Tropospheric delay correction of VLBI stations for the real-time trajectory determination of the Chang'E-5 spacecraft

The Chang'E-5 (CE-5) spacecraft was launched on 24 November 2020 with the purpose to implement unmanned lunar surface sampling and return. Very long baseline interferometry (VLBI) technique played an important role in real-time precise trajectory determination and attitude determination of the CE-5 spacecraft in the Earth to Moon transfer, circumlunar, landing, and ascending phases. However, tropospheric delay is one of the main error sources for VLBI observations which has to be corrected accurately for precise trajectory determination. To deal with this error properly, a prediction model (TRO_P) and a method with Global Navigation Satellite System observations (TRO_G) are proposed for tropospheric zenith delay correction for real-time and 30 min latency trajectory determination of the CE-5 spacx1ecraft, respectively. The results demonstrate that the mean root mean square (RMS) of residual error of VLBI delay and delay rate for TRO_P are 0.62 ns and 0.75 ps/s at low elevation angle, respectively. Moreover, the improvement for the mean RMS of VLBI delay using TRO_G is 39.5% meaning from 0.43 to 0.26 ns compared with that using the method with meteorological data (TRO_S) at low elevation angle. This study can provide a reference for tropospheric delay calibration for trajectory determination of the spacecraft using VLBI or other techniques.