Tonight’s PBS lineup is devoting all its space to outer space. First up, at 8 pm. ET, is A Year in Space, about astronaut Scott Kelly, who is just completing a year in space – as compared to his twin brother, Mark, also an astronaut, who has stayed home on Earth. And scientists do plan to compare the twins once Scott gets back on terra firma, because that’s the entire point of this year-long experiment. It also sounds like the first act of a ready-made science-fiction thriller,