The electromechanical angle computer inside the B-52 bomber's star tracker

Before GPS, the B-52 bomber used an automated celestial navigation system called the Astro Compass. At its core was the Angle Computer, an electromechanical analog computer that physically modeled the celestial sphere to solve the navigational triangle — converting star coordinates from a global reference frame into local azimuth and altitude values. The device used a half-sphere mechanism with a movable star pointer driven by inputs for declination, local hour angle, and latitude, outputting azimuth and altitude via synchro transmitters. The post explains celestial navigation concepts including the celestial sphere, sidereal hour angle, declination, and the line-of-position technique, while detailing why digital computers were rejected in favor of this mechanical approach in the early 1960s.