Viking 1 made the first truly successful landing on Mars on 20 July 1976 and sent back the first pictures from the surface. Its lander worked for more than six years, until a faulty command from Earth cut the link in November 1982.
Why they were built
Viking was a pair of complex deep-space probes designed to reach Mars and look for evidence of life. Each spacecraft had two parts: an orbiter of 2,339 kg and a lander of 978 kg. The orbiters photographed the planet and relayed data; the landers carried cameras, a seismometer, a weather station, an X-ray fluorescence spectrometer, a gas chromatograph mass spectrometer and a biology laboratory fed by a robot arm.
Swapped before launch
Before launch, the batteries of the spacecraft meant to fly first were discharged, so NASA swapped it for the second one, which launched as Viking 1 on 20 August 1975. After three course corrections it entered Mars orbit on 19 June 1976.
Landing on the Golden Plain
Orbiter photos showed the planned site in Chryse was rougher than expected, so the lander was retargeted to the western slopes of Chryse Planitia, the Golden Plain. It separated at 08:32 UT on 20 July 1976, sampled the air on the way down, and set down at 11:53:06 UT at 22.483° N, 47.94° W, about 28 km from its target.
The Soviet Mars 3 lander had made a survivable landing in 1971, but contact was lost seconds after touchdown, so Viking 1's was the first truly successful landing.
Looking for life
The lander photographed its surroundings in three colours and took a 300-degree panorama of gently rolling plains. It measured temperatures from −86 °C before dawn to −33 °C in the afternoon. Its seismometer did not work.
On 28 July 1976 the robot arm scooped the first soil samples into the biology laboratory. The combined results from four samples could have been read as a weak positive sign of life, but the gas chromatograph found no organic compounds, a negative result.
Six years on Mars
The primary mission ended in November 1976, followed by extended and continuation missions. The lander kept sending daily, then weekly, weather reports. In January 1982 it was renamed the Thomas Mutch Memorial Station, after the leader of the Viking imaging team.
On 11 November 1982 a faulty command sent from Earth interrupted communications, and attempts to regain contact failed. Together the two Viking landers returned 4,500 photos of their landing sites, and the orbiters 52,663 images of Mars.
