Crocco's Multiplanetary Trajectory

[1] Even though Walter Hohmann had already calculated the most energy-efficient trajectory between two similar circular orbits (the Hohmann transfer orbit) at the beginning of the century,[2] an Earth-Mars-Earth round trip utilizing this flight path would have made it a necessity to remain on the surface of Mars for a duration of 425 days, waiting for the planets to align and the next launch window to open, in addition to 259 days for both the journey to Mars and the return to Earth.

[3] Crocco searched for an orbit with the following properties: With proper selection of a certain launch window, this would also have allowed the spacecraft to return one year after departure.

Crocco realized that the flight trajectory may be disrupted by the gravitational fields of Mars and Venus, delaying or ultimately preventing return to Earth.

Crocco was well aware of the planet's gravitational effects, but his mission profile is neither using them to accelerate nor decelerate, instead limiting itself to utilizing them for trajectory stabilizations.

[6] Still, it is mistakenly widely assumed that G. A. Crocco would have been the inventor of the gravity assist, which was first presented in 1961 by the American mathematician Michael Minovitch as a method[7] to allow for the exploration of the outer planets which had been deemed nearly impossible beforehand.

A simplified Depiction of Crocco's Multiplanetary Trajectory. The black Ellipse depicts the trajectory, while the blue, red and green curves represent the Orbits of Earth, Mars and Venus respectively. The positions of the planets are marked on the date of Departure from Earth and at the date the spacecraft passes at the shortest distance to the respective planet.