To:sot_shift from: Dan Schwartz date: 29 July 99, 0830 EDT Subject: SOT shift report, Shift A7 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii -------- Shift A7. Start at 210:01:30 GMT = 0930 pm 28 July 99 End 9:20am 29 July SOT Lead DAS Spac/Aspect WAP,RAC FOT/Sci liason EM HRC MJ,AK,JG,MVZ,SSM,GA,JHC ACIS PPP,MWB,PGF,MP (Times will be given in GMT on day 210. In general times are rough, not precise.) PLAN Finish ACIS dark current measurements. DONE Activate vacuum monitor and take measurement. DONE Perform HRC-I initial turn-on. Collect HRC-I background (NOT DONE) Collect HRC-I cal source data (NOT DONE) Exercise HRC antico veto enable/disable; center blank enable/ disable; and edge blank enable/disable. DONE EVENTS Finish ACIS dark current measurements at 0300. Vacuum monitor reads 9.3 x 10^-5 torr. Turn off at 03:52. HRC shield 1 HV full on, 03:49. Rates about 4500 per sec. Start HRC-I high voltage turn-on, 04:07. See occasional events at 04:46:14, at HV=1200v. Hold at HV = 1350. Getting about 140 per sec count rate, of which >= half are cosmic rays, but residual counting rate is higher than expected. HRC team decides to stay at this voltage step and monitor performance for the duration of time until radiation belt passage. (Expect to operate at 1550v) Change OBSID to 62987 for antico tests. Rate drops to ~60 per sec with antico enable. Skip Cal source deploy. Set OBSID = 62983 for center/edge blank tests, ~06:12. Utilize a new OBSID, 62959, at ~06:32, to continue monitoring the HRC-I performance at HV = 1350v. Load ACIS event histogram patch, SOP_61007, and start a science run to accumulate histograms of the internal calibration source, at ~08:35. Back to Format 1 at 09:48. Large number of telemetry dropouts start around 08:40. Clear up suddenly for no reason. Command backup IRU into the low rate mode at 09:40. Use PCAD subformat. This is a preliminary to performing assessments of the affects of slosh, and of Chandra pointing stability. Start CAP 103 to assess jitter after a 52 deg yaw. Execute maneuver at 11:50. SSR dump complete at 13:02 NOTES/ISSUES/PROBLEMS Because of a clash in planned SCS slot usage between ACIS and HRC, ACIS did not load the event histogram patch and start accumulating histograms prior to the HRC activities. HRC-I background collection, and HRC-I internal cal source data were not taken, because the HRC-I has not yet been set to its expected operating high voltage. HRC Replan for tomorrow night, 211:00:00, will spend a couple of hours turning on HRC-I HV again and seeing if the rates have decreased, then proceding with the slow turn-on of HRC-S, and truncating the HRC-S data collection in order to finish activities a 211:10:00 as previously planned. ACIS notes a considerable area (few percent, by eyeball) of the CCDs are affected by cosmic ray events. In general these will be easily recognized and removed by ground processing, but their effect on dead time must be considered in the ground processing. Also, it is noticed that some cosmic ray events produce an extended halo of charge. SIM Flexure heating. Flight notes 126 and 127 discuss the heating of the -Z SIM focus mechanism flexure at pitch angles 35 and 45 degrees. This creates a large gradient to the other two flexures, inducing a tilt error. If this is significant, i.e., if it extends to pitch angles even further than 45 deg from the sun, then the flexures could all be controlled at some higher set point temperature. A tiger team developed a plan to assess these options: Observe the temperature rise at 55 and 65 degree pitch angles. Roll -10 degrees to attempt to measure fid light position changes relative to 90 deg pitch. Set the flexure thermal control points at 25 degC and 30 degC to verify control margin. Slosh criteria and evaluation. We met with PCAD and TST lead to discuss the requirement for image stability and establish a criterion for the jitter allowed to be induced by slosh. To produce an equal contribution as the ACIS pixel quantization to the image size, would allow a rate up to 0.147 arcsec/sec. But because of the potential value of conserving extra fuel, we suggested allowing up to 0.25 arcsec/sec motion before considering to dump residual IPS fuel. Wrote flight note 130, further detailing the stray light analysis. ------------------------------------------------------- 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 -------------------------------------------------------