Another Delay for Viking

"It may be that we don't understand Mars at all, or that all the areas of Mars are likely to be bad. But we shall find a place to land, I think ..."

If Viking Project Manager James S. Martin Jr. sounded plaintive last week, there was good reason. After studying photographs and radar scans of Viking's first alternative landing site on Mars' Chryse Planitia, the Plains of Chryse, he scrubbed a landing scheduled for July 17 and started studying a new site for a touchdown that could not take place until next week at the earliest. The postponement, following last month's decision to cancel Viking's scheduled July 4 landing, raised concern among scientists at the Jet Propulsion Laboratory's Mission Control Center; it further reduced the time left for Viking 1 to carry out its tasks before Viking 2 arrives.

Close Look. Earlier in the week scientists had been reasonably confident that the first alternative site, about 500 miles northwest of the original touchdown area, would prove safe for landing. Pictures from Viking's camera --which can "see" details down to the size of a football field each time the orbiter swoops to within 1,000 miles of Chryse--showed what seemed to be a relatively smooth area between two heavily cratered strips. It appeared to be less hazardous than the original site, which is crisscrossed by crevasses and steep escarpments that could swallow the lander or cause it to turn over.

Follow-up examination by the giant radar antenna at Arecibo, Puerto Rico, quickly dispelled that notion. The radar data indicated that the landscape was littered with boulders ranging from 3 ft. to 15 ft. in diameter. Despite pressure from biologists anxious to begin Viking's life-seeking experiments, Martin decided that the risks at the second site were too great for the 1,270-lb., three-legged lander; to lose it on landing would leave the billion-dollar Viking mission totally dependent on Viking 2.

After ruling this site out, the scientists turned to a third site some 900 miles west-northwest of the original target area. Preliminary radar data suggested that the new landing zone is smoother than the other two, but Viking scientists wanted detailed photographs of the area before making a final decision. To get them, controllers at J.P.L. last week "tweaked" Viking's thrusters to bring the periapsis (low point) of its orbit directly over the new landing site. If the photographs confirm that Chryse Planitia is relatively smooth, Viking will land on July 20.

In making his decisions, Martin is confronted by a complex series of deadlines. Some biologists are worried that the "chicken soup"--a nutrient-rich broth that will be used to moisten samples of Martian soil to determine if they contain organisms--will not keep long enough for all of the experiments scheduled. Even more vexing, Viking 2 is scheduled to arrive at Mars and go into orbit on Aug. 7. That will crowd the schedule of the Viking 1 lander, which will not begin to conduct its experiments until eight days after it lands. Each of the experiments requires an eleven-or twelve-day cycle, and if one of the experiments shows some promising results, it will have to be repeated twice more before scientists can state with confidence that there is life on Mars.

The arrival of Viking 2 could also confront scientists with an embarrassment of riches. J.P.L. does not have the communications capacity to operate and control both spacecraft and landers simultaneously. One must wait idly, either in orbit or on the Martian surface, while the other works.

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