ACIS Instrument Support - Monthly Progress Report for October-December 2025

0.  Management

  ...  Completed annual performance reviews of the MIT ACIS team.

1.  ACIS Characterization

1.3 Monitor scientific on-orbit performance of ACIS

  ...  On November 11 there was a series of X-class flares.  The final X5 solar flare was following 10 minutes later by a rapid rise in energetic particles.  The particle rate on ACIS was very high and led to a TXings radiation safing action. The ensuing CME was a direct hit.  ACIS safing was nominal and we estimate that the ACIS CCDs were saved from a fluence of 8.8e9, well exceeding the orbital limit of 2e9. This was the first TXings trigger due to the "very high" rate test -- all previous triggers have been due to the "increasing rate" test.  In this case, ACIS was in science idle between observations and missed seeing the initial rise in rates.  The "very high" test was added to TXings in 2022 for exactly this situation.

  ...  Reviewed CAP1795, collecting ECS data during the post-Nov 11 radiation safing action.

  ...  Examined science and housekeeping data from ObsID 30162, at the time of the Nov 11 radiation safing action.  Event rates were extremely high, saturating telemetry.  Bias maps were noisy, due to incomplete particle track removal.

  ...  Reviewed radiation shutdown memos from June and September 2025.

  ...  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).

  ...  Prepared slides for and presented ACIS status at Chandra Quarterly in November.

2.  Engineering

2.1 Instrument hardware engineering performance

  ...  Continue to monitor long term ACIS instrument performance.  Engineering trending is nominal.

  ...  The EEPROM checksum was verified in the OCT0625A, NOV0825A, and DEC0825A loads. Will continue to run monthly.  MIT telemetry processing will automatically check the results and send out an alert if the checksum is unexpected.

  ...  Supported CXC SOT examination of the ACIS door mechanism sensor monitoring algorithm

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

2.2 Flight software maintenance

  ...  ACIS flight software patch H-K-L uploaded on August 15, 2025. First new patch set since September 2023.
  
   ...  We continue to monitor threshold crossing rates.  The current set of TXing parameters were uploaded on Aug 15, 2025.  New commands were required for TXings revC but the rate limits are nearly the same as used previously, uploaded on Oct 20, 2024.

  ...  Continued work with MKI IT to migrate acis.mit.edu, the last ACIS Solaris machine, to Linux hardware. We are using this opportunity to also create a warm backup for maaxnew.mit.edu, which hosts the ACIS telemetry pipeline data archive. Testing of all EGSE functions has been successfully completed. The switch from the Solaris to Linux (CentOS) was completed in January. A future switch from CentOS to Rocky Linux will take place in 2026.

  ...  Modified the ACIS QEMU flight software simulator for use with an Apple M4 silicon laptop running Mac OS Tahoe.

2.3 Instrument science performance

  ...  Participated in monthly ACIS operations meetings. Confirmed optimal values for TXings parameters, monitored the TXings proxy during radiation events, confirmed continued fault-free performance of ACIS FSW version 61.

  ...  Continued documentation of ACIS EGSE networking security.

  ...  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

  ...  Confirmed frametime efficiency calculations in the POG are correct.

  ...  Discussed new language in the POG about the FI CCD requirement.  Supported wordsmithing of a related mission planning guideline.

  ...  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

  ...  Supported planning telecon for IACHEC 2026 meeting.

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

  ...  Technical reviewer for joint XMM/CXO proposals.

  ...  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. 

4.2 Generation of commands for ACIS observations

  ...  Continued working with USINT to verify or update parameters for the cycle 27 problematic ACIS configurations. The initial list had 108 ObsIDs from 11 programs, which is now down 5 observations to from 2 programs, both untriggered peer-reviewed ToOs.

  ... Checked timing of Next-In-Line mode and TXings during the HRC-I restart activity in December.

  ...  Reviewed OCT2025A, NOV1425A, DEC2225A command loads; OCT2025 (x2), NOV1425, NOV1725, DEC2225 (x3), DEC2925 final OR lists; OCT2025 (x2), NOV1725, DEC2225, DEC2925 preliminary schedules; and OCT2725, NOV0325, NOV2425, DEC0125, JAN1226 LTS OR lists. 

  ...  Checking on automated processes associated with SACGS.