In ESB, at the end of Hoth's attack, Vader saw the Falcon take off.

He's looking for Luke Skywalker. For him, Luke is on the ship, according to this:

"Our pursuit ships have sighted the Millennium Falcon, my lord. It has entered an asteroid field.” “Asteroids don’t concern me, Admiral,” Vader said as he slowly clenched his fist. “I want that ship, not excuses. How long until you will have Skywalker and the others in the Millennium Falcon?”

(ESB - Novelisation)

Why is he certain that Luke is onboard of the Falcon? He hasn't seen him...

Has he sensed, via the Force, that a Skywalker was onboard?

If so, was it not Luke, but rather Leia?

  • This appears to be an embellishment by the novel as only a shortened version of the dialog is in the film.
    – TheLethalCarrot
    Sep 20, 2019 at 15:54
  • The dupe indicates that Vader didn't sense anything. He merely assumed that Luke was on board.
    – Valorum
    Sep 20, 2019 at 16:08