John C. Smith has a master’s in celestial mechanics (the motion of heavenly bodies) and has spent more than twenty years at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., designing missions to explore the planets. He has worked on successful missions to Venus, Earth and Mars and has been part of the Cassini/Huygens mission to Saturn and Titan for 16 years. He is the designer of the four-year “tour” of the Saturn system that began in 2004 and recently contributed to the design of a two-year extended mission through 2010.