In late 1964 an aircraft took off for the first time that revolutionized aviation. It was sleek, sophisticated, technologically cutting edge and looked more like something that might appear out of Bruce Wayne’s bat cave than a traditional aircraft – it was, of course, the SR-71 Blackbird.
The SR-71 was an aircraft that set a new benchmark and one that served the United States Air Force faithfully for almost 35 years. During its lifespan, it was world’s fastest and highest-flying air-breathing operational manned aircraft, with a fastest recorded speed of 3,529.6 km/h (2,193.2 mph) and highest recorded altitude of 25,929 metres (85,069 feet) – which is roughly halfway up to where the Earth’s stratosphere begins. It goes without saying that the SR-71 was an absolutely astonishing aircraft – but just wait and see what’s coming next.
The SR-72, which we shall call ‘the Son of Blackbird, is now inching ever closer to its grand appearance – though still perhaps a decade away until it enters full service. Solid information regarding this new aircraft is sadly scant at this point as almost all of it is still classified and still under development, but we do have enough to piece together a somewhat clear picture of what the SR-72 might look like. An aircraft which, if the rumoured speeds are anything to go by, should be able to reach anywhere on the planet in an hour or less.
A Coverage Gap
When the SR-71 took its final bow in 1999, it did so without a direct successor in place. While other aircraft could cover some of its roles, it was clear that there was a coverage gap between surveillance satellites, manned aircraft, and unmanned aerial vehicles for intelligence, surveillance and reconnaissance (ISR) and strike missions.
Let’s just quickly jump back and see what kind of aircraft the SR-71 was to better understand what might come next. By the way, we have already done a video on the SR-71 here on Megaprojects so this will be a brief explanation – if you’re looking to really get stuck in then why not head on over to that video after this.
The SR-71 was a long-range, high-altitude, Mach 3+ strategic reconnaissance aircraft which first flew in 1966 before being retired in 1999. That was actually its second retirement, the first of which came in 1990 but because of how things were in the Middle East and North Korea, the old boys were rolled out for another decade.
The aircraft was almost exclusively used for high-altitude reconnaissance and most of its service history is shrouded in secrecy. Pilots who flew the aircraft have spoken of missions averaging 3-4 hours, though on several occasions that reached well over 11 hours. SR-71s were famously used during the Yom Kippur War in 1973 between Israel and its Arab neighbours. President Nixon was eager to see whether Israeli and Arab forces had pulled back to where they said they had and so ordered several Blackbirds to take a look.
The SR-71s departed the East Coast of the United States and delivered the damning photographic evidence directly back to Nixon. Neither the Israelis nor Arabs forces were where they said they were. Nixon called all of the countries directly to announce his inside knowledge and shortly after forces from both sides slunk back to where they were supposed to be and the war came to a close shortly after.
During its operational history, an estimated 800 missiles were fired at various SR-71s, all of which missed. That’s not to say that it didn’t experience its fair share of accidents, especially during development, but in terms of getting in and getting out of enemy territory quickly and efficiently, it was unparalleled.
When the end came for the SR-71 (for the second time) in 1999 it was a little unclear what came next. The increased use of satellites and drone technology left some questioning whether the U.S would ever again need a high-altitude, high-speed reconnaissance aircraft in quite the same way.
But how things can change. The rise of anti-satellite weapons, anti-access/area denial tactics, and counter-stealth technologies have meant that the idea of a roaring aircraft flying at the edge of space that could quickly penetrate enemy territory has come back into fashion.
SR- 72 – Early Development
Reports began creeping out in 2007 about a possible successor to the SR-71 and one which would be at least twice as fast, reaching speeds of more than six times the speed of sound (6,400 km/h – 4,000 mph). But it wasn’t until 2013 that things appeared to be confirmed when Lockheed Martin official Robert Weiss publicly stated that the company was developing a hypersonic plane to which he referred to as the SR-72. The company also released concept art depicting an aircraft that looked more like a spacecraft than a plane.
The aircraft is currently being developed at the Lockheed Martin Skunk Works Division, a semi-secretive department responsible for many of the most astonishing aircraft that have appeared over the last 70 years – but this would be quite a step, even for them.
The aircraft is thought to be roughly the same size as an SR-71, measuring around 30 metres (100 ft) in length. The major difference however will be that the SR-72 will be unmanned, whereas its older brother came with a crew of 2. The other major difference is that the SR-72 won’t simply be the eyes in the skies and will also have a strike role, most likely using the latest hypersonic missile technology.
It’s thought that the SR-72 will be powered by two engines. The first of which, a turbine engine, will power the aircraft until it reaches a speed of between Mach 2 and Mach 3 (that’s between 2,469 km/h – 3,704km/h – 1,534 mph – 2,301 mph), while the second, a dual-mode ramjet, will provide power for the aircraft’s hypersonic speeds.
After the excitement of the announcement, there followed a lull in information regarding the SR-72, with some questioning whether the technology to push a plane to Mach 6 even existed yet. The biggest obstacle seemed to be the overlap between the two engines. A typical turbo-jet engine has a top speed of around Mach 2.2 (2,716km/h – 1,687 mph, while the scramjet engine has a lowest possible operating speed of roughly Mach 4 (4,939 km/h – 3,069 mph. So as you can see there is a considerable gap between the two.
In 2014 things took a bit of a twist when NASA became involved with the project and awarded Lockheed Martin a $892,292 contract to study the possibility of using a Turbine Based Combined Cycle (TBCC) propulsion system which combines both the turbojet engine and the ramjet engine.
The Two Engines
The turbojet was first envisioned by a Frenchman by the name of Maxime Guillaume in 1921, though his design was never actually built. The Heinkel He 178 was the first aircraft to use the technology in 1939 and it’s fair to say we haven’t looked back since.
A turbojet is an airbreathing jet engine and comes with a gas turbine and a propelling nozzle. Inside the turbine is a compressor and combustion chamber and it is when the compressed air from the compressor is heated, with the help of the burning fuel in the combustion chamber, it expands throughout the turbine. The exhaust fills the propelling nozzle and is forced out of the back, providing the aircraft with its thrust.
Most engines that we see today use technology similar to this, but as we’ve seen this type of engine comes with a speed limit. One option is to include an afterburner which is often seen in the most modern military aircraft. This is an additional combustion chamber added to the turbine which can dramatically increase speed, but typically uses around 4 times the amount of fuel that a non-afterburner mode uses.
Before we jump straight to a scramjet it makes sense to start with its little brother, the ramjet. While you might think the ramjet with its significantly higher speeds might be a modern invention then think again. The concept actually dates back to 1913 and a French inventor René Lorin, though it would be some time before a working model emerged.
The ramjet uses forward motion to compress incoming air without the aid of compressors. For this reason, ramjets cannot operate from a standing start and vehicles that use it have often needed an assisted take-off, sometimes involving a rocket assist which is essentially a rocket strapped to the aircraft that powers it up to a high speed at which point the ramjet can engage and take over. These types of engines work best at supersonic speeds around Mach 3 (2,300 mph; 3,700 km/h) and can go all the way up to Mach 6 (4,600 mph; 7,400 km/h).
The scramjet is the upgrade of a ramjet. While they share many similarities, the major difference is that the scramjet involves combustion that takes place in supersonic airflow. A ramjet slightly decelerates the air to subsonic speed before combustion, whereas with a scramjet the entire process is carried out at supersonic speeds. The result – extraordinary speed. This kind of technology is still being developed, but the theoretical speeds involved are quite mind-blowing. It’s thought scramjets may eventually be able to operate between Mach 12 (14,000 km/h; 8,400 mph) and Mach 24 (25,000 km/h; 16,000 mph). But as I said, this technology is still very much in its infancy and it’s very likely we have some way to go before we see speeds like that.
OK, back to the SR-72. As I mentioned, there were a few years when very little, if anything was known about the development of this aircraft. But in 2017 and 2018 a series of tantalising announcements were made that pointed to some significant breakthroughs.
At the American Institute of Aeronautics and Astronautics’ annual SciTech Forum in 2018, Lockheed Vice President Jack O’Banion appeared to suggest that through major advances in 3D printing and computer modelling great strides had been made with the SR-72. His presentation came with a new artist’s rendering of the aircraft while he went on to add,
“Without the digital transformation, the aircraft you see there could not have been made. In fact, five years ago, it could not have been made,”
He went on to add that they could now digitally print the engine with an incredibly sophisticated cooling system integrated into the material of the engine itself. As you can imagine, his words were light on arrival dates or even how far along the project is, but he seemed to suggest that a prototype or concept demonstrator already exists. Lockheed carefully skirted the issue after the speech by its vice-president, neither denying nor confirming the progress made on the SR-72.
What we Know Today
It’s very possible that some kind of prototype of the SR-72 already exists. The internet is awash with images of aircraft that may or may not be the Son of Blackbird. Lockheed has stated that they aim to have a concept demonstrator in the air by sometime in the mid-2020s, with a service arrival date now tentatively set for 2030.
So I’m afraid we’re going to have to wait a while for this one. Those in the aviation industry are clear on just what a massive leap forward this would potentially be, but also what enormous obstacles lie ahead. Cost is a massive issue and in 2016 the former CEO of Lockheed Martin, Marillyn Hewson, said that after the breakthrough they believe a demonstrator, roughly the same size as an F-22 Raptor, could be built for less than $1 billion. The fact that she chose that massive number to work with, tells us just how dramatically expensive this is going to be.
Then there’s the question of weaponry. Lockheed has said the aircraft will be able to use hypersonic missiles, most likely Lockheed Martin’s High-Speed Strike Weapon (HSSW) which is itself still in development with a rumoured speed of Mach 5 (6,174 km/h – 3,836 mph). The combination of an aircraft travelling well over six times the speed of sound and a missile travelling five times faster than sound is a scary prospect indeed.
The final point is how they will be controlled. We already know that the SR-72 will almost certainly not be manned, which leaves the question of whether they will be remotely controlled like many drones – or – and this is really taking a leap into the unknown – will it utilize some kind of AI technology that controls some or all of the aircraft?
Unfortunately, we know painfully little about the SR-72 outside of some mouthwatering comments made by Lockheed and some sci-fi looking artist drawings. If this aircraft is really going to be capable of what we think it will be, this could be one of the most significant forward steps in aviation history. But don’t hold your breath just yet.