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GLAST Large Area Telescope LAT Pre-Shipment Review NCRs and Waivers Pat Hascall

Gamma-ray Large Area Space Telescope. GLAST Large Area Telescope LAT Pre-Shipment Review NCRs and Waivers Pat Hascall Systems Engineering Stanford Linear Accelerator Center. NCR Introduction. Presentation focus is on the main hardware related NCRs that remain open

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GLAST Large Area Telescope LAT Pre-Shipment Review NCRs and Waivers Pat Hascall

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  1. Gamma-ray Large Area Space Telescope GLAST Large Area Telescope LAT Pre-Shipment Review NCRs and Waivers Pat Hascall Systems Engineering Stanford Linear Accelerator Center NCRs and Waivers

  2. NCR Introduction • Presentation focus is on the main hardware related NCRs that remain open • Impact assessment for those NCRs identified as “Can Not Duplicate” (CND) will be discussed. • Several NCRs were left open for Environmental Testing at NRL and will be closed when final data review is completed after TV (Documentation of analysis or minor rework/inspection) • NCRs are classified into categories for discussion purposes • NCR Summary List of all open NCRs is presented for reference NCRs and Waivers

  3. NCR Category Definitions Open NCR’s classified into categories for discussion purposes: NCRs and Waivers

  4. NCR Resolution Definitions Open NCR’s classified into categories for discussion purposes: NCRs and Waivers

  5. NCR Resolution vs Category NCRs and Waivers

  6. NCRs For Discussion NCRs and Waivers

  7. NCR 855LATC Verify Errors CND, QAR • Issue • Calorimeter and Tracker front-end register (RC and FE) was not read successfully • Analysis • Issue in 16 of 3805 LATC configurations • Affects about 10 bits of ~ 2 million bits written/read in each LATC execution • Mostly at the start of commissioning: • Fourteen happened in first 290 runs • One in run 777 • One in run 1426 • None in last 2400 write/reads • None using FSW B0.6.9 (2120 runs) • Have not been able to replicate on the testbed • Resolution Plan • Mitigation plans in FSW • JIRA FSW-653 (B0.6.10) adds a reset to the calorimeter at power up • JIRA FSW-729 adds a retry by LATC when a verify error occurs, to be implemented if the problem reappears • Impacts on On-orbit performance • With no action, the LAT will not start the physics acquisition and one orbit worth of data would not be collected NCRs and Waivers

  8. NCR 922Housekeeping Telemetry Stopped QAR • Issue: • During a charge injection test, LAT housekeeping process (LHK) has twice emitted an error and subsequently did not create telemetry packets successfully • Analysis: • Review by FSW indicates a possible cause that the LHK and LCI (LAT Charge Injection) process may be in contention for memory • Was reproduced on testbed, analysis in progress • Resolution Plan: • Find and correct FSW error • Impacts on On-Orbit performance: • Loss of housekeeping data until restart NCRs and Waivers

  9. NCR 946ACD Free 5 Power Up CND, QAR • Issue: • ACD Free Board 5 was not responsive to commands after power up • Analysis: • Other power up parameters (voltages and currents) reviewed with no abnormalities seen • Occurred once in over 275 power ups (122 using redundant GASU) • Two possible causes • Look-at-me from redundant GASU did not reach or might have been decoded improperly on the Free board in which case it would only respond to commands from the primary (unpowered) GASU • Custom power up sequence (compensates for an old bug in ASIC primary/redundant switching code) did not result in successful power up in redundant mode • Resolution Plan: • Cycle power to FREE card (interim solution) • Add functionality to FSW to be able to send Look-at-me command to a FREE card without power cycling (JIRA FSW 718 adds capability, targeted for B1.0.0) • Impacts on On-Orbit performance: • Extend power up sequence timeline slightly NCRs and Waivers

  10. CPU Reboots CND, QAR • Issue • EPU and SIU reboots seen on 7 occasions (next chart has details) • Analysis • Several of these have likely causes relating to EGSE • Two recent reboots have occurred without the EGSE symptoms • Rate is 7 in about 1800 hours, or once per 250 hours • Existing data does not give sufficient information to determine the cause • Resolution Plan • FSW diagnostic software to be loaded that will help diagnose the cause of the reboots by identifying which tasks are executing • Records most recent 1024 task switches • Can be read out in primary or secondary boot • Run LAT on a non-interference basis at observatory to accumulate run hours • Impacts on On-orbit performance • Loss of data and LAT housekeeping telemetry until SIU is rebooted, potential for SC directed loadshed • Loss of ½ the science data until EPU is rebooted NCRs and Waivers

  11. CPU Reboots (Continued) No clear pattern has developed NCRs and Waivers

  12. NCR 957EPU 0 CPU Junction Temperature • Issue: • After applying vacuum, EPU 0 CPU junction temperature was higher than the other CPUs by up to 28 degrees and reached 104 degrees during bakeout. Telemetry returned to normal after repressurization. • Analysis: • Not observed at unit test or ambient level LAT testing • Possible causes • Degradation of thermal connection from heat sink to CPU • CPU on-chip sensor defective (unlikely) • Thermal analysis of board and tests on similar hardware support first hypothesis (disconnected heat sinkn test and analysis results consistent with observed temperature rise) • Under this condition, thermal and reliability margin still exceeds requirements • Expected junction temperature for this box at hot is 80 degrees • No potential for electrical side effects • Heatsink is brazed to the rail, and is adjacent to a empty slot • Epoxy is not electrically conductive • Board is conformal coated • Resolution Plan: • Use as is • Impacts on On-Orbit performance: • None NCRs and Waivers

  13. NCR 975Datagram Time Tags • Issue: • Some datagrams have a time tag that is 4.2 seconds “fast” • Analysis: • Rate is about 1 in 10000 datagrams • Likely FSW bug • Analysis in progress • Will reproduce on testbed • Could potentially be worked around on the ground • Resolution Plan: • Find bug and fix it • Impacts on On-orbit performance • None, if fixed • May use GSW mitigation until FSW error is found and fixed NCRs and Waivers

  14. Open NCRs NCRs and Waivers

  15. Open NCRs NCRs and Waivers

  16. Open NCRs NCRs and Waivers

  17. Open NCRs NCRs and Waivers

  18. LAT Waivers (1/3) NCRs and Waivers

  19. LAT Waivers (2/3) NCRs and Waivers

  20. LAT Waivers (3/3) NCRs and Waivers

  21. SC-LAT ICD Waivers NCRs and Waivers

  22. NCR and Waiver Summary • The LAT Team is confident that none of the NCRs or Waivers presented are significant enough to prevent the LAT from shipping. • The LAT Team recommends proceeding with the LAT shipping as planned. NCRs and Waivers

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