ESA’s Jupiter Icy Moons Explorer, Juice, launched the 14th April 2023, will make detailed observations of the giant gas planet and its three moons – Ganymede, Callisto and Europa – with a suite of the state-of-the-art instruments.
The spacecraft is carrying a number of instruments for studying different aspects of the Jovian system. The Radar for Icy Moon Exploration (RIME), one of the Italian-led instruments on board the mission, is a radar sounder optimized for the penetration of the Galilean icy moons up to a depth of 9 km.
During the first in history gravity assist flyby of the Earth-Moon system, which took place successfully between August 19 and 20, the radar was activated and performed a wide range of tests.
RIME is a low-frequency radar sounder designed to detect the characteristics of the surface and subsurface of celestial bodies. It was designed to measure the interior of Jupiter's icy satellites namely Ganymede, Europa and Callisto. These measurements have never been made before on Jupiter's Galilean moons. In addition to the study of the geology of Ganymede, Europa and Callisto, the radar has the unique ability to detect the possible presence of pockets of water in the subsurface layers. This is of particular importance for the entire mission since the main objective of JUICE is to understand the conditions of habitability of the icy moons.
The instrument was built by a consortium of institutions led by Thales Alenia Space (Rome) under the responsibility of the Italian Space Agency (ASI) and with the contribution of NASA's Jet Propulsion Laboratory under the scientific leadership of the University of Trento.
“During the lunar flyby, RIME was operated to acquire, for the first time since the launch of JUICE, data from the surface of a celestial body. Tests were performed by varying the radar parameters with the aim of better characterizing the functioning of RIME. These data will be extremely valuable for calibrating the instrument and optimizing the signal analysis techniques necessary for the planned scientific activities,” comments Lorenzo Bruzzone, professor at the University of Trento and Principal Investigator of the team that designed, developed and tested RIME. “The measurements collected,” continues Bruzzone, “will also allow us to tune the processing algorithms to reduce the effects of radio frequency interference generated by the probe’s subsystems in the radar band.” Tests carried out since launch have shown that the spacecraft’s power subsystem emits unexpected interference that potentially disturbs the quality of the radar data. “Thanks to the intense work of the RIME team engineers in recent months, data acquisition methods and signal processing techniques have already been developed that are capable of drastically reducing the effects of noise.”
"The RIME team is gratified that the instrument is functioning properly and that radar echoes have been obtained from the lunar surface," said Jeffrey Plaut, Co-Principal Investigator of RIME at NASA's Jet Propulsion Laboratory. "Coordination among the mission operations and instrument teams allowed us to get a valuable glimpse of RIME radar data while we continue our journey to the icy moons."
“Juice travel to Jupiter continues thanks to the never attempted flyby maneuver around the Earth-Moon system. The flyby has shown that Juice and its instrumentation are all performing well” comments Alessandra Tiberia, engineer at the Italian Space Agency and Project Manager of the RIME team. “Specifically, RIME has returned high quality echoes of the Moon surface. Furthermore it has been operated in listen-only mode to measure radio signals generated by terrestrial transmissions that are useful for calibration and has provided data on the Earth’s ionosphere. As someone said: “Sometimes the journey is as good as the destination”.
Figure 1 - The figure presents part of the first series of echoes measured by RIME of the lunar surface, and the digital elevation model (DEM) of the area with the spacecraft groundtrack indicated by a white line. The radargram has been generated with preliminary pre-processing (RFI noise mitigation, range compression and simple pre-summing only) and is not focused yet. It shows the surface of the Moon in the area of the flyby, which is a very rough area characterized by large variations of topography as shown in the DEM.
Figure 2 - The figure presents the spectrogram measured by the RIME in listen-only mode during part of the flyby of the Earth. Many different radio frequency sources are detected and visible in the data.