ACS Side-2 Performance Update
STScI TIPS Meeting
20-July-2006
Ken Sembach
1
ACS Timeline
Date (2006)
Event
June 19
ACS 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 21
ACS 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 23
ACS 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.
2
ACS Timeline (continued)
Date (2006) Event
July 2
Intercept of SMS with ACS activities.
July 3
Successful 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 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.
3
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)
4
CEB Power Switching
All relays independent and switched by individual RIU commands
LVPS1
ASPC1
(video)
MEB2
ASPC2
(video)
Clock1
(CCD control)
MEB1
LVPS2
Clock2
(CCD control)
Timing
(main control)
CEB
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
Simplified – multiple diode
busses in hardware
Legend:
5V only
5
Anomaly Review Board Investigated Possible Failures
Case #
Failure Mode
Anomaly
match
based on
ETU testing
Implicates
Expected Telemetry
+5V
+15V
-15V
+35V
+5V
+15V
-15V
+35V
1
All Nominal
No
Problem intermittent or
+15V open beyond TLM
sample point
2
+15V open
(external)
YES
LVPS #3 Board
+5V
0V
-15V
0V
3
+15V open
(internal)
YES
MFL2815D
+5V
0V
-18V to
-20V
0V
4 or 5
-15V open
(external or
internal)
No
MFL2815D or LVPS #3
+5V
+15V
0V
+35V
6
+15V shorted
(internal or
external)
YES
MFL2815D or LVPS #3 or
MEB Backplane or
Harness to CEBs
+5V
0V
-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
+5V
0V
0V
0V
Fault within MFL2815D
Fault on LVPS #3 Board, not in MFL2815D
Fault mode matches on orbit anomaly signature
6
ACS Resumes Exploration of the Universe
7
ACS Side-2 Orbital Verification Programs
Program
Analysis
10735
Cox
SBC MAMA Recovery
4 (I)
10737
Mack /
Gilliland
CCD Stability Monitor
5 (E)
10738
Program Name
Mack /Bohlin Earth Flats
10752
Sahu / Lallo
11005
Sirianni /
Lucas
11006
Cox
11007
Welty
11008
Sirianni
11009
Welty
Orbits
2 (I)
Cycle 14 Focus Monitor
1 (E)
Functional Test - MEB2 Switch
35 (I)
SBC Filter Wheel Checkout
7 (I)
ACS Side 2 Dump Test and Verification of ACS
Memory Load
1 (I)
ACS CCDs Side-2 Temp Setpoint
4 (I)
ACS Science Data Buffer Check/ Self-Tests for
CS Buffer RAM and MIE RAM
8 (I)
8
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
9
Dark Current / Hot Pixels
WFC1
Side-2 (-81 C)
Side-1 (-77 C)
WFC2
Side-2 (-81 C)
Side-1 (-77 C)
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).
WFC1
WFC2
Dark Current: (e/pix/hr)
Side-2 (-81 C)
Side-1 (-77 C)
10.2
18.4
8.6
15.7
Ratio
(-81 C / -77 C)
0.55
0.55
10
WFC Hot Pixel Contamination (%)
Threshold
(e-/pix/sec)
Side1
(-77 C)
Side2
(-81 C)
(-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)
Ratio
Side-1 (-77 C)
Side-2 (-81 C)
Note: 100x80 pix region, first day after annealing (only pixels brighter than 0.08 are shown)
11
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)
12
WFC Bias Jumps
A
Typical case
A
B
B
1 DN
C
C
D
D
Image stretched to show bias jumps.
1 DN
13
WFC Bias Jumps
A
Worst case
A
B
B
1 DN
C
C
D
D
Image stretched to show bias jumps.
1 DN
14
WFC Bias Jumps
• 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
15
Sensitivity
• Small sensitivity decrease (expected)
seen after lowering WFC setpoint
• Sensitivity measured using stellar
photometry and internal flatfields
Filter
Gain
Side-2 Change in QE
F435W
2
F475W
2
-2.1%
F606W
1,2
-1.2%
F625W
2
-0.9%
F775W
2
-1.1%
F814W
1,2
-2.6%
-1.1%
-2.2%
(Internal)
-1.7%
(Internal)
A 4096x4096 composite WFC/F606W image of a
portion of globular cluster 47 Tuc obtained on
Side-2 (4 x 339 sec).
16
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
Constant Library
Library + Perturbation
Empirical library PSF
for WFC/F606W
-1
-5
On average, 22.4% of light falls in
central pixel (+15%, -12%)
+3
+1
-1.0
-0.5
Photometry
supported to
0.005 mag
+6
+2
+0.3
Astrometry
supported to
0.01 pix in
both x and y
+7
+3
+0.5
Same as
on Side-1
% Residual
17
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)
18
Coronagraphic Spot Position
Side-2
Motion on Side-2
is well within
historical Side-1
envelope of positions.
19