Hardly any spacecraft is launched today into low-Earth orbit without an onboard GPS receiver for either operational orbit determination and timing and/or science-driven orbit determination and timing. It is by far the most efficient and most accurate tracking technology currently available to Earth-orbiting spacecraft, with no competing technology in sight. The increasing availability of other GNSS constellations and stronger signals (e.g. GPS L5, Galileo signals) will only increase the availability and accuracy of the technology, and will likely push GNSS-based navigation into higher orbital regimes, all the way to geostationary orbits and beyond. Concerns about the vulnerability of terrestrial GPS applications due to jamming or spoofing generally do not apply in orbit.
This chapter addresses the fundamentals of GNSS-based orbit determination in accessible terms while providing an expert perspective on the many obvious and not so obvious challenges facing the practitioner of orbit determination or the consumer of the solutions.
The chapter highlights the unique aspects of the technique relative to conventional terrestrial positioning, and describes the challenges posed by the orbit determination problem, the typical scenarios in which they arise, and the trade space of specialized solutions. Key elements of the art and science of orbit determination are discussed for a wide variety of applications.
Table of Contents:
62.2 Formulation of the Orbit Determination Problem
62.3 The First Step in Solving the POD Problem: Linearization
62.4 Types of Orbit Determination Approaches: Kinematic, Dynamics, and “In Between”
62.5 The Critical Role of the Reference GNSS Orbit and Clock States
62.6 POD Solution Validation
62.7 LEOs, MEOs, and HEOs
62.8 Formation Flying and Relative Positioning
62.9 Elements of the Art
62.11 Orbit Determination for Earth Science
62.12 Synergy with Other Data Types
62.13 Onboard Orbit Determination
62.14 Case Study: Jason-3 Mission
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