Lockheed Martin revealed a planned successor to the legendary SR-71 Blackbird. Except this SR-72 will be a drone, will fly nearly twice as fast as the Blackbird and be capable of carrying weapons. And that will make it the most exotic airplane ever constructed.
If it gets constructed, that is. According to Aviation Week's Guy Norris, the detailed design has been ongoing for years in cooperation with engine builder Aerojet Rocketdyne, but whether it actually gets built is still up in the air.
Hypersonic demonstrators to date have all been powered to speed by rocket boosters, including the same massive rockets used to launch satellites into space. The new design is closely based on the canceled HTV-3X Blackswift, an ambitious proposal to build a plane capable of taking off from a regular runway like a regular aircraft, accelerate to speed and stay there, then land as normal. It's harder than it sounds, and though Lockheed says it has solved one of the trickier problems - transitioning the engine from slow to supersonic to hypersonic flight - the company declines to say how. Other issues, including dealing with the considerable heat generated at hypersonic speeds, are still up in the air. Lockheed says a smaller, single-engine, optionally-manned demonstrator aircraft would precede building the SR-72.
Hypersonic flight is so difficult that all of humanity's accumulated hypersonic flight time is measured in minutes. It is so unique that each new attempt, including those that fail, is considered a successful experiment. The SR-71 flew at high supersonic speeds, which required several strokes of engineering genius.
The Blackbird was fast, with an official speed around Mach 3.2 and an unofficial speed a bit higher, and moderately stealthy, but still slow and detectable enough that if seen at long range there was time to move mobile objects under cover. Lockheed is betting that the SR-72's Mach 6 will simply be too fast to react.
The new aircraft will be capable of flying Mach 6 by essentially fusing two propulsion systems into one. It will have two regular jet engines, which compress air, inject fuel and push the mixture out the back to create thrust, but those stop working at a certain speed. To go faster requires a supersonic-combustion ramjet (scramjet), where essentially the air is moving fast enough to compress itself through a carefully-designed inlet before igniting fuel and pushing it out the back.
The SR-71 and its A-12 forbearer were among the most iconic and exotic aircraft in existence. Built in secrecy in the 1960s for the Central Intelligence Agency and flight tested at Groom Lake, Nevada (the infamous ‘Area 51'), the Blackbird was used for secret strategic reconnaissance, succeeding the high-flying but slow U-2. The SR-71 took pictures over such hostile targets as the Soviet Union, China and North Vietnam amongst others during its long career, but it was extremely expensive. The program was ended first in 1990 but returned shortly thereafter, finally making its last flight in 1998.
The public line is that increasingly capable satellites made the SR-71 obsolete, but satellites move in predictable orbits. Even a series of secret stealth satellites (canceled after considerable budget overruns) would be limited. Rumors of a secret SR-71 replacement are persistent - the supposed ‘Aurora' program -- but no verifiable evidence has emerged. That means if the SR-72 gets built, it will be the top dog, the wildest airplane ever made.