0 Assigned ID: 7230 ----- Attempting Submission 1 (Wed Apr 15 22:34:41 GMT 2026) ----- HST Phase I Proposal 7230 successfully submitted. Receipt: # 7230-1 0 ----- Attempting Submission 1 (Tue Aug 18 18:31:51 GMT 2026) ----- Enabling New Horizons Observations of Distant Scattered Disk Objects This program would observe up to three Target of Opportunity Scattered Disk Objects (SDOs) discovered in 2025 observations by the Vera C. Rubin Observatory (Rubin) in order to enable them to be observed up close by the New Horizons spacecraft. The Scattered Disk occupies a vast area of solar system beyond 55 AU, and the New Horizons spacecraft is the only facility now or in the foreseeable future that observe SDOs at distances less than 1 AU and phase angles up to 120 degrees (SDOs can only be seen at <2 degrees phase from Earth). These high-phase observations of SDOs would enable studies of their shapes and surfaces, critical for understanding both their origin in the Giant Planet zone and how SDOs presently evolve to become comets. The 2025 Rubin observations are presently being analyzed for any objects that may be observable by New Horizons. The ground based astrometry from Rubin and follow up from Subaru is sufficient to tell if an SDO is possibly observable from New Horizons, but not sufficient to actually enable those observations. The proposed HST observations would provide sufficient quality astrometry to enable the New Horizons observations of these SDOs without further follow up. Adding to the urgency, New Horizons is moving rapidly out of the solar system, and every year these SDO observations become harder to perform. The purpose of this proposal is to observe up to three Kuiper Belt Objects (KBOs) to obtain astrometry to improve their orbit enought that can be observed by New Horizons in 2027-2030. Those targets are not currently known, but will be deifned by the end of the calendar year 2026. Nominally, two orbits are allocated per target, for a max of three targets. Any targets would be roughly in the same area of the sky (within a degree or so) as the one already confirmed 2027 New Horizons target, 2020 KV11, and so we used the orbit of that KBO as nominal placeholder for planning purposes. We would update the Phase II with the correct orbits (by entering the orbital elements directly) before triggering the TOO. The nominal plan has the objects separated by 30 days, though there could be some flexibility in that timing (depending on the sky motion of the KBO) if required for schedulability. All the visits are the same, using a 4-point box dither with the full frame WFC3/UVIS and the F350LP broadband filter. We need a few Gaia DR3 stars in the field for absolute astrometry, but the expected star density is high enough that this is unlikely be a problem. Dr. Simon B. Porter is an expert in HST KBO observation and analysis, has led several HST proposals investigating binary KBOs (GO-14616 and SNAP-15821), performing astrometry in support of the New Horizons mission (GO-16183, GO-16924) and the astrometry of Pluto satellites (GO-17835), and is a New Horizons CoI. Dr. Susan D. Benecchi is an expert in KBO photometric and color observation and analysi and was for PI for color observations of New Horizons target KBOs (GO-12535, GO-12887, GO-13311, GO-13663, GO-14092) as well as the only Earth-based lightcurve of the New Horizons flyby target Arrokoth (GO-14627), and is a New Horizons CoI. Dr. Anne J. Verbiscer is an expert in KBO photometric analysis and was PI on HST observations of the moons of Saturn (GO-10357) and the moons of Pluto (GO-15261 and GO-15505) and is a New Horizons CoI. Dr. Wesley Fraser is the PI of the Col-OSSOS program that has provided the first colors for faint SDOs, has led multiple HST KBO programs (GO-12234 and GO-16167) and is a New Horizons Collaborator. Dr. JJ Kavelaars is an expert in observing and discovering KBOs from ground based facilities, led HST programs to recover New Horizons targets (GO-15108 and GO-15492) and is a New Horizons CoI. Dr. Alan Stern is an expert in the Kuiper Belt and is the New Horizons PI. Solar System Astronomy 6 false false false false false false false SUPPORTED SOLAR SYSTEM ASTEROID New Horizons KBO 1 TYPE=ASTEROID,A=100.783874222854,E=0.099773153155,I=3.314572022986,O=166.914905426798,W=331.176766747966,M=141.121051314833,EQUINOX=J2000,EPOCH=29-MAY-2020:11:22:33,EpochTimeScale=UTC EARTH SOLAR SYSTEM ASTEROID New Horizons KBO 2 TYPE=ASTEROID,A=100.783874222854,E=0.099773153155,I=3.314572022986,O=166.914905426798,W=331.176766747966,M=141.121051314833,EQUINOX=J2000,EPOCH=29-MAY-2020:11:22:33,EpochTimeScale=UTC EARTH SOLAR SYSTEM ASTEROID New Horizons KBO 3 TYPE=ASTEROID,A=100.783874222854,E=0.099773153155,I=3.314572022986,O=166.914905426798,W=331.176766747966,M=141.121051314833,EQUINOX=J2000,EPOCH=29-MAY-2020:11:22:33,EpochTimeScale=UTC EARTH WFC3/UVIS Imaging No No F350LP WFC3/UVIS Imaging No No F350LP WFC3/UVIS Imaging No No F350LP WFC3/UVIS Imaging No No F350LP WFC3/UVIS Imaging No No F350LP WFC3/UVIS Imaging No No F350LP POS-TARG OTHER 0.173 LINE 0.112 false false 81.785 4 23.884 BOX 1 false /tmp/OPVisit13319501849666039605.xml Timing link suitability includes constraints ([02 After 01 by 30.0 to 1000.0 days]) The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18426 :visit-id "01" :proposal-version -1 :trans-version "20260618" :date "17-Aug-2026 12:44:59.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18426 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18426 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2598 :al-overhead-at-end 0 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 /tmp/OPVisit16682379463680640430.xml Timing link suitability includes constraints ([02 After 01 by 30.0 to 1000.0 days]) The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18426 :visit-id "02" :proposal-version -1 :trans-version "20260618" :date "17-Aug-2026 12:45:00.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18426 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18426 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2598 :al-overhead-at-end 0 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 /tmp/OPVisit14236581435579017037.xml Timing link suitability includes constraints ([04 After 03 by 30.0 to 1000.0 days]) The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18426 :visit-id "03" :proposal-version -1 :trans-version "20260618" :date "17-Aug-2026 12:45:00.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18426 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18426 :visit-id "03" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2598 :al-overhead-at-end 0 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 /tmp/OPVisit10693009821297550658.xml Timing link suitability includes constraints ([04 After 03 by 30.0 to 1000.0 days]) The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18426 :visit-id "04" :proposal-version -1 :trans-version "20260618" :date "17-Aug-2026 12:45:01.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18426 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18426 :visit-id "04" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2598 :al-overhead-at-end 0 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 /tmp/OPVisit16714232841641712831.xml Timing link suitability includes constraints ([06 After 05 by 30.0 to 1000.0 days]) The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18426 :visit-id "05" :proposal-version -1 :trans-version "20260618" :date "17-Aug-2026 12:45:01.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18426 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18426 :visit-id "05" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2598 :al-overhead-at-end 0 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 /tmp/OPVisit8943132296777037843.xml Timing link suitability includes constraints ([06 After 05 by 30.0 to 1000.0 days]) The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18426 :visit-id "06" :proposal-version -1 :trans-version "20260618" :date "17-Aug-2026 12:45:02.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18426 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18426 :visit-id "06" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2598 :al-overhead-at-end 0 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0