Pulsed Laser Links for Small Satellite PNT and Networking

Danielle E. Coogan, Tyler Ritz, Myles Clark, John W. Conklin

Abstract: Satellite constellations are growing in size and in utility for applications as diverse as providing reliable, low-latency internet service to rural areas and Earth science missions. This expansion of satellite constellations brings attention to the need for responsive and reliable satellite communication. Current research focuses on using pulsed laser communications as the method of relaying time signals instead of the radio frequency (RF). The upcoming CLICK (CubeSat Laser Infrared CrosslinK) missions (Massachusetts Institute of Technology, University of Florida, NASA Ames Research Center) [1] will demonstrate a space-craft-to-spacecraft laser communication link and time-transfer. For pre-flight technology assessment of missions such as CLICK, a simulation of a spacecraft constellation in Earth orbit has been created to estimate clock synchronization and precision orbit determination based on measured instrumentation performance. We have developed a novel MATLAB-based numerical simulator to model spacecraft-to-spacecraft laser time-transfer and estimate the offset between the spacecraft clocks over time. This simulation includes timing errors associated with laser pulse generation and detection, as well as non-Gaussian clock drift models. The two on-board clocks modeled are a cesium-based Chip-Scale Atomic Clock (CSAC) and a rubidium-based Miniature Atomic Clock (MAC), both produced by Microchip [2][3]. An example case of two spacecraft in a circular, low-Earth orbit receiving GPS position, GPS timing, and laser pulse timeof-flight measurements is simulated. The positions and velocities of the two spacecraft at a reference epoch and the constant clock model coefficients are estimated. Polynomial models of different orders were used as clock models. The effect of clock model order on the root-mean-square (RMS) of the clock error is apparent in the case using GPS and lasing measurements, showing that the clock model improves with increasing clock model order. Results compare the estimated clock model of a mission operation that only uses GPS measurements and a mission operation that uses both GPS and laser pulse time-of-flight measurements between spacecraft referenced to their on-board CSACs. Including lasing measurements reduces the RMS clock model error to approximately half the RMS of the cases with only GPS measurements. This simulation tool can be used to optimize the lasing operations schedule based on mission timing performance objectives.
Published in: Proceedings of the 34th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2021)
September 20 - 24, 2021
Union Station Hotel
St. Louis, Missouri
Pages: 4002 - 4011
Cite this article: Coogan, Danielle E., Ritz, Tyler, Clark, Myles, Conklin, John W., "Pulsed Laser Links for Small Satellite PNT and Networking," Proceedings of the 34th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2021), St. Louis, Missouri, September 2021, pp. 4002-4011.
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