Starting in 1960, NASA began working on a series of unmanned probes to Mars (and Venus) that was named the Voyager Program. This program (not to be confused with Voyager 1 and Voyager 2, which were sent toward the outer planets) was planned to set the stage for manned landings on Mars in the 1980s.
Originally NASA had proposed a direct lander using a variant of the Apollo Command Module launched atop a Saturn 1B rocket with a Centaur upper stage. With the discovery by Mariner 4 in 1965 that Mars had only a tenuous atmosphere, the mission was changed to have both an orbiter and lander. The orbiters would have been a modified Mariner probe identical to that employed for Mariner 8 and Mariner 9, while the landers were to be modified Surveyor moon probes that landed through the use of aeroshells and a combination parachute/retro-rocket landing systems.
Politics involving the use of specific boosters played a role in the unravelling the program. As mentioned above, Voyager was to be launched originally on a Saturn 1B-Centaur combination. In mid-October 1965, NASA announced that development of the Saturn 1B-Centaur would be terminated, with Voyager being launched on a Saturn V booster instead. The Titan IIIC was looked at as an alternative booster, but was determined to be too weak to carry the payload weight.
And yet, the Saturn V was too powerful a rocket for just one Voyager mission. JPL, which had been managing the program since the beginning, had operated under the assumption that it would launch a fly-by test mission in 1969 and two complete missions in 1971 and 1973. The use of a Saturn V booster would mean that the two missions would have to be launched together on the same rocket. Moreover, the program would become too costly because the increased payload capability of the Saturn V booster would "escalate the cost of the spacecraft," and it would be too big a technological leap over the Mariners that were then being planned and launched.
On December 22, 1965, JPL was notified that there would be no 1971 mission; the earliest Voyager would now fly would be 1973. According to this plan, both spacecraft would orbit Mars and release large landing capsules that would search for evidence of Martian life. Work on the Voyager spacecraft would "go on a low back burner basis for the next year and a half to two years before [it was picked] up again." JPL would continue design work on landing capsules with support from Langley and Ames, but the next phase of the procurement cycle would be delayed "for some time."
In 1968, funding was cut for the Voyager Mars Program (along with the larger Apollo Applications Program, of which the Voyager Mars Program was only a part). $150 million had been requested in the 1967 budget to begin hardware development for Voyager. However, only $10 million was allocated, largely because the Apollo and Surveyor programs were reaching critical periods in their maturation, which left the planetary mission budgets taking the largest cuts. In essence, there was not enough money for both the moon and the planets. In 1971, the mission was cancelled completely, primarily on the grounds that launching both probes on the same rocket was both expensive and risky.
Despite the cancellation, the trials and tribulations of the Voyager Mars Program laid the foundation for the very successful Viking Program of the 1970s.
The above diagram shows the proposed Voyager lander as of September 1966. The lander's design was quite similar to that of the Viking landers, which would reach Mars in 1976. Similar elements included the tripod landing gear, large direct-link high-gain antenna, smaller relay antenna, and radioisotope thermoelectric generators. The 1966 design already had a boom soil sampler and a television camera, but the scientific experiments would need more definition for a biological mission. The plan across the legs of the Voyager lander was nearly twice that of the Viking; likewise, the proposed weight was about twice that of Viking.