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Lockheed Martin SR-72
The Lockheed Martin SR-72, commonly referred to as "Son of Blackbird", is an American hypersonic concept intended for intelligence, surveillance, and reconnaissance (ISR). It was proposed privately in 2013 by Lockheed Martin as a successor to the retired Lockheed SR-71 Blackbird. As of 2025, no confirmed flight tests have occurred and the SR‑72 remains a design concept with speculation persisting about potential service entry in the 2030s.
The SR-71 Blackbird was retired by the United States Air Force in 1998, eliminating a unique and valuable intelligence, surveillance, and reconnaissance (ISR) capability. Although most fifth-generation jet fighters and planned drones intended for enemy airspace rely on anti-radar stealth technologies, Professor Justin Bronk, a senior research fellow in airpower and technology at the Royal United Services Institute (RUSI), argues that the rise of anti-access/area denial tactics and counter-stealth technologies renders speed more promising than stealth for penetrating protected airspace.
The first unconfirmed reports about the SR-72 emerged in 2007, when various sources reported that Lockheed Martin's Advanced Development Programs (ADP) division, Skunk Works, was developing an aircraft capable of flying at six times the speed of sound, or Mach 6 (4,000 mph; 6,400 km/h; 3,500 kn), for the United States Air Force—about twice as fast as the SR-71.
Since 2006, Lockheed Martin had been working to develop a suitable engine with Aerojet Rocketdyne. After the HTV-3X (DARPA FALCON Project) was cancelled in 2008, Aerojet Rocketdyne applied its scramjet (supersonic combustion ramjet) technology to the SR-72's engine design. The SR-72 was envisioned to have an air-breathing propulsion system that could operate at subsonic, transonic, supersonic, and hypersonic speeds. Turbojet engines can function from zero speed and typically perform best up to Mach 2.2. Ramjets, which rely on aerodynamic compression with subsonic combustion, perform poorly below Mach 0.5, are most efficient around Mach 3, and can operate up to about Mach 6. (The SR-71's engines shifted to low-speed ramjets by redirecting airflow around the core and into the afterburner at speeds exceeding Mach 2.5.) Scramjets can cover the high-supersonic-to-hypersonic range. The SR-72 was to employ a turbine-based combined cycle (TBCC) system, with a turbine engine for low speeds and a scramjet for high speeds. The engines would share an inlet and nozzle but have separate airflow paths.
At speeds of Mach 5 and above, aerodynamic heating generates temperatures sufficient to melt conventional metallic airframes, prompting engineers to consider making critical components from composites such as the high-performance carbon, ceramic, and metal mixes used in intercontinental ballistic missiles (ICBMs) and the retired Space Shuttle.
On November 1, 2013, Aviation Week & Space Technology published an article on the SR-72's development. Public interest in the news was so intense that it overwhelmed the magazine's servers. Lockheed Martin officials announced plans to build an optionally piloted scaled demonstrator, about 60 feet (~18 meters) long—comparable in size to a Lockheed Martin F-22 Raptor—powered by a single full-scale engine to achieve Mach 6 for several minutes. They projected it would be ready by 2018 for flight testing aligned with the High Speed Strike Weapon timeline. The production version of the SR-72, company officials said, would resemble the SR-71 in size at over 100 ft (30 m) long, share its range, and enter service by 2030. It was intended to follow the U.S. Air Force's hypersonic roadmap, targeting a hypersonic strike weapon by 2020 and a penetrating ISR aircraft by 2030. Lockheed officials noted they had discussed the project with government officials but had not secured funding for the prototype or engine.
On November 13, 2013, Air Force Chief of Staff General Mark Welsh expressed the Air Force's interest in hypersonic flight, noting it would shorten an adversary's reaction time to operations. He highlighted it as one of several capabilities that could counter advanced air defenses. Welsh acknowledged the service was pursuing hypersonic technology but lacked the materials to build a full-sized aircraft like the uncrewed SR-72. He also clarified that the Air Force had not engaged with Lockheed Martin regarding the SR-72.
By December 2013, the Air Force declined to fund the SR-72 program. Facing budget constraints, the service chose instead to develop the Northrop Grumman RQ-180 stealth UAV—anticipated to be less costly and complex to design and produce—for ISR missions in contested airspace.
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Lockheed Martin SR-72
The Lockheed Martin SR-72, commonly referred to as "Son of Blackbird", is an American hypersonic concept intended for intelligence, surveillance, and reconnaissance (ISR). It was proposed privately in 2013 by Lockheed Martin as a successor to the retired Lockheed SR-71 Blackbird. As of 2025, no confirmed flight tests have occurred and the SR‑72 remains a design concept with speculation persisting about potential service entry in the 2030s.
The SR-71 Blackbird was retired by the United States Air Force in 1998, eliminating a unique and valuable intelligence, surveillance, and reconnaissance (ISR) capability. Although most fifth-generation jet fighters and planned drones intended for enemy airspace rely on anti-radar stealth technologies, Professor Justin Bronk, a senior research fellow in airpower and technology at the Royal United Services Institute (RUSI), argues that the rise of anti-access/area denial tactics and counter-stealth technologies renders speed more promising than stealth for penetrating protected airspace.
The first unconfirmed reports about the SR-72 emerged in 2007, when various sources reported that Lockheed Martin's Advanced Development Programs (ADP) division, Skunk Works, was developing an aircraft capable of flying at six times the speed of sound, or Mach 6 (4,000 mph; 6,400 km/h; 3,500 kn), for the United States Air Force—about twice as fast as the SR-71.
Since 2006, Lockheed Martin had been working to develop a suitable engine with Aerojet Rocketdyne. After the HTV-3X (DARPA FALCON Project) was cancelled in 2008, Aerojet Rocketdyne applied its scramjet (supersonic combustion ramjet) technology to the SR-72's engine design. The SR-72 was envisioned to have an air-breathing propulsion system that could operate at subsonic, transonic, supersonic, and hypersonic speeds. Turbojet engines can function from zero speed and typically perform best up to Mach 2.2. Ramjets, which rely on aerodynamic compression with subsonic combustion, perform poorly below Mach 0.5, are most efficient around Mach 3, and can operate up to about Mach 6. (The SR-71's engines shifted to low-speed ramjets by redirecting airflow around the core and into the afterburner at speeds exceeding Mach 2.5.) Scramjets can cover the high-supersonic-to-hypersonic range. The SR-72 was to employ a turbine-based combined cycle (TBCC) system, with a turbine engine for low speeds and a scramjet for high speeds. The engines would share an inlet and nozzle but have separate airflow paths.
At speeds of Mach 5 and above, aerodynamic heating generates temperatures sufficient to melt conventional metallic airframes, prompting engineers to consider making critical components from composites such as the high-performance carbon, ceramic, and metal mixes used in intercontinental ballistic missiles (ICBMs) and the retired Space Shuttle.
On November 1, 2013, Aviation Week & Space Technology published an article on the SR-72's development. Public interest in the news was so intense that it overwhelmed the magazine's servers. Lockheed Martin officials announced plans to build an optionally piloted scaled demonstrator, about 60 feet (~18 meters) long—comparable in size to a Lockheed Martin F-22 Raptor—powered by a single full-scale engine to achieve Mach 6 for several minutes. They projected it would be ready by 2018 for flight testing aligned with the High Speed Strike Weapon timeline. The production version of the SR-72, company officials said, would resemble the SR-71 in size at over 100 ft (30 m) long, share its range, and enter service by 2030. It was intended to follow the U.S. Air Force's hypersonic roadmap, targeting a hypersonic strike weapon by 2020 and a penetrating ISR aircraft by 2030. Lockheed officials noted they had discussed the project with government officials but had not secured funding for the prototype or engine.
On November 13, 2013, Air Force Chief of Staff General Mark Welsh expressed the Air Force's interest in hypersonic flight, noting it would shorten an adversary's reaction time to operations. He highlighted it as one of several capabilities that could counter advanced air defenses. Welsh acknowledged the service was pursuing hypersonic technology but lacked the materials to build a full-sized aircraft like the uncrewed SR-72. He also clarified that the Air Force had not engaged with Lockheed Martin regarding the SR-72.
By December 2013, the Air Force declined to fund the SR-72 program. Facing budget constraints, the service chose instead to develop the Northrop Grumman RQ-180 stealth UAV—anticipated to be less costly and complex to design and produce—for ISR missions in contested airspace.