(The following information appears in "NASA, The First 25 Years: 1958-1983," NASA, U.S. Government Printing Office,Washington, D.C., 1983, p. 99.)
Viking was designed to orbit Mars and land and operate on its surface. Two identical spacecraft consisting of an orbiter carrying a sterilized lander were launched in 1975 from Cape Canaveral and cruised through space for almost a year.
August 20, 1975
Began orbiting Mars, June 19,1976
Landed July 20
September 9, 1975
Began orbiting Mars, August 7,1976
Landed September 3
Viking's primary mission ended November 1 5, 1976,1 1 days before Mars passed behind the Sun. After conjunction in mid-December 1976, telemetry and command communications were reestablished, and the extended mission operations began. Orbiter 1 continued working until the summer of 1980. Orbiter 2 ended its mission in July 1978, and Lander 2 in April 1980. Lander 1 was the longest-lived; it operated until November 1982.
With but one exception, the science instruments acquired more data than was expected: (1) Biology experiments analyzed Martian soil and discovered chemical activity, but no evidence of life, (2) measurements were made of some physical and magnetic properties of the soil and the composition and physical properties of the upper atmosphere; (3) there was nearly continuous monitoring of weather at the landing sites where surface temperatures ranged from 29°C ( - 20°F) in the afternoon to -84°C (-120°F) at night; (4) there were dust storms, but wind velocities were low; (5) the north polar ice cap is composed of water ice.
The first color photographs showed the Red Planet truly red, the color due to oxidized iron. The total number of pictures exceeded 4,500 from the landers and 52,000 from the orbiters. The landers provided the first close-up look at the surface, monitored variations of atmospheric opacity over a full Martian year, and determined the mean size of the aerosols. The orbiter cameras observed new terrain and provided clearer detail on known features, including some color and stereo observations, and mapped about 97 percent of the surface.