chandra x-ray observatory cxc acis ops team december 13, 2007 1 controlling the acis fp temperature:...

Chandra X-Ray Observatory CXC

ACIS Ops team December 13, 20071

Controlling the ACIS FP Controlling the ACIS FP Temperature: Temperature:

I.I. Turning off the DH Heater During Turning off the DH Heater During Perigee Passages with Rear Sun Perigee Passages with Rear Sun

OrientationsOrientationsII.II. Turning Off the DH Heater Turning Off the DH Heater

During a Forward Sun During a Forward Sun OrientationOrientation

ACIS Ops TeamACIS Ops Team



New Proposed Test• turn off the DH heater for an entire perigee passage at forward Sun attitude OR during a series of calibration observations of E0102 at forward Sun in FEB0408 week

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 starting in the JAN0708 week

€

≥

What Are We Asking For Today ?



DePasquale (SAO),

Vogrin (NGST) predicts a steady state temperature of -69 to -71 C at the HRC position and pitch angle of ~150

Cool ACIS DH for an Entire Perigee Passage

Results of the 18 Nov 2007 Test

BeginEnd



DePasquale (SAO)

Side A temperature, 1CBAT

Minimum temperature achieved

-69.8 C

Results of the 18 Nov 2007 TestCool ACIS DH for an Entire Perigee Passage

End

Begin



DePasquale (SAO)

Side B temperature, 1CBBT

Minimum temperature achieved

-69.8 C


Begin

End



DePasquale (SAO)

FP cooled while there was significant Earth in the ACIS radiator FOV and the Camera Body was cooling and the FP cooled rapidly to -119.7 C after the perigee passage


Begin

End



Summary of DH Cooling TestsSummary of DH Cooling Tests

Minimum Temperatures and Fit ResultsMinimum Temperatures and Fit Results



Summary of Entire Perigee DH Cooling TestSummary of Entire Perigee DH Cooling Test

• 1CBAT and 1CBBT reached a minimum temperature of -69.8 C

• no evidence that the primary survival heater turned on

• appears unlikely that the ACIS Camera Body can cool below -69.8 C if the DH heater is off for the entire perigee passage, the SIM is at HRC-S, and the pitch angle is ~150 degrees

• based on this, ACIS Ops considers it safe to turn off the DH heater for all perigee passages as long as the pitch angle is greater than 140



What is Needed to Implement this in the JAN0708 Load ?What is Needed to Implement this in the JAN0708 Load ?

• New MP guideline which describes when the commands to turn off and turn back on the DH side B heater can be inserted for a given perigee passage

• Modification to the ACIS load review SW to check that the pitch angle during perigee is larger than 140 degrees for at least 55 ks during the perigee passage

• Engineering directives written to the OC/CC informing them of the times when the Dh heater is off and to expect off-nominal 1CB[AB]T temperatures

• GRETA, ACIS Ops & SOT MT&A limits modified for 1CB[AB]T to a Red Low value of -74.0 C

• Contingency CAP developed and approved (CAP 1053) to turn on the DH side B heater in the case that SCS 107 has run and stopped the loads before the heater is turned on and in the case that 1CBAT < -72.2 C

• plan is to turn off the DH heater for all perigee passages which satisfy these criteria, hopefully leading up to the day that the DH heater can be turned off at all times



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)



New Test: Turn Off the DH side B Heater in a Forward Sun Orientation

• Vogrin’s model predicts that the Forward Sun orientation is a colder orientation for the ACIS Camera Body and DH

• It is possible the Camera Body will get colder than -69.8 C in a forward Sun orientation

• two possibilities in February 2007, one is a group of E0102 calibration observations (~80 ks at a pitch of 65.1 degrees) in the FEB0408 week and the other is perhaps a perigee passage at forward pitch

• Scenario would be very similar to the 18 November 2007 DH cooling test, we would ask for additional COMs to monitor the Camera Body temperatures more frequently and would have CAP 1053 ready to run to turn on the heater in the case that 1CBAT < -72.2 C



Possible Outcomes

1) 1CBAT >= -72.2 C - conclude it is safe to turn off the DH side B heater in forward Sun orientations

2) 1CBAT < -72.2 C - turn the DH side B heater back on and investigate why the primary survival heater did not turn on as expected



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



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 -70.5 C -75.5 C -74.0 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

chandra x-ray observatory cxc acis ops team december 13, 2007 1 controlling the acis fp temperature:...

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