Time - Frequency transfer and orbit determination systems for space applications

Time and frequency transfer, when combined with orbit determination (OD), underpins a wide range of applications — from positioning, navigation, and timing (PNT), to precision metrology, geodesy, and tests of fundamental physics. This thesis explores the synergy between these two domains across three case studies, each targeting a distinct scientific and operational objective. First, within the framework of ESA’s Moonlight initiative, the research contributes to the definition of a Lunar Radio Navigation System (LRNS) architecture. The work focuses on synchronous time transfer using coherent transponders and common-view ground station coordination to ensure ephemeris and clock prediction accuracy for lunar users. A trade-off study on the onboard frequency reference was performed, supported by a semi-analytical method for generating multicoloured clock noise from Allan deviation profiles. Simulation results guided the selection of clock and message update strategies to ensure compliance with ESA’s PNT performance requirements. Second, in collaboration with the Italian Metrology Institute (INRIM), the thesis proposes a passive implementation of Two-Way Satellite Time and Frequency Transfer (TWSTFT). This technique enables UTC(k) synchronization for passive users using only a TV broadcast antenna and softwaredefined radio (SDR).By incorporating orbital dynamics and path delay modelling, the method demonstrates nanosecond-level time transfer capability, offering a scalable and robust alternative toGNSSbased time distribution. Third, the work addresses the Interstellar Probe (ISP) mission concept — a future deep-space mission aimed at heliosphere exploration. Through simulated two-way ranging campaigns, the study assesses the probe’s potential to test General Relativity at unprecedented distances (10- 1000 AU). Constraints on the Nordtvedt parameter are evaluated at the 10−5 level, and sensitivity to a Yukawa-type deviation from Newtonian gravity is shown to be competitive with existing limits on the graviton Compton wavelength (10−14 km). Together, these contributions demonstrate the versatility and strategic value of integrating timefrequency and orbit determination techniques — not only for current space infrastructure, but also as enabling technologies for future scientific missions and the advancement of gravitational physics.