Delta VLBI data performance in the Galileo spacecraft Earth flyby of December 1990

The performance of the delta very long baseline interferometry (Delta VLBI) data type during the recent Earth flyby of the Galileo spacecraft is presented. First, the data are given significance by showing why the mission design requires an accurate flyby. Then, the data's performance is analyzed, including its operational features, as well as its accuracy. Finally, the effectiveness of these data in improving the accuracy of flyby is shown. Comparisons are made between the expected and actual performances of the data. The processing time, reliability, and accuracy of these data were very good, and a solid gain was made in the encounter accuracy.