1. Chandra X-Ray Observatory CXC ACIS Ops team February 28, 2008 1 Controlling the ACIS FP Temperature: Turning off the DH Heater During ALL Perigee Passages ACIS Ops Team

2. Chandra X-Ray Observatory CXC ACIS Ops team February 28, 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 DH heater for ALL perigee passages regardless of pitch angle What Are We Asking For Today ?

3. Chandra X-Ray Observatory CXC ACIS Ops team February 28, 2008 3 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

4. Chandra X-Ray Observatory CXC ACIS Ops team February 28, 2008 4 DePasquale (SAO) Colder Camera Body results in a colder FP temperature Results of the 4/5 Feb 2008 Test FP Temperature during the test

5. Chandra X-Ray Observatory CXC ACIS Ops team February 28, 2008 5 DePasquale (SAO) Min temperature -72.2 C ~59 ks at tail-Sun ~110 ks at forward-Sun Some 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

6. Chandra X-Ray Observatory CXC ACIS Ops team February 28, 2008 6 DePasquale (SAO) Results of the 6/7 Feb 2008 Test FP Temperature during the test

7. Chandra X-Ray Observatory CXC ACIS Ops team February 28, 2008 7 Summary of Tests at Forward-Sun 1CBAT and 1CBBT reached a minimum temperature of -69.8 C in the first test after 48 ks at forward-Sun and -72.2 C in the second test after 110 ks at forward-Sun (in both cases after cooling for the entire perigee passage at tail-Sun) time constants at forward-Sun orientations are very similar to those in tail-Sun orientations (30-55 ks, see fits to all cooling tests at: http://cxc.harvard.edu/twiki/bin/view.cgi/AcisOps/CoolingTests) http://cxc.harvard.edu/twiki/bin/view.cgi/AcisOps/CoolingTests minimum temperature of -72.2 C at forward-Sun is consistent with Vogrin’s model ACIS Fid lights are operating nominally after these tests a cold Camera Body keeps the FP colder in general and allows a faster recovery after perigee passage CAP1053 is available on-console to be run in case the Camera Body gets colder than expected it is safe to turn off the DH heater for an entire perigee passage at any pitch angle Conclusion

8. Chandra X-Ray Observatory CXC ACIS Ops team February 28, 2008 8 Future Plans we plan to come back to the FDB to ask for approval to turn off the DH heater for good and we will discuss the data which indicate that the primary survival heater may have turned on during test #2 the DH heater will be turned off for good once the DS has implemented the SW which accounts for a variable Camera Body temperature, release is currently scheduled for April 2nd