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Unexpected Swarm A GPS receiver reboot on 26 July 2018

31 July 2018

The Swarm A GPS receiver rebooted on 26 July 2018 at 05:07:02 UTC autonomously. The GPS receiver data and time synchronization were available again at 05:29:47 UTC. The satellite's orbit and attitude seem unaffected by the anomaly. While the investigation is ongoing, it seems that there is no impact on the good health of the GPS receiver.

The pulse-per-second (PPS) signal that is nominally generated by the GPS receiver and used by the Swarm instruments to synchronize the measurements, stopped when the GPS receiver rebooted. After a few seconds, the on-board computer (OBC) started generating a substitute PPS signal based on its internal clock. During the transition several PPS signals were not generated, which caused the EFI instrument to switch off, while the other instruments kept operating. The EFI was switched on in the afternoon on 26 July, so that nominal operations of the Langmuir probes and thermal ion imagers (TII) could be resumed on 26 and 27 July, respectively.

The GPS receivers loaded the default settings during the reboot, which affected in particular the GPS antenna field-of-view and PLL bandwidth of the L2 tracking loop. The intended settings were restored on 27 July 2018 in the afternoon. Further, the generation of a data packet of the GPS receiver that is required by the L1b processor for producing orbit and attitude data products was re-enabled on 30 July 2018.

Data products have been recovered from 27 to 29 July.