In the latter part of the 21st century the people of Earth were just beginning to explore the universe beyond their solar system.  A highly advanced scientific vessel, the Phantom Star, was commissioned for the express purpose of traveling to Earth's nearest neighboring system.  Twenty days into the mission it disappeared.  No wreckage was ever found.  This would have been a major setback to the space program at one time, but need drove humanity to seek out a new way of life among the stars.