Development of the Stanford GNSS Navigation Testbed for Distributed Space Systems

摘要

Distributed Space Systems (DSS) promise advances in space science, earth and planetary science, as well as on-orbit servicing and space situational awareness. In order to mimic a large spacecraft with gigantic and reconfigurable aperture, DSS rely on precise knowledge of the relative position/velocity of the co-orbiting satellites. Especially in Earth's orbit, Global Navigation Satellite Systems (GNSS) can provide centimeter-level or better relative navigation solutions through differential carrier-phase processing techniques on cooperative satellites. The development of these GNSS functionalities and the verification of their capability to meet next-generation space mission requirements necessitate a high-fidelity testing environment. This research presents the design, development, and verification of the Stanford GNSS navigation testbed for spacecraft formation-flying and rendezvous. Key aspects of the system architecture are illustrated, including the orbital dynamics simulation, the GNSS signal and measurement generation, and the algorithms/software for advanced navigation applications. Each subsystem of the testbed is thoroughly verified through comparisons with flight data from space missions, live signals from static scenarios, and realistic hardware-in-the-loop simulations. Specifically, orbit propagation results are compared against precise flight dynamics products from the PRISMA formation-flying mission. A cross-verification method is introduced to validate the GNSS signal simulator and a software receiver emulator using a live signal source. In particular, an Extended Kalman Filter is used to quantify the distribution of pseudorange and carrier-phase measurement residuals from each signal source. The measurement residual statistics, along with satellite tracking performance, are then used as comparison metrics to verify that all stimulation methods are consistent with one another. After verification of the testbed, a commercial-off-the-shelf GNSS receiver is characterized using a zero-baseline test in order to quantify the measurement noise and assess its capability to support precision navigation on nanosatellites. Finally, the testbed is used to assess the performance of the Distributed multi-GNSS Timing and Localization system (DiGiTaL), a precision navigation payload for small satellite swarms under development at Stanford in collaboration with NASA Goddard Space Flight Center.