Viking 1
Viking 1 was the first of two spacecraft (along with "Viking 2") sent to Mars as part of NASA's Viking program. On July 20, 1976, it became the second spacecraft to soft-land on Mars, and the first soft lander to successfully perform its mission. (The first spacecraft to soft-land on Mars was the Soviet Union's Mars 3 on December 2, 1971, which stopped transmitting after 14.5 seconds.) "Viking 1" held the record for the longest Mars surface mission of days (over 6¼ years) or Martian solar days, until that record was broken by "Opportunity" on May 19, 2010.
List of unmanned NASA missions
The Viking program consisted of a pair of American space probes sent to Mars—Viking 1 and Viking 2. Each vehicle was composed of two main parts, an orbiter designed to photograph the surface of Mars from orbit, and a lander designed to study the planet from the surface. The orbiters also served as communication relays for the landers once they touched down. Viking 1 was launched on August 20, 1975, and the second craft, Viking 2, was launched on September 9, 1975, both riding atop Titan III-E rockets with Centaur upper stages. By discovering many geological forms that are typically formed from large amounts of water, the Viking program caused a revolution in scientific ideas about water on Mars.