In 1956 Gaetano Crocco proposed trajectories for a Mars flyby mission that would require half the energy, one third the time, and only a single rocket burn as opposed to the traditional Hohmann Mars expedition scenario. No specific spacecraft design was described, but the mission profile was used by the Soviets and Americans in their early manned spacecraft designs.
Crocco, an Italian astronomer, proposed a single-impulse Mars flyby on a one-year orbital trajectory. However in order to maintain the correct solar orbit for a free return to earth, it was necessary to get no closer to Mars than 1,290,000 km to Mars during the flyby. However Crocco found that it a Venus flyby was included in the mission plan, a closer approach to Mars was possible. This led to proposal for an Earth-Mars-Venus-Earth profile with launch in June 1971.