1. Chandra X-Ray Observatory CXC ACIS Ops team November 1, 2007 1 Controlling the ACIS FP Temperature: Turning off the DH Heater During Perigee Passages ACIS Ops Team

2. Chandra X-Ray Observatory CXC ACIS Ops team November 1, 2007 2 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 If the test above is successful:

3. Chandra X-Ray Observatory CXC ACIS Ops team November 1, 2007 3 Summary of DH Cooling Tests Minimum Temperatures and Fit Results

4. Chandra X-Ray Observatory CXC ACIS Ops team November 1, 2007 4 Summary 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

5. Chandra X-Ray Observatory CXC ACIS Ops team November 1, 2007 5 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

6. Chandra X-Ray Observatory CXC ACIS Ops team November 1, 2007 6 Side B temperature, 1CBBT First ACIS DH Cooling Test: Perigee Passage How fast can the Camera Body get cold ? Begin End

7. Chandra X-Ray Observatory CXC ACIS Ops team November 1, 2007 7 DePasquale (SAO), commanded by SOP_61014_DA HTR_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 ?

8. Chandra X-Ray Observatory CXC ACIS Ops team November 1, 2007 8 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 PR2NA 2238.2-71.1-69.81CBAT1CBBT ACIS Det. Hsg. Survival RD7NA 2238.2-73.6-72.51CBAT1CBBT Trinh(NGST)

9. Chandra X-Ray Observatory CXC ACIS Ops team November 1, 2007 9 One Concern primary 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 ?

10. Chandra X-Ray Observatory CXC ACIS Ops team November 1, 2007 10 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 -- contingency CAP to execute SOP_61014_DAHTR_B_ON will be ready to run TimeElapsed TimeEvent 323:07:000.0DH side B heater is turned off 323:13:1015000 sAOS, verify heater is off 323:14:1018600 sLOS 323:15:4531500 sAOS, verify temperatures 323:16:4535100 sLOS 323:21:15 51300 sAOS, verify temperatures 323:22:4056400 sside B heater turned on 323:23:1058200 sLOS

11. Chandra X-Ray Observatory CXC ACIS Ops team November 1, 2007 11 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

12. Chandra X-Ray Observatory CXC ACIS Ops team November 1, 2007 12 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

13. Chandra X-Ray Observatory CXC ACIS Ops team November 1, 2007 13 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 Limit Changes MnemonicCurrent Yellow LowNew Yellow LowCurrent Red LowNew Red Low 1CB[AB]T-70.5 C-72.2 C-75.5 C-74.7 C Camera Body Temp 1DAHBCU0.80 A0.0 A0.20 A0.0 A DA Htr Current B 1DAHBVO10.5 V0.0 V3.5 V0.0 V DA Htr Voltage B 1DAHHBVO25.0 V0.0 VN/A/N/A DA Htr Input Voltage B 1DAHTBENEnbN/A DA Htr B Enb/Dis 1DAHTBONOnN/A DA Htr B On/Off