18152( 16) - 05-Mar-2026 15:35:40 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18152 Version: 16 Check-in Time: 05-Mar-2026 15:35:40 STScI Edit Number: 8 Title Monitoring Interstellar Object 3I/ATLAS Departing the Solar System ------------------------------------------------------------------------------------ Type Cycle GO/DD 32 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Man-To Hui Shanghai Astronomical Observatory, CAS Y CoI: Max Mutchler Space Telescope Science Institute Y CoI: Dr. David Jewitt University of California - Los Angeles Y CoI: Dr. Jessica Agarwal Technische Universitat Braunschweig N CoI: Dr. Yoonyoung Kim University of California - Los Angeles N ------------------------------------------------------------------------------------ Abstract While numerical models predict a large population of interstellar objects (ISOs) in the interstellar neighborhood of the solar system, few have been found. Discovered in early July 2025, 3I/ATLAS is only the third ISO identified in our solar system, following 1I/`Oumuamua and 2I/Borisov. These ISOs exhibited distinct properties that remain poorly understood, possibly stemming from diverse origins in their parent circumplanetary systems or varying evolutionary stages. To better understand the ISO population, we propose ten HST DD orbits using the WFC3 camera with the F350LP filter to study 3I on its outbound heliocentric trajectory. Our primary scientific objectives are: (1) to obtain high-precision astrometry to evaluate nongravitational effects, (2) to monitor and resolve near-nucleus morphology, (3) to extract the nucleus signal to constrain its size, and (4) to search for potential fragments. No ground-based facility can achieve our goals because of HST's superior angular resolution, sensitivity, and imaging stability. ------------------------------------------------------------------------------------ Observations Description ------------------------ We request ten DD orbits using HST/WFC3 with the F350LP filter to image 3I postperihelion. The broad F350LP filter provides maximum sensitivity to faint coma, enabling detailed study of 3I's near-nucleus dust morphology and better constraints on its nucleus. Individual exposures from the same orbit will be dithered and combined to facilitate the removal of background sources. 3I is projected close to the midplane of the Milky Way and the field star density is correspondingly high. Accurate photometry and astrometry will be obtained only by using multiple images to eliminate contamination by field objects. Similar techniques have been successfully applied to HST observations of 1I and 2I. We propose scheduling the ten orbits starting from late November 2025, when 3I emerges from the solar exclusion zone, with each visits spaced at heliocentric distance intervals of 0.5 au. The final orbit should be completed before the target reenters the solar exclusion zone in early May 2026. The time coverage and high-precision astrometry are both crucial for determining the trajectory of 3I and, in particular in determining the nongravitational acceleration and its heliocentric distance dependency. According to the WFC3 ETC, a single 260 s exposure achieves a signal-to-noise ratio (SNR) of 5 at V-band magnitude 26.5. In each orbit, five such exposures can be obtained. Combining these exposures 18152( 16) - 05-Mar-2026 15:35:40 - [ 2] will further increase the SNR by a factor of 2.2, corresponding to a gain of nearly 1 magnitude. Using the viewing geometry on 2025 December 1 as an example, a 1 km diameter bare nucleus with geometric albedo 0.04 is expected to have apparent magnitude V = 23, well within the capacity of HST. The combined HST image from the same orbit can be used to search for fragments down to 700 m in radius. JPL Horizons predicts the 1-sigma ephemeris uncertainty to be 10 at the time of the HST observations, small enough compared to the WFC3's field of view. As the target remains observable preperihelion, the ephemeris uncertainty will further decrease. Astrometry from the proposed observations will also be included to update the orbit. The accuracy of the HST astrometric measurements is expected to be at the 0.1" level. Therefore, there is no concern to the HST pointing for the proposed program. We understand that we cannot control the spacecraft roll angle, meaning that we will not be able to optimize the orientation such that the tail is directed along the diagonal of the detector. However, WFC3's FOV is far larger than the apparent size of the target that we should obtain exquisite data regardless of the HST roll angle. ------------------------------------------------------------------------------------ 18152( 16) - 05-Mar-2026 15:35:40 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 3 TARGET NAME: 3I-ATLAS-OCT10 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET interstellar object ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=COMET, Q=1.356065570996796, E=6.137350157289094, I=175.1128577937168 , O=322.1522849649193, W=128.0116082517727, T=29-OCT-2025:11:36:17, TTimeScale=TDB, EQUINOX=J2000, EPOCH=28-JUL-2025:00:00:00, EpochTimeScale=TDB ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 19 +/- 5 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 18152( 16) - 05-Mar-2026 15:35:40 - [ 4] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 4 TARGET NAME: 3I-ATLAS-NOV21 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET interstellar object ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=COMET, Q=1.35640569052028, E=6.139362564105249, I=175.1130622033269 , O=322.1561849782609, W=128.0095067807252, T=29-OCT-2025:11:34:25, TTimeScale=TDB, EQUINOX=J2000, EPOCH=30-JUL-2025:00:00:00, EpochTimeScale=TDB, R0=2.808 , DT=0. , A1=4.264217376709E-7, A2=2.000436019897E-7, A3=0. , ALN=0.1112620426, NM=2.15, NN=5.093, NK=4.6142, AMRAT=0. ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 16 +/- 5 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 18152( 16) - 05-Mar-2026 15:35:40 - [ 5] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 5 TARGET NAME: 3I-ATLAS-DEC1 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET interstellar object ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=COMET, Q=1.356404858629546, E=6.139346138450772, I=175.113090485184 , O=322.1566074986231, W=128.0099236586739, T=29-OCT-2025:11:34:27, TTimeScale=TDB, EQUINOX=J2000, EPOCH=04-AUG-2025:00:00:00, EpochTimeScale=TDB, R0=1. , DT=0. , A1=7.199572086334E-8, A2=4.569792747498E-8, A3=-3.925215303898E-9 , ALN=1., NM=2., NN=0., NK=0., AMRAT=0. ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 12 +/- 4 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 18152( 16) - 05-Mar-2026 15:35:40 - [ 6] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 6 TARGET NAME: 3I-ATLAS-DEC17 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET interstellar object ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=COMET, Q=1.356418761995381, E=6.139422831829797, I=175.1130917268881 , O=322.1566239181344, W=128.0096924001076, T=29-OCT-2025:11:34:23, TTimeScale=TDB, EQUINOX=J2000, EPOCH=07-AUG-2025:00:00:00, EpochTimeScale=TDB, R0=1. , DT=0. , A1=4.572104930878E-8, A2=1.862444758415E-8, A3=-5.019464492798E-9 , ALN=1., NM=2., NN=0., NK=0., AMRAT=0. ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 12 +/- 4 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 18152( 16) - 05-Mar-2026 15:35:40 - [ 7] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 7 TARGET NAME: 3I-ATLAS-DEC29 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET interstellar object ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=COMET, Q=1.356421182919772, E=6.139423907689657, I=175.1130967647645 , O=322.1567016652489, W=128.0097235988275, T=29-OCT-2025:11:34:27, TTimeScale=TDB, EQUINOX=J2000, EPOCH=11-AUG-2025:00:00:00, EpochTimeScale=TDB, R0=1. , DT=0. , A1=4.474215507507E-8, A2=1.700624108315E-8, A3=-5.324076414108E-9 , ALN=1., NM=2., NN=0., NK=0., AMRAT=0. ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 12 +/- 4 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 18152( 16) - 05-Mar-2026 15:35:40 - [ 8] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 8 TARGET NAME: 3I-ATLAS-JAN26 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET interstellar object ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=COMET, Q=1.356424890557981, E=6.139409161771214, I=175.1131128947683 , O=322.1569360020026, W=128.0098740554459, T=29-OCT-2025:11:34:38, TTimeScale=TDB, EQUINOX=J2000, EPOCH=20-AUG-2025:00:00:00, EpochTimeScale=TDB, R0=1. , DT=0. , A1=4.533728599548E-8, A2=1.745203018188E-8, A3=-5.953273177147E-9 , ALN=1., NM=2., NN=0., NK=0., AMRAT=0. ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 12 +/- 4 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 18152( 16) - 05-Mar-2026 15:35:40 - [ 9] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 9 TARGET NAME: 3I-ATLAS-MAR5 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET interstellar object ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=COMET, Q=1.356481057231181, E=6.141351449317625, I=175.1164570850441 , O=322.1696089290778, W=128.0228697185194, T=29-OCT-2025:11:53:10, TTimeScale=TDB, EQUINOX=J2000, EPOCH=19-FEB-2026:00:00:00, EpochTimeScale=TDB, R0=1. , DT=9.478815 , A1=5.320206165314E-8, A2=1.148166060448E-8, A3=-6.854491829872E-9 , ALN=1., NM=2., NN=0., NK=0., AMRAT=0. ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 12 +/- 4 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 18152( 16) - 05-Mar-2026 15:35:40 - [ 10] Visit: 01 Visit Requirements: SCHED 30%; BETWEEN 24-NOV-2025:00:00:00 AND 06-DEC-2025:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 3I-ATLAS-OC WFC3/UVI ACCUM UVIS2-2K2 F350LP 3 260 S (780 T10 S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 2 3I-ATLAS-OC WFC3/UVI ACCUM UVIS2-2K2 F350LP 3 260 S (780 POS TARG 0.2, 0.2 T10 S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ 3I-ATLAS-OCT10 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 3I-ATLAS-OCT10 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB 3I-ATLAS-OCT10 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 3 none 1 N/A S 2C-SUB 3I-ATLAS-OCT10 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 3I-ATLAS-OCT10 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB 3I-ATLAS-OCT10 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 3 none 1 N/A S 2C-SUB 18152( 16) - 05-Mar-2026 15:35:40 - [ 11] Visit: 02 Visit Requirements: SCHED 30%; BETWEEN 08-DEC-2025:00:00:00 AND 15-DEC-2025:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 3I-ATLAS-NO WFC3/UVI ACCUM UVIS2-2K2 F350LP 3 260 S (780 V21 S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 2 3I-ATLAS-NO WFC3/UVI ACCUM UVIS2-2K2 F350LP 2 260 S (520 POS TARG 0.2, 0.2 V21 S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ 3I-ATLAS-NOV21 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 3I-ATLAS-NOV21 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB 3I-ATLAS-NOV21 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 3 none 1 N/A S 2C-SUB 3I-ATLAS-NOV21 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 3I-ATLAS-NOV21 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB 18152( 16) - 05-Mar-2026 15:35:40 - [ 12] Visit: 03 Visit Requirements: SCHED 30%; BETWEEN 22-DEC-2025:00:00:00 AND 29-DEC-2025:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 3I-ATLAS-DE WFC3/UVI ACCUM UVIS2-2K2 F350LP FLASH=5 2 170 S (340 C1 S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 2 3I-ATLAS-DE WFC3/UVI ACCUM UVIS2-2K2 F350LP FLASH=5 3 170 S (510 POS TARG 0.2, 0.2 C1 S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ 3I-ATLAS-DEC1 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 3I-ATLAS-DEC1 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB 3I-ATLAS-DEC1 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 3I-ATLAS-DEC1 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB 3I-ATLAS-DEC1 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 3 none 1 N/A S 2C-SUB 18152( 16) - 05-Mar-2026 15:35:40 - [ 13] Visit: 04 Visit Requirements: SCHED 30%; BETWEEN 05-JAN-2026:00:00:00 AND 12-JAN-2026:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 3I-ATLAS-DE WFC3/UVI ACCUM UVIS2-2K2 F350LP FLASH=5 3 170 S (510 C17 S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 2 3I-ATLAS-DE WFC3/UVI ACCUM UVIS2-2K2 F350LP FLASH=5 4 170 S (680 POS TARG 0.2, 0.2 C17 S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ 3I-ATLAS-DEC17 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 3I-ATLAS-DEC17 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB 3I-ATLAS-DEC17 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 3 none 1 N/A S 2C-SUB 3I-ATLAS-DEC17 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 3I-ATLAS-DEC17 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB 3I-ATLAS-DEC17 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 3 none 1 N/A S 2C-SUB 3I-ATLAS-DEC17 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 4 none 1 N/A S 2C-SUB 18152( 16) - 05-Mar-2026 15:35:40 - [ 14] Visit: 05 Visit Requirements: SCHED 30%; BETWEEN 14-JAN-2026:00:00:00 AND 18-JAN-2026:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 3I-ATLAS-DE WFC3/UVI ACCUM UVIS2-2K2 F350LP FLASH=5 3 170 S (510 C17 S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 2 3I-ATLAS-DE WFC3/UVI ACCUM UVIS2-2K2 F350LP FLASH=5 3 170 S (510 POS TARG 0.2, 0.2 C17 S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ 3I-ATLAS-DEC17 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 3I-ATLAS-DEC17 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB 3I-ATLAS-DEC17 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 3 none 1 N/A S 2C-SUB 3I-ATLAS-DEC17 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 3I-ATLAS-DEC17 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB 3I-ATLAS-DEC17 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 3 none 1 N/A S 2C-SUB 18152( 16) - 05-Mar-2026 15:35:40 - [ 15] Visit: 06 Visit Requirements: SCHED 30%; BETWEEN 22-JAN-2026:00:00:00 AND 24-JAN-2026:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 3I-ATLAS-DE WFC3/UVI ACCUM UVIS2-2K2 F350LP FLASH=5 3 170 S (510 C29 S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 2 3I-ATLAS-DE WFC3/UVI ACCUM UVIS2-2K2 F350LP FLASH=5 3 170 S (510 POS TARG 0.2, 0.2 C29 S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ 3I-ATLAS-DEC29 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 3I-ATLAS-DEC29 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB 3I-ATLAS-DEC29 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 3 none 1 N/A S 2C-SUB 3I-ATLAS-DEC29 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 3I-ATLAS-DEC29 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB 3I-ATLAS-DEC29 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 3 none 1 N/A S 2C-SUB 18152( 16) - 05-Mar-2026 15:35:40 - [ 16] Visit: 07 Visit Requirements: BETWEEN 09-FEB-2026:00:00:00 AND 23-FEB-2026:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 3I-ATLAS-JA WFC3/UVI ACCUM UVIS2-FIX F350LP FLASH=5 2 35 S (70 N26 S S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ 3I-ATLAS-JAN26 1 WFC3/UVI ACCUM UVIS2-FI F350LP none none 1 none 1 N/A S X 3I-ATLAS-JAN26 1 WFC3/UVI ACCUM UVIS2-FI F350LP none none 2 none 1 N/A S X 18152( 16) - 05-Mar-2026 15:35:40 - [ 17] Visit: 08 Visit Requirements: BETWEEN 09-FEB-2026:00:00:00 AND 23-FEB-2026:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 3I-ATLAS-JA WFC3/UVI ACCUM UVIS2-FIX F350LP FLASH=5 2 35 S (70 N26 S S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ 3I-ATLAS-JAN26 1 WFC3/UVI ACCUM UVIS2-FI F350LP none none 1 none 1 N/A S X 3I-ATLAS-JAN26 1 WFC3/UVI ACCUM UVIS2-FI F350LP none none 2 none 1 N/A S X 18152( 16) - 05-Mar-2026 15:35:40 - [ 18] Visit: 09 Visit Requirements: BETWEEN 30-MAR-2026:00:00:00 AND 27-APR-2026:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 3I-ATLAS-MA WFC3/UVI ACCUM UVIS2-FIX F350LP FLASH=5 2 35 S (70 R5 S S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ 3I-ATLAS-MAR5 1 WFC3/UVI ACCUM UVIS2-FI F350LP none none 1 none 1 N/A S X 3I-ATLAS-MAR5 1 WFC3/UVI ACCUM UVIS2-FI F350LP none none 2 none 1 N/A S X 18152( 16) - 05-Mar-2026 15:35:40 - [ 19] Visit: 10 Visit Requirements: BETWEEN 30-MAR-2026:00:00:00 AND 27-APR-2026:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 3I-ATLAS-MA WFC3/UVI ACCUM UVIS2-FIX F350LP FLASH=5 2 35 S (70 R5 S S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ 3I-ATLAS-MAR5 1 WFC3/UVI ACCUM UVIS2-FI F350LP none none 1 none 1 N/A S X 3I-ATLAS-MAR5 1 WFC3/UVI ACCUM UVIS2-FI F350LP none none 2 none 1 N/A S X 18152( 16) - 05-Mar-2026 15:35:40 - [ 20] Visit: 22 Visit Requirements: SCHED 30%; BETWEEN 08-DEC-2025:00:00:00 AND 15-DEC-2025:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 3I-ATLAS-DE WFC3/UVI ACCUM UVIS2-2K2 F350LP FLASH=5 3 170 S (510 C1 S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 2 3I-ATLAS-DE WFC3/UVI ACCUM UVIS2-2K2 F350LP FLASH=5 3 170 S (510 POS TARG 0.2, 0.2 C1 S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ 3I-ATLAS-DEC1 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 3I-ATLAS-DEC1 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB 3I-ATLAS-DEC1 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 3 none 1 N/A S 2C-SUB 3I-ATLAS-DEC1 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 3I-ATLAS-DEC1 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB 3I-ATLAS-DEC1 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 3 none 1 N/A S 2C-SUB 18152( 16) - 05-Mar-2026 15:35:40 - [ 21] Summary Form for Proposal 18152 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-2K2C-SUB, UVIS2-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=5 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 05-JAN-2026:00:00:00 AND 12-JAN-2026:00:00:00, BETWEEN 08-DEC-2025:00:00:00 AND 15-DEC-2025:00:00:00, BETWEEN 09-FEB-2026:00:00:00 AND 23-FEB-2026:00:00:00, BETWEEN 14-JAN-2026:00:00:00 AND 18-JAN-2026:00:00:00, BETWEEN 22-DEC-2025:00:00:00 AND 29-DEC-2025:00:00:00, BETWEEN 22-JAN-2026:00:00:00 AND 24-JAN-2026:00:00:00, BETWEEN 24-NOV-2025:00:00:00 AND 06-DEC-2025:00:00:00, BETWEEN 30-MAR-2026:00:00:00 AND 27-APR-2026:00:00:00, POS TARG 0.2, 0.2, SCHED 30% ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F350LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names 3I-ATLAS-DEC1, 3I-ATLAS-DEC17, 3I-ATLAS-DEC29, 3I-ATLAS-JAN26, 3I-ATLAS-MAR5, 3I-ATLAS-NOV21, 3I-ATLAS-OCT10 ------------------------------------------------------------------------------------------------------------------------------------