[31] Mars reappeared from behind the Sun, as viewed from Earth in mid-December 1976. This signaled the start of the so-called extended mission. Communication with all four spacecraft was reestablished. This phase of the mission was planned to continue through May of 1978, perhaps even longer.

The extended mission illustrates the general proposition that once a demanding problem has been solved-albeit with great difficulty-the second time is routine. Examples abound in the annals of exploration, particularly mountaineering. So it is with the extended mission. Complicated sequences of trenching and sample acquisition are carried out without fanfare. Many more pictures have been taken than during the primary mission. Before the Viking mission is completed we will have monitored the environment for almost a complete martian year, or one revolution about the Sun, a total of 687 Earth days. The scientific return is just now being cataloged. It will be years before the analysis is complete. In that sense, the Viking mission is still in its infancy.

Many of the persons who played an instrumental role in the primary mission have now gone. The new team is no less competent, but the excitement inevitably has been replaced by a workaday approach. I return to JPL frequently to examine the most recent collection of pictures, but I feel out of place, like a college graduate who returns to his campus and finds himself among a new generation, perhaps only a few years younger but still a world apart.

I was encouraged by a valued editorial advisor to close with a look toward the future. In fact, the events of the future are blurred. On a personal basis I realize that many of us who worked on Viking will never again be associated with a comparable journey of space exploration, not because we are in any way disenchanted but because it is time to move on to other things. That separation is bittersweet. The memories keep popping up at unexpected moments, and present ventures seem drab by comparison.

As to further unmanned exploration of Mars, preliminary plans exist for a rover mission in the late 1980s. A tractor-drive vehicle, slightly larger than Viking, could roam up to several hundred kilometers, sampling geological and biological environments inaccessible to Viking. This might be followed by an unmanned sample-return mission in the early 1990s, providing the first opportunity to analyze martian surface materials in great detail. But these missions exist only on paper. Neither has been approved and their large cost necessarily makes them vulnerable.

Even if the immediate future is uncertain, I have no doubts about the distant years. Some day man will roam the surface of Mars. Those wonderful Viking machines will be crated up, returned to Earth, and placed in a museum. Children in generations to come will stand before them and struggle to imagine the way it was on that first journey to Mars.

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