Celestial navigation works in the daytime. Star tracking was part of the SR-71 G&C system. The stellar inertial platform was aligned preflight with the aircraft

Celestial navigation works in the daytime. Star tracking was part of the SR-71 G&C system. The stellar inertial platform was aligned preflight with the aircraft at rest. Day or night made no matter. It had many initialization modes, at least one of which required tracking two stars within 5 minutes. It's alluded to at [1]. [1] https://www.sr-71.org/blackbird/manual/4/4-40.php https://www.sr-71.org/blackbird/manual/4/4-40.php