Viking 1 marks 50 years since NASA’s first Mars landing

NASA’s Viking 1 lander touched down on Mars on July 20, 1976, giving the agency its first successful landing on the planet 50 years ago. A current inflation-adjusted cost was not disclosed, but the Viking program ranks among NASA’s most expensive robotic missions when adjusted for inflation, and it established much of the operating model later Mars landers would follow.

Viking 1 was one of two Viking spacecraft sent to Mars. It launched on Aug. 20, 1975, and reached Mars orbit on June 19, 1976, before its lander separated for descent to Chryse Planitia. NASA initially aimed for a July 4 landing to align with the U.S. Bicentennial, but mission managers delayed the attempt after reviewing the proposed landing area and selected a safer site. The new date, July 20, also marked the seventh anniversary of Apollo 11’s lunar landing.

The spacecraft architecture paired an orbiter with a lander. The orbiter later served as a communications relay and was eventually shut down on Aug. 7 after its attitude-control gas was depleted. The lander became the longest-lived part of the Viking program, lasting far beyond its planned 90-day prime mission.

A durable lander with a cautious descent system

Viking 1 entered the Martian atmosphere behind an ablative heat shield, then used parachutes to slow its descent. Retro-rockets fired just above the ground, allowing the three-legged spacecraft to reach the surface safely.

Once on Mars, the lander used a robotic arm to collect and analyze soil, including experiments in an onboard biological laboratory. NASA’s position is that the Viking biology experiments did not produce definitive evidence of life. The agency has said the instruments found “unexpected and enigmatic chemical activity” in Martian soil, but no clear proof of living microorganisms near the landing sites.

That conclusion has not ended debate. Some researchers have continued to argue that the Viking data may have contained signs of biological activity, though NASA’s official interpretation remains more cautious.

Viking 1 also carried cameras that returned surface imagery from Mars, as well as antennas that allowed communication through the orbiter and directly with Earth. Its power system was a Radioisotope Thermoelectric Generator, using heat from plutonium-238 decay to generate electricity. That RTG was central to the mission’s long life, keeping the lander operating until its final transmission on Nov. 11, 1982.

The mission ended with a software mistake

Viking 1 might have operated longer if not for an error during efforts to extend the life of its batteries. By January 1982, three of the lander’s four nickel-cadmium batteries were showing wear. Engineers first tried deep-discharge conditioning, but the improvement was limited and temporary.

A later plan changed the battery-charging sequence so that the lander would charge against a known voltage rather than discharge for a set period. Engineers expected the reduced charging frequency and duration to preserve battery life. On Nov. 19, 1982, the revised sequence was uploaded. The expected signal did not arrive.

NASA declared a spacecraft emergency on Nov. 20. The new sequence had been written into memory locations used for the lander’s high-gain antenna pointing parameters, leaving the antenna no longer aimed at Earth. Attempts to reestablish contact continued for four months, but failed. The Viking Lander Monitor Mission ended in March 1983.

Viking 1 was not the first spacecraft to soft-land on Mars. The Soviet Union’s Mars 3 achieved that in 1971, but transmitted for only about 20 seconds after touchdown. Viking 1’s years of operations, imaging and surface science gave NASA a durable Mars platform seven years after the first crewed lunar landing.

This story draws on original reporting from The Register.