oppler effect in TianQin time-delay interferometry

he current design of space-based gravitational wave detectors utilizesheterodyne laser interferometry in inter-satellite science measurements.Frequency variations of the heterodyne beatnotes are predominantly caused bythe Doppler effect from relative satellite motion along lines of sight.Generally considered to be outside the measurement band, the Doppler effectappears to have been largely overlooked in literature on numerical simulationsof time-delay interferometry (TDI). However, the potential impact on theeffectiveness of TDI should be assessed. The issue is particularly relevant toTianQin that features geocentric orbits, because of strong gravity disturbancesfrom the Earth-Moon system at $<1\times 10^{-4}$ Hz. In this paper, based onhigh-precision orbital data obtained from detailed gravity field modeling, weincorporate the Doppler shift in the generation of TianQin's beatnote phasesignals. To remove the large-scale Doppler phase drift at $<1\times 10^{-4}$Hz, we develop a high-performance high-pass filter and consider two possibleprocessing sequences, i.e., applying the filter before or after TDIcombinations. Our simulation results favor the former and demonstratesuccessful removal of the low-frequency gravity disturbances for TianQinwithout degrading the TDI performance, assuming 10 m pseudo-ranginguncertainty. The filtering scheme can be used in developing the initialnoise-reduction pipeline for TianQin.