Leveraging Commercial Broadband LEO Constellations for Navigating

Tyler G. Reid, Andrew M. Neish, Todd F. Walter, Per K. Enge

Abstract:	There has been resurgent interest in building large low Earth orbiting (LEO) constellations of satellites on a new and bigger scale. Their aim is delivering Internet to the world by providing truly global and robust broadband coverage. Players such as OneWeb, SpaceX, Samsung, and Boeing all have proposals for such a system. Each plans on launching constellations of 600 to over 4000 satellites, dwarfing the 1400 operational satellites currently in orbit. This sheer number of satellites, along with their global coverage, gives rise to opportunities not only for broadband but also as a platform for providing navigation services. Here we explore how such a LEO constellation could be leveraged for augmentation of GPS for navigation and even as a full standalone backup. LEOs have the advantage of being closer to the Earth compared to GNSS systems in medium Earth orbit (MEO), thus experiencing less path loss and potentially delivering stronger signals. This makes them more resilient to jamming. LEO spacecraft also have much faster motion in the sky, passing overhead in minutes instead of hours in MEO. This gives rise to more multi-path rejection, as reflections are no longer static over short averaging times. The addition of these constellations adds a wealth of geometric diversity. We examine how these LEO constellations can be piggybacked to deliver navigation services in the form of a hosted payload. The full architecture is explored, from user geometry and signal in space ranging errors (SIS URE) to position errors as well as how such a payload could be conceived. This can be done more economically as better satellite geometry allows for degraded SIS URE to achieve comparable performance to GPS today. We explore the use of chip-scale atomic clocks (CSAC) on the satellites for precise timing as well as the GPS ephemeris message to enable backwards compatibility. Constellation-wide orbit determination methods are also discussed. Ultimately, all elements and are brought together to show the possible system performance that is achievable. This is in an effort to leverage infrastructure coming on the horizon to further protect, toughen, and augment the PNT that we are increasingly reliant upon.
Published in:	Proceedings of the 29th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2016) September 12 - 16, 2016 Oregon Convention Center Portland, Oregon
Pages:	2300 - 2314
Cite this article:	Reid, Tyler G., Neish, Andrew M., Walter, Todd F., Enge, Per K., "Leveraging Commercial Broadband LEO Constellations for Navigating," Proceedings of the 29th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2016), Portland, Oregon, September 2016, pp. 2300-2314. https://doi.org/10.33012/2016.14729
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