NASA’s Dawn spacecraft is scheduled to go into orbit around the main belt asteroid 4 Vesta in July 2011. Currently the project is using a 3-σ pole position uncertainty of Vesta of 12? for spacecraft trajectory design. We have determined that with an additional set of Hubble observations at Vesta’s next opposition in February 2010, that the pole position uncertainty can be reduced by a factor of 4. This will reduce both cost and risk to the Dawn mission, and is likely to increase the stay time at Vesta and will add to the scientific return of the mission. The requested observing window in February 2010 is the last and single best opportunity that can benefit the Dawn mission, but it is before the start of the next HST Cycle.

The primary goal of this observation is to measure the rotational pole of Vesta. For this purpose, we need to obtain images in the wavelengths where Vesta has the highest contrast, and to have a complete and as uniform as possible rotational coverage. For this purpose, we will follow the sequence of previous HST observation of Vesta (GO-10799). We will separate the total 7 orbits into two groups. The first group has 4 orbits, executed continuously. The second group has 3 orbits, and should start 30 orbits after the completion of the first group, and executed continuously, in order to well interlace with the first group in rotational phase of Vesta. The observation should be scheduled close to the opposition of Vesta, which occurs around Feb 23, 2010, in order to obtain the highest spatial resolution in low solar phase angles. When implementing the sequence, we realize that, thank to the sub-array model of WFC3, we can include a secondary goal in the observation, to map the surface with the same filters as used in previous HST observations to gain higher resolution. The timing requirement for this secondary goal is the same as for pole measurement. In addition, we discovered that there will be some exposures with overlapping rotational phase coverage. We can therefore utilize those exposures to realize the third and fourth goals, which are to search for satellites around Vesta, and to take some snapshots of Vesta in the UV wavelengths that have never been observed before. In order to get short overhead for high-speed imaging, we will take advantage of the 512x512 subarray mode, except for satellite search exposures, which will use full-frame. We will use two filters for pole measurement, the F469N and F373N; two filters for surface mapping, the F673N and F953N; the wide R-band filter F606W for satellite search; and F336W, F275W, and F225W for UV snapshots. The exposure times in seconds are listed below: F953N 12 F673N 1.2 F606W 10 F469N 4.0 F373N 12 F336W 1.7 F275W 15 F225W 80 The detailed sequence is optimized for uniform rotational coverage of Vesta for exposures through F373N, F469N, F673N, and F953N filters. If there is any way to hide the long overhead following each of the full-frame exposure in orbit 4, 5, 6, 7, then we can insert one more sub-array exposure in those orbits. This will cover the gap in the rotation of Vesta and substantially improve the rotational coverage. If possible, we would like to continue exploring that possibility. Also, if after the actual scheduling, it is found that we have longer unused visibility in our orbits, we would like to fill them in. SOLAR SYSTEM 0 false 0.0 0.0 false false false false false false SUPPORTED SOLAR SYSTEM Surface brightness 4.46 mag/arcsec2, angular diameter 0.518 arcsec ASTEROID Asteroid 4 Vesta TYPE=ASTEROID,A=2.361937325265019,E=0.08872920479890047,I=7.134420968509158,O=103.9148645013264,W=149.8368094343074,M=253.5042125123777,EQUINOX=J2000,EPOCH=04-JAN-2010:00:00:00 EARTH WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F336W Using ephemeris for target 12049-01-VESTA ephemeris data for target 12049-01-VESTA does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 08.306 to 11.001. ephemeris interval: 09.334 to 11.335 Timing link suitability includes constraints ([Sequence (01 02 03 04) within 0.3 days]) The scheduling data was generated by CASM 17.5. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12049 :visit-id "01" :proposal-version -1 :trans-version "20090915" :date "04-Feb-2010 17:19:16.0" :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 139792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12049 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12049 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2885 :al-overhead-at-end 0 :internal-dur-at-end 191 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3236 :pcs-gap 0 ) true 1 0 Using ephemeris for target 12049-02-VESTA ephemeris data for target 12049-02-VESTA does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 08.306 to 11.001. ephemeris interval: 09.334 to 11.335 Timing link suitability includes constraints ([Sequence (01 02 03 04) within 0.3 days]) The scheduling data was generated by CASM 17.5. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12049 :visit-id "02" :proposal-version -1 :trans-version "20090915" :date "04-Feb-2010 17:20:47.0" :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 139792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12049 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12049 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2893 :al-overhead-at-end 0 :internal-dur-at-end 191 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3236 :pcs-gap 0 ) true 1 0 (Tic-Visit :proposal-id 12049 :visit-id "03" :proposal-version -1 :trans-version "20090915" :date "04-Feb-2010 17:50:19.0" :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 139792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12049 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12049 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2893 :al-overhead-at-end 0 :internal-dur-at-end 191 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3236 :pcs-gap 0 ) true 1 0 Using ephemeris for target 12049-04-VESTA ephemeris data for target 12049-04-VESTA does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 08.306 to 11.001. ephemeris interval: 09.334 to 11.335 Timing link suitability includes constraints ([Sequence (01 02 03 04) within 0.3 days] [05 After 04 by 2.1 to 2.1 days]) The scheduling data was generated by CASM 17.5. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12049 :visit-id "04" :proposal-version -1 :trans-version "20090915" :date "04-Feb-2010 17:32:02.0" :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 419792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12049 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12049 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2903 :al-overhead-at-end 0 :internal-dur-at-end 497 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3236 :pcs-gap 0 ) true 1 0 Using ephemeris for target 12049-05-VESTA ephemeris data for target 12049-05-VESTA does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 08.306 to 11.001. ephemeris interval: 09.334 to 11.335 Timing link suitability includes constraints ([Sequence (05 06 07) within 0.2 days] [05 After 04 by 2.1 to 2.1 days]) The scheduling data was generated by CASM 17.5. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12049 :visit-id "05" :proposal-version -1 :trans-version "20090915" :date "04-Feb-2010 17:50:35.0" :trans-errors '(:WARNINGS 1 :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 419792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12049 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12049 :visit-id "05" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2851 :al-overhead-at-end 0 :internal-dur-at-end 497 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3236 :pcs-gap 0 ) true 1 0 Using ephemeris for target 12049-06-VESTA ephemeris data for target 12049-06-VESTA does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 08.306 to 11.001. ephemeris interval: 09.334 to 11.335 Timing link suitability includes constraints ([Sequence (05 06 07) within 0.2 days] [Sequence (06 07) within 0.2 days]) The scheduling data was generated by CASM 17.5. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12049 :visit-id "06" :proposal-version -1 :trans-version "20090915" :date "04-Feb-2010 17:50:54.0" :trans-errors '(:WARNINGS 1 :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 419792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12049 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12049 :visit-id "06" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2851 :al-overhead-at-end 0 :internal-dur-at-end 497 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3236 :pcs-gap 0 ) true 1 0 Using ephemeris for target 12049-07-VESTA ephemeris data for target 12049-07-VESTA does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 08.306 to 11.001. ephemeris interval: 09.334 to 11.335 Timing link suitability includes constraints ([Sequence (05 06 07) within 0.2 days] [Sequence (06 07) within 0.2 days]) The scheduling data was generated by CASM 17.5. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12049 :visit-id "07" :proposal-version -1 :trans-version "20090915" :date "04-Feb-2010 17:51:04.0" :trans-errors '(:WARNINGS 1 :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 419792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12049 :visit-id "07" :obset-id "07" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12049 :visit-id "07" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2851 :al-overhead-at-end 0 :internal-dur-at-end 497 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3236 :pcs-gap 0 ) true 1 0