>>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.
>>jjk166+Fg1
But the ICBMs did. They also had star trackers to help them navigate, and they needed more robust maps than just the Sun and Canopus, since they had to be able to fly 24hrs a day, 365 days a year. Different problem space.