Two Touches of Venus

After lonely, four-month journeys through the void, two ingeniously contrived spacecraft--one Russian, the other American--reached Venus last week. Methodically investigating the cloud-shrouded planet, they successfully radioed their findings back across 50 million miles of space to scientists on earth. The dual performance was perhaps the most impressive demonstration yet of the technical progress made by man during his first decade of space flight.

Diving directly into the planet's dense, murky atmosphere, Russia's 2,427-lb. Venus 4 ejected an egg-shaped, instrument-crammed capsule. Although the mother ship was quickly incinerated by the frictional heat of its plunge, the capsule was insulated by an ablative coating that gradually burned off as it heated. At an altitude of 15.5 miles, when its velocity had been sufficiently slowed by Venusian "air" resistance, the capsule automatically deployed a parachute and began drifting slowly toward the surface. As it descended through the whirling gases, the capsule sniffed them, noted their composition, temperature and pressure, and dutifully reported them back to earth.

Atmosphere Profile. America's 540-Ib. Mariner 5 took a less direct approach, swinging to within 2,480 miles of the Venusian surface and then briefly disappearing behind the planet before heading toward a permanent orbit around the sun. As Mariner drew close, its instruments searched for a Venusian magnetic field and an accompanying radiation belt, and peered down into the upper atmosphere to determine its height and temperature profile. As the spacecraft swung behind Venvis, its radio signals passed through the Venusian atmosphere on their way to earth. By measuring the effect the intervening gases had on the strength, frequency and path of these signals, scientists could estimate both the density and pressure of the atmosphere.

In Moscow, scientists lost little time in revealing the details of what Venus 4 had found. Although the temperature at 15.5 miles was an uncomfortable but bearable 104DEG F., they reported, it gradually increased as the capsule drifted lower, reaching a scorching 536DEG F. by the time that transmissions ceased some 90 minutes later.

But the Russians failed to clarify--and perhaps do not know--whether the signals stopped after the capsule reached the Venusian surface or while it was still descending, leaving open the possibility that even higher temperatures exist at lower altitudes. (Data recorded by Mariner 2 in 1962 and by radiotelescope observations have indicated Venusian surface temperatures as high as 800DEG F.) In any event, there seems little doubt that extreme heat finally silenced the capsule, either by damaging its parachute and causing it to plunge to destruction or simply by frying its electronic components.

The Soviet capsule also measured Venusian atmospheric pressures up to 15 times as great as the earth's and determined that the atmosphere consists almost entirely of carbon dioxide, which, scientists believe, is spewed out by volcanic activity. No trace of nitrogen (which constitutes 78% of the earth's atmosphere) and only 1.5% of oxygen and water vapor were detected. In readings made before Venus 4 entered the atmosphere, the Russians could find no evidence of a Venusian magnetic field and radiation belt.

Scientific Chagrin. Mariner 5 accumulated and recorded so much data that at week's end it was still being played back and transmitted to Pasadena's Jet Propulsion Laboratory. From preliminary glimpses at Mariner's telemetry, JPL's scientists confirmed Venus 4's discovery of a halo or corona of hydrogen around Venus and agreed that the atmosphere is indeed "dense." They also reported that there had been some fluctuations in the magnetic field surrounding Mariner as it swung past Venus, but that this did not necessarily mean the detection of a Venusian magnetic field.

Although U.S. scientists were confident that Mariner's findings, when fully evaluated, would rival those of Venus 4 in importance, they were clearly chagrined at the Soviet success in sending an operational instrumented capsule through the atmosphere of another planet, years before the U.S. is scheduled even to attempt such a feat. Russia, they note, has already attempted 18 probes to Mars and Venus--compared with only five for the U.S.--and appears to be willing to pay the great costs of planetary exploration. Congress, on the other hand, has continuously snipped away at NASA's budget, leaving the U.S. only four planned planetary probes: a pair of Mars photographic flybys in 1969 and possibly a pair of Martian instrumented soft landings in 1975.

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