Accurate ground-to-ground laser time transfer by diffuse reflections from tumbling space debris objects

摘要

The optical two-way time transfer between two widely separated laser ranging ground stations in common view of a space debris target can be achieved from diffuse laser pulse reflections. The round-trip time-of-flight measurements augmented by the detection and epoch timing of diffusely scattered laser light from the second ground station allows accurate clock comparisons, provided that the mean location of the point of reflection on the target structure can be recovered with sufficient fidelity. We have set up a target delay model that derives the tumbling motion of rocket bodies from a combination of laser ranging and photometric measurements. Combined with the simultaneously measured short arc orbit, we obtain the applicable in situ propagation delay for the time transfer signal between the two ground stations in order to establish the clock offset between them. We show an example where the uncertainty of this clock synchronization for a time-of-flight comparison already reaches 3 ns. We point out that there is still significant room for improvement.