Illustration of the Mariner 2 spacecraft

PASADENA, California--The Mariner Venus spacecraft of 1967 may combine with the Mariner Mars spacecraft, vintage 1964, in a novel experiment planned for this summer and fall by Caltech Jet Propulsion Laboratory scientists for the National Aeronautics and Space Administration.

This month, September and early October before Mariner V is scheduled to fly by Venus, JPL scientists will attempt to get readings solar plasma and space magnetism from both Mariner V and Mariner IV while they are in the same direct line with Earth and the sun.

The two spacecraft would be about 70 million miles apart with Earth roughly in the middle, on a line drawn from the Sun. The unique lineup could be capitalized on assuming that Mariner IV's radio transmitter would still be operating.

"And we have no reason to believe it won't be," says Conway W. Snyder, Mariner Venus project scientist. The Mars Mariner's signal came through loud and clear only last week on the Caltech-JPL 210-foot antenna at the nearby Goldstone, California, Deep Space Station. At that time Mariner IV was more than 75 million miles from Earth.

From as far as 215 million miles, Mariner IV has reported scientific data to Earth for 2-1/2 years.

Mariner V was launched from Cape Kennedy on June 14 with encounter of the planet set for October 19.

The periods of conjunction that will be studied are from about August 10 to 21 and roughly September 1 to October 10. On September 7, Mariner IV will be only 29,167,000 miles from the Earth in its elliptical swing, and Mariner V will be roughly 20.5 million miles distant.

By the time Mariner V encounters Venus it will be 49.5 million miles away and Mariner IV, moving slowly, will have fallen behind Earth, 34 million miles out.

The JPL space scientists hope to record shock waves and other disturbances in the solar wind or magnetic field encountered by each spacecraft during August. The solar plasma streams out from the sun at rates of 200 to 500 miles per second, according to previous experiments on Mariner II and other spacecraft.

Later, during September and October, the two-spacecraft readings will be concerned with concentrations of solar high- energy particles. Attempts will be made to measure the speed and direction of streams of electrons and protons.

These high-energy particles move at almost the speed of light (186,000 miles per second), and hence can travel from Mariner V to Mariner IV in a matter of minutes. The August readings, because of the slower plasma stream, would require up to a day and a half to record.

This would be the most spectacular use of Mariner IV since it flew by Mars on July 14, 1965, and returned 22 pictures of that planet from a distance of 6,118 miles. The time of the project twin-spacecraft experiments would be nearly three years after the Mariner IV launching on November 28, 1964.

Among the other half-dozen major experiments scheduled to be accomplished by Mariner V are radio occultation measurements of the density and the composition of the heavy Venus atmosphere.

Other instruments will seek data on temperatures, electron density and possible radiation belts around the Earth's sister planet. Scientists also will attempt to obtain more accurate figures on Venus' mass, orbit and general position vis a vis Earth in the solar system. Venus orbits the Sun at a mean distance of 67.2 million miles. Earth orbits at a mean 92.9 million miles.

In sum, the scientific findings of Mariner V could con- tribute some leading answers--not final, of course, but helpful-- to the interesting questions:

How much is our sister planet really like Earth?

What chance is there of finding life on Venus via robot landers?

And, ultimately, would there be any point in sending a manned spacecraft to Venus in the future?

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