Sep_27_1999_M66.txt Shift M66 Start at 1999:270:11:00 GMT = 1999 Sep 27 7:00am EDT End 1999 Sep 27 12:00pm EDT SOT Lead Robert Cameron ACA/SC FOT-SI ACIS Yousaf Butt HRC-SI (Times: hhmm or ddd:hhmm, not precise.) Plan: Recovery from safe mode entry. Eclipse passage. ACIS CTI measurement after radiation passage. Recovery of the mission timeline. We started the shift AOS. S/C state: 1100 GMT -------- PCAD MODE= Normal Sun Mode NSUN,SPNT Stars: = 7 (had been 8 from ACA full-field search) FIDS = 0 RA = 79.2059 est. DEC = 45.9794 est. ROLL = 98.062 est. Format = 4 OBSID = 0 SIM FA = -535 SIM TSC = -99608 (HRC-S) HETG ANG = 81, 82 (out) LETG ANG = 82, 80 (out) HRC = safed ACIS = video boards off; FP @-110C EVENTS day 270 ACTIVITY -------------- -------- 2000 LOS 2346 AOS 1999:270:13:38:07.683 EE1RADZ0 ELECTRON1 RADIATION ENTRY0 1999:270:16:25:44.632 PENTRY EARTH SHADOW (PENUMBRA) ENTRY 1999:270:16:27:54.632 EONIGHT EARTH SHADOW (UMBRA) ENTRY 1999:270:17:35:34.632 EODAY EARTH SHADOW (UMBRA) EXIT 1999:270:17:36:54.632 PEXIT EARTH SHADOW (PENUMBRA) EXIT 1999:270:19:15:03.372 EPERIGEE ORBIT PERIGEE 1999:270:19:42:07.683 EP2RADZ0 PROTON2 RADIATION ENTRY0 1999:270:20:16:07.683 XP2RADZ0 PROTON2 RADIATION EXIT0 1999:270:20:48:24.828 EASCNCR ORBIT ASCENDING NODE CROSSING 1999:270:23:56:07.683 XE1RADZ0 ELECTRON1 RADIATION EXIT0 NOTES/ISSUES/PROBLEMS --------------------- Further details on the cause of the bright-star hold: The p18 command load had a segmented observation for obsid 123. The quaternion for 123 was incorrect, with a 0.6 degree roll error. However, the star catalog for 123 was built for the correct quaternion. It was realized that the ACA would be able to find the stars with such a roll error. But PCAD zeroed out the star position errors, caused by the catalog/quaternion mismatch, and introduced a quaternion error, which caused the failure to find stars at the end of the next maneuver. In addition, the p18 load had a 2-day offset in the time of the maneuver to the first 123 observation. This observation never happened, but fortunately was followed by a second 123 observation at the same attitude. The OFLS at present cannot correctly handle segmented observations, and the FOT Mission Planners will explicitly countermand such observations until the OFLS is fixed. A full-field ACA search was commanded (CAP 454A) to find 8 stars, for fine attitude initialization. Current attitude (approx.): RA = 292.742 Dec = -85.236 Roll = 288.951 1400: 2 of the 8 stars have been lost so far. It remains to be seen how well we can hold the X-axis pointing and stars during the perigee passage, with its disturbance torques. It is not known if the Earth will occult the ACA during perigee. An ATS has been loaded to perform only eclipse operations. Chandra will remain in normal sun mode through the radiation zone passage. A second ATS will be built and uploaded before 2000 GMT to perform ACIS post-radiation CTI measurements. Operations CXO Status Report 9/27/99 7AM ---------------------------------------- During the last 24 hours the spacecraft experienced a bright star hold and safe mode event. Following trouble shooting and assessment, the spacecraft was returned from safe mode to normal sun mode and readied for the next eclipse scheduled at 12:30PM 9/27. The ACIS was commanded to the next-in-line position for radiation belt passage. During the safe mode entry and recovery to normal sun mode the spacecraft performed as expected. The spacecraft entered bright star hold at 9AM 9/26 following a maneuver with a large attitude error due to an incorrect quaternion in the command load. Safe mode entry occurred at 6:57PM 9/26 following an operator error during fine attitude initialization to recover from bright star hold. Safe mode recovery to normal sun mode was completed at 4:10AM 9/27. Full analysis is being performed on the sequence of events leading to safe mode, however initial assessment indicates modifications to flight and ground software and ground procedure are required. Following fine attitude initialization, the plan is to re-intercept the GTO observing plan after appropriate load review and procedure revision.