Characterizing clock-induced errors in laser-communication-based inter-satellite ranging

High-precision inter-satellite ranging is critical for formation flying, autonomous navigation, and scientific measurements in small-satellite missions. Laser communication terminals (LCTs) offer an opportunity to perform both data transfer and ranging, but their dual-use imposes stringent requirements on onboard clocks and timing electronics. This paper investigates the impact of clock-induced timing errors on two-way LCT-based ranging between CubeSats operating around the near-Earth asteroid 99942 Apophis. A methodology is developed to unify clock noise specifications provided in datasheets, generating realistic timing errors across microsecond-to-hour integration periods. Using high-fidelity orbital simulations, two orbital configurations—coplanar and non-coplanar—are analyzed to evaluate how relative satellite geometry influences the propagation of clock errors into range measurements, orbit determination, and the estimation of Apophis’ gravitational parameter. Results demonstrate that inter-satellite links (ISLs) can reduce orbit determination errors along directions weakly constrained by Earth-based Doppler—from 1–3 m to 0.1–0.3 m in coplanar formations, and even further in non-coplanar formations—corresponding to improvements of one to two orders of magnitude. Subsystem-level noise, such as detector jitter and time tagging, can still limit achievable precision, even with high-performance clocks. The methodology provides a framework applicable to a broad range of small-satellite missions, guiding the selection of clocks, formation geometry, and system design to optimize both navigation performance and science return.