft.
These data will be crucial for understanding one of the most extreme environments in the Solar System, testing the limits of space electronics, and improving radiation models that still carry major uncertainties.
CREDIT spacecraft: ESA/ATG medialab; Jupiter: NASA/ESA/J. Nichols (University of Leicester); Ganymede: NASA/JPL; Io: NASA/JPL/University of Arizona; Callisto and Europa: NASA/JPL/DLR
Another major focus of the mission will be the interaction between radiation and Jupiter’s icy moons (Europa, Ganymede and Callisto), worlds of particular interest because they may conceal liquid oceans beneath their frozen surfaces. In this context, RADEM will help investigate how radiation affects the icy surfaces, whether there are local changes in the particle environment around these moons, and what implications these processes may have for these potentially habitable oceans.
Ganymede will play a special role in the mission: the final nine months of JUICE will be devoted to orbiting this moon, allowing for more detailed observations of this unique world.
LIP’s contribution to RADEM is part of a broader area of research and development dedicated to studying the radiation environment in space and its effects - SpaceRad. The work carried out in this field is aligned with ESA’s roadmap for “Space Radiation Environment and Effects” and covers expertise across all the technologies identified there.