ACIS Instrument Support - Monthly Progress Report for Februrary/March 2025


1.  ACIS Characterization

1.3 Monitor scientific on-orbit performance of ACIS

  ...  There was one TXings trigger shutdown on March 24, due to a bright source dithering on and off of the CCD mimicking the sharp rise of a radiation event.  Shutdown was nominal.  Previous observations using similar configurations did not cause a TXing shutdown, but used the short dither period that was standard until a few years ago.  ACIS and the HETG teams are discussing plans for changing the configuration for the remainder of that program,

  ...  Continued monitoring of ACIS CTI, gain, trailing pixel pulseheight, detector efficiency, corner pixel distribution, spectral line centroid and width, and focal plane temperature. Updated monitoring web pages.  (http://space.mit.edu/~cgrant/monitor.html).


2.  Engineering

2.1 Instrument hardware engineering performance

  ...  Continue to monitor long term ACIS instrument performance.  Engineering trending over the past 60 days is (mostly) nominal.

  ...  The ACIS Door Potentiometer, 1DACTAT, has begun to occasionally toggle below its former yellow low limit. The value has walked around over 25 years, particularly in the past few years.  It is not believed that the door itself is moving.  The yellow low (caution low) limit was reduced in January.  This month the red low (warning low) limit change was been approved by MPCWG and FDB to prevent alerts at the current values.

  ...  1DACTBT, the temperature at the top of the DA collimator, violated its yellow (caution) high limit in February due to general spacecraft warming.  The yellow and red limit updates were approved by TWG and FDB to prevent unnecessary violation alerts.

  ...  The EEPROM checksum was verified in the FEB1025A and MAR1025B loads. Will continue to run monthly.  MIT telemetry processing will automatically check the results and send out an alert if the checksum is unexpected.

  ...  Continued weekly physical audit of the ACIS Engineering Unit lab. Weekly audits were nominal. 

2.2 Flight software maintenance

  ...  ACIS flight software patch H-J-K uploaded on September 19, 2023.  First new patch set since August 2022.

  ...  ACIS flight software patch H-K-L documentation was signed off by the MIT team.  (https://acisweb.mit.edu/pub/ACIS_Patch_H-K-L.pdf) The only change is an update to TXings which fixes the bug in exposure time calculation that caused the false trigger during the Crab pulsar observation in October (SPR 162).  ACIS command packets were built, tested, and installed in the ODB.  Started work on Chandra FSW WG presentation.  Reviewed the FOT produced command loads for the uplink and the SOT SOP.  Uplink is expected sometime this summer.

   ...  Edited ACIS patch command packet creation procedure to include updates required for new MIT network configuration, plus clearing up some areas of uncertainty.

   ...  We continue to monitor threshold crossing rates.  The current set of TXing parameters were uploaded on Oct 20, 2024.

2.3 Instrument science performance

  ...  Participated in monthly ACIS operations meetings.  Discussed TXing trigger during bright source observation, status of FSW patch development, focal plane temperatures during perigee passages, development of a TXing proxy, and 1DACTAT limits.

  ...  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.


3.  CXC Support

3.1 Provide user support

  ...  ACIS memo listing calibration ObsIDs and observation characteristics (ACIS Memo #165) will no longer be updated.  Functionality is replaced by web page (http://acisweb.mit.edu/asc/evt-page.html), which provides the same information but is more automated.

3.2 Provide data analysis support

  ...  Participated in discussion of ACIS gain changes.  Likely to be some combination of multiple factors influencing charge transfer inefficiency including reduced sacrificial charge during solar maximum, increased radiation damage during solar maximum, and increased temperature variability revealing calibration problems.

  ...  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 Wayside OCC.  Restarted both EGSE machines routinely.  One required a COG reset after network maintenance work.

  ...  Supported BUOCC demo on February 25.

4.2 Generation of commands for ACIS observations

  ...  Reviewed status of remaining cycle 26 configurations with issues.  Discussed with USINT.

  ...  Reviewed FEB1025A, MAR1025A, MAR1025B command loads; FEB1025, MAR1025(x3) final OR lists; FEB1025, MAR1025(x2) preliminary schedules; and FEB2425(x2), MAR1025, MAR2425 LTS OR lists.

  ...  Checking on automated processes associated with SACGS.