Slovak Detector Tested in Earth’s Van Allen Radiation Belts
The JUICE spacecraft, which launched toward Jupiter in April 2023, returned to its home planet Earth in August 2024 for its first gravity assist after following an elliptical orbit around the Sun. These close flybys of planets in the Solar System, also known as "gravity slingshots," accelerate the probe, aiming to reach Jupiter by July 2031. Three more gravity assists will be required, with the next one involving Venus, followed by two more Earth flybys.
During last year’s close flyby of Earth at an altitude of 6,840 km above the Pacific Ocean, the spacecraft took the opportunity to test and calibrate several of its scientific instruments. Among them was the PEP (Particle Environment Package), which includes the ACM (Anti-Coincidence Monitor) detector, constructed at the Institute of Experimental Physics of the Slovak Academy of Sciences (SAS) in Košice, with support from Slovakia's PECS
“The ACM detector’s task is to detect energetic electrons in Jupiter's magnetosphere, which can penetrate deeply through the shielding of scientific instruments. The ACM enables the distinction between these disruptive electrons and low-energy plasma particles, which is essential for high-quality scientific data recording,” said Ján Baláž, the detector's designer from the Institute of Experimental Physics, SAS.
As part of the close Earth flyby, the spacecraft twice crossed the outer Van Allen radiation belt, where Earth’s magnetic field traps high-energy electrons. Recent data analysis and calibration with the onboard RADEM radiation monitor confirm that the ACM detector performs as expected, reliably registering energetic electrons and their secondary products that penetrate deeply into the PEP instrument.
“During this phase of the mission, the ACM detector operated with a single energy threshold of 90 kilo-electronvolts (keV). For even better calibration, we plan to scan the entire energy range from 54 keV to 320 keV. However, Venus in August 2025 won’t be helpful for this purpose, as it lacks a magnetic field and therefore has no Van Allen belts. We will have to wait for the next Earth flyby in September 2026,” the scientist explained.
Source: Ján Baláž, Institute of Experimental Physics, SAS, jan.balaz@saske.sk