The Lockheed SR-71 “Blackbird” is a long-range, high-altitude, Mach 3+ strategic reconnaissance aircraft that was operated by the United States Air Force.
It was developed as a black project from the Lockheed A-12 reconnaissance aircraft in the 1960s by Lockheed and its Skunk Works division. American aerospace engineer Clarence “Kelly” Johnson was responsible for many of the design’s innovative concepts.
During its career, the SR-71 Blackbird gathered intelligence in some of the world’s most hostile environments. The SR-71 was conceived to operate at extreme velocities, altitudes, and temperatures: actually it was the first aircraft constructed with titanium, as the friction caused by air molecules passing over its surface at Mach 2.6 would melt a conventional aluminum frame.
No Blackbird has ever been lost or damaged due to hostile action: in fact, even though according to Airman Magazine over 4,000 missiles have been fired at the SR-71 during its service life, none of them hit.
How was the Blackbird able to outrun, or otherwise successfully avoid, Surface-to-Air Missiles (SAMs)? or Why the SR-71 Blackbird was never Shootdown?
‘It’s an issue with intercept geometry,’ says famous writer, former Naval Aviator and Aerospace Eng Tim Hibbets on Quora. ‘[For instance] the SA-2 missile had about Mach 3.5 worth of giddy-up versus the nominal Mach 3.2 of the SR-71. That’s great, but the SAM had to launch, accelerate, climb, and track to the plane. This took time; time that the pilot was using to transit the danger zone (cue music). Here’s a graphic showing the effective envelope of the SA-2 against a moving target.
So, you can see that engaging against a Mach 1 target is a child’s play, with the comrades with coffee cups pushing buttons on Studdly McFighter while he’s still out past 20 nm, all the way to 2 miles for a normal altitude. Meanwhile, the dudes with the spacesuits just have to stay outside that little red bit in order to keep pulling in-flight pay. And mind, they are getting radar warnings and simply have to turn a little left or right if they aren’t feeling sporty about it.
Also, realize the Blackbird is transiting that four nautical mile window in about 6 seconds. It’s enough to make a SAM operator cry.
More info on the graphic featuring the effects of speed and altitude on SA-2 SAM is provided on Stack Exchange.
The Intercept geometry in fact is the bubble of space in which the SA-2 missile can be effective against a specific target [aircraft]. Crucial is the detection range of the radar system guiding the missile, given here 40 nm.
Since the SA-2 has only a limited time to ascend to the altitude of the target and to close in, the combination of speed and altitude of the SR-71 (1854 kt, moving at more than 30 nm per minute) leaves only very small intercept geometry. Moreover, the Blackbird has to overfly the missile launcher almost directly to be vulnerable. If the SR-71 flies above 90.000 ft and Mach 3.2 (or employs effective countermeasures), it will be unassailable by the SA-2.
By contrast, if an aircraft is flying only Mach 1 at 60.000 ft (which equals 573.6 kt, moving at less than 10 nm per minute), its course can go past the launcher with a 25 nm offset and being in range of the Fan Song – SA-2 combination.