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[124-127] Acquisition of soil samples for analysis within the Lander was the single most demanding Viking activity, requiring the integrated contributions of many scientists and engineers. In the course of the mission the surface sampler arm was deployed many times; numerous trenches were dug and many samples were delivered to instruments within the spacecraft. Figures 154 and 155, which show the extended sampler arm on Viking 2 from the vantage point of both cameras, capture the essence of a sampling operation. Figure 156 shows the same region after several trenches have been dug and one rock pushed a short distance. The trenches are visible at the far left and far right. The displaced rock, nicknamed Mr. Badger after a character in Wind in the Willows, is near the middle of the picture. Mr. Badger is seen in its original position in figure 155. We were fortunate that martian surface materials were unconsolidated and relatively easy to shovel. Figures 157 through 161 show the progressive excavation of an area at the Lander 1 site known as Sandy Flats. Over a period of 10 months, more than a dozen individual trenching operations at Sandy Flats were completed. After it had been determined that the upper soil was biologically sterile, some scientists speculated that organisms might exist deeper in the soil where they would be protected from deadly ultraviolet radiation. The thesis was tested by repeatedly digging at the same spot until a hole more than 15 cm in depth was excavated (fig. 161). In one sense this was a sophisticated engineering task, requiring complicated sequences of sampler arm commands. In another sense it was reminiscent of childhood exercises with sand and shovel. At any rate, it was to no avail. Samples yielded negative biological results. Figures 162 through 164 record sampling of a duricrust layer at the Lander 2 site. Figures 162 and 163 are two views of the area before sampling. Because this small exposure of duricrust was nestled between large blocks, engineers were concerned that the sampler arm might be damaged by inadvertently striking one of the boulders. Stereoscopic analysis of picture pairs indicated that the duricrust was accessible, but that the arm would come very close to several potentially disabling obstacles. Our nervousness was dispelled only when we received a picture showing the virtual obliteration of the duricrust patch (fig. 164). In the search for martian organisms it was suggested that material from under rocks might be an attractive environment for organisms (protected from the sterilizing effects of the solar ultraviolet). Figures 165 through 167 show a boulder (nicknamed "Notch Rock") at the Lander 2 site that was successfully nudged to one side. Figure 165 is the "before" picture. Figure 166 shows the sampler arm midway through its pushing operation. Figure 167 shows the completed activity. The rock has been moved approximately 3 cm. A small depression is visible in front of the rock where it had previously been partially buried by surface material. Again, no organisms were found. The decision to push a rock with the relatively fragile sampler arm was preceded by many days of careful analysis and consideration of potential risks. During a long meeting at which we discussed the relative merits of several candidate rocks, a foreign scientist, visiting JPL, sat briefly in the back of the room. Already impressed with the exotic spaceage technology in evidence throughout the laboratory, a puzzled frown crossed his face as he listened to a group voting for a favorite rock. | ||
