1. TIPS/JIM 20 Aug 20091 ACS Status Update Norman Grogin (TIPS/JIM 20 Aug 2009) WFC Post-SM4 Performance Recap Day 174 Suspend : Determinations and Corrective Actions Spotlight : WFC Bias Striping (Characterization & Mitigation) Review of Latest SMOV Findings Outline

2. TIPS/JIM 20 Aug 20092 Metric January 2007 (measured) May 2009* (projected) Problematic* Post SM4 (measured) Read noise (e-; gain = 2) C&S: 5.5DSI: 4.0> 10DSI: 3.9-4.7 C&S: 4.4-5.7 Dark current (e-/pix/hr) 10.715> 10020-25 Hot pixels (%)0.681.1> 1.51.1 Full well depth (e-)84,000 < 40,000~80,000 Non-linearity (%)< 0.1 > 0.5 2 s) CTE (@ 1620 e-)0.9999490.999921< 0.99990.99989 Cross-talk4x10 -5 > 4x10 -4 1x10 -4 Bias shift** (%)0.02< 0.1> 0.20.02-0.30 (before correction) WFC Performance Metrics * Projected and problematic values from Gilliland et al. 2008 (TIR ACS 2008-04). **Residual bias shift after analytical correction of signal-dependent effect.

3. TIPS/JIM 20 Aug 20093 ACS suspended on 23 June as result of 2 Error Status Buffer messages:  ACS 955: CEB Command Max Retries Exceeded  ACS 1002: NED ASIC Not Alive Status at time of suspend:  No observations executing or lost  All monitored currents and voltages normal  ASIC & FPGA properly initialized & functioning after SMS 173 reboot  Error occurred during NED collection cycle (CS to ASIC comm broken)  HST orbital position far from SAA Tiger Team formed on 24 June and identified 2 possible causes:  ASIC Status Line raised (informs FPGA of bit anomaly or comm error)  FPGA reset in response to SEU of power regulator Day 174 Suspend: Revisited

4. TIPS/JIM 20 Aug 20094 FPGA/ASIC Relationship

5. TIPS/JIM 20 Aug 20095 Day 174 Suspend: Back-story ASIC Status Line scenario not favored because it produces only ACS 955 ESB message, does not explain ACS 1002 ( “ ASIC Not Alive ” ) failure Radiation test reports now available show ambient heavy-ion flux sufficient to upset power regulator once every ~100 days  SEU causes small voltage drop that triggers Power On Clear circuit  FPGA and ASIC both reset; only FPGA reboots  Scenario explains both ACS 955 and ACS 1002 ESB messages Initial assessment (presented by D. Golimowski at 16 Jul 2009 TIPS): Plausible, but this outcome of has 0.1% probability after ion hit because it occurs in small (2 ms) window of 2 s NED collection cycle.

6. TIPS/JIM 20 Aug 20096 Day 174 Suspend: Resolution Revised assessment (subsequent to TIPS presentation on 16 Jul 2009): Further investigation of FSW and ESTIF testing revealed scenario in which raised Status Line produces both 955 and 1002 error messages with reasonable probabilities. GSFC subsequently discovered that cause of raised Status Line was single- bit comm error, which is automatically corrected by hardware. Status Line supposed to be raised only for double-bit comm errors. Incorrectly set bit in error response register  register now patched MO and Project considering proposal to alter FAC and FSW to allow “ slow suspend ” of ACS after future occurrences of 955 errors to enable dumps of FPGA and ASIC memory before power shutdown. Estimated delivery time: 2.5 months.

7. TIPS/JIM 20 Aug 20097 WFC Bias “Striping” Bias striping pattern varies between WFC chips and between frames 1/f noise (1mHz to 1Hz) generated with ASIC during bias voltage offsetting Striping appears constant across rows of CCD : ~removable in S/W No measurable effect on ~bright-src photometry, but could be worrisome for studies at low surface brightness (and low background)

8. TIPS/JIM 20 Aug 20098 ACS/WFC Bias Image: before correctionACS/WFC Bias Image: after correction De-striping the BIAS: Before/After

9. TIPS/JIM 20 Aug 20099 Superbias Quality Striping averages away at nearly N 1/2 Stripe-mitigated superbias only marginally noisier than pre-failure superbias Superdark similarly amenable to stacking Testing underway for end-user app to de-stripe science images (similar to the WFPC2 wdestreak)

10. TIPS/JIM 20 Aug 200910 ACS News Roundup WFC crosstalk (A. Suchkov): –Pre-failure: Avg. ghosting on victim amps is ~1-2 e-/pix. –Post-repair: Visually indistinct but still present for high fluxes WFC DARK & BIAS monitoring (T. Desjardins, P.-L. Lim): –Now “warm” pixels = 0.04 ≤ DC < 0.08 e-/s; +40 hot&warm pix/day –Bias level drifting ~linearly at 0.02 e-/day SIAF (C. Cox): New aperture definitions installed. Pixel area map (A. Fruchter): –Two new header keywords for Multidrizzle (no end-user impact). Pipeline calib. files (R. Bohlin, C. Cox, T. Desjardins, R. Lucas, J. Mack, A. Maybhate, M. Mutchler, et al.) –WFC Flatfields, Gain ratios coming soon (old Flatfields are ~same) –Plan is for all calib. files to be in place for post-ERO operations

11. TIPS/JIM 20 Aug 200911 Summary All SBC and WFC SMOV programs have been executed and data analysis is nearly complete. No significant post-SM4 performance issues discovered. Day 174 Suspend traced to FAC bug, now patched. Update to FAC/FSW planned to implement “ slow suspend ” for memory dumps before shutdown. Low-level bias striping in WFC is being characterized & mitigation strategies being tested. “ Clean ” superbias/superdark will be in pipeline as of 9 Sep 09. Both SBC and WFC have had successful and spectacular “ first light ” external observations. (Pretty pictures still embargoed -- sorry!) ACS now proceeding with WFC and SBC GO Science  Farewell to Tyler Desjardins (RIA in AWT), departing STScI for grad school. You will be sorely missed!