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.
Exploration of Mars
In August 2012, NASA selected "InSight", a $425 million lander mission with a heat flow probe and seismometer, to determine the deep interior structure of Mars. Two flyby CubeSats called MarCO were launched with "InSight" on 5 May 2018 to provide real-time telemetry during the entry and landing of "InSight". The CubeSats separated from the Atlas V booster 1.5 hours after launch and traveled their own trajectories to Mars. "InSight" landed successfully on Mars on 26 November 2018.
Other future mission concepts include polar probes, Martian aircraft and a network of small meteorological stations. Longterm areas of study may include Martian lava tubes, resource utilization, and electronic charge carriers in rocks. Micromissions are another possibility, such as piggybacking a small spacecraft on an Ariane 5 rocket and using a lunar gravity assist to get to Mars.