Space: RENDEZVOUS WITH THE RED PLANET

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FOR five months the little spacecraft sped through the interplanetary void.

Last week, on the 157th day of an arcing, 242-million-mile journey across the solar system Mariner 6 reached its destination. In the closest approach to Mars ever achieved by a man-made object, the U.S. spacecraft flew within 2,130 miles of earth's planetary neighbor.

On command from its computer, Mariner 6's electronic gear poured out an endless stream of data from the red planet—information about the density and composition of its atmosphere and its varying surface temperatures. On board the ungainly, 850-lb. ship, whose four solar panels gave it the look of a stubby windmill, tiny transmitters also sent back to earth, some 60 million miles away, the best close-up portrait man has ever had of Mars. At week's end, an identical twin named Mariner 7 moved into position for similar electronic observations. Mariner 6 aimed its close-up cameras on Martian equatorial regions, Mariner 7 at the planet's south polar area. Together they were programmed to photograph about 20% of the Martian surface.

Canals and Craters

Despite ingenious techniques of optical and radio telescopy, astronomers have piled up more questions about Mars than answers. What is the true nature of those strange seasonal dark-enings? Are the white polar caps composed of frozen water or, as many astronomers believe, dry ice (frozen carbon dioxide)? Do those long controversial "canals" really exist, or are they optical illusions? The 1965 flight of Mariner 4 showed that Mars is pocked by moonlike craters, apparently as a result of meteor bombardment. But the unmanned probe did not determine whether Mars can support anything remotely like earthly life.

Seeking to answer that age-old puzzle, scientists from Caltech's Jet Propulsion Laboratory at Pasadena crammed Mariners 6 and 7 with vastly improved electronic gear, ranging from tape recorders to miniature computers to extraordinarily sensitive infra-red and ultraviolet measuring equipment. The total cost of the Mariners and their launch vehicles: $148 million.

Though Mariner 6 needed only one mid-course correction throughout its long journey, and Mariner 7 was almost on target, the flights were not completely trouble-free. Last week one of Mariner 6's infra-red spectrometers balked just as it was supposed to search out the gases and vapors in the Martian atmosphere. JPL technicians explained that the spectrometer, which should be cooled to below — 400° F. to operate efficiently, refused to chill at all. Mariner 7 caused even greater concern at Mission Control when it went off the air entirely for seven hours. Apparently struck by a tiny meteoroid, the spacecraft lost its fix on the star Canopus and its directional antenna spun away from earth. A new roll-and-search command went up from Pasadena. Mariner 7 obeyed, and though performing at less than capacity, its radio functioned again.