Determining trajectory of balloon motion in Venusian atmosphere by very long-base interferometry method

As part of the Vega project two balloon probes were released into the Venusian atmosphere from flyby vehicles. These balloons carried transmitters operating in the 18 cm wavelength range. The method of differential radio interferometry with a very long base (VLBI) was used for ensuring the necessary accuracy in measuring coordinates and velocity. Almost all the major radio telescopes in the world participated in this program, but an analysis of data collected using the Ussuriysk-Yevpatoriya base is the major consideration. After discussing determination of the model of motion of these balloons on the basis of Doppler frequency measurements using one telescope, the determination of the mean trajectory of balloon motion from interference frequency measurements is illustrated. It is shown that in the southern Venusian hemisphere the Vega-2 balloon moved at a mean velocity of 66 m/s; the latitudinal component of velocity was 3.4 plus or minus 0.5 m/s and was directed to the north. The Vega-1 balloon velocity in the Northern Hemisphere was 69 m/s and was directed virtually parallel to the equator. In certain cases there were changes in signal frequency corresponding to oscillation of the suspended instrument package with a period of about 7.4 seconds.