1. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 1 Controlling the ACIS FP Temperature: Turn Off the ACIS DH Heater ACIS Ops Team

2. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 2 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 Change to Standard Operations turn off the ACIS DH heater as the new standard configuration What Are We Asking For Today ? 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

3. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 3 ACIS FP Temperature over the Mission Bissell (NGST), 8 hr averages of FP temperature, 30 day running average Review from Sep 6, 2007 FDB Presentation: Why Are We Doing This ?

4. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 4 ACIS FP Temperature over the Mission Grant (MIT)

5. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 5 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

6. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 6 ACIS FWHM vs. FP Temperature Grant (MIT) FWHM of FI CCDs is a sensitive function of FP temperature

7. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 7 ACIS FP Temperature over the Mission Grant (MIT)

8. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 8 Expected Improvement with the DH Heater off Joe Vogrin’s and Neil Tice’s 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 Vogrin’s 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

9. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 9 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/ view.cgi/AcisOps/CoolingTests

10. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 10 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.

11. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 11 DePasquale (SAO), min temperature -69.8 side A/B ~63 ks at tail-Sun ~48 ks at forward- Sun Cool ACIS DH for an Entire Perigee Passage and during E0102 observations Results of the 4/5 Feb 2008 Test

12. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 12 DePasquale (SAO) Colder Camera Body results in a colder FP temperature Results of the 4/5 Feb 2008 Test FP Temperature during the test

13. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 13 DePasquale (SAO) Min temperature -72.2 C ~59 ks at tail-Sun ~110 ks at forward-Sun Evidence the primary survival heater turned on Results of the 6/7 Feb 2008 Test Cool ACIS DH for an Entire Perigee Passage, some E0102 observations and some HRC observations

14. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 14 DePasquale (SAO) Results of the 6/7 Feb 2008 Test FP Temperature during the test

15. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 15 DePasquale (SAO) 1CBAT during the end of the 6/7 Feb 2008 Test 1CBAT goes from -72.2 C to -69.8 C every 3ks

16. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 16 DePasquale (SAO) More than one sample in first case but only one sample in the second case Zoom of the First Two Instances in which 1CBAT increased to -69.8 C

17. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 17 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

18. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 18 Location of 1CBAT and Survival Heater and SSTS Tice (LMA)

19. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 19 ACIS Detector Housing Survival Heater Geometry HR7, HR8: 22 W @ 29 V Prime survival -71.1 °C Rdnt survival -73.6 °C RT7 & RT8 are SSTS 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)

20. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 20 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

21. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 21 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.

22. Chandra X-Ray Observatory CXC ACIS Ops team March 27, 2008 22 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