Mission Type: Lander, Orbiter
Launch Vehicle: Titan IIIE-Centaur (TC-3 / Titan no. E-3 / Centaur no. D-1T)
Launch Site: Cape Canaveral, Fla., USA
NASA Center: Jet Propulsion Laboratory, Langley Research Center
Spacecraft Mass: 3,527 kg
Spacecraft Instruments:
Orbiter:
1) imaging system
2) atmospheric water detector
3) infrared thermal mapper
Lander:
1) imaging system
2) gas chromatograph mass spectrometer
3) seismometer
4) x-ray fluorescence
5) biological laboratory
6) weather instrument package (temperature, pressure, wind velocity)
7) remote sampler arm
Aeroshell:
1) retarding potential analyzer
2) upper-atmosphere mass spectrometer
References:
Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, by Asif A. Siddiqi, NASA Monographs in Aerospace History No. 24

NSSDC Master Catalog, http://nssdc.gsfc.nasa.gov/nmc/

Viking-A was scheduled to launch before Viking-B, but had to launch second due to a problem with its batteries that had to be repaired.

After a successful launch and a midcourse correction on 19 September 1975, Viking 2 entered orbit around Mars on 7 August 1976, nearly a year after launch.

As with Viking 1, photographs of the original landing site indicated rough terrain, prompting mission planners to select a different site at Utopia Planitia near the edge of the polar ice cap where water was located, that is, where there was a better chance of finding signs of life.

The lander separated from the orbiter without incident on 3 September 1976 and, after atmospheric entry, landed safely at 22:37:50 UT about 6,460 kilometers from the Viking 1 landing site. Touchdown coordinates were 47.968° north latitude and 225.71° west longitude

Photographs of the area showed a rockier, flatter site than that of Viking 1. The lander was in fact tilted 8.5° to the west. The biology experiments with scooped-up soil produced similar results to that of its twin -- inconclusive on the question of whether life exists or ever has existed on the surface of Mars. Scientists believed that Martian soil contained reactants created by ultraviolet bombardment of the soil that could produce characteristics of organisms living in Earth soil.

The orbiter continued its successful imaging mission, approaching as close as 28 km to the Martian moon Deimos in May 1977. A series of leaks prompted the termination of orbiter 2 operations on 24 July 1978, while lander 2 continued to transmit data until 12 April 1980. In total, the two orbiters returned 51,539 images of Mars at 300 meters resolution, that is, about 97 percent of the surface. The landers returned 4,500 photos of the two landing sites.