Study of Single Event Effects on Commercial off-the-shelf GPS Receivers Onboard FORMOSAT-7/COSMIC-2 Constellation in Low-Earth Orbit

The FORMOSAT-7/COSMIC-2 (F7/C2) is a joint Taiwan-US collaboration mission, launched on 25 June 2019, that follows the FORMOSAT-3/COSMIC mission, aiming to provide next-generation global navigation satellite system (GNSS) radio occultation data to global users. The mission comprises six identical small satellites with an inclination angle of 24°, launched to the parking orbit of 720 km first, and then transferred to the mission orbit of 550 km. Each satellite bus is equipped with two commercial off-the-shelf global positioning system receivers (GPSR) for positioning, navigation, and timing functions. After commissioning, the GPSR often generates "GPS Receiver Warm Start Requested (WSR)" messages, which can be considered as a type of single event effect (SEE). The SEEs result from the radiation and energetic particles in the space environment, which may sometimes lead to the failure of the mission. More than 7,000 WSR events have been recorded in the 3 years after launch, presenting a valuable opportunity to investigate SEE using commercial off-the-shelf GPSR hardware. Furthermore, the F7/C2 mission is the first satellite constellation that enables scientists to study SEEs at different altitudes of Low-Earth orbit. This study investigates and discusses the cumulative rate, distribution of WSRs, and their relationships with altitude and the geomagnetic field. The high-probability warning area for SEE occurrence is also reported based on the geomagnetic field, with corresponding strength around 21,200/20,550 nT at both orbits, which can be regarded as the border of South Atlantic Anomaly (SAA) area. Furthermore, the weighting center and the drift of the SAA in longitudinal direction are simultaneously interpreted. Additionally, the study analyzes the relationships of occurring WSRs and space weather with the disturbance of the Earth's magnetic field (Kp index) and the solar activity (F10.7 index).