COS SMOV Morning Update
4 June 2009
COS NUV HV Turn-on:
full ramp-up Dark Exposures
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Apparently nominal HV ramp-up and operation; recommend ops request
to clear event flag 2, continue with SMOV operations
Two test exposures (program 11355 visit 4)
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Voltage ramp exposure: final count rate consistent with subsequent dark
Nominal voltage [-2050v(MCP) / -800v(PC)] integration :
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– Exp 1 : 3090 sec during full ramp-up sequence (red track in figure below)
– Exp 2: 450 sec at full operating voltage (blue track in figure below)
– Rate: 29.8 (13395. counts / 450. secs) ;
– No obvious morphology.
Consistent with expected higher background on-orbit, but not as high as predicted.
COS NUV HV Turn-on:
Operating Voltage Dark Exposure
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Dark count rate = 30 cps.
This is substantially lower than initial predictions (~225-450 cps)
Possibly due to lower window temperature (~13C versus nominal
predicted cold op of 17C), or to shorter initial decay timescale for
COS window.
Much too early to form significant conclusions
Important to analyze behavior over time in upcoming dedicated NUV
dark monitoring program 11466 within predicted nominal operating
temperature range (cold op = 17C; hot op = 31C).
Dark-count Levels: STIS and COS
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Ball measures of window samples from same boules as flight detectors:
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STIS:
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Irradiated by Sr90 source for 30 minutes (phosphorescence rate after 5000 sec)
STIS (boule STE6): 70 counts / sec
COS (boule STF8): ~18 counts/sec
STIS (STE6)/COS (STF8)= ~4:1
Ball SER COS-NUV-001 (3 June 1998); Ball SER COS-NUV-031 (18 June 2002)
– CEI specification: 130 counts/sec (1.25 e-4 counts/sec/pixel)
– Ground TV dark rate:
• 6-7 counts/sec (per Randy Kimble)
• “substantial improvement over spec,” ref: Kimble et al 1998, ApJ, 493, L83
– On-orbit dark rate (STIS cycle 17 IHB):
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COS:
• 0.86 – 1.70 E-3 counts/sec/pixel;
• corresponds to ~900-1780 counts/sec from entire detector
– CEI specification: at I&T ~4.2 counts/sec (4.0 e-6 counts/sec/pixel)
– Ground TV dark rate (from entire detector ):
• TV03: 2.68 counts/sec
• TV06: 3.38 counts/sec
– On-orbit COS dark rate (from entire detector):
• Anticipated: 225-450 counts / sec (1/4 of STIS value)
• As measured in 11355 visit 4 exposure 2 (450 sec): ~30 counts/sec
Upcoming COS SMOV Timeline
• Day 155 (Thurs 4 June):
– 11355 visit 5 (COS07) NUV Fold Test
• 1135505 155:17:51:54 - 155:18:50:33 UT
– 11356 visit 1 of 13 (COS23) FUV HV Turn-on
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Turn FUV detector on, but do not ramp voltage, dump DCE memory
1135601 155:21:05:00 - 155:21:07:31
sets event flag 3
OPS request required: clear NSSC-1 COS event flag 3 prior to visit 2
• Day 156 (Fri 5 June):
– 11356 visit 2 of 13 (COS23) FUV HV Turn-on
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Set at HVLOW
1135602 156:16:55:20 - 156:17:14:11
sets event flag 3
OPS request required: clear NSSC-1 COS event flag 3 prior to visit 3
Upcoming COS SMOV Timeline
• Day 157: Sat 06 June
– 11467: NUV functional test
• 146701 157:00:00:00 - 157:02:20:06
– Evaluate image and spectrum locations; prepare updates of TA parameters to
be uploaded with SMS173 (input needed by day 167)
– 11466: 3 visits (of 11) NUV darks
• 1146601 157:07:00:00 - 157:08:01:34
• 1146602 157:09:39:50 - 157:11:07:27
• 1146603 157:16:22:05 - 157:17:48:56
– 11356 visit 3 of 13 (COS23) FUV HV Turn-on;
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ramp from HVLOW to first specified value, dump DCE, wave , dark exp
OPS request required: clear NSSC-1 COS event flag 3 set in 1135602
1135603 157:20:52:00 - 157:21:28:28
No event flag set; leave SI at HV level for 4 hours; then execute 1135604
– Contingency OPS request in place to place FUV in INHIBIT if anomaly
• science data