The SR-71 used an Astroinertial Navigation System that used stars to keep the navigation information accurate as the plane flew over long distances. Normally an inertial navigation system degrades in accuracy over time and distance due to small errors building up and something called gyro drift. The NAS-14V2 used a catalog of known stars and a gimballed telescope to identify specific stars (even during a cloudy day) and determine the position of the stars in relation to the aircraft. Using this information the position of the aircraft can be used to revise the inertial navigation system’s data every so often so the accuracy is much better.
And this was required because the SR-71 started flying in 1966, and the first GPS satellite didn’t launch until 1978. The full GPS constellation wasn’t finished until 1990.
The SR-71 used an Astroinertial Navigation System that used stars to keep the navigation information accurate as the plane flew over long distances. Normally an inertial navigation system degrades in accuracy over time and distance due to small errors building up and something called gyro drift. The NAS-14V2 used a catalog of known stars and a gimballed telescope to identify specific stars (even during a cloudy day) and determine the position of the stars in relation to the aircraft. Using this information the position of the aircraft can be used to revise the inertial navigation system’s data every so often so the accuracy is much better.
And this was required because the SR-71 started flying in 1966, and the first GPS satellite didn’t launch until 1978. The full GPS constellation wasn’t finished until 1990.