Characterization of Expected Multipath Error for the NICER X-Ray Telescope Payload

Viliam Klein, Penina Axelrad and Jeanette Veldman

Abstract:	GPS has become the instrument standard for positioning and timing onboard many low Earth orbit (LEO) satellites. The Neutron star Interior Composition ExploreR (NICER) is a soft X-ray timing spectrometer payload for the International Space Station (ISS) that will meet its timing requirements through a combination of microcontroller oscillators and a GPS disciplined one pulse per second (1-PPS) signal. This paper presents an analysis of the expected pseudorange and time solution errors caused by multipath in the complex ISS environment. The specific timing requirement and the many challenges presented by the NICER environment make this particular interesting case study for analysis using an Advanced GNSS Multipath Model (AGMM). The AGMM incorporates CAD drawings of the structures involved, and accounts for dynamic motion of the solar panels and radiators on the ISS, as well as the articulation of the NICER payload. Simulations show the impact of blockages, reections and diraction from a number of key surfaces on the ISS. Example results indicate that clock bias solution errors caused by multipath are well below 10 ns most of the time, with some errors in the 10-20 ns range when large multipath and poor GPS satellite visibility occur together. The simulation tool developed for this study has the exibility to support similar analyses for a variety of spaceborne GNSS applications.
Published in:	Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014) September 8 - 12, 2014 Tampa Convention Center Tampa, Florida
Pages:	2448 - 2456
Cite this article:	Klein, Viliam, Axelrad, Penina, Veldman, Jeanette, "Characterization of Expected Multipath Error for the NICER X-Ray Telescope Payload," Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014), Tampa, Florida, September 2014, pp. 2448-2456.
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