FPGA Implementation for Time Transfer and Ranging in the COMPASSO Mission – In-Orbit Validation for Next Generation GNSS

Kurzfassung

To address the growing demand for precise global positioning in commercial and scientific applications, the German Aerospace center (DLR) proposed the Kepler concept to increase the end-user performance of the Global Navigation Satellite System (GNSS) service. By utilizing optical links between satellites for precise time transfer and ranging Kepler enhances the performance, enabling down to mm-level accuracy, as well as the robustness of the GNSS Galileo. The COMPASSO mission of the DLR is an in-orbit validation of Kepler key technologies. Two iodine clocks, a frequency comb and a laser terminal for optical time transfer and ranging are evaluated, paving the way for future space applications. Hosted on the Bartolomeo platform of the International Space Station (ISS), COMPASSO is scheduled for launch in 2027 and will operate for 1.5 years. Time transfer and ranging evaluation is performed via bi-directional transmission of pseudo random noise spreading sequences at 9.6 GChip/s as well as establishing a 75 Mbit/s data link between ISS and the optical ground station of the DLR Oberpfaffenhofen. By leveraging FPGA technology, the performed digital signal processing (DSP) can be referenced onto the highly stable iodine clock or oven-controlled crystal oscillator reaching target ranging accuracy level. Appropriate measures to ensure stable and reliable operation in space as well as allow for in-orbit FPGAware updates of used SRAM based FPGA technology are implemented. Control as well as telemetry and telecommand tasks are taken over by an embedded LEON3 softcore processor. This presentation provides an overview of the COMPASSO mission, with a focus on the FPGA selection, design and implementation. Design decisions and lessons learned are shared, offering insights into the challenges of scientific missions and taking novel technology into space. Concluding, a look ahead exploring new design opportunities and taking developments in the market into account is given.