What would a birthday party be without cake, music and toasts? Thirty-five years ago today, NASA’s Voyager 1 spacecraft launched on its mission of exploration. It is now the most distant human-made object and the second-longest operating spacecraft. (Voyager 2 is the longest.) NASA’s Jet Propulsion Laboratory, Pasadena, Calif., which manages the Voyager spacecraft, held a celebration Sept. 5.