Aug_17_1999_M27.txt Shift M27 Start at 1999:229:18:00 GMT = 1999 Aug 17 2:00pm EDT End 1999 Aug 17 10:00pm EDT See http://asc.harvard.edu/acis/SOT_reports/sot-shift.html, or /proj/ascwww/AXAF/extra/science/htdocs/acis/SOT_reports/Aug_17_1999_M27.txt. SOT Lead Ed Kellogg SOT SC/ACA Rob Cameron FOT-SI HRC-SI John Chappell, Jerry Austin ACIS-SI Paul Plucinsky, Ed Boughan (Times will be given in GMT on day 229. not precise.) EVENTS PLAN DONE OBSID -------------- ---- ---- ----- Start shift (2pm EDT 17 Aug 1999) 1800 1800 1226 Additional ACIS load 1268 Madrid AOS 1815 1815 Start CAP 290A, config HRC protected SCS's, optimize HRC-I antico, put HRC in NIL 1838 62449 Complete CAP 190 A 1935 Vacuum 4.1e-6 torr 2000 In safe mode! 2017 CTU VCDU counter reset 1999:229:20:17:56.175 2017 Complete SOP 40006, indicates safe mode 2040 Dump OBC-A error log 2142 ACIS cold radiator temp -115.9 C 2340 End shift (2pm EDT 12 Aug) day 228 1800 NOTES/ISSUES/PROBLEMS --------------------- As soon as we saw safe mode, SOC did SOP 40006. After ~20 min, he concluded that Chandra was in a safe condition. Chandra made a transition to Normal Point Mode during a compound maneuver, instead of staying in Normal Maneuver Mode. PCAD reported there were several undesirable command overlaps, resulting in loading a new quaternion too early, which gave a huge attitude/rate error. PCAD stated they hadn't appreciated the timing issues. As of 2049 hrs, the SIM is parked at 23336 steps on the translation table axis, midway between the ACIS and HRC positions. The X location is -594, the same as before we went to safe mode. HRC HV was shut down. ACIS was stopped, and its temperature is normal. Pitch angle is 110 degrees, OK. Later, pitch angle went to 90, as expected for safe mode. 2121 We asked TST to run CAP 206 to disable all the HRC HV SCS's in the OBC-B configuration, since it comes on with them all enabled. 2147 Error log dump confirms PCAD attitude/rate error. More details from 6 pm EDT review meeting - The 3rd daily load was built on OFLS 7 between 1700-1730 GMT, activated ~1830-1900. We may have violated a 10 sec delay CARD constraint between maneuvers. Pete Quast restated the presently understood cause: the ATS for a compound maneuver had a transition from normal maneuver mode to normal point mode prior to the end of the first maneuver. The quaternion had already been updated to the next pointing direction, 120 degrees away, so a large error value occurred, which triggered the attitude/rate error. Marilyn Newhouse said that we had identified a need for a settle time between maneuvers in the constraints file of OFLS, but the value in the file was zero. After much discussion, it was decided to pursue parallel paths - examine data to improve our confidence that the above is the cause of safe mode and is the only problem, try to duplicate it on ASVT, and prepare to execute SAP 56002, recovery from safe mode when we are sure we know the cause of safe mode. At the 9 pm EDT meeting it was decided to use SOP 5C030, Core Swap, modified, to recover from safemode. This might be ready for use in ~4 hours, but we must take into account crew readiness and TLM outages to plan the actual time of execution. We still need to make a permanent change in the algorithm for generating the DOT so that there will be a 3 min delay between ACIS stop science (AA00000000) and commanding the next OBSID, to allow ACIS to send down data that are transmitted after AA00000000 but belong with the previous obsid. This was communicated to CXC MP, Pat Slane.