Comment by throw0101c

The sensor was sensitive enough that it could detect stars during daylight:

* https://theaviationgeekclub.com/the-sr-71-blackbird-astro-na...

* https://www.twz.com/17207/sr-71s-r2-d2-could-be-the-key-to-w...

* https://en.wikipedia.org/wiki/Missile_guidance#Astro-inertia...