To travel from one planet to the other, the so-called « Hohmann » trajectory is the best in terms of mass transported, energy expended, and mechanical and thermal stresses at departure and arrival. However, traversing a Hohmann orbit requires 8 to 9 months. This is too long on account of human factors and, above all, radiation exposure. Reducing the duration necessitates increased propellant consumption, and they would have to be produced on Mars.