In 1976 Viking 2 began orbiting the red planet.
The two Viking Mission Spacecraft, Viking 1 and Viking 2, both comprised Orbiter and Lander craft. Once they arrived close to Mars they began to orbit the planet taking high resolution images of the surface and sending them back to Earth. Once analysed by NASA they were able to determine suitable landing zones and then give the command for the Lander to separate and touchdown on the surface. The Orbiter would remain in orbit taking photos and various measurements such as atmospheric data and infrared thermal images. The Landers became the first United States space craft to land on the surface and they took samples of rock and detected the weather conditions of the planet.
Viking 2 launched on the 9th of September 1975 from Cape Canaveral Air Force Station, Florida (20 days after Viking 1) and after almost a year travelling at speeds exceeding 20,000 km/hour it reached Mars and began its orbital path on the 7th of August 1976. After several weeks orbiting the red planet and sending images back to earth NASA finally decided on a landing location. On the 3rd of September 1976 the Viking 2 Lander separated from the Orbiter and began its descent and landing safely on the same day in an area known as Utopia Planitia (the largest known impact crater in the solar system with the approximate diameter of 3,300km).
The Lander began its mission which included the search for life. Although no evidence of life was found the Lander did find carbon, nitrogen, hydrogen, oxygen and phosphorus which are all the elements required for life as we know it.
The Orbiter continued to take high resolution images of Mars and managed to map the entire surface in great detail.
Both Viking missions were due to end on the 15th of November 1976 but they managed to operate far beyond their original mission objectives. The Viking 2 Orbiter ran out of the gas required for its orbital control and positioning of its solar panels on the 25th of July 1978. Due to this mission control sent a signal for the Orbiter to shutdown Viking Orbiter 2’s transmitter which also ended communications with the Lander. The last data transmission from Viking 2 reached Earth on the 11th of April 1980 and this is considered the end of Viking 2’s mission.
The Viking 1 Orbiter began running out of the same gas in 1978 but the mission control shutdown certain systems to conserve power and so Viking 1 managed to keep transmitting until the 7th of August 1980. The last data transmission from Viking 1 reached Earth on the 11th of November 1982 but mission control attempted to regain transmission for six months finally calling an end to the mission on the 21st of May 1983.