[EricRobodox]

Mars every two years. Thats why there are launch windows. But yes, planet allignment is*most always*, and thats an assumption, to be in the proposal. Thats why they are proposed so early, so they can hit it. Keep in mind ATLO (Assemble, Test, and Launch Operations), which is when they assemble the flight hardware, takes place about a year or two before launch (at least it is for MSL), compared to the entire mission being started sometimes 10 years before launch.