Astro-Naughts Defying Gravity Sundays at 10 PM, ABC “Threshold” Written by Sheri Elwood Directed by Peter Howitt Defying Gravity wants to be a hipper, updated version of Star Trek, but it’s more like Lost in space right now. There’s the same sense of isolation countered with innumerable, vivid flashbacks, the same menace lurking just out of sight, the sense that the characters have less freedom of choice than they appear to. I get it that this is a scripted show modeled, like Lost, on the idea of a reality show–people are dumped into a hostile, confined environment and told to survive. But the romance…