Controlling the ACIS FP Temperature: Turning off the DH Heater During Perigee Passages

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



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:



Summary of DH Cooling TestsSummary of DH Cooling Tests

Minimum Temperatures and Fit ResultsMinimum Temperatures and Fit Results



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



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



Side B temperature, 1CBBT

First ACIS DH Cooling Test: Perigee Passage

How fast can the Camera Body get cold ?

Begin

End



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 ?



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)



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 ?



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



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



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



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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Controlling the ACIS FP Temperature: Turning off the DH Heater During Perigee Passages