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Demonstrates enhanced positional precision in deep space probes, suggesting improved mission success.
China's Tianwen‐2 probe, launched on 29 May 2025, will sample asteroid 2016 HO3 and exploring comet 311P. The precise positioning of the Tianwen‐2 probe will benefit its mission goals. Phase‐referencing VLBI imaging offers significant potential to improve the positional precision of deep space probes. However, traditional phase‐referencing VLBI imaging assumes a nearly constant angular position, thereby limiting positioning precision for moving targets, particularly with sparse arrays or long‐duration observations. To enhance the tracking precision of moving targets, an improved Kinematic Phase‐Referencing (KPR) VLBI method is investigated. By directly integrating a kinematic orbital model—parameterized by polynomial coefficients—into the phase‐referencing VLBI process, KPR‐VLBI removes the need for the nearly constant‐position assumption. Observations of the Tianwen‐2 probe were carried out using the five stations of the Chinese VLBI Network to validate the KPR‐VLBI method. Results indicate that the final angular position precision is at the sub‐milliarcsecond level, which is primarily constrained by tropospheric and ionospheric errors as well as calibrator position errors, while the 1σ formal error of angular position is better than 10 micro‐arcseconds. Furthermore, compared with conventional phase‐referencing VLBI imaging, KPR‐VLBI is able to effectively suppress sidelobes arising from the target motion in synthesized images, thereby leading to more reliable results.
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Tong et al. (2026) studied this question.
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