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Test balloons near Venus an international success

By Robert C. Cowen / June 25, 1985



Scientists and engineers of the international team that tracked two instrumented balloons which were dropped into Venus's atmosphere by Soviet spacecraft are calling this unique project an outstanding success. French space scientist Jacques Blamont explains that it is still too early to report what the probes have discovered. Nevertheless, he says, the trackers ``have done good work.'' He adds, ``We are essentially convinced that the data are good.''

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This is also an achievement for East-West scientific cooperation. Though US-Soviet scientific contacts are at a low point, the Deep Space Tracking Network of the NASA Jet Propulsion Laboratory (JPL) anchored the French-led tracking effort.

The probes were carried by the Soviet Vega 1 and 2 spacecraft. They entered the Venusian atmosphere June 10 and 14. Launched respectively last Dec. 15 and 21, Vega 1 and 2 are now on a course to intercept Halley's comet next March. Venus's gravity deflected the Vegas onto the desired course, giving them a boost of extra energy as they passed by the planet.

Each probe package separated into a lander and a free-floating balloon as it fell. According to reports from Moscow, the landers have also returned much useful data on the planet's surface, where the 850 degrees F. temperature is hot enough to melt lead and the atmospheric pressure is some 100 times as great as sea-level pressure on Earth. Again, however, little has yet been announced publicly as to what has been found.

Soviet tracking stations were adequate for the landers. But the helium-filled balloons, with French-designed instrument gondolas hanging 40 feet below them, required worldwide service. They were designed to drift with the Venusian wind in equatorial regions some 34 miles above the planet's surface. Precision tracking by several widely spaced antennas was needed to fix the three-dimensional position of the balloons and to determine wind speed to within an accuracy of two miles an hour.

To meet this need, the French space agency CNES (Centre National d'Etudes Spatiales) organized a 14-unit international tracking network to supplement the six-antenna net of the Soviet Union. NASA agreed to contribute its three major tracking facilities at Goldstone, Calif., Canberra, and Madrid. NASA experts met with Soviet specialists to work out the requirements. During the actual tracking, however, JPL communicated with the CNES center in Toulouse, France, which, in turn, had direct contact with the Soviet Union.

Designed to operate for about two days, the two balloon instrument packs returned data for about 46 hours, according to JPL. Planetary scientists will be studying both these data and those from the landers, looking especially for signs of vulcanism.

Radar mapping, previous probes, and instruments on the US Pioneer Venus spacecraft still orbiting the planet strongly suggest that Venus is at least as volcanically active as our own planet Earth. The middle level of Venus's largely carbon dioxide atmosphere, where the balloons have traveled, contains sulfuric acid clouds and sulfurous gases. A number of scientists suspect volcanoes have injected this sulfurous material.

In particular, Larry W. Esposito of the University of Colorado at Boulder has noted that there was an unexpectedly high concentration of sulfur dioxide and sulfuric acid in the middle Venusian atmosphere when Pioneer Venus arrived in 1978. That concentration has dropped steadily since then. Dr. Esposito suggests that a powerful volcanic eruption took place just before Pioneer reached the planet.

Thus vulcanism is likely to be a major topic when scientists from East and West meet in Toulouse in August to discuss the new balloon and lander data. Meanwhile, Vega 1 and 2 continue on toward their Halley rendezvous with an international set of instruments, including French and US contributions, on board.

A Tuesday column. Robert C. Cowen is the Monitor's natural science editor.