0 Assigned ID: 6934 ----- Attempting Submission 1 (Tue Nov 04 18:13:52 GMT 2025) ----- HST Phase I Proposal 6934 successfully submitted. Receipt: # 6934-1 No additional comments. Thank you for your assistance. -1603583177 ----- Attempting Submission 1 (Tue Nov 11 19:37:38 GMT 2025) ----- Kallichore (Jupiter XLIV) is a faint irregular satellite of Jupiter and the closest of the outer moons to the nominal JUICE trajectory. Refining its poorly constrained orbit is essential to assess the feasibility of a potential close JUICE flyby. On December 15, 2025, Kallichore will occult a relatively bright star along a well-placed ground track across Europe. We request two single-orbit HST/WFC3-UVIS visits to obtain high-precision astrometry of Kallichore in the days preceding this event. These observations will reduce the predicted shadow-path uncertainty from hundreds to a few tens of kilometers, enabling a coordinated ground-based campaign and providing key input for JUICE navigation and mission planning. Moreover, the ultra-precise astrometry will further improve our understanding of the dynamical evolution and physical properties of Jupiter's irregular satellites. We request two single-orbit visits with WFC3/UVIS, scheduled for November 30 and December 4, 2025, separated by four days to maximize temporal coverage. Each visit will obtain eight 97-s exposures using the UVIS2-2K2C-SUB aperture and the F606W filter, selected for its combination of high throughput and well-characterized PSF. Observations will be executed in non-sidereal tracking mode, following the predicted motion of Kallichore. A box-dither pattern will be applied between exposures to improve PSF sampling and mitigate detector artifacts. Simulations with the HST Exposure Time Calculator (G2V spectrum, high background) indicate an SNR > 14 per frame, including a post-flash level of 17 electrons to mitigate charge-transfer efficiency losses. We verified with the HST Exposure Time Calculator that stars fainter than magnitude 17 will not be saturated. The fields include at least three non-saturated Gaia DR3 stars suitable for differential astrometry. PI Juan Luis Rizos is a planetary scientist at the Instituto de Astrofisica de Andalucia (IAA-CSIC), Spain, whose main research focus is the study of small bodies in the Solar System. He has extensive experience in data analysis from both ground-based telescopes and space missions. He has conducted spectrophotometric studies of bodies such as Ceres, the asteroid Bennu, and the comet Tempel 1. He has also been a member of NASA's OSIRIS-REx and DART mission teams, where he analyzed surface properties, and currently is a member of ESA's JUICE mission to Jupiter's moons. Co-I Benjamon Proudfoot has extensive experience in modeling the orbits of TNO binaries and predicting stellar occultations of TNO companions. He has published several papers and PI'd several HST programs focused on TNO binary science. He is the lead developer of MultiMoon, the tool that will be used to model the binary orbit. Co-I Simon B. Porter provides important expertise in HST image analysis. He was the PI of the HST program to acquire precise astrometry of Arrokoth before the series of successful stellar occultations. He is the developer of the absolute astrometry tools that will be used for this effort. Co-PI Jose Maria Gomez-Limon has proven expertise in using FORS2 data to update stellar occulations by small bodies in the Solar System. He has also expertise in reducing and analyzing stellar occultation data and organizing stellar occultation campaigns. Co-PI Alvaro Alvarez-Candal works with visible to near-infrared (spectroscopic and photometric) observations of asteroids, Centaurs, and TNOs. Lately, he has been developing tools to make the largest photometric databases aimed at helping with the analysis of data from next-generation large sky surveys. Co-PI Altair R. Gomes-Junior is an early-career scientist at the Federal University of Uberlandia (Brazil). He is an expert in Planetary Science with the use of astrometric and photometric techniques and has been contributing in the characterization of Solar System Bodies through stellar occultations. He is the PI of the approved proposals for the observation of stellar occultations by the CHEOPS Space Telescope, including the successful observation of the occultation by Triton in October 2022. He is also the head of development of the open-source python package used for the analysis of stellar occultations SORA (Stellar Occultation Reduction and Analysis). Co-I Luisa Maria Lara is a Full Professor at the at the IAA-CSIC, where she specializes in planetary science, particularly in the study of planetary and cometary atmospheres using physico-chemical modeling, remote sensing, and in situ data. She has played/plays a major role in missions such as ESAs Rosetta, BepiColombo, and JUICE, contributing both scientifically and technically to instrument development and mission planning. Co-I Olivier Witasse is a planetary scientist at the European Space Agency and serves as Project Scientist for the Jupiter Icy Moons Explorer (JUICE) mission. He oversees the scientific coordination of these projects and fosters collaboration within Europes planetary science community. Dr Witasse has extensive experience in managing space missions and integrating ground-based observations. His research portfolio spans studies of Venus, Earth, Mars and its moons Phobos and Deimos, Jupiter and Europa, Saturn and Titan, as well as comets and asteroids. The Co-PI Paul Hartogh (PI of SWI), also member of the JUICE mission team, contribute to this proposal in direct support of its scientific goals and successful execution. Solar System Astronomy 0 false SUPPORTED SOLAR SYSTEM The V-magnitude flux was obtained from the Minor Planet Center's Natural Satellites Ephemeris Service. From November 27, 2025 onward, the flux is below 23.6. SATELLITE irregular STD=JUPITER STD=KALLICHORE NOT OCC OF KALLICHORE BY JUPITER FROM EARTH, SEP OF KALLICHORE IO FROM EARTH GT 10", SEP OF KALLICHORE EUROPA FROM EARTH GT 10", SEP OF KALLICHORE GANYMEDE FROM EARTH GT 10", SEP OF KALLICHORE CALLISTO FROM EARTH GT 10" EARTH WFC3/UVIS Imaging No No F606W POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 1 false 1762883772599 Using ephemeris for target 18215-01-KALLICHORE ephemeris data for target 18215-01-KALLICHORE does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 25.244 to 27.120. ephemeris interval: 25.304 to 27.305 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. 1764522137000 280.06055342172203 (Tic-Visit :proposal-id 18215 :visit-id "01" :proposal-version -1 :trans-version "20250624" :date "11-Nov-2025 18:56:12.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 563088 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18215 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18215 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2590 :al-overhead-at-end 0 :internal-dur-at-end 652 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 1763380112749 Using ephemeris for target 18215-02-KALLICHORE ephemeris data for target 18215-02-KALLICHORE does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 25.244 to 27.120. ephemeris interval: 25.304 to 27.305 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. /System/Volumes/Data/solaris/user1/williamj/hst/work/cycle33/OP-cache/18215-v02.xml (Tic-Visit :proposal-id 18215 :visit-id "02" :proposal-version -1 :trans-version "20250624" :date "17-Nov-2025 06:48:32.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 563088 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18215 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18215 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2590 :al-overhead-at-end 0 :internal-dur-at-end 652 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0