Design and development of a GNSS spaceborne receiver for Earth Observation satellites orbit determination

In the recent years, the use of GNSS receivers for on-board satellite orbit determination has become a common solution in new satellite design, as it considerably simplifies the overall architecture if compared to traditional orbit determination systems such as radiometric tracking. In most cases, the satellite positioning requirements can be met with a single-frequency solution that provides position accuracy in the order of 15m. As part of the ALMASat-EO project, being carried out at the Microsatellite Lab of the University of Bologna, for the development of a small satellite for Earth observation in the middle range image resolution, a new GNSS receiver for precise orbit determination has been designed and developed. The receiver itself is a dual front-end software defined receiver, based on the Xilinx Virtex5 FPGA. The first prototype features 64MB of 200MHz DDR2 SDRAM and 16MB of Flash memory. Synchronization and tracking algorithms are design starting from software simulation, to guarantee tracking accuracy around 5° using third order tracking loops. Position estimation accuracy around 1m in the along-track and normal component, and 2m in the vertical component, is obtained using reduced dynamic filtering algorithm based on the Extended Kalman Filter.