----- Submission 1 (Mon Dec 13 19:19:38 GMT 2004) ----- Assigned ID: 1021 ----- Submission 1 (Mon Jul 12 15:06:14 GMT 2004) ----- Phase I Proposal 1021 (phase13-DD) successfully submitted. Saturn's Inner Satellites at True Opposition We request one HST orbit to observe Janus, Epimetheus, Mimas, and Enceladus with WFPC2 exactly at opposition, when the Earth transits the center of the solar disk seen from Saturn on UT 13/14 January 2005. Data obtained at this unique viewing geometry are essential to determining physical properties of the moon's surface, related to its emplacement and evolution, and critical for the interpretation of photometric data obtained by Cassini at higher phase angles. This single observation will be the capstone of 9 years of legacy HST WFPC2 observations of the saturnian system (Cycles 6-12, R. French, PI) from which we have constructed precise, multiwavelength phase curves which demonstrate how the reflectance of these satellites varies with solar phase angle from 0.07 to 6.4 degrees. Each satellite exhibits a dramatic increase in brightness, or "opposition effect", as phase angles decrease below 1 degree. Since 1998 (Cycle 7) the minimum observable phase angle at opposition has decreased each year to 0.07 degrees in Cycle 12; however, the absolute minimum observable phase angle, about 0.02 degrees (limited by the angular size of the Sun viewed from Saturn), has not been accessible until Cycle 13. Using the same set of broadband filters for continuity with our previous programs, we will place observations made during the Earth transit on the existing UVBRI phase curves and establish the amplitude of each satellite's opposition surge. From these observations we will determine surface properties such as porosity, grain size distribution and particle opacity using radiative transfer models. While the Cassini spacecraft will obtain images at larger phase angles, it will miss entirely the narrow brightness surge near opposition due to orbital constraints. Because these inner satellites will be either lost in or contaminated by the glare of the fully open rings, they are not accessible to ground-based telescopes. The 2005 opposition prese nts the only opportunity for HST to observe the saturnian system during this rare planetary alignment. The next transit of Earth across the solar disk seen from Saturn occurs in 2020; the next central transit occurs in 2049.
Visit 01 and 02 perform guide star acquisition tests for Visits 03 and 11. Visit 03 perfoms a Fixed Head Star Tracker (FHST) update with no ORIENT restrictions so Visit 11 can execute without a FHST update. The time critical observations of VIsit 11 must occur while the Earth transits the solar disk seen from Saturn. In this single visit, the first HST images of Saturn, its rings, and inner satellites at true opposition will be obtained using the F1042M, F336W, F439W, F555W, F675W, and F814W filters. SOLAR SYSTEM 0 false 0.0 false false false false false AVAILABLE UNIDENTIFIED UNDESIGNATED Near the place in the sky were Saturn will be at the time that visit 11 executes. J2000 00 00 0.0000 +00 00 0.00 J2000 UNIDENTIFIED UNDESIGNATED Near the place in the sky were Saturn will be at the time that visit 11 executes. J2000 00 00 0.0000 +00 00 0.00 J2000 SOLAR SYSTEM OFFSET Saturn Offset STD=SATURN WFPC2 Imaging No F336W WFPC2 Imaging No F439W WFPC2 Imaging No F555W WFPC2 Imaging No F675W WFPC2 Imaging No F814W Perform a guide star acquisition test for one the guide stars to be used in visit 11. (Tic-Visit :proposal-id 10357 :visit-id "01" :proposal-version -1 :trans-version "20041107" :date "12-Dec-2004 10:58:37.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 44816 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10357 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10357 :visit-id "01" :orbit-number 1 :pcs-time 289 :si-vis-utilization 180 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3258 :pcs-gap 0 ) false 1 0 Guide star acquistion test for one of visit 11's guide stars. Perform guide star acquisition tests for the guide stars to be used in visits 02 and 11. (Tic-Visit :proposal-id 10357 :visit-id "02" :proposal-version -1 :trans-version "20041107" :date "12-Dec-2004 10:58:29.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 44816 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10357 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10357 :visit-id "02" :orbit-number 1 :pcs-time 289 :si-vis-utilization 180 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3258 :pcs-gap 0 ) false 1 0 Guide star acquistion test for one of visit 11's guide stars. Visit 11 has problems scheduling in the desired orbit because of unfavorable windows for Fixed Head Star Tracker (FHST) updates. If the less restrictive visit 03 is scheduled just before visit 11, the FHST update will take place sooner; and there will not be an need for an FHST update between the two visits. (Tic-Visit :proposal-id 10357 :visit-id "03" :proposal-version -1 :trans-version "20041107" :date "12-Dec-2004 10:57:57.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "02" :si-bright-earth-limb-angle 20.0 :data-volume 44816 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10357 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10357 :visit-id "03" :orbit-number 1 :pcs-time 365 :si-vis-utilization 180 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3236 :pcs-gap 0 ) false 1 0 (Tic-Visit :proposal-id 10357 :visit-id "11" :proposal-version -1 :trans-version "20041107" :date "16-Dec-2004 09:00:41.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 672240 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10357 :visit-id "11" :obset-id "11" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10357 :visit-id "11" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2589 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) false 1 0