the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Feb 2026
Juice-SWI during the Lunar-Earth-Gravity-Assist (LEGA). II. Instrument operations
Abstract. The Jupiter Icy Moons Explorer (Juice) embarked in 2023 on a 8-year interplanetary journey to Jupiter and its icy moons. The Submillimetre Wave Instrument (SWI) is one of the ten science instruments aboard the spacecraft. SWI is a sophisticated and first-of-its-kind payload visiting the outer solar system, featuring dual-band tunable receivers, two independent pointing mechanisms, and spectrometers capable of high resolution (up to a resolving power of 107). It is designed to support the diverse science objectives of the Juice mission targeting Jupiter's middle atmosphere, icy-moon's exospheres as well as near sub-surface thermophysical properties. For this purpose the Juice mission adopts a complex trajectory tour within the Jovian system, which further necessitates a sophisticated, mission-driven operations concept for SWI. This presents significant planning, operations and commanding challenges which are described in this paper in the context of the Lunar and Earth Gravity Assist (LEGA). After the development and ground calibration of the instrument, the SWI Team has designed a comprehensive calibration strategy applicable during the Cruise Phase of Juice. Among the various opportunities for calibration, including the Near-Earth Commissioning Phase and more than ten Payload Checkout Windows, the LEGA offers the means not only to improve the calibration of the instrument, but also to validate the operational strategy of future icy moon flybys.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-584', Anonymous Referee #1, 27 Feb 2026
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RC2: 'Comment on egusphere-2026-584', Anonymous Referee #2, 10 Mar 2026
This is a very well written detailed description of the plan for the Juice SWI instrument operations throughout the mission and initial testing of the operational planning and execution during LEGA. I compliment the authors on laying out such a clear and highly detailed paper.
General Comments:
- Is there any interaction of the jovian radiation environment and the signal quality of science measurements for SWI? Many other instruments suffer from increased background/noise in their measurements due to Jovian radiation. It may be nice to add a comment about that somewhere just for clarity. If by chance, there is some interaction/increase of noise due to the radiation then a question would be how does SWI plan to deal with that throughout the mission.
- lines 170 and 185: I don’t have any experience with how the brightness maps of Jupiter look in the GHz range, but in just about every other wavelength range there are large fluctuations of the brightness of Jupiter vs latitude (banding) and even longitude (especially in the 5 micron region). If there are brightness variations, how can you trust pointing to the half power point will place you precisely at the limb? In addition, to what flux accuracy (50% +/-???) and what pointing accuracy does your flux accuracy work out to?
- In Figure 2, how does the spacecraft pointing performance (spice reconstructed kernels) feed into the data analysis? Maybe there is another arrow from spacecraft data which leads to a Naif SPICE box where the actual performance of the spacecraft pointing is captured?
- As an addendum, how is the pointing information of the SWI telescope captured in the data? Will there be SWI delivered spice kernels that give the position of the telescope relative to the spacecraft for all times the instrument is on during the mission?
- Line 343 begs the question, why did SWI only perform 166 of its 225 planned observations?
- Line 348, Maybe it was the first time the Earth was observed at frequencies around 1200 GHz form space, but I would suspect the Earth atmosphere has been probed at these wavelengths from the ground before, no? Maybe just adding “from space” after “Earth was observed”?
- The mentioned safe mode event on line 408, is this specific instrument safe mode anomaly? I believe so, maybe lead “safe mode event” with “instrument” to be completely clear.
- Not sure whether it is worth detailing the cause of the safe mode during ObsID 314, but you sort of leave the reader curious.
Detailed comments:
- Line 29, remove “of” after “will include”
- Line 36, maybe “enabling determination of their sources” rather than “enabling to determine their sources”
- Line 53: maybe “The telescope is equipped” rather than “The instrument TRU” which sounds a bit redundant since I think the TRU is the instrument.
- Line 65: possible change “thereby” to “and”
- You state in line 78 there are “6” basic instrument operational modes but then list 7 modes.
- Line 170: add “is” after “to know where the instrument”
- Line 173: add space “models(Cavalie…”
- Line 235: “almost only SWI….” This bit reads rather oddly and I’m not sure how important the point is. For one, I assume most of the in-situ instruments were happily observing during this period. I suggest removing or maybe trying to be a bit more specific like (SWI was the only remote sensing instrument capable of observing the Earth during the days following closest approach due to spacecraft pointing restrictions) or something like that.
- Remove random @ symbol in line 398
Citation: https://doi.org/10.5194/egusphere-2026-584-RC2
Video supplement
Juice-SWI ObsID 242 - AT scan Ladislav Rezac and Thibault Cavalié https://doi.org/10.5446/72321
Juice-SWI ObsID 243 - CT scan Ladislav Rezac and Thibault Cavalié https://doi.org/10.5446/72322
Juice-SWI ObsID 257 - Limb scan Ladislav Rezac and Thibault Cavalié https://doi.org/10.5446/72323
Juice-SWI ObsID 282 - Limb stare Ladislav Rezac and Thibault Cavalié https://doi.org/10.5446/72324
Juice-SWI ObsID 373 - 2D map Ladislav Rezac and Thibault Cavalié https://doi.org/10.5446/72325
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This is generally very well-written and appropriately detailed. Therefore, I have relatively few comments, and encourage that it be accepted subject to some minor corrections.
Typos/Rephrasing:
Pg.2, line 48: "at two wavelengths" should be "in two wavelength bands"
Pg. 18, line 397: "calibr@te" should be "calibrate"
Comments:
I don't see it mentioned, but are users of the observation planning tools notified if there is a possibility that the observations may point near the sun (if not in the solar occultation mode) or a non-target body (i.e. Jupiter will be in the background of a Ganymede scan)?
Pg. 9, Line 240. I assume this also true for the calibration modes, since you want to make sure your cold sky pointings do not look at a planet or moon.
Pg. 7 Line 174-176: If I understand this right, what is happening is that the instrument begins a scan across Jupiter, notes at some point a nadir signal (based on pointing, not measurements?), continues a scan until half of that power is reached, and then stops the scan and begins integrating on target? It seems, without further details, like this approach could suffer failures under un-anticipated conditions. If there is further detail on this operation mode (or if this has been done before, etc.), a reference would be sufficient, otherwise, I would appreciate further elaboration on the specifics (including replicating a few details from appendices). Clearly initial tests have worked, as shown in the figures/videos, but strange things can happen in Jupiter's radiation environment.