November 6, 2013
Lockheed Martin’s Skunk Works has confirmed that it is developing the SR-72 spy plane. The successor to the SR-71 Blackbird, which was capable of Mach 3.5, the SR-72 will be a hypersonic unmanned aircraft capable of Mach 6, or just over 4,500 mph. At hypersonic speeds, the SR-72 will be able to traverse any continent in around an hour — meaning, if they’re strategically positioned around the world on aircraft carriers, the US military can strike or surveil any location on Earth in about an hour. It is also suspected that the SR-72′s hypersonic engine tech — some kind of hybrid scramjet — will find its way into the US military’s High Speed Strike Weapon (HSSW), a missile that can theoretically strike anywhere on Earth in just a few minutes.
The SR-72, despite the similar name, is a completely new plane. At the moment, the SR-72 is still only a concept, though Lockheed has now confirmed that the plane is in active development. An optionally piloted scale version of the plane with a single engine will be built in 2018, with test flights scheduled for 2023. If all goes to plan (funding hasn’t yet been secured by Lockheed Martin), a full-size SR-72 (about 100 feet long) will be built and tested by 2030. As it stands, the current plan is for the SR-72 to be unmanned. It will be a very, very large drone.
While the SR-72 will undoubtedly be a paragon of stealth and fashioned from monolithic crystals of titanium wrapped in carbon fiber, its defining feature is its operational speed of Mach 6 — or 4,567 mph (7,350 kph). At this speed, the SR-72 can cross the Atlantic (or Europe or China or…) in about an hour — or circumnavigate the planet in six hours. At an operational altitude of around 80,000 feet (24,300 meters) and Mach 6, the SR-72 will be almost impossible to shoot down.
To reach Mach 6, some aeronautic magic needs to occur, otherwise we would’ve built a Mach 6 aircraft years ago. Basically, turbofan engines — like you would find in every big airliner — are only really efficient up to around Mach 2.5. Ramjets can then take you to around Mach 4, but then they too lose their efficiency. To get to Mach 6, Lockheed’s Skunk Works lab — which has developed such luminaries as the U-2, SR-71, F-22, and F-35 — is working with Aerojet Rocketdyne to create a turbojet/scramjet hybrid engine that uses a turbine at low speeds, and a scramjet (supersonic combustion ramjet) at higher speeds. Like the SR-71, these engines will have the same inlet and nozzle, with some kind of mechanical system that shifts the airflow between the two portions of the engine as airspeed changes. Whereas a ramjet decelerates incoming air to subsonic speeds, a scramjet is supersonic throughout, allowing for much higher air speeds (no one knows quite how fast, but we’re talking about at least Mach 10).
