Three Imperial stormtroopers discuss the destruction of the Death Star on the first anniversary of its exploding:
Of course Palpatine must have known! The logic is inescapable. Why else would Darth Vader have been in his Tie fighter and not in the Death Star when Luke Skywalker blew it to kingdom come? Personally, I always thought it was because he was needed as the villain for the next couple of movies and so he had to escape, but that’s just me.