The Viking Program: The History and Legacy of NASA's First Missions to Mars

Several years before Mariner 9's successful orbiting mission, NASA had begun designing missions for unmanned landings on Mars that would use a spacecraft consisting of an orbiter module and a landing module. The design of the modular spacecraft came from NASA's successful use of a similar spacecraft delivery system for the Apollo program's manned missions to the Moon.

The Viking 1 landing on Mars had originally been scheduled to coincide with the nation's bicentennial on July 4, 1976, but th...