Am I right in thinking it didn't matter which star it locked onto, and it didn't need to know which star it was? Would it be a problem if it locked onto another celestial body (e.g. Venus)?
The system could also use planets or even the sun for navigation. A special filter was used with the sun to avoid burning out the photomultiplier tube.
https://theaviationgeekclub.com/the-sr-71-blackbird-astro-na...