Calibration method of spacecraft–inertial sensor center-of-mass offset for the Taiji gravitational wave detection mission under science mode

Accurately calibrating the center-of-mass (CoM) offset between the spacecraft (SC) and the inertial sensor test mass (TM) is crucial for space-based gravitational wave (GW) antennas, such as LISA and Taiji. Existing calibration methods generally require dedicated spacecraft maneuvers, which can interrupt science data continuity and compromise inter-satellite laser-link stability. This paper presents a maneuver-free CoM-offset calibration scheme that directly uses standard science-mode readouts from inertial sensors, interferometers, and differential wavefront sensors. A high-fidelity closed-loop DFACS simulation is developed to generate 25 days of synthetic science-mode readouts, and an extended-state adaptive Kalman filter is constructed to estimate the CoM offset while augmenting systematic bias terms and colored readout-noise states as nuisance states. To support the weak-excitation identification mechanism, a Fisher-information-based estimability analysis is further performed for the augmented closed-loop system. Nominal Monte Carlo (MC) simulations are used as the final statistical calibration-performance assessment, yielding empirical RMSE values of 2.9×10⁻⁴–1.3×10⁻³m for the six CoM-offset components. A separate model-mismatch MC study for b₁O¹ shows RMSE values of 2.39×10⁻³, 8.52×10⁻⁴, and 5.51×10⁻⁴m, with mean errors below 0.6 mm. The results demonstrate that the proposed method enables millimeter-level, maneuver-free CoM-offset calibration during science operation and retains practical robustness under representative model mismatch.