Word: touchdownes
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...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...
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...
...chances of a successful landing at 70%. Unlike the Apollo lunar module, which could be maneuvered out of harm's way by the astronaut pilot as it neared the moon's surface, the unmanned Viking lander must descend along a preprogrammed path all the way to its touchdown. If it encounters a large boulder, a deep crevice, too steep a slope or high winds upon landing, the craft could topple over and be forever silenced. It might conceivably even sink, antennas and all, into soft ground or a deep layer of dust...
...rocket fuel is also hydrocarbon-free to avoid confusing Viking's life-seeking instruments. When the first Viking foot pad touches Martian soil, it will trip a sensor that shuts off the engines. Eighteen minutes later controllers will know, by signals sent from the lander, if a successful touchdown has been made...
Viking will not wait for any congratulatory messages from Pasadena. Within seconds after touchdown, with almost unseemly haste, it will automatically point a camera down and take a picture of one of its foot pads and the surrounding soil. Scientists programmed this quick shot so that they could at the very least learn about grain sizes, erosion and other surface conditions near Viking's feet in the event that some catastrophe befalls the craft soon after the landing. Six minutes later, like a wary human set down on alien soil, Viking will look cautiously up from its foot...