ACS Status Update
STScI TIPS Meeting
19-October-2006
Ken Sembach
1
ACS/HRC Timeline
• ACS Suspended Saturday, September 23, 2006
• Telemetry showed that the HRC ASPC2 board was missing its
+35V input
• This voltage is needed for CCD bias level and reset drain
operation.
• Loss of +35V believed to leave HRC unusable
• Lots of discussion about this - more on this if you want to know
• An ACS-free SMS was implemented the following week
• Thanks to scheduling team, PCs, and NICMOS Team for getting as
much science as possible planned for that week
• ARB was convened to determine cause of suspension
• Failure of A2/A3 contacts to close in K1 relay
• Solder joints from K1 relay to ASPC2 board
• Problem is unrelated to June 2006 Side-1 electronics failure
2
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.
Simplified – multiple diode
busses in hardware
Legend:
5V only
3
K1 relay
ASPC2
(C,D half of CCD)
ASPC1
(A,B half of CCD)
4
Relay Operation
Pushes Telemetry Pole
D
C
Glass Beads:
Used to push on
movable contact
Rocker Assembly
A
B
Glass Beads:
Used to push on
movable contact
Pushes +35V Pole
Pivot point
Contact made by
spring action of
movable center arm
to relaxed state
Shown in LVPS2
Selection Position (X coil
commanded last)
(LVPS2 A3
+35V)
D1
A2
(LVPS1 A1
+35V)
D2
D3
Contact made by
pushing action of
rocker arm
5
ACS/HRC Timeline
• WFC returned to service on October 1, 2006
• Not affected by HRC relay issue
• HRC returned to service on October 15, 2006
• Single toggle of relay restored electrical contact
• ARB has recommended never toggling problematic relay again
• SBC is functional but powered off
• ARB is examining options for bringing SBC on line
• Previous use of SBC required toggle of problematic HRC relay to allow
HRC to be turned off for SBC observations
• Power / current / thermal issues are being worked
• Option 1: CCDs and SBC on simultaneously
• Option 2: CCDs off when SBC is on
6
ACS/HRC Post Recovery Performance
• Internal bias and dark exposures from ACS Daily Monitor
Program (10758) have been examined
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Data were obtained after the ACS anneal on October 16, 2006
Data were read out through the C amplifier
Both GAIN=2 and GAIN=4 data were obtained.
Readnoise and dark current track historical averages
Bias levels are slightly higher than historical average, but this is
expected
• Bias level typically higher for a short time (few hours) after anneals
• Bias level is expected to drop back to historical average by next set of
observations
• No impact on science data or performance
• Data look perfectly normal, with no anomalies noted (Marco
Sirianni)
7
ACS/HRC Bias Images (16-Oct-2006)
The two bias images above were obtained after resumption of HRC operations.
Both were obtained with GAIN= 2 after the ACS anneal. These bias images look
perfectly normal. The data were read out through the C amplifier.
8
ACS/HRC Readnoise and Bias Level (GAIN=2)
The above plots show the readnoise (left) and bias level (right) for historical
Side-2 data [blue points] and post-recovery data [yellow points]. The solid red
lines are the historical averages, and the dotted red lines indicate the historical
±3 sigma excursions.
9
ACS/HRC Readnoise and Bias Level (GAIN=4)
The above plots show the readnoise (left) and bias level (right) for historical
Side-2 data [blue points] and post-recovery data [yellow points]. The solid red
lines are the historical averages, and the dotted red lines indicate the historical
±3 sigma excursions.
10
ACS/HRC Post Recovery Performance
• First post-recovery science data were obtained October 18,
2006
• G800L observations of SN1987A (Kirshner SAINTs program;
GO10867)
• Historical data were pulled for comparison
• Exposures dithered to remove cosmic rays
• Data look perfectly normal, with no anomalies noted (Ron
Gilliland)
11
ACS/HRC Science Images (18-Oct-2006)
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