Bobcat-1: The Ohio University CubeSat for Inter-Constellation Time Offset Determination

Sabrina Ugazio, Kevin Croissant, Brian Casey Peters, Frank van Graas

Peer Reviewed

Abstract:	The determination of Global Navigation Satellite Systems (GNSS) inter-constellation time offset is still an open issue, and it would be particularly useful for those users with limited sky visibility. The increasing number of operative GNSS satellites is enabling more opportunities even for in-space users; users in the GNSS Space Service Volume (SSV) can exploit a PVT solution for orbit determination. However, it must be considered that users in the high SSV (GEO and HEO orbit) have a limited visibility of GNSS satellites. Even if four satellites in view are sufficient to determine a PVT solution when using a single GNSS constellation, when multiple constellations are involved it must be considered that an unknown is added for every different constellation considered, to estimate the time offset between constellations. As a result, when only one satellite is available from a constellation, there is no improvement in the positioning performance. This limitation could be overcome if the time offset among GNSS constellations would be provided to GEO users by an external source. The solution of the problem related to inter-constellation time offset is still on-going, and different approaches are under evaluation, implying a ground- network of GNSS receivers. The estimate exploiting in-space measurements from a CubeSat is an innovative technology to be explored. Bobcat-1, the Ohio University CubeSat, will be a “stepping-stone” to a Master clock in space. Bobcat-1 has been selected to be launched through the NASA CubeSat Launch Initiative and is scheduled to be in space by the end of 2020. Even if the mission’s primary objective will be the GNSS inter-constellation offset estimate, Bobcat-1 will also enable scientific studies, such as for example ionosphere TEC measurements applying a gradient algorithm. The focus of this paper is on the mission planning description, describing the analysis of the advantages that GEO satellites will get if provided with GNSS inter-constellation time offset estimates.
Published in:	Proceedings of the ION 2019 Pacific PNT Meeting April 8 - 11, 2019 Hilton Waikiki Beach Honolulu, Hawaii
Pages:	318 - 325
Cite this article:	Ugazio, Sabrina, Croissant, Kevin, Peters, Brian Casey, van Graas, Frank, "Bobcat-1: The Ohio University CubeSat for Inter-Constellation Time Offset Determination," Proceedings of the ION 2019 Pacific PNT Meeting, Honolulu, Hawaii, April 2019, pp. 318-325. https://doi.org/10.33012/2019.16808
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