Assisted Snapshot GNSS Position, Navigation, and Timing for LEO Satellites

This paper presents a novel conceptual design for a low Size, Weight, Power, and Cost (SWaP-C) snapshot Global Navigation Satellite System (GNSS) positioning system for Low Earth Orbit (LEO) CubeSats to enhance their Space Situational Awareness (SSA). Assisted GNSS (aGNSS) strategies allow for small snapshot collections of GNSS signals to be used for full position, velocity, and timing solutions at low-power usage. Key limitations of commercial GNSS receivers for CubeSats and the benefits of aGNSS strategies are discussed. Conceptual designs for the receiver architecture for power-efficient implementation are presented. Computation times and power usage are tested with common microprocessors for major functions and algorithms utilized in the full implementation. Methodologies for initial orbit determination and predictions are discussed to enable computation of aGNSS solutions in a dynamic LEO environment, with examination of the importance of an accurate drag parameter and fit span considerations. Strategies that allow efficient updates to GNSS ephemerides by utilizing a Commercial Off-The-Shelf (COTS) GNSS receiver are explored. Tests of propagation accuracy and the consistency of aGNSS availability are performed with real GNSS data acquired from a LEO satellite in orbit. Major functionalities are presented for further exploration of a snapshot GNSS system customizable to the needs of a variety of LEO satellites, with a focus on CubeSat class missions.