SR71 used a pre-GPS navigation system via stars even in daylight https://theaviationgeekclub.com/the-sr-71-blackbird-astro-nav-system-aka-r2-d2-worked-by-track

SR71 used a pre-GPS navigation system via stars even in daylight https://theaviationgeekclub.com/the-sr-71-blackbird-astro-nav-system-aka-r2-d2-worked-by-tracking-the-stars-and-was-so-powerful-that-it-could-see-the-stars-even-in-daylight/ https://theaviationgeekclub.com/the-sr-71-blackbird-astro-na... Mounted behind the SR-71 RSO’s cockpit, this unit (that was affectionately dubbed “R2-D2” after the Star Wars movie came out in 1977), computed navigational fixes using stars sighted through the lens in the top of the unit. These fixes were used to update the inertial navigation system and provided course guidance with an accuracy of at least 90 meters (300 feet). Some current aircraft and missile systems use improved versions as a backup to GPS. HN discussion: https://news.ycombinator.com/item?id=37651171 https://news.ycombinator.com/item?id=37651171