1. 1 ACS Side-2 Performance Update STScI TIPS Meeting 20-July-2006 Ken Sembach

2. 2 ACS Timeline Date (2006)Event June 19ACS suspends at 17:15 UTC. Tiger Team formed. June 20 ACS Suspend Status Meetings start. Analysis of ACS data prior to suspension shows that it looks normal. SMOV preparations begin in case switch to Side-2 is necessary. June 21ACS CEB Anomaly Review Board created. June 22 Observing timeline intercepted with SMS containing no ACS activities. Tiger Team passes off investigation to ARB. ACS transitioned to Operate mode on Side-1 as recommended by TT. June 23ACS Team decides to recommend WFC temperature setpoint change. June 27 ARB recommends switch-over to Side-2. ARB endorses WFC temperature setpoint change. June 29 FRR for switch-over to Side-2 held - Switch-over approved. New FSW uploaded to ACS. June 30 Uplink and realtime switch to Side-2. CCD electronics boards powered. ACS safed for SMS intercept on July 2.

3. 3 ACS Timeline (continued) Date (2006)Event July 2Intercept of SMS with ACS activities. July 3Successful checkout of ACS memory / dumps. July 4 WFC temperature setpoint lowered from -77 C to -81 C. Successful resumption of CCD calibration and science observations. July 7 ARB lifts moratorium on SBC observations. ARB considers risks/benefits of ACS Side-1 testing. July 11ARB votes that risks to ACS assets outweigh benefits of Side-1 testing. July 12Press release for first Side-2 science observation released. July 13HST Project concurs that Side-1 tests should not be done at this time. July 16SMS contains SBC SMOV activities. July-AugustAnalysis of SMOV / science data in progress.

4. 4 ACS Suspends What was observed All ones were read back from WFC and HRC CCD Electronics Box (CEB) A/D telemetry FIFOs Status buffer messages : +15V and +5V supply voltages at high limits 36 CEB limit-checked parameters were found to be out-of-limits ACS current decreased 1.2-1.8 amps (no current spike in ACS) Anomaly lasted about 7 seconds before ACS suspended Ruled out WFC and HRC CEB interface optocouplers in common package WFC and HRC CEB FIFO read control CEB A/D converters Space weather-induced damage (excessive radiation)

5. 5 CEB Power Switching LVPS1 LVPS2 CEB Clock1 (CCD control) Clock2 (CCD control) All boards are needed for operation of the entire detector. Single fault affects at most half the science data. One CEB each for WFC and HRC ASPC1 (video) ASPC2 (video) Timing (main control) Simplified – multiple diode busses in hardware MEB1 MEB2 Legend: 5V only All relays independent and switched by individual RIU commands

6. 6 Anomaly Review Board Investigated Possible Failures Case #Failure ModeAnomaly match based on ETU testing ImplicatesExpected Telemetry +5V+15V-15V+35V 1All NominalNo Problem intermittent or +15V open beyond TLM sample point +5V+15V-15V+35V 2 +15V open (external) YESLVPS #3 Board+5V0V-15V0V 3 +15V open (internal) YESMFL2815D+5V0V -18V to -20V 0V 4 or 5 -15V open (external or internal) NoMFL2815D or LVPS #3+5V+15V0V+35V 6 +15V shorted (internal or external) YES MFL2815D or LVPS #3 or MEB Backplane or Harness to CEBs +5V0V -6V to -8V 0V 7 -15V shorted (internal or external) No MFL2815D or LVPS #3 or MEB Backplane or Harness to CEBs +5V +8V to +11V 0V +30V to +35V 8 or 9 MFL2815D inhibited or internally destroyed No (additional testing in progress) MFL2815D+5V0V Fault within MFL2815DFault on LVPS #3 Board, not in MFL2815DFault mode matches on orbit anomaly signature

7. 7 ACS Resumes Exploration of the Universe

8. 8 ACS Side-2 Orbital Verification Programs ProgramAnalysisProgram NameOrbits 10735CoxSBC MAMA Recovery4 (I) 10737 Mack / Gilliland CCD Stability Monitor5 (E) 10738Mack /BohlinEarth Flats2 (I) 10752Sahu / Lallo Cycle 14 Focus Monitor1 (E) 11005 Sirianni / Lucas Functional Test - MEB2 Switch35 (I) 11006CoxSBC Filter Wheel Checkout7 (I) 11007Welty ACS Side 2 Dump Test and Verification of ACS Memory Load 1 (I) 11008Sirianni ACS CCDs Side-2 Temp Setpoint4 (I) 11009Welty ACS Science Data Buffer Check/ Self-Tests for CS Buffer RAM and MIE RAM 8 (I)

9. 9 ACS WFC Temperature Setpoint Change HRC TEC setpoint maintained at -80 C WFC TEC setpoint lowered from -77 C to -81 C after Side-2 switch Lower WFC setpoint should improve science 2005 Aft Shroud Cooling System study Fewer hot pixels (and fewer anneals needed) Shorter charge transfer tails Gain in sensitivity for deep exposures is ~ 0.1 magnitudes (or equivalently, about 20% in observing time) Lowering temperature now consolidates recalibration activities for Side-2 switch and temperature change Change would likely have been needed within the next 12-24 months

10. 10 Dark Current / Hot Pixels Note: The white histogram is wider because only 4 images were used instead of 40. In both cases the tail of the histogram is for 1 single day, the first day after the anneals of July 14 (white) and June 15 (yellow). Side-2 (-81 C) Side-1 (-77 C) Side-2 (-81 C) Side-1 (-77 C) WFC1 WFC2 Dark Current: (e/pix/hr)Ratio Side-2 (-81 C)Side-1 (-77 C)(-81 C / -77 C) WFC110.218.40.55 WFC28.615.70.55

11. 11 Note: 100x80 pix region, first day after annealing (only pixels brighter than 0.08 are shown) Side-2 (-81 C)Side-1 (-77 C) WFC Hot Pixel Contamination (%) Threshold (e - /pix/sec) Side1 (-77 C) Side2 (-81 C) Ratio (-81C /-77C) >0.0122.29.00.41 >0.043.81.30.34 >0.081.60.60.37 >0.101.10.50.45 Ratio of Hot Pixels (-77 C / -81 C)

12. 12 Gain Ratio WFC: Gain=1 and Gain=2 (default) Side-2 Ratio Same as on Side-1 to 1 part in 10 4 (47 Tuc data) Quad-quad gains are consistent to 1 part in 10 3 (internal flats)

13. 13 WFC Bias Jumps A B CD A B CD 1 DN Typical case Image stretched to show bias jumps.

14. 14 WFC Bias Jumps A B CD A B CD 1 DN Worst case Image stretched to show bias jumps.

15. 15 WFC Side-1 (Gain=2, default) Jump detected in 1/40 images Jump detected only on Amplifier B Side-2 (Gain=2, default) Jump detected in 7/35 images Jump detected on 2 or 4 amplifiers simultaneously Side-2 (Gain=1) Jump detected in 5/35 images Jump detected only on 1 amplifier at a time, mostly Amp B HRC No bias jumps observed on Side-1 or Side-2 WFC Bias Jumps

16. 16 Sensitivity Small sensitivity decrease (expected) seen after lowering WFC setpoint Sensitivity measured using stellar photometry and internal flatfields A 4096 x 4096 composite WFC/F606W image of a portion of globular cluster 47 Tuc obtained on Side-2 (4 x 339 sec). FilterGainSide-2 Change in QE F435W2-2.6% -2.2% (Internal) F475W2-2.1% F606W1,2-1.2% F625W2-0.9% F775W2-1.1% F814W1,2-1.1% -1.7% (Internal)

17. 17 Point Spread Function Astrometric and photometric analysis of WFC Side-2 47 Tuc data (J. Anderson) Temporal change noted was well within normal orbit-orbit and epoch-epoch ranges No evidence for additional underlying spatial dependence of PSF Empirical library PSF for WFC/F606W Constant -5 +6 +7 On average, 22.4% of light falls in central pixel (+15%, -12%) Library Library + Perturbation +3 +1 +2 +3 -0.5 +0.3 +0.5 % Residual Photometry supported to 0.005 mag Astrometry supported to 0.01 pix in both x and y Same as on Side-1

18. 18 Mechanisms Affected by Side-2 Switch Fold mirror / cal door / coronagraphic spot Resolvers and electronics Positions are within usual ranges seen for Side-1 motions. Filter wheels Resolvers and electronics Filter Wheel #1: positions are the same as on Side-1 Filter Wheel #2: currently a small offset w.r.t. Side-1 (investigating) Shutter LEDs, photodiodes, and electronics No test performed yet Post-flash illumination LED No test performed yet (low priority)

19. 19 Coronagraphic Spot Position Side-2 Motion on Side-2 is well within historical Side-1 envelope of positions.