Planning of the JUICE/JANUS camera observations during the first ever Lunar-Earth Gravity Assist

Abstract. The Jupiter Icy Moons Explorer (JUICE) spacecraft, launched in April 2023, will reach the Jovian system in July 2031 and will conduct an extensive science campaign of the Jupiter system, with a strong focus on Jupiter itself and of its icy Galilean satellites. During its cruise phase the spacecraft performed a double gravity assist maneuver (Moon–Earth) in August 2024, followed by a "farewell" observational sequence on 9 September 2024. These events constitute the Lunar Earth Gravity assist (LEGA) campaign. JANUS, the high resolution optical camera of JUICE, used this opportunity to perform an imaging campaign under realistic illumination, viewing geometry and thermal conditions that closely mimic the forthcoming Jupiter operations. JANUS acquired a total of 461 images in full frame, lossless mode, covering the complete set of 13 spectral filters (340–1080 nm). This paper summarizes the end‑to‑end workflow from the definition of scientific and engineering constraints, through the design and ground‑segment validation of the observation sequences, to the acquisition, processing and preliminary analysis of the LEGA data. The campaign demonstrated that a rapid thermal‑pre‑warm strategy using the spacecraft survival heaters can bring the JANUS optics to the required −20 °C thermal stability significantly limiting the power draw but preserving image quality. Exposure times were limited by a 1/4‑pixel smearing criterion; nevertheless, exposure times ranging from 0.22 ms to 163 ms yielded adequate signal‑to‑noise ratios across all filters, and full 13‑filter colour sequences were successfully obtained at high ground‑track speeds. A series of images acquired with increasing compression ratios showed no perceptible degradation, establishing a realistic data‑volume budget for the science phase. Simultaneous measurements by MAJIS, NavCam and the external Earth‑observation satellites enabled a three‑way cross‑calibration that will improve the absolute radiometric accuracy of JANUS. The LEGA experience shows that extending payload operations during cruise‑phase flybys dramatically enhances calibration quality, cross‑instrument synergy and scientific return. These lessons will directly inform the planning of the remaining JUICE Earth flyby windows (September 2026 and January 2029) and provide a best‑practice template for the Jupiter phase of the mission.

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Journal
Annales Geophysicae
Published
2026-10-30
DOI
https://doi.org/10.5194/angeo-44-1243-2026
Citations
1
Primary Topic
Astronomy and Astrophysical Research
Type
article
Field-Weighted Citation Impact
2.77

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article

Planning of the JUICE/JANUS camera observations during the first ever Lunar-Earth Gravity Assist

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1 citations
Annales Geophysicae
Astronomy and Astrophysical Research
2.77
article

Planning of the JUICE/JANUS camera observations during the first ever Lunar-Earth Gravity Assist

Livio Agostini, C. Tubiana, Ganna Portyankina, Alice Lucchetti, T. Roatsch, Inès Belgacem, R. Hueso, Alessio Aboudan, R. Politi, Elke Kersten, Manish R. Patel, Michael Aye, Ry Evill, F. Trauthan, P. Palumbo, Vincenzo Della Corte, Nicole Schmitz, Luca Penasa, Angelo Zinzi, Benoît Seignovert, Luisa Maria Lara, Stubbe Faurschou Hviid, Thomas Bilotta, Matthew Read, Angela Dietz, Thomas Cornet, Klaus‐Dieter Matz, Jose Maria Castro
article en
1 citations

Abstract

Abstract. The Jupiter Icy Moons Explorer (JUICE) spacecraft, launched in April 2023, will reach the Jovian system in July 2031 and will conduct an extensive science campaign of the Jupiter system, with a strong focus on Jupiter itself and of its icy Galilean satellites. During its cruise phase the spacecraft performed a double gravity assist maneuver (Moon–Earth) in August 2024, followed by a "farewell" observational sequence on 9 September 2024. These events constitute the Lunar Earth Gravity assist (LEGA) campaign. JANUS, the high resolution optical camera of JUICE, used this opportunity to perform an imaging campaign under realistic illumination, viewing geometry and thermal conditions that closely mimic the forthcoming Jupiter operations. JANUS acquired a total of 461 images in full frame, lossless mode, covering the complete set of 13 spectral filters (340–1080 nm). This paper summarizes the end‑to‑end workflow from the definition of scientific and engineering constraints, through the design and ground‑segment validation of the observation sequences, to the acquisition, processing and preliminary analysis of the LEGA data. The campaign demonstrated that a rapid thermal‑pre‑warm strategy using the spacecraft survival heaters can bring the JANUS optics to the required −20 °C thermal stability significantly limiting the power draw but preserving image quality. Exposure times were limited by a 1/4‑pixel smearing criterion; nevertheless, exposure times ranging from 0.22 ms to 163 ms yielded adequate signal‑to‑noise ratios across all filters, and full 13‑filter colour sequences were successfully obtained at high ground‑track speeds. A series of images acquired with increasing compression ratios showed no perceptible degradation, establishing a realistic data‑volume budget for the science phase. Simultaneous measurements by MAJIS, NavCam and the external Earth‑observation satellites enabled a three‑way cross‑calibration that will improve the absolute radiometric accuracy of JANUS. The LEGA experience shows that extending payload operations during cruise‑phase flybys dramatically enhances calibration quality, cross‑instrument synergy and scientific return. These lessons will directly inform the planning of the remaining JUICE Earth flyby windows (September 2026 and January 2029) and provide a best‑practice template for the Jupiter phase of the mission.

Annales GeophysicaeVol. 44(2)
Centre National de la Recherche Scientifique (FR), European Space Operations Centre (DE), University of Padua (IT), University of the Basque Country (ES), The Open University (GB), Agenzia Spaziale Italiana (IT), Astronomical Observatory of Capodimonte (IT), European Space Agency (FR), Leonardo (Italy) (IT), Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR) (DE), European Space Astronomy Centre (ES), Institute for Space Astrophysics and Planetology (IT), Laboratoire de Planétologie et Géosciences (FR), Instituto de Astrofísica de Andalucía (ES), Osservatorio Astronomico di Padova (IT), Observatoire des Sciences de l'Univers Nantes Atlantique (FR), Freie Universität Berlin (DE), National Institute for Astrophysics (IT), Nantes Université (FR)
Eusko Jaurlaritza, Agenzia Spaziale Italiana, Agencia Estatal de Investigación
Openalex Percentile: Top 9%
Astronomy and Astrophysical Research
2.77
DOIOpen Access PDFOpenAlex
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