An Equivalent Calculation Method of VLBI Instantaneous Time Delay Rate

Radial velocity needs to be introduced into the instantaneous time delay rate model of VLBI, which will increase the partial derivative calculation of the velocity term in the observation matrix, and the state transition matrix will also have an extra state transition part of the velocity term. The calculation amount of the state transition matrix accounts for a major proportion in the precise orbit determination, so it is of great significance to reduce its scale for improving the operating efficiency of orbit determination software. An instantaneous delay rate equivalent calculation method is proposed, which requires only the position and avoids the velocity term and its partial derivative. Compared with the instantaneous time delay rate model, this method reduces the state transition matrix from 6 × 6 dimensions to 3 × 6 dimensions, and reduces the calculation amount of software while ensuring the accuracy. The measured data of the Earth-Mars transfer segment of “Tianwen-1” is used to verify the effectiveness and accuracy of the method.