Astronauts and scientists will discuss everything from extraterrestrial life to passenger flights into outer space at a public meeting this week on space travel to Mars. The experts are gathering on Georgia Tech’s campus to tell a presidential commission about the goal of returning astronauts to the moon and flying from there to Mars. “It’s doable, but it will be a challenge,” said Georgia Tech professor Robert Braun, who has worked with NASA on previous Mars missions. “What we would like to do is use the moon as a science lab basically to prove that humans can live and work on another planet.” From there, humans could travel on to Mars.