On Mars: Exploration of the Red Planet. 1958-1978

[421] Viking was a success, both as a flight project and as a scientific investigation. Excellent hardware performance was the key to a fruitful mission. Project specifications called for a return of scientific data from the landers for a minimum of 90 days; hut by the end of the primary mission on 15 November 1976, at solar conjunction, Viking lander 1 had been operating on the surface for 128 days, Viking lander 2 for 73 days. After a month-long rest while Mars disappeared from Earth's view as the planet swung behind the sun, the landers were awakened in mid-December 1976 for the extended mission, which lasted until 1 April 1978. The extended mission gave Viking scientists time to collect additional data on nearly every aspect of Mars science for which the landers had been programmed.1
April and May 1978 were months of transition for the Viking project. Under NASA management directives, the project was transferred to the Jet Propulsion Laboratory by the Viking staff at Langley Research Center. Old Viking hands, like G. Calvin Broome, project manager and mission director for the extended mission, left the project, and personnel from JPL took their places. Kermit Watkins, recognized for his role in preparing the Viking orbiter for flight, became project manager for what was called the continuation mission. Viking project scientists Gerald Soffen, who had accepted a new position at NASA Headquarters, was replaced by Conway Snyder.
Original plans had called for terminating the Viking mission after completion of the extended phase, but the spacecraft were functioning so satisfactorily in the spring of 1977 that the agency reconsidered the request of Viking science teams for an extension of the mission's activities. A continuation mission also received the strong endorsement of the Science Steering Group at its June 1977 meeting, but the major problem was money. Mission managers would have to reduce expenditures to a level that would continue operations without any additional funds in fiscal 1978. Once again, everyone tightened fiscal belts, and the project moved forward. 2
Hardware problems on the Viking spacecraft began in the fall of 1977. In September, the second traveling-wave-tube amplifier on Viking lander 2 failed, and without this amplifier unit it could not communicate with Earth through the orbiter. Then a gas leak developed in the attitude control system of Viking orbiter 2, which required disabling half the control system to prevent further propel ant loss. In February 1978, a more serious leak developed, losing about 22 percent of the remaining gas. As [422] a third leak in March further depleted the supply. Later that month, the flight controllers placed orbiter 2 in a roll-drift to prevent any further problems of this sort. Some atmospheric water observations were made by orbiter 2 in June and July, 25 July the spacecraft began to drift out of alignment with the sun, and no propellant was left to correct its attitude. At 6:01 a.m. UMT on 25 July 1978 (11:01 p.m. PDT, 24 July), orbiter 2 ceased operating during orbit 706-1049.5 days after launch from Earth. 3
Lander 2 could communicate with Earth only via orbiter 1, while lander 1 could make direct contact. According to the continuation mission team, with these capabilities the landers could continue responding until December 1978, the start of another solar conjunction. But the scientists wanted to squeeze still more from the hardware. Mike Carr and his colleagues on the orbiter imaging team, the most vocal advocates of continuing the mission, wanted to obtain more high-resolution photographs of potential landing sites for the next Mars mission. Remembering just how harrowing the site selection and certification process had been for Viking, they argued that they needed to get as many images of the surface as the hardware would permit. In addition, they wanted to study Martian weather and atmosphere closely from January to April 1979, because this season would be similar to the one in which they had observed dust storms during 1977. 4
Two serious limitations affected extending Viking any further than December 1978. Funds, of course, were critical, as they had always been, but also the communications loads imposed on the Deep Space Network by the Pioneer-Venus and Voyager-Jupiter missions meant that Viking could have only a limited amount of time on the air to transmit scientific information from Mars to Earth. The ability of JPL's mission control center and its Deep Space Network to squeeze the Viking transmissions into the schedule became one of the overriding factors in the continued life of Viking. In April 1979, Conway Snyder, in a memorandum to all the Viking scientists, projected that operations would come to an end in July of that year. He noted that the mission had provided the team "with a long and interesting road," and he was pleased that they had all been able to travel it together. But he also suggested that the mission might "afford us a few more surprises yet before the end." 5
The end did not come in 1979. Viking lander 2 was shut down on 12 April 1980 after 1316.1 days on the surface. Orbiter 1 was silenced by a command from JPL on 7 August 1980, because it, too, was about out fuel. Three of the four spacecraft were silent, but lander 1 remained active and would likely continue its transmissions to Earth for some years. Each week, the team at JPL would query the spacecraft for weather information and periodically ask for surface pictures so the specialists could monitor the Martian landscape in front of the lander for any changes. 6
Statistical evidence of success includes 51 539 orbital images of the Red Planet and more than 4500 images from the landers. About 97 percent of the [423] planet was photographed at a resolution of about 300 meters, while 2 percent of the planet was seen at a resolution of 25 meters or better. Together, the two landers returned more than 3 million weather reports by August 1980. Total orbital infrared observations exceeded 100 million. For generations, discussions about Mars had included such traditional topics as canals, waves of darkening, and blue clearings. But with NASA's explorations of Earth's near neighbor, man had at his disposal "a plethora of hard data about the large variety of geological features on the planet, about the composition of the surface, the atmosphere, and the polar caps, and about many aspects of Martian meteorology, including temperatures, pressures, tides, dust storms, and the abundance and transport of water vapor." Scientists, mission planners, and hardware specialists expected to spend much of the 1980s analyzing this information and preparing for another mission to Mars in the 1990s that would yield "as great a quantum jump in our understanding of this complex and fascinating planet" as did Mariner and Viking. 7