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

TL;DR

This paper presents an accurate pseudorange model and a novel Kalman filter algorithm for clock synchronization and light-travel-time estimation in space-based gravitational-wave detectors, achieving submeter accuracy essential for data processing.

Contribution

It introduces a realistic pseudorange model in the barycentric reference frame and a specialized Kalman filter algorithm to disentangle pseudoranges and synchronize clocks in space-based GW detectors.

Findings

Achieves submeter accuracy in clock synchronization and light-travel-time estimation.

Provides a realistic pseudorange model for space-based GW detectors.

Demonstrates the effectiveness of the proposed algorithm with data simulations.

Abstract

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.