What is meant by a Mars “launch window”?
Due to the trajectories ships must follow when going from Earth to Mars, certain relative positions of the two planets allow for maximum speed with minimum propulsion costs. Whenever such a set of relative positions occurs — approximately once every 26 months — a “window” of opportunity opens for a “launch” to Mars. The most recent window was in August of 2005; the next one will open in October of 2007.
