In spite of recent progress, the role of distant galaxies in cosmic reionization has been difficult to pin down. A powerful way to make progress is to move beyond counting high redshift sources and study the stellar properties of the population instead. Accurate knowledge of the average star formation density and its recent history in the universe at this epoch is necessary to determine whether these galaxies emit enough hard photons to reionize the Universe. This requires measuring rest frame optical light, which only Spitzer can probe at these redshifts, for a large enough sample of typical galaxies. At least 50 typical sources with Spitzer imaging are needed to determine the star formation rate (SFR) density directly from stellar mass measurement (rather than estimated from the luminosity function) to 25% accuracy. Unfortunately, the depth needed to reach typical z>~7 galaxies is impractical in a blank field survey. To address this cosmic puzzle, we will obtain ultra−deep Spitzer imaging of the fields behind 10 of the most powerful and well calibrated cosmic telescopes. Cluster−scale gravitational lenses acting as cosmic telescopes enable the study of intrinsically lower luminosity galaxies than would otherwise be possible. This will be a crucial Legacy complement to the existing IRAC deep surveys and shallower cluster studies, and will open up new parameter space parameter space by probing intrinsically fainter objects than existing cluster surveys and much improved sample variance over deep field surveys. It will allow us to study the properties (e.g. star formation rates and stellar masses) of a large number of galaxies (50 at z~7 and 10 at z~8) for the first time, thus meeting our goal of reconstructing the cosmic SFR with sufficient accuracy. Presence (or absence) of established stellar population will be measured by Spitzer for the largest sample to date. Together these findings will allow us to identify the dominant sources of the bulk of ionizing photons necessary to drive reionization. HST 13 orbits for RCS2−2327.4−0204 (ACS/F814W − 3 orbits, WFC3/F098W − 3 orbits, WFC3/F125W − 3 orbits, WFC3/F160W − 4orbits) Dither Pattern: Cover chip gap in ACS ACS-DITHER-LINE (default)+ACS-DITHER-BOX (within each orbit) WFC3: Here we use 4 different orientations (approximate relative rotations 0, 90, 180, 270deg), which allow us to cover a larger area with the parallels. We mix the IR-DITHER_UVIS pattern (only half of the positions because of the rotations) with an extension of the IR-DITHER-BOX-MIN (to which we added points at dx=1.5pix, dy=-3.5pix and dx=-3pix, dy=-1pix) creating the following points (offsets in arcsec): 1: -11.947 17.457 2: -12.150 17.760 3: -11.608 17.942 4: -11.405 17.639 5: -11.744 17.033 6: -12.354 17.336 7: 11.071 17.744 8: 10.868 18.047 9: 11.410 18.229 10: 11.613 17.926 11: 11.274 17.320 12: 10.665 17.623 Together with the different rotations this provides an approximately square area covered by the WFC3/IR observations. For optimal overlap and data quality we change filters during orbits. The dithers were put in as pos-targ as otherwise orbit planner wouldn't allow efficient sampling. The overall orientation is defined via the ACS observations, where the optimal orientation (~50-55deg) provides maximal overlap with existing data. COSMOLOGY 12 false 0.0 0.0 false false false false SUPPORTED CLUSTER OF GALAXIES HIGH REDSHIFT CLUSTER RICH CLUSTER J2000 ACS/WFC Imaging No No F814W WFC3/IR Imaging No No F098M WFC3/IR Imaging No No F125W WFC3/IR Imaging No No F160W POS-TARG DITHER 0.265 LINE 0.187 false false 69.05 4 20.67 ACS-WFC-DITHER-BOX 2 false The scheduling data was generated by CASM 20.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13177 :visit-id "01" :proposal-version -1 :trans-version "20121031" :date "14-Nov-2012 15:27:28.0" :trans-errors '(:WARNINGS 2 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "30" :si-bright-earth-limb-angle 40.0 :data-volume 4873104 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13177 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13177 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2440 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 2773 :pcs-gap 167 ) (Tic-Orbit :proposal-id 13177 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2552 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 2773 :pcs-gap 167 ) (Tic-Orbit :proposal-id 13177 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 2552 :al-overhead-at-end 0 :internal-dur-at-end 999 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 2773 :pcs-gap 167 ) false 3 0 The scheduling data was generated by CASM 20.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13177 :visit-id "02" :proposal-version -1 :trans-version "20121031" :date "14-Nov-2012 15:13:00.0" :trans-errors '(:WARNINGS 1 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "30" :si-bright-earth-limb-angle 40.0 :data-volume 6196112 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13177 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13177 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2440 :al-overhead-at-end 0 :internal-dur-at-end 1037 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 2773 :pcs-gap 167 ) (Tic-Orbit :proposal-id 13177 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2558 :al-overhead-at-end 0 :internal-dur-at-end 1075 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 2773 :pcs-gap 167 ) (Tic-Orbit :proposal-id 13177 :visit-id "02" :orbit-number 3 :pcs-time 222 :si-vis-utilization 2551 :al-overhead-at-end 0 :internal-dur-at-end 1075 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 2773 :pcs-gap 167 ) false 3 0 The scheduling data was generated by CASM 20.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13177 :visit-id "03" :proposal-version -1 :trans-version "20121031" :date "14-Nov-2012 15:13:06.0" :trans-errors '(:WARNINGS 1 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "30" :si-bright-earth-limb-angle 40.0 :data-volume 6196112 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13177 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13177 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2440 :al-overhead-at-end 0 :internal-dur-at-end 1037 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 2773 :pcs-gap 167 ) (Tic-Orbit :proposal-id 13177 :visit-id "03" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2558 :al-overhead-at-end 0 :internal-dur-at-end 1075 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 2773 :pcs-gap 167 ) (Tic-Orbit :proposal-id 13177 :visit-id "03" :orbit-number 3 :pcs-time 222 :si-vis-utilization 2551 :al-overhead-at-end 0 :internal-dur-at-end 1075 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 2773 :pcs-gap 167 ) false 3 0 The scheduling data was generated by CASM 20.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13177 :visit-id "04" :proposal-version -1 :trans-version "20121031" :date "14-Nov-2012 15:13:10.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 40.0 :data-volume 4119136 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13177 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13177 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2440 :al-overhead-at-end 0 :internal-dur-at-end 1037 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 2773 :pcs-gap 167 ) (Tic-Orbit :proposal-id 13177 :visit-id "04" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2551 :al-overhead-at-end 0 :internal-dur-at-end 1075 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 2773 :pcs-gap 167 ) false 2 0 The scheduling data was generated by CASM 20.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13177 :visit-id "05" :proposal-version -1 :trans-version "20121031" :date "14-Nov-2012 15:13:13.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 40.0 :data-volume 4119136 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13177 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13177 :visit-id "05" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2440 :al-overhead-at-end 0 :internal-dur-at-end 1037 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 2773 :pcs-gap 167 ) (Tic-Orbit :proposal-id 13177 :visit-id "05" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2551 :al-overhead-at-end 0 :internal-dur-at-end 1075 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 2773 :pcs-gap 167 ) false 2 0