Synchronization and Syntonization of Formation Flying Cubesats Using the Namuru V3.2 Spaceborne GPS Receiver

E.P. Glennon, J.P. Gauthier, M. Choudhury, A.G. Dempster, K. Parkinson

Abstract:	The growing popularity of cubesats has delivered for the first time the opportunity to develop space missions at very low cost. These also include 2U and 3U cubesats, with the increased mass and volume of these larger formats allowing significantly enhanced capability. 3U cubesats can even include thrusters and reaction wheels in addition to the solar panels, batteries, telemetry and command and control systems that may be found on such platforms. The availability of small, cheap, and capable spacecraft, coupled with the fact the launchers often carry multiple cubesats for deployment presents the opportunity to fly pairs or triplets of satellites in formation, which may be beneficial in some applications, such as bistatic radar. This in turn requires a capability to not only fix the absolute and relative positions of the spacecraft, but depending on the mission may also require an ability to synchronize and syntonize them as well. The Namuru V3.2 FPGA based GPS receiver has been developed specifically for the Boeing Colony II 3U cubesat platform and a mission that satisfies many of these requirements. In this paper, we focus on describing the timing synchronization and syntonization aspects of the receiver, with particular regard on how it may operate in low earth orbit (LEO). These timing aspects of the receiver include the use of disciplined voltage-controlled temperature-compensated crystal oscillators (VC-TCXOs) rather than ordinary TCXOs in order to eliminate sawtooth timing errors and to support the syntonization requirement. Algorithmic modifications necessary to account for the differences between the LEO and terrestrial scenarios are discussed. Finally, we also present results obtained by testing the navigation and timing outputs of the receiver using hardware based Spirent GPS simulators running LEO scenarios and high quality universal frequency counters/timers.
Published in:	Proceedings of the ION 2013 Pacific PNT Meeting April 23 - 25, 2013 Marriott Waikiki Beach Resort & Spa Honolulu, Hawaii
Pages:	588 - 597
Cite this article:	Glennon, E.P., Gauthier, J.P., Choudhury, M., Dempster, A.G., Parkinson, K., "Synchronization and Syntonization of Formation Flying Cubesats Using the Namuru V3.2 Spaceborne GPS Receiver," Proceedings of the ION 2013 Pacific PNT Meeting, Honolulu, Hawaii, April 2013, pp. 588-597.
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