On to the Red Planet

For a few days last week, it seemed as if the U.S. and Soviet Russia were racing each other to Mars. No sooner had the U.S. launched Mariner IV from Cape Kennedy than the Russians put up Zond (for Probe) II. Scientists speculated that the Soviets' more powerful rockets might have given the Red spacecraft enough extra push to carry it past Mariner on the 228-day, 325 million-mile voyage to the red planet. But the race was not so much a contest between nations as it was a confrontation with the inexorable geometry of planetary orbits. Both Russia and the U.S. had rushed their spacecraft aloft to get them through the one-month "window" during which Mars is most favorably positioned for an earth-launched rocket.

Whether Zond had enough zip to overtake Mariner was not clear. But the question seemed academic. Even if Zond gets there first, it may not be able to manage its mission; its power supply seems to be failing.

A Little Sticky. Mariner had different difficulties. Just as planned, one of its bright-eyed optical sensors locked on the sun, the craft's prime navigational reference and power source for its solar cells. But when another sensor began searching the heavens for a second reference point--the giant, blue-white star Canopus--Mariner got confused and began looking around in all directions.

First, the star-sighter locked on Alderamin. Then it fixed its gaze on Regulus. Another roll on its axis, and Mariner picked out Naos, then a multistar cluster near Naos. Finally, when Mariner was 360,000 miles from earth, its electronic eye found a star bright enough to send the proper radio report: Mariner had locked on Canopus.

The fix came none too soon. Besides being a guide on the way to Mars, Canopus also served to aim Mariner's directional radio antenna back toward earth, enabling Jet Propulsion Laboratory scientists to calculate the craft's flight path. Knowing that path, the rocketeers were able to plan a correction for Mariner's original course, which would have taken it past the red planet at a distance of 151,000 miles--too far for it to shoot any meaningful television pictures. But shortly before that correction could be made last week, Mariner went into an unexpected roll. JPL had to wait until the craft righted itself before carrying out the "midcourse" maneuver designed to turn Mariner ever so slightly toward Mars. The maneuver was accomplished, and again Mariner found Canopus. How accurate the course correction was, scientists will not know for days.

Many Hazards. But even a successful mid-course correction will not guarantee a successful mission. There are still some 323 million miles to go. The 138,000 parts on board are subject to radiation damage, and to unexplained failure caused by undetected flaws. Only if Mariner survives all such hazards, can the U.S. count on its purple-winged spacecraft taking the first detailed photos of mysterious Mars.

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