Jet Propulsion Laboratory (U.S.). Spacecraft Data Systems Section.

Project Viking was approved by NASA Administrator Thomas O. Paine on December 4, 1968. It followed in the aftermath of the cancellation of the Voyager Project to Mars (the name Voyager was, of course, used for a later planetary mission to the outer planets) earlier that year. Viking was originally to be launched in 1973, and was referred to as "Viking 1973." In January 1970, the launch date was postponed to 1975, the next available Mars launch window, as an alternative to a cancellation of the mission itself.

Project Viking consisted of two orbiters and two landers. The Jet Propulsion Laboratory (JPL) was assigned to design and build the two Viking Orbiters and to conduct mission communications using the Deep Space Network. JPL was also used as the command center for the mission. Overall responsibility for the management of Project Viking was at NASA's Langley Research Center at Hampton, VA. Langley turned management of Project Viking over to JPL towards the end of the mission, in April 1978.

An early milestone in the Viking Project was the preliminary design review (PDR), a formal review held October 19-20, 1971, at the end of the conceptual phase for the design of the orbiter systems. Once the basic soundness of all aspects of the orbiter was approved, the next milestone was the critical design review (CDR) held July 9-10, 1973.

Three Viking Orbiters were built. VO-1 was originally considered solely as a proof-test orbiter. However, in September 1974, VO-3 had its systems tests cancelled. VO-3 was put into storage, and VO-1 was re-designated as a flight unit. It was planned to have a third launch, in 1977, only if both Viking launches were not successful. A VO 75 proof test model was stored at the JPL Edwards Facility until that facility's material disposition at shutdown in 1995.

On August 13, 1975, a week before the planned launch of Viking 1, a faulty control valve on the Viking Orbiter was replaced, and caused a slight delay in the launch. It was decided to remove Viking A from the launcher and replace it with Viking B which could take ten days to accomplish. A delay beyond August 21 would jeopardize a possible Mars landing on July 4, 1976. A July 4 landing was desired, in part to take advantage of the American Bicentennial that day. Viking 1 was launched on time, on August 20, 1975, and arrived in Mars orbit on June 19, 1976. The prime landing site, at Chryse Planitia, was found to be a channeled floor with jagged, irregular edges, and many craters, unsuitable terrain for a safe landing. On June 27, 1976, the decision was made to delay a landing until after July 4. The Viking 1 Lander eventually touched down at another spot on Chryse Planitia on July 20, 1976. Viking 2 was launched in September 1975, and the Viking 2 Lander landed at Utopia Planitia in September 1976.

The Viking 1 orbiter ceased operations on August 17, 1980 after 1485 orbits of Mars due to running out of attitude control gas. The Viking 2 orbiter ceased operations on July 25, 1978, after 706 orbits due to a leak in its propulsion system.

From the description of Project Viking Computer Command Subsystem Document Collection, 1969-1977. (Jet Propulsion Laboratory Library and Archives). WorldCat record id: 733100113