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Opportunity at Air Force Research Laboratory (AFRL)

Relativistic Time Synchronization for Satellite Crosslinks


Space Vehicles Directorate, RV/Space and Planetary Sciences

RO# Location
13.40.01.C0064 Kirtland Air Force Base, NM 871175776


Name E-mail Phone
Pham, Khanh Dai 505.846.4823


With an outlook towards flexible Global Positioning System (GPS)-surrogate technologies, this research opportunity focuses on time transfer and synchronization approaches for satellite constellations equipped with crosslink capabilities. Specifically, scientific breakthroughs are needed for time signals of onboard clocks to be transferred and synchronized through crosslinks, including gravitational effects such as Shapiro delays. The endpoints of these crosslinks are satellites with clocks in orbital motions (e.g., moving at 3 km per second for Geo-synchronous Orbits and 7 km per second for Low Earth Orbits). What follow are some technical challenges of interest, including (1) modeling, simulation, and analysis of relativistic time transfers in radio and/or optical clocks; (2) compensation of Shapiro delays and other propagation effects; (3) distributed time transfer mechanisms in radio and/or optical crosslinks; (4) stability and consensus in remote time dissemination; and (5) accurate processing of crosslink data for time synchronization accuracy and convergence.



Pham KD: “Stochastic Power Controls for Distributed Pulse-Coupled Synchronization”. IEEE Aerospace Conference, doi: 10.1109/AERO.2017.7943841, Big Sky, MT, 2017

Kirchner D: “Two-Way Time Transfer via Communication Satellites”. Proceedings of IEEE 79(7): 983-990, 1991

Miller J, et al: “NASA Architecture for Solar System Time Distribution”. Proceedings of IEEE Frequency Control Symposium: 1299-1303, 2007

Xie Y: “Relativistic Time Transfer for Inter-satellite Links”. Frontiers in Astronomy and Space Sciences 3: 2016


GPS denied; Time synchronization; Distributed time transfer; Onboard processing; Crosslinks; Shapiro delay; Synchronization accuracy; Propagation effects;


Citizenship:  Open to U.S. citizens
Level:  Open to Postdoctoral and Senior applicants
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