During Viking operations I was the director of Science Analysis and Mission Planning. Among my duties was the management of the Landing Site Certification activities. When it became clear that we were going to reject the pre-selected site and essentially certify a new landing location from orbit, Jim Martin and the mission director, Tom Young, gave me the responsibility of defining and coordinating the plan for selecting the new site. The guidelines were straightforward, and challenging to say the very least. Our task was to certify and land at a safe site, if at all possible, before the MOI activities of the second Viking began on July 28 or so. The resulting plan kept several possible options open at all times until the final site selection was made. Spacecraft maneuvers were scheduled as often as necessary to make certain that the proper observations were taken in a timely manner. We also organized a vast data analysis activity that included daily assessment of both Earth-based radar data and the wealth of new images and other information being acquired by the Viking orbiter.

I’m certain that I was not the only Viking flight team member who was not able to sleep on the night of July 18. Both the anticipation and the apprehension were palpable in the Viking operations area throughout the day on July 19. Everyone was well aware that the Soviet Union had tried four times to land a spacecraft on Mars. All four had been failures. Many of us had devoted six or more years of our lives to the design, development, and implementation of Viking. We believed that we had done everything possible to maximize the probability of success of the mission. Had we done enough? We were about to find out.

Just before two o’clock in the morning in California on July 20 we received telemetry indicating that the Viking lander had successfully separated from its orbiter. The spacecraft that would land on Mars was now on its own—it was not possible to send the lander any more commands. The lander computer software, which had been tested repeatedly for this critical phase of the mission, would be responsible for both its deorbit maneuver that would put the vehicle on a path to enter the Martian atmosphere, and the entire entry, descent, and landing sequence.

The telemetry indicated that the deorbit maneuver was nearly perfect. We waited together, our hopes riding on a vehicle over a hundred million miles away, for almost three hours as Viking approached its rendezvous with Mars. When the lander reached the aeroshell phase of its atmospheric entry, the data from Mars was processed in real time and displayed on the monitors in the mission operations area. We watched, mesmerized, as each point on the graphic display of the descent fell almost exactly on top of the nominal curve. We listened as Al Hibbs in the pressroom narrated the major events of the descent for the press and the listening world. At eleven minutes after five o’clock in the morning the telemetry indicated that the terminal descent engines had fired. Forty seconds later, we heard the shouts from mission control. "Touchdown! We have touchdown!"