Avco study of 1965 for an Advanced Mariner spacecraft on flyby/lander missions to Mars in 1969-1971 using an Atlas-Centaur with the Centaur burning 30% Flox. Not continued with after the use of fluorine in the Centaur upper stage was cancelled. Instead NASA flew the Atlas-Centaur Mariner Mars flyby missions in 1969, the Mariner Mars orbiter missions in 1971, and finally the Titan 3E-boosted Viking orbiter/landers in 1975.