ACIS Instrument Support - Monthly Progress Report for January 2002

1. ACIS Characterization

1.1 Characterize and model radiation damage in ACIS CCDs

  ...  Continued collection of raw data in "cuckoo" clocking mode which allows for more efficient telemetry of raw data. 

       * CL34-37, 1 successful run of no-squeegee cuckoo clocking on I3 Node 3 (focal plane temperature too warm for three runs)

  ...  Continued analysis of no-squeegee cuckoo data.  Sacrificial charge analysis shows that while precursors at all distances contribute to CTI differences, only the closest precursors (within 100 pixels) significantly degrade spectral resolution.  Work continues on defining filters and corrections factors that would improve over-all performance.

  ...  Continued lab testing of radiation damaged CCD shows a fat zero from optical light can be used to fill traps and improve CTI and FWHM.  The improvement is the same for optical charge deposited 80 msec or 8 secs before transfer which implies that the effective capture times must be much shorter.  Significant improvement is seen even with very small charge packets (10 e-).

1.2 Design and characterize alternative CCD readout modes

  ...  Continued study of charge injection to measure CTI using ACIS electronics in the lab.  Flight version of SRAM/PRAM for sacrificial charge measure of CTI is undergoing testing on the ACIS engineering unit.  A flight test is planned in the next few months.
 
1.3 Monitor scientific on-orbit performance of ACIS

 [...  Conducted fifth CTI measurement in alternating exposure mode with frame times of 4.0 and 3.2 seconds (ObsID 61327, 31 Jan).  This test will be used to calibrate and search for time variation in the detrending factor used by MIT and CXC to remove the influence of background variability on measured CTI.  Analysis forthcoming.  (see http://space.mit.edu/~cgrant/cti/altexp.html)

  ...  Continued monitoring of ACIS CTI.  No significant changes detected. Updated CTI web page (http://space.mit.edu/~cgrant/cti/)

  ...  Continued study of ACIS background, both quiescent and flares, for multiple SIM and grating positions.

 [...  Investigated possible new on-board grade filters suggested by CXC Cal to reduce background and telemetry saturation.

 [...] Updated plots of ACIS gain in the bottom twenty rows of each CCD as a function of time.  All CCDs stable with a slow decline in gain slope (ADU/eV) except for I2 which continues to vary.  Updated web page (http://space.mit.edu/~cgrant/gain/)

1.4 Update and improve CCD simulation

  ...  Continued work on detailed physical model of FI CCD including CTI and sacrificial charge.

 [...  Reanalyzed HIREFS calibration data of S3 to better understand gain function at very low energies (< 277 eV).


2. Engineering

2.1 Flight software maintenance

  ...  Investigation of ACIS t-plane latchup anomaly which took place on Oct. 29 and November 4.  This is the second and third occurence since launch (first was June 27, 2000).  Designed and tested a generic t-plane latchup recovery CAP both on the engineering unit and on-board.

 [...  Investigated FEP_IO_ERROR seen in telemetry after SCS 107 execution on 11 Jan.  Four out of twenty-three SCS 107 executions have similar errors caused by insufficient delay times between commands.  One of these caused a BEP reboot.  Possible actions are increasing delay times in SCS 107 or better monitoring of flight software version number.  Ongoing.

2.2 Instrument hardware engineering performance

  ...  Continue to monitor long term ACIS instrument performance and find, with one exception, that all hardware engineering parameters are stable.

       * Degradation of the SIM thermal environment is evident in the increasing temperature of the PSMC (Power Supply and Mechanism Controller).  In the 2-1/2 years since launch, the peak lid temperature has risen 9C and the peak DEA power supply board temperature has gone up 8C -- all internal PSMC power is radiated to the SIM walls.  If the current trends stay constant, we will see the PSMC exceed its Yellow temperature limits within the next year (30C for the lid, 50C for the DEA electronics board).  In approximately 3 years we will hit the Red limits.  There is no known failure mechanism which kicks in at that point, but we will simply have reached an operating temperature beyond which we have no environmental test data on the flight unit.

       * The increasing temperature of the SIM environment could, of course, start to make it more difficult to control the focal plane temperature, but we do not currently expect that to be a problem.  The warm radiator seems to continue to have enough control authority to isolate the detector housing from it's environment.  Further, the DEA and DPA boxes show  only a 1C change in their peak temperatures since launch and they are operating some 20C from their respective Red limits.

       * The performance of the cold radiator and the focal plane temperature control continue to operate nominally, but we cannot measure the available margin -- and track any trend in possible degradation -- without turning off the focal plane temperature control for about 20,000 seconds while the earth is entirely out of the radiator field of view.  It is a test we could run for "free" during a radiation-induced safe-hold of the Observatory.  (Since the focal plane would cool from -120C to -123C, the mechanical stress induced on the CCDs would be minimal.)

2.3 Instrument science performance

 [...] Investigated ACIS bias map stability.  See ACIS Memo #196 "Stability of Averages of ACIS Bias Files" at http://space.mit.edu/ACIS/iacis.html.

  ...] Investigated anomalously high count rate on S4 CCD during ObsID 1585 on November 19.  High count rate due to increase in "streaking" along rows.  Analysis of streak frequency with time shows some correlation to S3 amp_rej rates in quiescence, plus irregular flaring.  The flaring behavior is supressed when ACIS is not in the focal plane, so soft protons may cause the flares. (see http://space.mit.edu/~cgrant/s4.html)

  ...  Continued daily quick-look processing of ACIS telemetry and maintained Web interface to ACIS real-time data.

  ...  Continued to publish the "annotated DOT" timeline reports.

  ...  Continued to develop flight s/w algorithms to implement "Squeegee" clocking mode and to report precursor charge from ACIS CCDs.

  ...  Participated in ACIS operations meetings

  ...  Participated in ACIS telecon

 [...] Reviewed ACIS status in a presentation to the ACIS IPI team.

2.3 Participate in Chandra activities

 [...] Supported testing of CAP #774 - a generic CAP designed to recover from a threshold crossing plane latchup on ACIS.  Including,
       * CAP review
       * Real-time support, both command checking and data analysis


3. CXC Support

3.1 Provide user support

  ...  Updated ACIS memo listing calibration ObsIDs and observation characteristics (ACIS Memo #165).

3.2 Provide data analysis support

  ...  Participated in CXC Cal/Ops RMF discussion group.

  ...  Continued to maintain ACIS calibration database of ground and flight data products


4. OCC Support

4.1 Use of MIT/ACIS EGSE at OCC

  ...  Continued support and maintenance of ACIS EGSE software and hardware at the OCC.