DPA-A Anomalous Shutdown¶

What is it?¶

The DPA-A shuts down anomalously, presumably due to a spurious command.

When did it happen before?¶

The DPA-A has shut down 4 times over the mission:

• October 26, 2000: 2000:300:15:40, obsid 979
• December 19, 2002: 2002:353:20:26, obsid 60915
• January 12, 2015: 2015:012:00:01, obsid 52186
• December 9, 2016: 2016:344:07:40, obsid 17615

Will it happen again?¶

It appears likely that the anomaly will occur again if the mission continues.

How is this anomaly diagnosed?¶

Within a major frame (32.2 seconds), one should see:

• 1DPPSA (DPA-A Power Supply On/Off) change from 1 to 0 (On to Off)
• 1DPP0AVO (DPA-A +5V Analog Voltage) drop to 0.0 +/- 0.3 V
• 1DPICACU (DPA-A Input Current) drop to < 0.2 A (this value is noisy, so take an average)
• DPA-A POWER should go to zero
• 1DP28AVO (DPA-A +28V Input Voltage) is expected to have a small uptick, ~0.5 V, consistent with the load suddenly dropping to zero
• The software and hardware bilevels will likely not have normal values if BEP side A is active.

All other hardware telemetry should be nominal. The current values for these can be found on our Real-Time Telemetry pages. Older data can be examined from the dump files or the engineering archive.

What is the response?¶

Our real-time web pages will alert us and the Lead System Engineer will call us. We need to:

• Send an email to the ACIS team at the official anomaly email address. If it is off-hours, call Peter and Bob.
• Send an email to sot_red_alert announcing that the ACIS team is aware of the DPA-A shutdown and is investigating, and that a telecon will be called when more information is available.
• Contact the GOT Duty Officer to inform that we need the dump data as soon as possible and to email or call us when the dump file is available.
• Process the dump data and make sure that there is nothing anomalous in the data BEFORE the shutdown. We want to know if a new occurrence looks just like the previous occurrences. If yes, it should appear as if in one frame the DPA-A turned off.
• Once analysis of the dump data is complete, convene a telecon at the next reasonable moment with the ACIS team and review the diagnosis. The MIT ACIS team (Peter Ford, Bob Goeke, Mark Bautz, and Bev LaMarr) should also be included in the discussion, either in the telecon or via email. If the diagnosis is consistent with previous DPA-A anomalies, proceed with the recovery. If the diagnosis is not consistent with previous DPA-A anomalies, stop and start a more involved analysis with the ACIS team.
• As soon as the time of the shutdown is known, inform sot_yellow_alert.
• Identify whether or not additional comm time is needed and if so ask the OC/LSE to request it.
• Send an email to sot_red_alert and call a telecon with the FOT, SOT, and FDs to brief them on the diagnosis and the plan to develop a CAP to recover.
• Prepare a CAP and submit it for review to capreview AT ipa DOT harvard DOT edu, and cc: acisdude. It will also be necessary to call the OC/CC to determine which number should be used for the CAP. This CAP will have the following steps:
  • Power on the DPA side A (SOP_ACIS_DPAA_ON)
  • If Chandra is heading into the radiation belts, it may be necessary to also issue a WSVIDALLDN command to power off the video boards (1A_WS007_164.CLD)
  • Reload the patches and restart DEA housekeeping (SOP_ACIS_SW_STDFOPTG)
  • Reset the focal plane temperature to -121 \(^\circ{\rm C}\) (SOT_SI_SET_ACIS_FP_TEMP_TO_M121C)
• Execute the CAP at the next available comm. Reloading the flight software patches can take a half an hour, so ensure that there is enough time in the comm to execute the entire procedure.
• Write a shift report and distribute to sot_shift to inform the project that ACIS is restored to its default configuration.

Impacts¶

• Until the DPA-A is powered back on, science operations will be interrupted.
• The warmboot of the BEP will reset the parameters of the TXINGS patch to their defaults. They can be updated in the weekly load through a SAR.
• After recovery from a DPA-A shutdown, the power status may be in an unusual state (e.g., lower than expected input current) due to FEPs being off. This situation should resolve itself with the next observation.

Relevant Procedures¶

Relevant Notes/Memos¶

• Flight Note 394
• Flight Note 417
• Flight Note 563