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Review of ACS-R Performance
During SMOV4
David Golimowski (STScI)
3 Sep 2009
SMOV Status 9/3/09
David Golimowski
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ACS-R SMOV Timeline (1)
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•
ACS-R hardware successfully installed on 16 May 2009 during EVA-3
•
WFC and SBC passed Aliveness and Functional Tests; HRC not recovered
•
Day 146 (26 May): WFC 12-hour anneal performed; pre- and post-anneal dark
frames show little change indicating that 18 month hiatus at ambient -10 C
was sufficient to anneal nearly all temporary hot pixels.
•
Day 148 (28 May): WFC Optimization Campaign commenced
•
Day 150 (30 May): SBC UV contamination check; BEA exit deemed safe
•
Optimization Campaign showed that all pre-failure settings remained valid for
CEB-R operations and that no changes in default settings were warranted.
SMOV Status 9/3/09
David Golimowski
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ACS-R SMOV Timeline (2)
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Optimization Campaign truncated on 3 June 2009 after Iteration 2
 Performance matched or exceeded projections and expectations
 VOD offsets of < -1 V produce anomalous behavior in amps C and D
that mimics charge-injection but was unexplained by Tiger Team
 HSTMO and Project elect to proceed with WFC default configuration
and continue “off-line” investigation of VOD anomaly
•
Dual-Slope Integrator selected as default mode of ASIC pixel sampling
•
Low-frequency bias variations and signal dependent “bias shift” can be
effectively removed during post-image processing with Teledyne algorithm
•
Bias striping pattern varies among quadrants and between frames; caused by
1/f noise (1 mHz to 1 Hz) generated with ASIC during setting of bias voltage
offset. Striping is constant across rows of CCD and is removable.
SMOV Status 9/3/09
David Golimowski
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ACS-R SMOV Timeline (3)
•
Day 166: Suspend due to failed SIC&DH toggle test (15 June 2009)
•
Day 174: Suspend due to ASIC comm error and power down
(23 June 2009)
•
All WFC and SBC SMOV programs executed by end of SMS 193
(12 July 2009)
•
WFC enabled for science in SMS 194; first GO (SNAP) images on
16 July 2009
•
ACS ERO successfully executed on 17 July 2009
•
CCD Daily Monitor transitioned from SMOV to Cycle 17 calibration
phase on 31 Aug 2009
SMOV Status 9/3/09
David Golimowski
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WFC Bias and Dark Frames
Superbias - 1 full anneal cycle
(7/7/09-8/3/09; 34 frames)
SMOV Status 9/3/09
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Superdark - 1/2 anneal cycle
(derived with latest CCDTAB)
David Golimowski
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Bias Stripe Removal
(before)
SMOV Status 9/3/09
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(after)
David Golimowski
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VOD (Reset Drain) Anomaly
VDD: +27V, VLG: -3V
(defaults)
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Bias
VOD: +14V
(default is +15V)
Illumination 1
Illumination 2
SMOV Status 9/3/09
David Golimowski
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Bias and Read Noise Monitor
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Amp D, gain=2.0
SMOV Status 9/3/09
David Golimowski
8
WFC Linearity and Full Well
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Photon Transfer Test from Iteration 1 of O.C.
(Amplifier D, Dual-Slope Integrator)
SMOV Status 9/3/09
David Golimowski
9
WFC Performance Summary
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January 2007
(measured)
May 2009*
(projected)
Problematic*
Read noise
(e-; gain = 2)
C&S: 5.5
DSI: 4.0
10
DSI: 3.9-4.7
C&S: 4.4-5.7
Dark current (e-/pix/hr)
10.7
15
100
20-25
Hot pixels (%)
0.68
1.1
1.5
1.1
Full well depth (e-)
84,000
84,000
40,000
~80,000
Non-linearity (%)
< 0.1
< 0.1
0.5
< 0.2
Metric
Post SM4
(measured)
(exp time > 2 s)
CTE (1620 e-)
0.999949
0.999921
0.9999
0.99989
Cross-talk
4x10-5
4x10-5
4x10-4
1x10-4
Bias shift** (%)
0.02
< 0.1
< 0.2
0.02-0.30
(before correction)
* Projected and problematic values from Gilliland et al. 2008 (TIR ACS 2008-04) .
**Residual bias shift after analytical correction of signal-dependent effect.
SMOV Status 9/3/09
David Golimowski
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WFC Dark Current History
12 hr anneal
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6 hr anneal
-77 C -81 C
SMOV Status 9/3/09
David Golimowski
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WFC CTE History
SMOV Status 9/3/09
David Golimowski
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SMOV Light Leak Test
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
Multi-SI proposal (11515; Biagetti & Sembach) to check external
images for contamination from COS and WFC3 calibration lamps

Stray light streak noted in ACS/WFC F814W images regardless of
whether the COS or WFC3 lamps are on or off

Streaks also seen in pre-SM4 images and F814W images of 47 Tuc
(SMOV4 Prop 11397)

Streak absent in images from other broadband filters

Morphology and wavelength dependence strikingly similar to
WFC3/UVIS glint seen in TV

Caused by scattering from CCD surface and reflection from window
and beveled edges of camera housing
SMOV Status 9/3/09
David Golimowski
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WFC and WFC3 Glints
ACS/WFC F814W
SMOV Day 219
SMOV Status 9/3/09
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WFC3/UVIS Thermal Vac
ISR 2007-21
David Golimowski
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ACS Anomalies &Suspends (1)
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SIC&DH Anomaly (HSTAR 11880)
•
Day 166 (15 June): SI commanding lost after failure of SIC&DH toggle
•
Tiger Teams investigated:
 Dangers of overexposing SI detectors during Bright Earth crossings,
SAA crossings, and slews across bright stars
 Potential polymerization of contaminants on UV-channel optics
•
Implications for ACS:
 No danger to WFC CCD
 SBC MAMA vulnerable to catastrophic damage during BE crossings
 Impact of SAA on MAMA unknown because HV normally turned off
 ACS optics exposed to 100s of hrs of BE crossings with no ill-effects
•
SBC concerns resolved by 486 FSW revision that automatically shuts down
MAMA HV after future (expected) SIC&DH anomalies
SMOV Status 9/3/09
David Golimowski
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ACS Anomalies &Suspends (2)
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ASIC Anomaly (HSTAR 11895)
•
Day 174 (23 June): ACS suspended after 2 Error Status Buffer messages
during NED collection cycle :
 ACS 955: CEB Command Max Retries Exceeded
 ACS 1002: NED ASIC Not Alive
•
Tiger Team 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
•
Radiation test reports show ambient heavy-ion flux sufficient for SEU every
~100 days, but only 0.1% chance of causing observed ESB sequence
•
Status Line probably raised by single-bit comm error, which is automatically
corrected by memory scrub. Should be raised only for double-bit comm errors.
Incorrectly set bit in error response register  register now patched
SMOV Status 9/3/09
David Golimowski
16
Other Items
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•
WFC focus initially -2.5 m off nominal. OTA secondary mirror was moved
on 20 July 2009 to make other SIs confocal with WFC
•
SIAF update program showed WFC aperture had moved < 1 arcsec in both
x and y, with negligible rotation.
•
Internal and external analyses of WFC amplifier cross-talk are mutually
consistent. No perceptible difference in cross talk between pre- and postSM4 images at all signal levels.
•
SBC performance:
 MAMA dark and flat images unchanged from pre-SM4 states
 OTA breathing effects on encircled energy unchanged from pre-SM4
state
 UV contamination check revealed 2-3% drop in sensitivity for
 < 140 nm after SM4; no change in sensitivity at longer wavelengths.
SMOV Status 9/3/09
David Golimowski
17
SBC UV Contamination
F125LP
Bright Earth photopolymerizes
contaminants onto pickoff mirror
Pre SM4 (short)
Post SM4 (short & long)
F150LP
Delta Mag (Pre-Post SM4)
F115LP = -0.034 +/- 0.017
F125LP = -0.014 +/- 0.013
F140LP = -0.019 +/- 0.015
F150LP = 0.002 +/- 0.015
F165LP = 0.008 +/- 0.015
SMOV Status 9/3/09
David Golimowski
18
Forward Plan
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First delivery of WFC calibration reference files (superbias, superdark,
CCDTAB) to CDBS will occur TODAY in advance of ERO release on 9/9
•
Determine by next week final cadence of CCD Daily Monitor to produce
temporally well-sampled reference images with minimal bias striping
•
Complete software for removing bias stripes and signal-dependent “bias
shift” in WFC images. Deliver software as standalone packages to users.
•
HST Project approved modifications of 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. Delivery in October.
•
VOD anomaly and its possible beneficial use to mitigate CTE through
charge-injection will be investigated
SMOV Status 9/3/09
David Golimowski
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