To:sot_shift from: Dan Schwartz date: 06 Oct 99 , 11:00am EDT Subject: SOT shift report, Shift L75 -------- See http://asc.harvard.edu/acis/SOT_reports/sot-shift.html, or /proj/ascwww/AXAF/extra/science/htdocs/acis/SOT_reports/Oct_06_1999_L75.txt. Shift L75. Start at 279:11:00 GMT = 07:00am 06 Oct EDT End 11:00am 06 Oct SOT Lead DAS Spac/Aspect FOT/Sci liason HRC ACIS (Times will be given in GMT on day 279. In general times are rough, not precise.) PLAN Continue running load P20d. Doing an ACIS-S/HETG observation of SN1987a. Next Comm at 17:00 to 18:00 GMT (1-2pm) EVENTS NOTES/ISSUES/PROBLEMS At start of shift, Chandra's state from the last LOS, 279:12:27, was as follows: PCAD MODE = NPNT CONTROL LAW FLAG = NPNT Stars: = 5 FIDS = 3 RA = 83.900 deg DEC = -69.292 deg ROLL = 71.886 deg Format = 2 OBSID = 124 SIM FA = -467 SIM TSC = 75623 (ACIS-S) HETG = IN LETG = out HRC HV is OFF We have used the following new OBSID, in a CAP to change the ACIS event mode to Faint 3x3 readout. It has been running VF 5x5 readout during OBSID 124. This observation is ACIS-S/HETG observation of SN 1987a. OBSID 1387 will otherwise be identical to OBSID 124. The CAP, 465, is to be executed during the 17:00 to 18:00 comm pass. There are two underlying problems here: Why was this grating observation set up with the 5x5 in the first place? Second, the process of getting such a late change into the system is not appropriate. What was the complete chain of communication from the observation PI through the Chandra User Support, and is this how it should be? Report from the 9am ops standup: We sailed through yesterday's eclipse, power profiles as expected. A review was given of the gyro phenomena observed on day 269. IRU unit A, gyro number 2, had its current jump one or two bits, from 102 ma to 104 ma, at GMT 267:13:05. This led to an immediate change of the yaw bias estimated on board, from ~0.4305 deg/hr and gradually drifting down to 0.4245 deg/hr over a two hour period. The Pitch bias started changing at ~14:30 from 0.2938 deg/hr to become 0.3038 deg/hr about two hours later (16:30). Roll bias didn't change, which is consistent with the fact that Unit A gyro 2 does not have any components in the spacecraft X-axis. It is thought that the small current change could be due to drag on the rotor from a drop of oil being released from the lubricant reservoir onto the bearings. This reasonably might cause the bias change, either from direct mechanical effects, or from the small heating effect of the increased current. These changes of current and drift rate are at least 5 times smaller than the threshold at which the gyro design engineer thinks we need to pay attention. So we have no concern from that particular incident. NONETHELESS, we recognize historical problems with gyros, and the FOT WILL continue to monitor and evaluate all such changes. Following safe mode recovery, the change in gyro bias rates was associated with the fact that the gyros were NOT updated in the on-board Kalman filter for a considerable time, following their power cycling due to the safe mode event. We have a 4pm EDT telecon today to discuss the safe modes issues that Rob Cameron is pursuing. Use the ACIS meet-me line, today only. ------------------------------------------------------- Dan Schwartz, MS #3 das@head-cfa.harvard.edu phone: (617)495-7232 FAX: (617)495-7356 cell phone: (617)512-5627 pager: 800-759-8352 PIN 1636502 or e-mail 1636502@skytel.com -------------------------------------------------------