>>Out_of+R4
Not in any detail, but as a hand-waving explanation it keeps tracks of the Sun and the star Canopus, so by two fixed reference points you can have a known orientation.
>>potami+d01
The Sun is the brightest star and Canopus is the third brightest star (Sirius presumably is not in an appropriate position to be detected), so you don't really need a proper star tracker, you just need a brightness sensor.