ORLANDO, Fla. — A starship without an engine?

It may seem a fantastical notion, but hardly more so than the idea of building a starship of any kind, especially with NASA’s future uncertain at best.

Yet here in Orlando, not far from the launching site of the space program’s most triumphant achievements, the government’s Defense Advanced Research Projects Agency, or Darpa, drew hundreds this month to a symposium on the 100-Year Starship Study, which is devoted to ideas for visiting the stars.

Participants — an eclectic mix of engineers, scientists, science fiction fans, students and dreamers — explored a mix of ideas, including how to organize and finance a century-long project; whether civilization would survive, because an engine to propel a starship could also be used for a weapon to obliterate the planet; and whether people need to go along for the trip. (Alternatively, machines could build humans at the destination, perhaps tweaked to live in non-Earth-like environs.)

“The space program, any space program, needs a dream,” said one participant, Joseph Breeden. “If there are no dreamers, we’ll never get anywhere.”