A Strategic Design Of Differential VLBI Observation Of Spacecraft

Differential VLBI alternatively observes a target and a reference object. By subtracting the observations it gives the differential quantity. This technique could result in very high precision in the relative position determination because the subtraction removes most of the error sources from the observation of the target, and so let the differential VLBI technique play an important role in the deep space exploration. However, the reference source may not be available especially before, during or after the maneuver or capture perid because the prerequisite as the angular distance between the target and the reference object should be very small in order to maintain the high precision. Based on the analysis of the archive observations from astrometric and geodetic VLBI experiments, in this dissertation, a strategic design of the implementation of differential VLBI is developed by using observations of several reference sources spreading out in a circular band centered at the target and interpolating the non-geometric delay in the target direction. Compared to the traditional differential VLBI, in our design the high precision in the relative position determination is retained while the limitation in the angular distance is extended as well as the effect of the observation uncertainties of a single reference source on the reduction results is repressed. Data analysis shows that by using our design a precision of about 1ns in the correction of the non-geometric delay could be obtained at both S and X band. Our analysis in this dissertation could also be referred in the application studies of differential VLBI in the fields related to the position determination of weak radio sources.