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ACS Side-2 Performance UpdateSTScI TIPS Meeting

20-July-2006

Ken Sembach

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ACS TimelineDate (2006) Event

June 19 ACS suspends at 17:15 UTC. Tiger Team formed.

June 20ACS 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 21 ACS CEB Anomaly Review Board created.

June 22Observing 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 23 ACS Team decides to recommend WFC temperature setpoint change.

June 27ARB recommends switch-over to Side-2.ARB endorses WFC temperature setpoint change.

June 29FRR for switch-over to Side-2 held - Switch-over approved.New FSW uploaded to ACS.

June 30Uplink and realtime switch to Side-2. CCD electronics boards powered.ACS safed for SMS intercept on July 2.

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ACS Timeline (continued)Date (2006) Event

July 2 Intercept of SMS with ACS activities.

July 3 Successful checkout of ACS memory / dumps.

July 4WFC temperature setpoint lowered from -77 C to -81 C.Successful resumption of CCD calibration and science observations.

July 7ARB lifts moratorium on SBC observations. ARB considers risks/benefits of ACS Side-1 testing.

July 11 ARB votes that risks to ACS assets outweigh benefits of Side-1 testing.

July 12 Press release for first Side-2 science observation released.

July 13 HST Project concurs that Side-1 tests should not be done at this time.

July 16 SMS contains SBC SMOV activities.

July-August Analysis of SMOV / science data in progress.

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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)

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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

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Anomaly Review Board Investigated Possible FailuresCase # Failure Mode Anomaly

match based on

ETU testing

Implicates Expected Telemetry

+5V +15V -15V +35V

1 All Nominal NoProblem intermittent or

+15V open beyond TLM sample point

+5V +15V -15V +35V

2+15V open (external)

YES LVPS #3 Board +5V 0V -15V 0V

3+15V open (internal)

YES MFL2815D +5V 0V-18V to

-20V0V

4 or 5-15V open (external or

internal)No MFL2815D or LVPS #3 +5V +15V 0V +35V

6+15V shorted

(internal or external)

YESMFL2815D or LVPS #3 or

MEB Backplane or Harness to CEBs

+5V 0V-6V to

-8V0V

7-15V shorted (internal or external)

NoMFL2815D 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 +5V 0V 0V 0V

Fault within MFL2815D Fault on LVPS #3 Board, not in MFL2815D Fault mode matches on orbit anomaly signature

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ACS Resumes Exploration of the Universe

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ACS Side-2 Orbital Verification ProgramsProgram Analysis Program Name Orbits

10735 Cox SBC MAMA Recovery 4 (I)

10737Mack /

Gilliland CCD Stability Monitor 5 (E)

10738 Mack /Bohlin Earth Flats 2 (I)

10752 Sahu / Lallo Cycle 14 Focus Monitor 1 (E)

11005Sirianni /

Lucas Functional Test - MEB2 Switch 35 (I)

11006 Cox SBC Filter Wheel Checkout 7 (I)

11007 WeltyACS Side 2 Dump Test and Verification of ACS Memory Load 1 (I)

11008 Sirianni ACS CCDs Side-2 Temp Setpoint 4 (I)

11009 WeltyACS Science Data Buffer Check/ Self-Tests for CS Buffer RAM and MIE RAM 8 (I)

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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

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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)

WFC1 10.2 18.4 0.55

WFC2 8.6 15.7 0.55

11Note: 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)

>0.01 22.2 9.0 0.41

>0.04 3.8 1.3 0.34

>0.08 1.6 0.6 0.37

>0.10 1.1 0.5 0.45

Ratio of Hot Pixels (-77 C / -81 C)

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Gain Ratio

• WFC: Gain=1 and Gain=2 (default)• Side-2 Ratio

• Same as on Side-1 to 1 part in 104 (47 Tuc data)• Quad-quad gains are consistent to 1 part in 103

(internal flats)

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WFC Bias JumpsA B

C D

A B

C D

1 DN

1 DN

Typical case

Image stretched to show bias jumps.

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WFC Bias JumpsA B

C D

A B

C D

1 DN

1 DN

Worst case

Image stretched to show bias jumps.

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• 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

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Sensitivity• Small sensitivity decrease

(expected) seen after lowering WFC setpoint

• Sensitivity measured using stellar photometry and internal flatfields

A 4096x4096 composite WFC/F606W image of a portion of globular cluster 47 Tuc obtained on Side-2 (4 x 339 sec).

Filter Gain Side-2 Change in QE

F435W 2 -2.6% -2.2%(Internal)

F475W 2 -2.1%

F606W 1,2 -1.2%

F625W 2 -0.9%

F775W 2 -1.1%

F814W 1,2 -1.1% -1.7%(Internal)

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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

-1

-5

+6

+7

On average, 22.4% of light falls in central pixel (+15%, -12%)

LibraryLibrary + Perturbation

+3

+1

+2

+3

-1.0

-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

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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)

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Coronagraphic Spot Position

Side-2

Motion on Side-2is well within

historical Side-1 envelope of positions.