Clock synchronization and light-travel-time estimation for space-based gravitational-wave detectors

• Main Authors: Reinhardt, Jan Niklas, Hartwig, Olaf, Heinzel, Gerhard
• Format: Journal Article
• Language: English
• Published: 19-08-2024
• Subjects: Physics - General Relativity and Quantum Cosmology
• DOI: 10.48550/arxiv.2408.09832

Space-based gravitational-wave detectors, such as LISA, record
interferometric measurements on widely separated satellites. Their clocks are
not synced actively. Instead, clock synchronization is performed in on-ground
data processing. It relies on measurements of the so-called pseudoranges, which
entangle the interspacecraft light travel times with the clock
desynchronizations between emitting and receiving spacecraft. For
interspacecraft clock synchronization, we need to isolate the differential
clock desynchronizations, i.e., disentangle the pseudoranges. This further
yields estimates for the interspacecraft light travel times, which are required
as delays for the laser frequency noise suppression via time-delay
interferometry. Previous studies on pseudorange disentanglement apply various
simplifications in the pseudorange modeling and the data simulation. In
contrast, this article derives an accurate pseudorange model in the barycentric
celestial reference system, complemented by realistic state-of-the-art LISA
data simulations. Concerning pseudorange disentanglement, this leads to an a
priori under-determined system. We demonstrate how on-ground orbit
determinations, as well as onboard transmission and on-ground reception time
tags of the telemetry data, can be used to resolve this degeneracy. We
introduce an algorithm for pseudorange disentanglement based on a nonstandard
Kalman filter specially designed for clock synchronization in systems where
pseudorange measurements are conducted in different time frames. This algorithm
achieves interspacecraft clock synchronization and light travel time estimation
with submeter accuracy, thus fulfilling the requirements of time-delay
interferometry.