在有2个探测器的深空探测中，利用同波束VLBI技术可解算高精度的差分相时延，进而同时提高2个探测器的测定轨精度。但是，差分相时延的解算条件严格，差分相位抖动较大时直接影响解算的成功率。针对这一问题，利用SELENE 两颗小卫星Rstar 和Vstar 的4个测站长达1年的同波束VLBI观测数据，统计得出了差分相位抖动与其对应的角距离的关系模型。该模型的建立，既有利于提高同波束VLBI 差分相时延的解算成功率，又对行星中性大气和电离层掩星观测研究具有重要的参考意义。%In deep-space exploration with two detectors, using the same-beam VLBI tech-nique can get high precision differential phase delay, thus the accuracy of orbit determina-tion can be much improved. However, the conditions of differential phase delay solution are much strict. Differential phase fluctuations may jeopardize the success of resolving differen-tial phase delay. To make it clear, conduct a statistic work of one year’s same-beam VLBI data which are got from two satellites (Rstar and Vstar) in SELENE pro ject. After a series of computing, a model for the relation between differential phase fluctuations φ and corre-sponding separation anglesθof two satellites was drawn. The model is described as a linear equation ofφ=2.69θ+1.09, where, the slope of 2.69 reflects the influence of earth neutral atmosphere and ionosphere, and the intercept of 1.09 deg reflects the effect of thermal noise. This model not only can help to resolve differential phase delay in the same-beam VLBI observation, but also can serve as a reference for the study of planetary atmosphere and ionosphere in occultation observation.
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