Space weather conditions during the Galaxy 15 spacecraft anomaly

On 5 April 2010, the Galaxy 15 spacecraft, orbiting at geosynchronous altitudes experienced an anomaly near local midnight when it stopped responding to any ground commands. The anomaly has been reported as due to a lockup of the field-programmable gate array (FPGA) within the spacecraft baseband communications unit during an onboard electrostatic discharge (ESD). This study evaluates the space weather conditions at the time of the Galaxy 15 anomaly. The study also compares the plasma and geomagnetic environments around the anomaly to space weather observations over the operational lifetime of Galaxy 15 up to the anomaly time. On 5 April, the Galaxy 15 spacecraft encountered severe plasma conditions while it was in eclipse and during the subsequent anomaly interval. These conditions included a massive magnetic field dipolarization that injected energetic particles from the magnetotail during a substorm observed by GOES and THEMIS satellites. Galaxy 15 was located at a near-optimum position and local time to experience the full impact of the injected energetic particles. During the largest previous storm experienced by Galaxy 15 in December 2006, evidence suggests that it would not have been exposed to the same level of space weather as on 5 April 2010. Hence, while Galaxy 15 was traversing the nightside on 5 April it likely experienced, for a short period, the most severe local plasma conditions it had encountered since launch. The most likely contributions to the ESD were interactions of the spacecraft with substorm-injected energetic particles facilitating spacecraft surface charging and deep dielectric charging.