At this time, von Braun also worked out preliminary concepts for a human mission to Mars that used the space station as a staging point. His initial plans, published in "The Mars Project" (1952), had envisaged a fleet of 10 spacecraft (each with a mass of 3,720 metric tonnes), three of them uncrewed and each carrying one 200-tonne winged lander in addition to cargo, and nine crew vehicles transporting a total of 70 astronauts. The engineering and astronautical parameters of this gigantic mission were thoroughly calculated. A later project was much more modest, using only one purely orbital cargo ship and one crewed craft. In each case, the expedition would use minimum-energy Hohmann transfer orbits for its trips to Mars and back to Earth.