Controlling the ACIS FP Temperature:

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• Controlling the ACIS FP Temperature
• Turn Off the ACIS DH Heater
• ACIS Ops Team

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What Are We Asking For Today ?
Change to Standard Operations

• turn off the ACIS DH heater as the new standard
  configuration

Results of Tests in FEB0408 Load

• two tests conducted during the FEB0408 load
  demonstrated that it is safe to turn off the DH
  heater at forward-Sun orientations, the Camera
  Body temperatures never dropped below -72.2 C in
  a 110 ks observation

Preparation for New Configuration

• CXC DS has implemented a new algorithm to
  correct aspect when the ACIS camera body
  temperature is fluctuating and the Fid Lights are
  moving

Approval today is contingent upon a successful
deployment of the new SW by the CXC DS, ie ACIS
Ops will not turn off the DH heater until the DS
gives the OK
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Review from Sep 6, 2007 FDB Presentation Why Are
We Doing This ?
ACIS FP Temperature over the Mission
Bissell (NGST), 8 hr averages of FP temperature,
30 day running average
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ACIS FP Temperature over the Mission
Grant (MIT)
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ACIS Gain vs. FP Temperature
Grant (MIT) 0.3 is the budget for the gain
calibration, 0.5 C increase in FP temperature
results in gain being out of the calibration
specification
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ACIS FWHM vs. FP Temperature
Grant (MIT) FWHM of FI CCDs is a sensitive
function of FP temperature
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ACIS FP Temperature over the Mission
Grant (MIT)
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Expected Improvement with the DH Heater off

• Joe Vogrins and Neil Tices analysis indicates
  that the FP temperature could be up to 3 degrees
  colder if BOTH the ACIS DH heater and the SIM FA6
  heater are off
• In Vogrins final analysis, he modeled a range
  of pitch angles from 45 to 172 degrees and the
  SIM at the ACIS and HRC positions, for the
  default heater configuration and for the DH
  heater and SIM FA6 heaters both off configuration
  
• In his initial analysis for a pitch angle of
  155, Vogrin modeled the effect of turning off the
  heaters separately. For that case, he found that
  turning off the DH heater reduced the ACIS FP
  temperature by 1.1 deg, turning off the SIM FA6
  heater reduced it by 0.4 deg, and turning off
  both the DH heater and SIM FA6 heater reduced it
  by 2.6 deg. Therefore, the reduction in the FP
  temperature by turning off both heaters is larger
  than the sum of the reductions of turning the
  heaters independently.
• In the intial analysis, Joe predicted that the
  1CBAT would drop to -66/-67 C. We know from our
  tests that 1CBAT gets as cold as -69.8 C for a
  pitch angle of 155 degrees, so we would expect
  more than 1.1 deg decrease in the FP temperature
  for this orientation from the DH heater alone
  being off

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Summary of DH Heater off Tests at
Rear-Sun Minimum T achieved is -69.8 C Full
results available at cxc.harvard.edu/twiki/bin/ v
iew.cgi/AcisOps/CoolingTests
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Summary of DH Heater Off Tests at Rear/Forward Sun
During second test, the Camera Body temperature
reached -72.2 C on side A and B for the first
time in the mission.
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Results of the 4/5 Feb 2008 Test
Cool ACIS DH for an Entire Perigee Passage and
during E0102 observations
DePasquale (SAO), min temperature -69.8 side
A/B 63 ks at tail-Sun 48 ks at forward-Sun
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Results of the 4/5 Feb 2008 Test
FP Temperature during the test
DePasquale (SAO) Colder Camera Body results in a
colder FP temperature
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Results of the 6/7 Feb 2008 Test
Cool ACIS DH for an Entire Perigee Passage, some
E0102 observations and some HRC observations
DePasquale (SAO) Min temperature -72.2 C 59 ks
at tail-Sun 110 ks at forward-Sun Evidence the
primary survival heater turned on
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Results of the 6/7 Feb 2008 Test
FP Temperature during the test
DePasquale (SAO)
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1CBAT during the end of the 6/7 Feb 2008 Test
1CBAT goes from -72.2 C to -69.8 C every 3ks
DePasquale (SAO)
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Zoom of the First Two Instances in which 1CBAT
increased to -69.8 C
DePasquale (SAO) More than one sample in first
case but only one sample in the second case
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DePasquale (SAO)
Table of Instances in which 1CBAT increased to
-69.8 C
Tick Time(DOY 39) Time(ks)
samples Diff(ks) 1 0.2171-2179
136.0521-136.1013 2 0.0
2 0.2551-2553
139.3321-139.3485 1 3.23 3
0.2885-2891 142.2185-142.2677
2 2.87 4 0.3208-3213
145.0065-145.0557 2 2.73 5
0.3527-3528 147.7617-147.7781
1 2.71 6 0.3826-3832
150.3529-150.4021 2 2.60 7
0.4142-4147 153.0753-153.1245
2 2.67 8 0.4441-4447
155.6665-155.7157 2 2.54 9
0.4726-4728 158.1265-158.1429
1 2.41 10 0.5003-5009
160.5209-160.5701 2 2.38 11
0.5292-5298 163.0137-163.0629 2
2.44 12 0.5577-5578
165.4737-165.4901 1 2.41 13
0.5854-5859 167.8681-167.9173 2
2.38
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Tice (LMA)
Location of 1CBAT and Survival Heater and SSTS
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ACIS Detector Housing Survival Heater Geometry
Trinh(NGST)

• HR7, HR8 22 W _at_ 29 V
• Prime survival -71.1 C
• Rdnt survival -73.6 C
• RT7 RT8 are SSTS
• Better than 1.19 C accuracy (_at_ -70 C ) for
  1YA94 SSTS that controls survival heater
• Located on Z face of Detector Housing (side A,
  1CBAT)
• Closest telemetry thermistor is 1CBAT (FM07)

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Did the Survival Heater Come on ?

• Regular cycles of 1CBAT up to -69.8 C every 3 ks
  are consistent with the survival heater cycling
  on and off
• Cycling between -72.2 C and -69.8 C is
  consistent with setpoint of primary survival
  heater of -71.1 C
• more frequent cycles up of 1CBAT than 1CBBT are
  consistent with survival turning on and off since
  survival heater is on side A
• more than one consecutive reading of 1CBAT at
  -69.8 C is consistent with the survival heater
  turning on as opposed to 1CBAT drifting slowly
  down to -72.2 C with occasional single ticks up
  to -69.8 C
• Neil Tice adds, The frequency of oscillation (1
  cycle per 40 minutes) in 1CBAT is consistent with
  the thermal time constant of the DH along with a
  22 W short duration (few minutes) heat pulse,

Conclusion

• It is likely that the primary survival heater
  did turn on
• All ACIS components and the Fid Lights operated
  nominally with the camera body at -72.2 C
• It is safe to turn off the DH heater for any
  spacecraft orientation and for the foreseeable
  future

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Implementation Commanding
-- realtime commanding preferred to maintain
flexibility -- very simple, CAP 1062 under
development which issues two ACIS HW commands to
turn off and to disable the heater 1HHTRBOF
and 1HHTRBDS -- contingency CAP 1063 under
development to turn on the DH side B heater in
case the Camera Body gets too cold, issues two
ACIS HW commands to turn the heater on
1HHTRBEN and 1HHTRBON
Status of CXC DS SW Update

• The DS7.6.11.6 release of CXCDS processing
  contains new aspect pipeline
• code that uses fid light and ACIS temperature
  telemetry to compensate for
• thermal contraction of the fid light mount as the
  DH temperature varies.
• This has been verified by processing all ACIS
  DH test obsids as well as two
• HRC observations.
• Detailed inspection of pipeline outputs showed
  the expected behavior of the
• correction code. Nominal aspect performance was
  recovered.

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Schedule for Implementation

• ACIS Ops waits for final approval from DS that
  SW has been deployed and is functioning as
  expected
• ACIS Ops schedules final CAP review to approve
  time of CAP execution
• We prefer to execute this during a perigee
  passage to minimize the
• temperature fluctuations during a science
  observation
• Earliest anticipated date of execution is Monday
  April 7th, perigee passage
• on that day which we could use
• Need to coordinate with MP, current plan is to
  not include any ACIS DH heater commands in the
  APR0708 load