Satellite communication constellations as sources of alternate PNT (position, navigation, and timing)

Position, Navigation, and Timing (PNT) applications are critical and embedded in all aspects of commercial and defense applications. The existing space-based solution of PNT yields Global Navigation Satellite Systems (GNSS), which provides highly accurate PNT reliably for any global user. A number of countries have implemented GNSS systems: GPS (US), GLONASS (Russia), Galileo (EU), and BeiDou (China). The sole reliance on the GPS system for US defense, unfortunately, creates a vulnerability if GPS were denied. The threat of GPS denial is forcing applications to consider methods of obtaining alternate PNT. The commercial satellite industry, with its emerging communication constellations in LEO, MEO, and GEO, enables new sources of space-based alternate PNT. Some commercial entities are providing alternate PNT as their primary service mission while others are providing communication services with secondary services in alternate PNT. In this paper, we will address and analyze emerging space-based sources of alternate PNT. A number of communication constellation providers have expressed interest in adopting alternate PNT solutions: SpaceLink, Starlink, Iridium, OneWeb, Amazon, and others. We will present a review and assessment of the different emerging alternate PNT solutions, their precision and timing accuracy beyond the existing GPS capability, and their targeted applications.