controlling the acis fp temperature: turning off the dh heater during perigee passages
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Chandra X-Ray Observatory CXC
ACIS Ops team November 1, 20071
Controlling the ACIS FP Controlling the ACIS FP Temperature: Temperature:
Turning off the DH Heater During Turning off the DH Heater During Perigee PassagesPerigee Passages
ACIS Ops TeamACIS Ops Team
Chandra X-Ray Observatory CXC
ACIS Ops team November 1, 20072
New Proposed Test• turn off the DH heater for an entire perigee passage
• monitor the Camera Body side A/B temperatures (1CB[AB]T)
• If both side A and B read -72.2 C or colder, contingency response is to turn the DH heater back on
Success Criteria
Change to Standard Operations
• The Camera Body side A (1CBAT) -72.2 C and side B (1CBBT) -72.2 C for the duration of the test
€
≥
• turn off the DH heater for all perigee passages for which the pitch angle is larger than 140 degrees
€
≥
If the test above is successful:
Chandra X-Ray Observatory CXC
ACIS Ops team November 1, 20073
Summary of DH Cooling TestsSummary of DH Cooling Tests
Minimum Temperatures and Fit ResultsMinimum Temperatures and Fit Results
Chandra X-Ray Observatory CXC
ACIS Ops team November 1, 20074
Summary of DH Cooling TestsSummary of DH Cooling Tests
• proposed test is most similar to the first test and NOT like the other tests during the CDF-S observations in which the SIM is at the ACIS position
• first test resulted in a minimum temperature of -69.8 C for both 1CBAT and 1CBBT in 37 ks
• extrapolation of first test predicts temperatures of 1CBAT=-71.6 C and 1CBBT=-70.0 C after 56 ks
• 90% CL on asymptotic temperatures is 1CBAT=-80.3 C and 1CBBT=-74.6 C
• primary survival heater should turn on at -71.1 C and secondary survival heater should turn on at -73.6 C
Chandra X-Ray Observatory CXC
ACIS Ops team November 1, 20075
DePasquale (SAO), Vogrin predicts a steady state temperature of -69 to -71 C at the HRC position and pitch angle of ~150
First ACIS DH Cooling Test: Perigee Passage
How fast can the Camera Body get cold ?
Begin
End
Chandra X-Ray Observatory CXC
ACIS Ops team November 1, 20076
Side B temperature, 1CBBT
First ACIS DH Cooling Test: Perigee Passage
How fast can the Camera Body get cold ?
Begin
End
Chandra X-Ray Observatory CXC
ACIS Ops team November 1, 20077
DePasquale (SAO), commanded by SOP_61014_DAHTR_B_ON
DH heater draws a maximum of 60 W, survival heaters draw 22 W
If the survival heater turns on, side A should respond faster than side B
First ACIS DH Cooling Test: Heating
How fast does the Camera Body warm ?
Chandra X-Ray Observatory CXC
ACIS Ops team November 1, 20078
Detector Housing Survival Heater
Geometry
•HR7, HR8: 22 W @ 29 V• Prime survival -71.1 °C• Rdnt survival -73.6 °C
•Better than 1.19 °C accuracy (@ -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)
Heater description
Pr or Red
Htr Bus
Enable Cmd
Disable Cmd
Heater Flight Telemetry Mnemonic
Heater Power at 29 volts (watts)
Heater Resistance (ohms)
Heater Close Set Point Temp (°C)
Heater Open Set Point Temp (°C)
Primary Heater Monitor Thermistor Mnemonic
Backup Heater Monitor Thermistor Mnemonic
ACIS Det. Hsg. Survival
PR 2 NA NA NA 22 38.2 -71.1 -69.8 1CBAT 1CBBT
ACIS Det. Hsg. Survival
RD 7 NA NA NA 22 38.2 -73.6 -72.5 1CBAT 1CBBT
Trinh(NGST)
Chandra X-Ray Observatory CXC
ACIS Ops team November 1, 20079
One Concern
• DH cools faster than predicted from earlier test
• primary survival heater fails to turn on and/or secondary survival heater fails to turn on
• thermostat for primary survival heater turns on at a temperature less than -71.1 C (how close are the temperatures read out by 1CB[AB]T and the survival heaters ?)
• SCS 107 interrupts the load before the command to turn the DH heater back on is executed and one of the above is true
The ACIS Camera Body and the Fid Lights get colder than -72.2 C. Fid Lights should not be allowed to drop below -76.0 C.
How could this happen ?
Chandra X-Ray Observatory CXC
ACIS Ops team November 1, 200710
Implementation-- DH heater will be commanded on and off in the load (has been executed 6 times in the load)
-- realtime COMs will be provided to monitor the Camera Body temperature during the second half of the perigee passage. FOT MP has identified COMs on DOY 2007:323 (Monday 19 November 2007)
-- contingency CAP to execute SOP_61014_DAHTR_B_ON will be ready to run
Time Elapsed Time Event
323:07:00 0.0 DH side B heater is turned off by the load
323:13:10 15000 s AOS, verify heater is off 323:14:10 18600 s LOS
323:15:45 31500 s AOS, verify temperatures 323:16:45 35100 s LOS
323:21:15 51300 s AOS, verify temperatures 323:22:40 56400 s side B heater turned on by the load 323:23:10 58200 s LOS
Chandra X-Ray Observatory CXC
ACIS Ops team November 1, 200711
Telemetry Verification
Camera Body temperature 1CBAT/1CBBT digitization is ~2.47 C
-59.9 C
-62.4 C
-64.8 C
-67.3 C
-69.8 C
-72.2 C
-74.7 C
1CB[AB]T
-71.1 C, primary survival heater set point
-73.8 C, secondary survival heater set point
-76.0 C, must not drop below
• side A (1CBAT) cools faster than side B (1CBBT)
• side B (1CBBT) warms faster than side A when the DH heater is used
• side A (1CBAT) should warm faster when the survival heater is used
Chandra X-Ray Observatory CXC
ACIS Ops team November 1, 200712
Telemetry Verification
Five possible cases:
1) 1CBAT > -72.2 C and 1CBBT > -72.2 C -- allow test to proceed
2) 1CBAT = -72.2 C and 1CBBT > -72.2 C -- allow test to proceed
3) 1CBAT > -72.2 C and 1CBBT = -72.2 C -- allow test to proceed
4) 1CBAT = -72.2 C and 1CBBT = -72.2 C -- terminate test
5) 1CBAT < -72.2 C and 1CBBT < -72.2 C -- terminate test
Chandra X-Ray Observatory CXC
ACIS Ops team November 1, 200713
Turn the DH Heater Off for Future Perigee Passages
• Keeping the Camera Body colder will keep the FP temperature colder• If the proposed test is successful, we want to turn off the DH heater for all perigee passages for which the pitch angle is greater than 140 degrees
Limit Changes
Mnemonic Current Yellow Low New Yellow Low Current Red Low New Red Low
1CB[AB]T -70.5 C -72.2 C -75.5 C -74.7 C Camera Body Temp
1DAHBCU 0.80 A 0.0 A 0.20 A 0.0 A DA Htr Current B
1DAHBVO 10.5 V 0.0 V 3.5 V 0.0 V DA Htr Voltage B
1DAHHBVO 25.0 V 0.0 V N/A/ N/A DA Htr Input Voltage B
1DAHTBEN Enb N/A DA Htr B Enb/Dis
1DAHTBON On N/A DA Htr B On/Off
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