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Operations CXO Status Report

Friday 29 May 2020 9.00am EDT

During the last week Chandra's observing schedule was interrupted by a spacecraft Safe Mode event that occurred at 10:17am EDT on May 24 and was detected at the scheduled contact which started at 5:10 pm EDT. The Safe Mode transition was nominal and all systems functioned as expected. The cause of the trip was an unintended command load interaction in the on-board software between re-enabling the PCAD momentum monitor after a grating move and the start of a maneuver sequence. The monitor re-enable subfunction delayed execution of the PCAD mode transition to Normal Maneuver Mode for approximately 4 seconds, allowing the target attitude update command to be executed while still in Normal Point Mode and causing the attitude safing monitor to trip. No hardware issues have been identified as contributing to Safe Mode entry.

Real-time procedures were executed over May 24-26 to recover from Safe Mode to OBC-A controlling in Normal Sun Mode and then recover to Normal Point Mode. As part of the Normal Sun Mode recovery, a maneuver to a cooling attitude was performed to prevent excessive spacecraft heating at the Normal-Sun attitude.

In order to perform a controlled eclipse entry and exit of the first eclipse of the season on May 27, a set of maneuver-only (non-science) loads were uplinked to the spacecraft during the 4 pm EDT contact on May 26. Chandra passed through this first eclipse with nominal power and thermal performance.

A new mission schedule and loads were approved and began operating at 9:48pm EDT on May 27. This anomaly resulted in 225.4 ks of science loss. Scheduled observations that were impacted by the Safe Mode will be rescheduled.

The schedule of targets for the next week is shown below and includes an observation of 4U 1630-47, which is a follow-up to a Target of Opportunity on May 15 and is coordinated with ATCA, and an observation of NGC7793 P13 which was accepted as a Director's Discretionary Time Target of Opportunity on May 11.



------------------------------------------
        Radiation Belts                     Jun  1
        NGC2276                ACIS-S
        J0446A                 ACIS-S       Jun  2
        Westerlund1            ACIS-I
        N132D                  ACIS-S
        Westerlund1            ACIS-I       Jun  3
        Radiation Belts                     Jun  4
        G1.9+0.3               ACIS-S
        NGC7793P13             ACIS-S
        G1.9+0.3               ACIS-S
        ALPHACEN               HRC-I        Jun  5
        N132D                  ACIS-S
        4U1630-47              ACIS-S/HETG
        Radiation Belts                     Jun  6
        G1.9+0.3               ACIS-S
        N132D                  ACIS-S       Jun  7

------------------------------------------

All spacecraft subsystems continued to support nominal operations.

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