... Star Atlas . ... stars . ... Kepler completes prime mission, begins extended mission . With the completion of the prime mission, Kepler now has collected enough data to begin finding Earth-sized planets with a one-year orbit around stars similar to the Sun. ... NASA is marking two milestones in the search for planets like Earth: the successful completion of the Kepler Space Telescope's 3.5-year prime mission and the beginning of an extended mission that could last as long as four years. ...