SWI observation strategy for the Jupiter Tour of the JUICE nominal science phase as exemplified by the latest ESA planning exercise

The Jupiter Icy Moons Explorer (JUICE) is the first L-class mission of the Cosmic Vision 2015-2025 program of the European Space Agency. JUICE was launched in April 2023 and embarked on an 8-year interplanetary transfer to reach Jupiter and its system. It will perform its Jupiter orbit insertion in July 2031 and start its nominal science phase. JUICE will orbit the planet about 60 times until its Ganymede orbit insertion (GOI) at the end of 2034. This Jupiter tour will comprise 2 close flybys of Europa, and many more flybys of Ganymede and Callisto. After starting the Jupiter tour in the equatorial plane of the planet, JUICE will spend many months in inclined orbits reaching inclinations of up to ~ 35 degrees before going back to the equatorial plane in preparation of GOI.

The payload of JUICE comprises 10 science instruments. One of the remote sensing instruments is the Submillimetre Wave Instrument (SWI), which was designed to study the composition, chemistry and dynamics of the atmospheres of Jupiter and the Galilean Moons. It will also investigate the surface properties of the moon surfaces. SWI is an off-axis single dish telescope with 29 cm diameter equipped with two perpendicular pointing mechanisms that allow to point ±72° along track and ±4.3° cross track from the nadir direction of the JUICE platform during the Jupiter tour. It is a heterodyne spectrometer and radiometer that can be tuned independently and simultaneously in two submillimetre bands (530-638 GHz and 1066-1286 GHz). The highest spectral resolution is achieved with the Chirp Transform Spectrometers that cover 1 GHz bandwidth with 10000 channels. SWI is thus a miniaturized observatory with all the inherent complexity implied for observation planning.

The JUICE Science Operation Center (JSOC) is conducting planning exercises every year before JOI. These exercises serve the purpose of developing the science observation implementation procedures and the relevant software tools (both at the ESA and instrument team levels) that will ensure smooth operations during the science phase. In parallel, the four JUICE science working groups are continuously consolidating and extending the JUICE science objectives. They also identify multi-instrument synergies and propose coordinated observation campaigns.

The latest planning exercise occurred in the first semester of 2026 and focused on two equatorial orbits, namely orbits 37 and 38, that include a close Ganymede flyby. It spans from 23 November to 20 December 2033, with the flyby occurring on 27 November 2033. The flyby inbound is mostly on the nightside and the outbound on the dayside, with a closest approach at ~900 km altitude. The orbits also provide opportunities for Io, Europa and Callisto observations with apparent sizes sufficiently large so that enable to map them.

The implementation of the JUICE observing plan follows a multi-step approach (observation plan, pointing timeline, instrument timeline) coordinated by JSOC. A significant effort by JSOC and the instrument teams concerned the identification and implementation of common/complementary observations in the design the spacecraft pointing profile to maximize the science return of the mission in these orbits and flyby. Following the latest JUICE science synergy workshop (ESAC, January 2026), several coordinated campaigns have been implemented in the 2026 planning exercise and helped making the implementation of the timeline more efficient. Of particular interest for SWI are the following coordinated campaigns: zonal winds, distant monitoring and auroral monitoring for Jupiter, and a coordinated mapping of the Ganymede dayside on the flyby outbound leg.

For what concerns SWI, the observation sequences pre-defined are complemented with other SWI observations, that can be either prime or ride-along observations. For Jupiter, those include: (i) temperature and winds observations with Jupiter limb scans, (ii) searches for isotopes and new species with limb stares and scans, (iii) temperature and composition measurements by means of regional mapping observations (including the auroral regions). During the flyby Ganymede, SWI will perform surface and exosphere regional mapping observations from the largest distances during the flyby and a series of limb stares and scans to investigate the composition, temperature and winds of its exosphere a few hours from closest approach. Moreover, SWI aims to conduct a monitoring of the Galilean Moons surfaces and exospheres on a daily basis, dedicating about 1 hour per day of operations, to investigate the various processes acting as sources and sinks for the exospheres. Finally, SWI will support observation campaigns initiated and led by other instruments and the latest planning exercise proposed several examples of those, like: (i) stellar and Earth radio occultations for which SWI will observe the temperature, composition and winds of the target at the latitudes/longitudes of the ingress/egress, and (ii) Io and Europa closest distance observations.