Five-year mission
Memory Beta, the wiki for licensed Star Trek content.
A five-year mission was a standard mission duration for Federation starships in the 23rd century. With bigger, faster and more enhanced vessels, ships could perform exploratory missions farther outside Federation space, and not need to dock at a starbase so often.
Five-year missions were usually conducted by larger Federation starships such as the Constitution class and Excelsior class.
Between 2245 and 2285, the USS Enterprise (NCC-1701) conducted 5 five-year missions, most famously under Captain James T. Kirk between 2265 and 2270.
During his career Robert April commanded four five-year missions, the Enterprise's first was under his command, and prior to that he conducted three missions in command of the USS Tiberius. (EV comic: "Flesh of My Flesh")
