Carroll: How much is a First Class stamp? codeine phosphate The timing of the mission also presents a challenge. The Tito plan would require that NASA and the private partners adopt the project wholeheartedly and immediately, with little wiggle room. The planetary alignment, which happens only once every 15 years, presents a narrow launch window. The mission would have to begin sometime between Christmas Day 2017 and Jan. 5, 2018 to take advantage of the orbital dynamics of the planets.