GARHEO Flight Experiment to Test GPS-Galileo Interoperability to Support Launchers and Space Missions

Abstract

On November 22, 2019, the UP-Aerospace Space Loft 14 (SL-14) sounding rocket was launched from Spaceport America in New Mexico, USA, on a suborbital flight with four payloads on board, including the GARHEO (GPS-GALILEO Receiver for Human Exploration & Operations) experiment to analyze GPS L1 and Galileo E1 signals under a highly dynamic environment. The mission followed a parabolic trajectory reaching 92 km altitude before returning to Earth. The experiment is a partnership agreement between ASI (Agenzia Spaziale Italiana) and the National Aeronautics and Space Administration (NASA). Qascom, a European aerospace company, contributed a space-qualified receiver capable of tracking multi- Global Navigation Satellite System (GNSS) signals. The objective is to validate the capability of GPS-Galileo signals to support launchers and space users. Being able to rely on signals from more than one GNSS constellation greatly improves signal coverage, and increases the diversity of system architecture, frequencies and geometry. SpaceLoft XL is a single-stage unguided sounding rocket. The standard configuration is 6.1 m in overall length, 26.4 cm in maximum diameter, and 354 kg maximum lift-off mass including the payloads. The nominal flight profile is a sub-orbital trajectory reaching 100 km altitude in 160 seconds, followed by four minutes under microgravity conditions. During the main flight phases (boost, re-entry, recovery, and landing), the payloads experience an axial acceleration up to 16G, and a radial acceleration up to 18.5G due to the spin of the launch vehicle. The GARHEO payload was installed in Payload Transportation System (PTS) slot number 4-1. A circular ring antenna was used for acquisition of the L-band GNSS signals. Preliminary analysis of the digitally-recorded GNSS signals indicates that the rapid acceleration was observed during lift off and booster separation. The results also demonstrate the impact to standard receivers under these dynamics and their difficulty to track signals. This paper presents how high-dynamics, including spin, impacts the signal-to-noise ratio (CN0) during acquisition and tracking, and how this affects the positioning performance. It includes the mission results and also provides recommendations for the design of future multi-GNSS receivers that are capable to track signals under high dynamics. The paper also discusses options for integrating GARHEO with the Autonomous Flight Termination Systems (AFTS). A key feature of the analysis is the ability to reproduce the recorded signals in a simulator to achieve realistic replay of mission scenarios. Validation of the capability of GPS-Galileo signals to support space users will, in turn, greatly improve the overall Positioning, Navigation, and Timing (PNT) performance. GARHEO builds on the success of another successful U.S.-Europe cooperation effort, the GARISS (GPS-Galileo Receiver for the International Space Station) project, which was completed in May 2019 and demonstrated a combined GPS/Galileo (L5/E5a) waveform on a software-defined radio on-board the space station.