Don't have all the answers, but last night, on the webcast, they were explaining that the spacecraft uses the stars for navigation [1].
In addition, instead of wasting valuable power for radio transmission, they send a simple tone back to Earth [2]. With that, they can determine if various events were successful (tones are sent at specific event times), also calculate the changes in speed/rotation using doppler shifts from the "tones" [3] (validating the engine fired, current spin, etc)