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.
Mars Direct
Upon reaching Mars, the upper stage would be jettisoned, with the Habitat Unit aerobraking into Mars orbit before soft-landing in proximity to the "Earth Return Vehicle". Precise landing would be supported by a radar beacon started by the first lander. Once on Mars, the crew would spend 18 months on the surface, carrying out a range of scientific research, aided by a small rover vehicle carried aboard their Mars Habitat Unit, and powered by the methane produced by the Earth Return Vehicle.