18397( 3) - 27-Aug-2026 17:58:31 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18397 Version: 3 Check-in Time: 27-Aug-2026 17:58:31 STScI Edit Number: 1 Title Testing The Refractory Sulfur Reservoir Hypothesis with the Next Interstellar Object ------------------------------------------------------------------------------------ Type Cycle GO 34 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. John W Noonan Auburn University Y CoI: Dr. Dennis Bodewits Auburn University N CoI: Dr. Martin A. Cordiner Catholic University of America N CoI: Dr. Nathan X. Roth American University N CoI: Dr. Davide Farnocchia Jet Propulsion Laboratory N CoI: Dr. Marco Micheli ESA, SSA-NEO Coordination Centre N ------------------------------------------------------------------------------------ Abstract Comets are the leftovers of the era of solar system formation and, as such contain some of the most primitive materials available for study. Interstellar comets allow us to probe the volatile and organic composition of a protoplanetary disk's cold midplane, where sub-mm and IR observations cannot penetrate. Within those disks, sulfur reservoirs are currently a major source of interest in the astrophysics community as less than 0.1% of the cosmic abundance of sulfur can be traced in gas species. Recent studies imply that the missing sulfur is trapped in refractory components, but which minerals are not yet clear. Ejected icy planetesimals offer unique opportunities to investigate sulfur-bearing species that would be locked in ice or dust in the midplane of these protoplanetary disks, revealed by an interstellar object's heating as it enters our solar system. With the first light of LSST it is highly anticipated that several more will be discovered in the next few years. The time domain observations measured with HST COS and JWST during the apparition of 2I/Borisov and 3I/ATLAS resulted in a more complete picture of the chemical composition of those volatiles present in another planetary system, but did not provide conclusive results on sulfur-bearing species. We propose a Target of Opportunity program to observe the next active interstellar object, which has yet to be discovered. We will quantify its CO, CS, S2, and atomic sulfur reservoirs, a combination of species that is unique to HST's far-ultraviolet (FUV) capability, and measure the sulfur-to-oxygen ratio while providing unparalleled sensitivity to the commonly occurring cometary species OH. ------------------------------------------------------------------------------------ Observations Description ------------------------ 1. Overall observational strategy We plan to observe the next active interstellar object with V<15 with two instrument settings, COS G160M CENWAVE 1589 A and STIS G230L, in two temporally separated epochs. The FOV will be centered at the comet. Therefore, we will use the same 4 visit (7 orbit) observing sequence (3 COS visits and one STIS visit) for each epoch. The sequence in each 2-orbit COS visit is: 18397( 3) - 27-Aug-2026 17:58:31 - [ 2] ACQ/IMAGE in NUV MIRROR A with PSA setting, 30 s exposure G160M FP-POS# 1794 s G160M FP-POS# 1794 s ACQ/IMAGE in NUV MIRROR A with PSA setting, 30 s exposure We will alternate the FP positions to cycle through all four FP-POS in each epoch. The first 2 visits in an epoch will cycle through FP-POS 1-4, one FP per orbit. For the third COS visit in each epoch the sequence is: ACQ/IMAGE in NUV MIRROR A with PSA setting, 30 s exposure G160M FP-POS1 897 s G160M FP-POS# 897 s The 3rd visit cycles FP-POS=1 and FP-POS=2 in a single orbit. The trailing ACQ/IMAGE used in for the first and second COS visits is eliminated to improve science overhead. This leads to a total exposure time in FP 1 and 2 each of 2691 s and 1794 s for each FP 3 and 4, for a total exposure time of 8970 s over 5 orbits. The exposure time is based on COS ETC run #COS.sp.1928787. The sequence for each 2-orbit STIS G230L visit is: ACQ in MIRROR with F28X50LP, 3 s exposure G230L with 52X0.5, 1900 s exposure IMAGE in MIRROR with F28X50LP, 3 s G230L with 52X0.5, 19000 s exposure IMAGE in MIRROR with F28X50LP This leads to a total exposure time of 3800s over two orbits. The exposure time is based on STIS ETC run #STIS.sp.1928799 2. Comet position uncertainty and acquisition: Upon discovery the next active interstellar object we will work rapidly to improve the ephemerides uncertainties. If it becomes clear that we should expect a 3-sigma uncertainty in RA or DEC in the range of 1.5" we will replace the primary ACQ/IMAGE in each COS visit with an ACQ/SEARCH pattern to ensure detection. ------------------------------------------------------------------------------------ 18397( 3) - 27-Aug-2026 17:58:31 - [ 3] TARGET LIST Generic Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Selection Criteria | Flux data No | Name | Description | | ------------------------------------------------------------------------------------------------------------------------------------ 1 ISO-4I SOLAR SYSTEM, COMET ACTIVE INTERSTELLAR COMET V = 12 +/- 5 Comments: We will trigger our ToO upon the detection of an active ISO, that is, with an hyperbolic orbit with a barycentric eccentricity significantly greater than unity as reported by the JPL Small-body Database, that has a perihelion within 2 au and reaches at least V=15. Activity will be defined as having a distinct coma upon detection that manifests as a nonstellar point spread function in discovery images and that persists in all follow-up observations. We will coordinate with the JWST ToO team to trigger on the same object and focus HST's capability near perihelion, where JWST may not be able to observe depending on the object's path through the solar system. ------------------------------------------------------------------------------------------------------------------------------------ 18397( 3) - 27-Aug-2026 17:58:31 - [ 4] Visit: 01 (Epoch 1 : FP1) Visit Requirements: SCHED 100%; GROUP 01, 02, 03, 04, 05, 06, 07 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I COS/NUV ACQ/IMA PSA MIRRORA 1 30 S (30 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I COS/FUV TIME-TA PSA G160M 1589 FP-POS=1, BUFFER-TIME=10000, 1 1700 S G LIFETIME-POS=LP10 (1700 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE ISO-4I 2 COS/FUV TIME-TA PSA G160M 1589 none none none none 1 N/A G 18397( 3) - 27-Aug-2026 17:58:31 - [ 5] Visit: 02 (Epoch 1 : FP2) Visit Requirements: SCHED 100%; GROUP 02, 01, 03, 04, 05, 06, 07 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I COS/NUV ACQ/IMA PSA MIRRORA 1 30 S (30 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I COS/FUV TIME-TA PSA G160M 1589 FP-POS=2, BUFFER-TIME=10000, 1 1700 S G LIFETIME-POS=LP10 (1700 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE ISO-4I 2 COS/FUV TIME-TA PSA G160M 1589 none none none none 1 N/A G 18397( 3) - 27-Aug-2026 17:58:31 - [ 6] Visit: 03 (Epoch 1 : FP3) Visit Requirements: SCHED 100%; GROUP 03, 01, 02, 04, 05, 06, 07 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I COS/NUV ACQ/IMA PSA MIRRORA 1 30 S (30 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I COS/FUV TIME-TA PSA G160M 1589 FP-POS=3, BUFFER-TIME=10000, 1 1700 S G LIFETIME-POS=LP10 (1700 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE ISO-4I 2 COS/FUV TIME-TA PSA G160M 1589 none none none none 1 N/A G 18397( 3) - 27-Aug-2026 17:58:31 - [ 7] Visit: 04 (Epoch 1 : FP4) Visit Requirements: SCHED 100%; GROUP 04, 01, 02, 03, 05, 06, 07 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I COS/NUV ACQ/IMA PSA MIRRORA 1 30 S (30 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I COS/FUV TIME-TA PSA G160M 1589 FP-POS=4, BUFFER-TIME=10000, 1 1700 S G LIFETIME-POS=LP10 (1700 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE ISO-4I 2 COS/FUV TIME-TA PSA G160M 1589 none none none none 1 N/A G 18397( 3) - 27-Aug-2026 17:58:31 - [ 8] Visit: 05 (Epoch 1 : FP1) Visit Requirements: SCHED 100%; GROUP 05, 01, 02, 03, 04, 06, 07 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I COS/NUV ACQ/IMA PSA MIRRORA 1 30 S (30 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I COS/FUV TIME-TA PSA G160M 1589 FP-POS=1, BUFFER-TIME=10000, 1 1700 S G LIFETIME-POS=LP10 (1700 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE ISO-4I 2 COS/FUV TIME-TA PSA G160M 1589 none none none none 1 N/A G 18397( 3) - 27-Aug-2026 17:58:31 - [ 9] Visit: 06 (Epoch 1: STIS G230L) Visit Requirements: GROUP 06, 01, 02, 03, 04, 05, 07 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I STIS/CCD ACQ F28X50LP MIRROR 1 3 S (3 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=99 1 1500 S -MAMA G (1500 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ISO-4I STIS/CCD ACCUM F28X50LP MIRROR 1 15 S (15 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A ISO-4I 2 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 1 N/A -MAMA G ISO-4I 3 STIS/CCD ACCUM F28X50LP MIRROR none none none 1 1 N/A ISO-4I 3 STIS/CCD ACCUM F28X50LP MIRROR none none none 2 1 N/A 18397( 3) - 27-Aug-2026 17:58:31 - [ 10] Visit: 07 (Epoch 1: STIS G230L) Visit Requirements: GROUP 07, 01, 02, 03, 04, 05, 06 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I STIS/CCD ACQ F28X50LP MIRROR 1 3 S (3 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=99 1 1500 S -MAMA G (1500 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ISO-4I STIS/CCD ACCUM F28X50LP MIRROR 1 15 S (15 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A ISO-4I 2 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 1 N/A -MAMA G ISO-4I 3 STIS/CCD ACCUM F28X50LP MIRROR none none none 1 1 N/A ISO-4I 3 STIS/CCD ACCUM F28X50LP MIRROR none none none 2 1 N/A 18397( 3) - 27-Aug-2026 17:58:31 - [ 11] Visit: 08 (Epoch 2 : FP1) Visit Requirements: SCHED 100%; GROUP 08, 09, 10, 11, 12, 13, 14 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I COS/NUV ACQ/IMA PSA MIRRORA 1 30 S (30 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I COS/FUV TIME-TA PSA G160M 1589 FP-POS=1, BUFFER-TIME=10000, 1 1700 S G LIFETIME-POS=LP10 (1700 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE ISO-4I 2 COS/FUV TIME-TA PSA G160M 1589 none none none none 1 N/A G 18397( 3) - 27-Aug-2026 17:58:31 - [ 12] Visit: 09 (Epoch 2 : FP1) Visit Requirements: SCHED 100%; GROUP 09, 08, 10, 11, 12, 13, 14 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I COS/NUV ACQ/IMA PSA MIRRORA 1 30 S (30 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I COS/FUV TIME-TA PSA G160M 1589 FP-POS=1, BUFFER-TIME=10000, 1 1700 S G LIFETIME-POS=LP10 (1700 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE ISO-4I 2 COS/FUV TIME-TA PSA G160M 1589 none none none none 1 N/A G 18397( 3) - 27-Aug-2026 17:58:31 - [ 13] Visit: 10 (Epoch 2 : FP2) Visit Requirements: SCHED 100%; GROUP 10, 08, 09, 11, 12, 13, 14 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I COS/NUV ACQ/IMA PSA MIRRORA 1 30 S (30 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I COS/FUV TIME-TA PSA G160M 1589 FP-POS=2, BUFFER-TIME=10000, 1 1700 S G LIFETIME-POS=LP10 (1700 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE ISO-4I 2 COS/FUV TIME-TA PSA G160M 1589 none none none none 1 N/A G 18397( 3) - 27-Aug-2026 17:58:31 - [ 14] Visit: 11 (Epoch 2 : FP3) Visit Requirements: SCHED 100%; GROUP 11, 08, 09, 10, 12, 13, 14 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I COS/NUV ACQ/IMA PSA MIRRORA 1 30 S (30 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I COS/FUV TIME-TA PSA G160M 1589 FP-POS=3, BUFFER-TIME=10000, 1 1700 S G LIFETIME-POS=LP10 (1700 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE ISO-4I 2 COS/FUV TIME-TA PSA G160M 1589 none none none none 1 N/A G 18397( 3) - 27-Aug-2026 17:58:31 - [ 15] Visit: 12 (Epoch 2 : FP4) Visit Requirements: SCHED 100%; GROUP 12, 08, 09, 10, 11, 13, 14 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I COS/NUV ACQ/IMA PSA MIRRORA 1 30 S (30 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I COS/FUV TIME-TA PSA G160M 1589 FP-POS=4, BUFFER-TIME=10000, 1 1700 S G LIFETIME-POS=LP10 (1700 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE ISO-4I 2 COS/FUV TIME-TA PSA G160M 1589 none none none none 1 N/A G 18397( 3) - 27-Aug-2026 17:58:31 - [ 16] Visit: 13 (Epoch 2: STIS G230L) Visit Requirements: GROUP 13, 08, 09, 10, 11, 12, 14 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I STIS/CCD ACQ F28X50LP MIRROR 1 3 S (3 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=99 1 1500 S -MAMA G (1500 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ISO-4I STIS/CCD ACCUM F28X50LP MIRROR 1 15 S (15 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A ISO-4I 2 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 1 N/A -MAMA G ISO-4I 3 STIS/CCD ACCUM F28X50LP MIRROR none none none 1 1 N/A ISO-4I 3 STIS/CCD ACCUM F28X50LP MIRROR none none none 2 1 N/A 18397( 3) - 27-Aug-2026 17:58:31 - [ 17] Visit: 14 (Epoch 2: STIS G230L) Visit Requirements: GROUP 14, 08, 09, 10, 11, 12, 13 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I STIS/CCD ACQ F28X50LP MIRROR 1 3 S (3 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=99 1 1500 S -MAMA G (1500 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ISO-4I STIS/CCD ACCUM F28X50LP MIRROR 1 15 S (15 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A ISO-4I 2 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 1 N/A -MAMA G ISO-4I 3 STIS/CCD ACCUM F28X50LP MIRROR none none none 1 1 N/A ISO-4I 3 STIS/CCD ACCUM F28X50LP MIRROR none none none 2 1 N/A 18397( 3) - 27-Aug-2026 17:58:31 - [ 18] Visit: 15 (Epoch 3 : FP1) Visit Requirements: SCHED 100%; GROUP 15, 16, 17, 18, 19, 20, 21 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I COS/NUV ACQ/IMA PSA MIRRORA 1 30 S (30 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I COS/FUV TIME-TA PSA G160M 1589 FP-POS=1, BUFFER-TIME=10000, 1 1700 S G LIFETIME-POS=LP10 (1700 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE ISO-4I 2 COS/FUV TIME-TA PSA G160M 1589 none none none none 1 N/A G 18397( 3) - 27-Aug-2026 17:58:31 - [ 19] Visit: 16 (Epoch 3 : FP1) Visit Requirements: SCHED 100%; GROUP 16, 15, 17, 18, 19, 20, 21 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I COS/NUV ACQ/IMA PSA MIRRORA 1 30 S (30 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I COS/FUV TIME-TA PSA G160M 1589 FP-POS=1, BUFFER-TIME=10000, 1 1700 S G LIFETIME-POS=LP10 (1700 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE ISO-4I 2 COS/FUV TIME-TA PSA G160M 1589 none none none none 1 N/A G 18397( 3) - 27-Aug-2026 17:58:31 - [ 20] Visit: 17 (Epoch 3 : FP2) Visit Requirements: SCHED 100%; GROUP 17, 15, 16, 18, 19, 20, 21 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I COS/NUV ACQ/IMA PSA MIRRORA 1 30 S (30 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I COS/FUV TIME-TA PSA G160M 1589 FP-POS=2, BUFFER-TIME=10000, 1 1700 S G LIFETIME-POS=LP10 (1700 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE ISO-4I 2 COS/FUV TIME-TA PSA G160M 1589 none none none none 1 N/A G 18397( 3) - 27-Aug-2026 17:58:31 - [ 21] Visit: 18 (Epoch 3 : FP3) Visit Requirements: SCHED 100%; GROUP 18, 15, 16, 17, 19, 20, 21 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I COS/NUV ACQ/IMA PSA MIRRORA 1 30 S (30 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I COS/FUV TIME-TA PSA G160M 1589 FP-POS=3, BUFFER-TIME=10000, 1 1700 S G LIFETIME-POS=LP10 (1700 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE ISO-4I 2 COS/FUV TIME-TA PSA G160M 1589 none none none none 1 N/A G 18397( 3) - 27-Aug-2026 17:58:31 - [ 22] Visit: 19 (Epoch 3 : FP4) Visit Requirements: SCHED 100%; GROUP 19, 15, 16, 17, 18, 20, 21 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I COS/NUV ACQ/IMA PSA MIRRORA 1 30 S (30 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I COS/FUV TIME-TA PSA G160M 1589 FP-POS=4, BUFFER-TIME=10000, 1 1700 S G LIFETIME-POS=LP10 (1700 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE ISO-4I 2 COS/FUV TIME-TA PSA G160M 1589 none none none none 1 N/A G 18397( 3) - 27-Aug-2026 17:58:31 - [ 23] Visit: 20 (Epoch 3: STIS G230L) Visit Requirements: GROUP 20, 15, 16, 17, 18, 19, 21 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I STIS/CCD ACQ F28X50LP MIRROR 1 3 S (3 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=99 1 1500 S -MAMA G (1500 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ISO-4I STIS/CCD ACCUM F28X50LP MIRROR 1 15 S (15 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A ISO-4I 2 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 1 N/A -MAMA G ISO-4I 3 STIS/CCD ACCUM F28X50LP MIRROR none none none 1 1 N/A ISO-4I 3 STIS/CCD ACCUM F28X50LP MIRROR none none none 2 1 N/A 18397( 3) - 27-Aug-2026 17:58:31 - [ 24] Visit: 21 (Epoch 3: STIS G230L) Visit Requirements: GROUP 21, 15, 16, 17, 18, 19, 20 WITHIN 7D; ON HOLD ; TOO MIN RESPONSE TIME 21.0D; TOO MAX RESPONSE TIME 60.0D On Hold Comments: We are on hold to activate for an active ISO that is observable by HST and will reach a minimum magnitude of 17. 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 ISO-4I STIS/CCD ACQ F28X50LP MIRROR 1 3 S (3 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ISO-4I STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=99 1 1500 S -MAMA G (1500 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ISO-4I STIS/CCD ACCUM F28X50LP MIRROR 1 15 S (15 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISO-4I 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A ISO-4I 2 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 1 N/A -MAMA G ISO-4I 3 STIS/CCD ACCUM F28X50LP MIRROR none none none 1 1 N/A ISO-4I 3 STIS/CCD ACCUM F28X50LP MIRROR none none none 2 1 N/A 18397( 3) - 27-Aug-2026 17:58:31 - [ 25] Summary Form for Proposal 18397 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X2, F28X50LP, PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV, STIS/CCD, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ, ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=10000, BUFFER-TIME=99, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4, LIFETIME-POS=LP10 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GROUP 01, 02, 03, 04, 05, 06, 07 WITHIN 7D, GROUP 02, 01, 03, 04, 05, 06, 07 WITHIN 7D, GROUP 03, 01, 02, 04, 05, 06, 07 WITHIN 7D, GROUP 04, 01, 02, 03, 05, 06, 07 WITHIN 7D, GROUP 05, 01, 02, 03, 04, 06, 07 WITHIN 7D, GROUP 06, 01, 02, 03, 04, 05, 07 WITHIN 7D, GROUP 07, 01, 02, 03, 04, 05, 06 WITHIN 7D, GROUP 08, 09, 10, 11, 12, 13, 14 WITHIN 7D, GROUP 09, 08, 10, 11, 12, 13, 14 WITHIN 7D, GROUP 10, 08, 09, 11, 12, 13, 14 WITHIN 7D, GROUP 11, 08, 09, 10, 12, 13, 14 WITHIN 7D, GROUP 12, 08, 09, 10, 11, 13, 14 WITHIN 7D, GROUP 13, 08, 09, 10, 11, 12, 14 WITHIN 7D, GROUP 14, 08, 09, 10, 11, 12, 13 WITHIN 7D, GROUP 15, 16, 17, 18, 19, 20, 21 WITHIN 7D, GROUP 16, 15, 17, 18, 19, 20, 21 WITHIN 7D, GROUP 17, 15, 16, 18, 19, 20, 21 WITHIN 7D, GROUP 18, 15, 16, 17, 19, 20, 21 WITHIN 7D, GROUP 19, 15, 16, 17, 18, 20, 21 WITHIN 7D, GROUP 20, 15, 16, 17, 18, 19, 21 WITHIN 7D, GROUP 21, 15, 16, 17, 18, 19, 20 WITHIN 7D, ON HOLD , SCHED 100%, TOO MAX RESPONSE TIME 60.0D, TOO MIN RESPONSE TIME 21.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G160M, G230L, MIRROR, MIRRORA ------------------------------------------------------------------------------------------------------------------------------------ Target Names ISO-4I ------------------------------------------------------------------------------------------------------------------------------------