The Starlight Commune

A group of retired professors from University of Hawaii discover a spherical astrolabe in an attic of a 19th century mansion on Molokai. It had been converted from a device for maritime navigation into a device for navigation through time. Accompanying the astrolabe was a 500-year-old book describing how the astrolabe was converted and what the result was. The professors decided to acquire more of the astrolabes, convert them per the book's instructions, and attempt to travel back to 15th century Mogadishu, Somalia. Trouble was, Chinese Admiral Xheng He's "Treasure Fleet" was in port, and several of the sailors decided to attempt to kidnap the professors and put them to work on the ships.
All the professors made it back to the future except one. Horacio Fuente was stranded. He married, raised a daughter, and tasked her with handing the spherical astrolabe to the Great Admiral, Vasco da Gama. But what if the Great Admiral discovers the true function of the device? How will she edit her dad's memoir to describe the astrolabe as nothing more than an ancient marine navigation device? Will her dad's wannabe time-traveling companions find the astrolabe in the future?