To:sot_shift from: Dan Schwartz date: 27 Sep 00, 12:00noon EDT Subject: SOT shift report 2000-09-27 L433 -------- See http://asc.harvard.edu/acis/SOT_reports/sot-shift.html, or /proj/ascwww/AXAF/extra/science/htdocs/acis/SOT_reports/Sep_27_2000_L433.txt. Shift L433. Start at 271:12:00 GMT = 08:00am 27 Sep EDT End 12:00 noon 27 Sep SOT Lead DAS Spac/Aspect FOT/Sci liason HRC ACIS (Times will be given in GMT on day 271. In general times are rough, not precise.) PLAN ---- Continue running load SEP2400c. Perform HRC-S/LETG observations of the star Sirius B for calibration, obsid 1452; of the Be star X Per to study the intervening dust, obsid 589; of the hottest white dwarf H1504+65, obsid 30; and of the nova V1494 Aql, obsid 2308. Next Comms: 271:03:00 to 04:00 271:12:55 to 13:55 271:22:10 to 00:10 272:09:10 to 11:10 272:20:10 to 22:10 273:06:30 to 07:30 273:16:20 to 17:20 274:00:30 to 01:30 274:06:50 to 08:50 274:17:00 to 18:00 Orbital events: 272:01:24 ORBIT APOGEE 273:09:08 ORBIT PERIGEE 274:16:51 ORBIT APOGEE 276:00:34 ORBIT PERIGEE 277:08:18 ORBIT APOGEE 278:16:02 ORBIT PERIGEE EVENTS ------ Status at LOS, 271:03:59, was as follows: PCAD MODE = NPNT CONTROL LAW FLAG = NPNT Stars: = 5 FIDS = 3 RA = 101.315 deg DEC = -16.725 deg ROLL = 94.498 deg Format = 1 OBSID = 1452 Sirius B SIM FA = -990 SIM TSC = -99616 (HRC-S) HETG = OUT (79.8 deg) LETG = IN ( 4.5 deg) HRC-S HV is ON EPHIN Geom = LARG E1300 = 0.0 LT 10.0 (RADMON P4GM = 0.3 LT 300. Triggers) P41GM = 0.0 LT 8.47 A-leak = 0.5480 mu-a B-leak = 0.0960 mu-a Ascending through 92783 km. ACIS focal plane temperature -118.9. 12:55 AOS Status at LOS, 271:13:54, was as follows: PCAD MODE = NPNT CONTROL LAW FLAG = NPNT Stars: = 5 FIDS = 3 RA = 58.869 deg DEC = 31.029 deg ROLL = 108.316 deg Format = 1 OBSID = 589 X Per SIM FA = -990 SIM TSC = -99616 (HRC-I) HETG = OUT (79.8 deg) LETG = IN ( 4.5 deg) HRC-S HV is ON EPHIN Geom = LARG E1300 = 0.0 LT 10.0 (RADMON P4GM = 0.0 LT 300. Triggers) P41GM = 0.0 LT 8.47 A-leak = 0.6880 mu-a B-leak = 0.1200 mu-a Ascending through 129083 km. ACIS focal plane temperature -119.9 NOTES/ISSUES/PROBLEMS From the 9am status meeting: OCT0200c load is approved, as of receipt of ACA approval this morning. On-board loads are good until 274:13:39. Products for the LETG bumper test are being checked on ASVT today. The test is planned for next Wednesday afternoon, EDT. Notes from splinter meeting on MUPS warm starts. This meeting was held yesterday afternoon. Jeff Shirer pointed out that the TRW propulsion design and development group had assumed only 76 cases of momentum unloading per year, which was a disconnect from the PCAD group estimate of about 350. (The SAO mission support team failed to note this disconnect.) So the thrusters were only qualified to 3 times the five year estimate, or 1222 firings. We are currently using about 152 firings per year, so we will exceed the qual level in about 8 years. The degradation occurs in the initial stages of firing, when the catalyst temperature is only 450 deg F. During firing the temperature builds up to 1100 deg F. The nature of the thruster failure is a gradual degradation in the impulse delivered per firing. Thus we can monitor, anticipate failure, and switch to the B side while we still have capability for A side control during safe mode. Jeff pointed out several steps by which we can reduce our number of firings. The primary difference between the propulsion prediction and the actual, is that the prediction assumed we would unload a large fraction of the momentum envelop each firing, namely 33 ft-lb-sec, whereas we tend to unload only small amounts, ~10 ft-lb-sec. One reason for unloading small amounts is conservatism, given the inability of the OFLS to accurately track momentum, and given the conservative PCAD solar pressure disturbance torque model which is about twice the actual torques. Jeff's ideas, coordinated with Dan Shropshire and the mission planners, involve using more accurate torques determined on-orbit to predict momentum buildup, letting more momentum build-up so that more is dumped per episode. This would be most efficient if we let the spacecraft auto-unload. The consequences of that would be loss of some minutes of data in the middle of science observations, and some TBD work to revise the CXC data system to recognize such episodes and use the data on both sides of the firing. Such and approach should not be taken without CXC data system inputs. Another scheme would be to manually offload as is done presently, but at higher levels of momentum build-up, and instead of offloading to nominally zero momentum as is now done we would try to bias the offload to be the negative of what is predicted to be built up in the next scheduled interval. These ideas will undergo further development, and be presented to the flight director's CCB at an appropriate time before starting work toward implementation. Initially they would have to be manually implemented via the Maneuver Constraint Checking tools which have been developed, but they would then be specified for a future release of the OFLS software. Quick look data: none this morning. ------------------------------------------------------- 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 -------------------------------------------------------