Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

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

Samuel Y. W. Low, Toby Bell, Simone D'Amico

TL;DR

The paper presents a complete end-to-end CDGNSS navigation software architecture (DiGiTaL v2) for Distributed Space Systems, emphasizing a mathematically rigorous, numerically stable CEKF with consider parameters to handle COM-to-PCO biases and crosslink uncertainties. It integrates GRAPHIC measurements for absolute positioning and crosslink SDCP for relative baselines, supported by a lightweight FDIR, modular software design, and compute-lean optimizations. A comprehensive, multi-fidelity test plan culminating in VISORS flight-like results demonstrates sub-centimeter relative position and sub-millimeter-per-second velocity accuracy, robust to crosslink outages and cycle slips. The work provides a transferable framework and verification methodology that can guide future DSS missions requiring precise onboard navigation using CDGNSS. Overall, it advances readiness for real-time, fault-tolerant CDGNSS navigation in distributed spacecraft architectures.

Abstract

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.

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

TL;DR

The paper presents a complete end-to-end CDGNSS navigation software architecture (DiGiTaL v2) for Distributed Space Systems, emphasizing a mathematically rigorous, numerically stable CEKF with consider parameters to handle COM-to-PCO biases and crosslink uncertainties. It integrates GRAPHIC measurements for absolute positioning and crosslink SDCP for relative baselines, supported by a lightweight FDIR, modular software design, and compute-lean optimizations. A comprehensive, multi-fidelity test plan culminating in VISORS flight-like results demonstrates sub-centimeter relative position and sub-millimeter-per-second velocity accuracy, robust to crosslink outages and cycle slips. The work provides a transferable framework and verification methodology that can guide future DSS missions requiring precise onboard navigation using CDGNSS. Overall, it advances readiness for real-time, fault-tolerant CDGNSS navigation in distributed spacecraft architectures.

Abstract

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.

Paper Structure

This paper contains 27 sections, 29 equations, 19 figures, 13 tables, 1 algorithm.

Table of Contents

  1. Introduction
  2. Navigation Requirements
  3. Requirements Generalizations and Assumptions
  4. Requirements Identification
  5. Implications of Precision Requirements on the Receiver Phase Center and Spacecraft Attitude
  6. Navigation Functional Architecture
  7. Overview of Architecture
  8. Stable and Regularized Consider Extended Kalman Filter
  9. Process Noise Modeling
  10. Measurement Noise Modeling
  11. Integer Ambiguity Resolution
  12. Navigation Fault Detection, Isolation, and Recovery
  13. Data Health Screening and Rejection
  14. Measurement Screening and Rejection
  15. Memoryless Estimation and Monitoring of Prefit Residual Statistics
  16. ...and 12 more sections

Figures (19)

  • Figure 1: Generalized modes that spacecraft in a distributed system may adopt.
  • Figure 2: Assumed interface architecture applied in the context of identifying interface requirements.
  • Figure 3: Mapping of navigation operating requirements to the spacecraft modes
  • Figure 4: Illustration of body-frame component position uncertainties in the VISORS spacecraft (Source: visors2023aas).
  • Figure 5: Navigation functional architecture based on CDGNSS with IAR, for a two-spacecraft state vector
  • ...and 14 more figures