NASA begins making detailed plans for a pair of orbiter/lander spacecraft, now named Viking, to be sent to Mars in the mid 1970s (possibly as early as 1973). With more recent Mariner missions having revealed a number of major challenges, including a thin atmosphere which won’t significantly slow a heavy object such as a landing vehicle, mission planners have to consider entirely new methods of reentry (as opposed to the Earthlike atmosphere that was expected as recently as 1964). The twin Viking spacecraft will not lift off until 1975.
