The Blackbird predated inertial navigation and GPS. And it went too fast for LORAN and other conventional aviation nav aids. And at the speeds it traveled, a few tenths of a degree of error in the flight path meant hundreds of miles of error at the point you needed the cameras to roll, at the point at which you were supposed to meet up with the tanker, etc. All very bad things. To solve it, Lockheed developed an automated star-tracking telescope system. It had enough memory for something like 15 constellations, and it could see the brightest stars even in full daylight. It worked, very well. It had a few drawbacks, though. Sometimes, if there were any small holes in the canopy of the covered revetments they housed the Blackbirds in prior to takeoff, as they "spun up" the star tracking system, it would see the small holes, interpret them as a constellation, lock on, and start throwing up all sorts of errors. BNefore it even released the brakes for taxi out to the runway. There is a myth that the Blackbird could not takeoff with full tanks of fuel. Not true, and on several missions, that was exactly what they did. They reason they didn't was that a full load of fuel increased the weight on the wheels by another 100,000lbs. This increased your takeoff run, it cut the "takeoff abort point" by a huge margin, because the brakes just couldn't slow all that down, and if they lost an engine on takeoff, they're options were severely reduced with regard to doing a go-around and coming in for landing. One engine, at full fuel load, even on full afterburner, could not maintain level flight with the landing gear down. It was far better to take off with minimal fuel, heat up, then meet up with a tanker and top off. The most critical time element in a Blackbird mission was take-off time. Ironically, despite being the fastest aircraft in the skies, the Blackbird could not make up for lost time in the air. Because it's cruise speed WAS it's max speed, an oddity in the aviation world. There are unsubstantiated reports of Blackbirds temporarily exceeding Mach 3.2 and flying higher than 85,000 feet, but it was only to outrun missiles. And the folks telling me these things usually then say, "It'd do it, but it wasn't happy doing it." Whereas it would happily cruise all day long at Mach 3.2 at 80,000-85,000 feet. In any event, she couldn't go much faster than 3.2 for long before important things, like the engines, began to melt. They couldn't make the old girl fly truly straight and level. The best the could get was a constant slight climb and descent. So if they were aiming for 80,000 feet altitude, they'd set it up for a slow climb to 85,000, then a slow descent to 75,000, repeat as needed.