arXiv subjects

Toby Bell

Publications and source records attributed to Toby Bell.

3 recordsLinked to original sources

arXiv2025

Flight-Ready Precise and Robust Carrier-Phase GNSS Navigation Software for Distributed Space Systems

This paper presents the full requirements analysis, design, development, and testing of high-precision navigation flight software for Distributed Space Systems (DSS) using Carrier Phase Differential GNSS (CDGNSS). Five main contributions are made. First, a survey of flown and upcoming DSS missions with stringent precision requirements is conducted, from which a thorough requirements analysis is distilled to guide development and testing. Second, a real-time navigation functional architecture is designed, and adopts a sparse and regularized Consider Kalman Filter with options for numerical stability in-flight. The filter rigorously accounts for uncertainties in process noise, measurement noise, and biases. It tracks float ambiguities with integer resolution where possible. The covariance correlation structure is preserved under all navigation modes, including contingencies and outages. Third, a lightweight, memoryless Fault Detection, Isolation, and Recovery (FDIR) module is developed to guard against anomalous measurements, providing statistical screening and ensuring robust navigation. Fourth, the software architecture is proposed for ease of integration, with strategies presented for modularity and computational efficiency tailored to constrained flight systems. Fifth, a comprehensive test campaign is conducted, mapped to a requirements verification matrix, spanning unit, interface, software-in-the-loop, and real-time hardware-in-the-loop tests, emphasizing gradual test fidelity for efficient fault isolation. Finally, flight-like results are demonstrated using the VISORS mission, due to the generalizability of the VISORS navigation operations, and the stringency which demands sub-centimeter relative position and sub-millimeter-per-second velocity accuracy. This architecture aims to serve as a reference for next-generation DSS missions adopting CDGNSS.

eess.SY↗

arXiv2025

Event-Driven Simulation for Rapid Iterative Development of Distributed Space Flight Software

This paper presents the design, development, and application of a novel space simulation environment for rapidly prototyping and testing flight software for distributed space systems. The environment combines the flexibility, determinism, and observability of software-only simulation with the fidelity and depth normally attained only by real-time hardware-in-the-loop testing. Ultimately, this work enables an engineering process in which flight software is continuously improved and delivered in its final, flight-ready form, and which reduces the cost of design changes and software revisions with respect to a traditional linear development process. Three key methods not found in existing tools enable this environment's novel capabilities: first, a hybrid event-driven simulation architecture that combines continuous-time and discrete-event simulation paradigms; second, a lightweight application-layer software virtualization design that allows executing compiled flight software binaries while modeling process scheduling, input/output, and memory use; and third, high-fidelity models for the multi-spacecraft space environment, including for wireless communication, relative sensing such as differential GPS and cameras, and flight computer health metrics like heap exhaustion and fragmentation. The simulation environment's capabilities are applied to the iterative development and testing of two flight-ready software packages: the guidance, navigation, and control software for the VISORS mission, and the Stanford Space Rendezvous Laboratory software kit for rendezvous and proximity operations. Results from 33 months of flight software development demonstrate the use of this simulation environment to rapidly and reliably identify and resolve defects, characterize navigation and control performance, and scrutinize implementation details like memory allocation and inter-spacecraft network protocols.

cs.SE↗

arXiv2023

Autonomous Guidance Navigation and Control of the VISORS Formation-Flying Mission

Virtual Super-resolution Optics with Reconfigurable Swarms (VISORS) is a distributed telescope mission for high-resolution imaging of the Sun using two 6U CubeSats flying in formation in a Sun-synchronous low-Earth orbit. An optics spacecraft carries a photon sieve acting as a high-resolution lens in the extreme ultraviolet spectrum, while the image passing through the sieve is focused on a detector spacecraft. This paper presents the newly conceived design of the on-board guidance, navigation and control (GNC) system, which is highly autonomous, robust, passively safe, and validated under realistic mission simulations. The primary objective of the GNC system is to establish a passively safe and high-precision formation alignment at 40-meter separation, with sub-centimeter relative navigation and position control accuracy, over repeated observations of 10-second duration. Science mission success rates are assessed via Monte-Carlo analyses under realistically modelled uncertainties stemming from sensing errors, maneuver errors, unmodelled dynamics, and erroneous knowledge of internal spacecraft components. Precise real-time relative navigation is achieved by carrier phase differential GPS with integer ambiguity resolution. Precise control over short baselines is achieved via closed-loop optimization-based stochastic model predictive control with centimeter-level accuracy. Control at far range and during approach is achieved by closed-form impulsive control with meter-level accuracy. Passive safety is enforced throughout the mission to mitigate collision risks even under critical subsystem failure. Beyond VISORS, this work also realizes the crucial insight that the described GNC architecture is generalizable to other distributed space missions where accuracy and fault-tolerant safety are key requirements, such as rendezvous, proximity operations, and swarming missions.

cs.RO↗