Lockheed Martin SR-72

The Lockheed Martin SR-72  is a conceptualized unmanned, hypersonic aircraft intended for intelligence, surveillance and reconnaissance proposed by Lockheed Martin to succeed the retired SR-71 Blackbird.

Design and development
The SR-72, proposed successor to the SR-71 Blackbird, retired in 1998, is expected to fill what is considered a coverage gap between surveillance satellites, subsonic manned aircraft, and unmanned aerial vehicles for intelligence, surveillance and reconnaissance (ISR) and strike missions. With the growth of anti-satellite weapons, anti-access/area denial tactics, and counter-stealth technologies, a high-speed aircraft could penetrate protected airspace and observe or strike a target before enemies could detect or intercept it. The proposed reliance on extremely high speed to penetrate defended airspace is considered a significant conceptual departure from the emphasis on stealth in 5th generation fighter programs and projected drone developments. There were unconfirmed rumors about the SR-72 dating back to 2007, when various sources disclosed that Lockheed Martin was developing a Mach 6 plane for the US Air Force. Such a development was confirmed on 1 November 2013, when the Skunk Works revelations were published about the development work on the SR-72 exclusively in Aviation Week & Space Technology. Public attention to the news was large enough to overwhelm the Aviation Week servers.

To attain such speeds, Lockheed Martin has been collaborating with Aerojet Rocketdyne since 2006 on an appropriate engine. The company is developing the system from the scramjet-powered HTV-3X, which was canceled in 2008. The SR-72 is envisioned with the ability to accelerate from standstill to Mach 6.0 using the same air-breathing hypersonic propulsion system, making it about twice as fast as the SR-71. Normal ramjets cannot typically operate over Mach 4.0, and turbofan engines can usually perform best up to Mach 2.2. The SR-71's specially designed engines converted to low-speed ramjets by redirecting the airflow around the core and into the afterburner for speeds greater than Mach 2.5. The SR-72 is to use a turbine-based combined cycle (TBCC) system to use a turbine engine at low speeds and a scramjet engine at high speeds. The turbine and ramjet engines share common inlet and nozzle, with different airflow paths in between.

An optionally-piloted scaled demonstrator is planned to be built in 2018. The demonstrator design is about 60 ft long, about the size of an F-22 Raptor, and is powered by one full-scale engine to fly it for several minutes at Mach 6. Flights of the demonstrator are to be conducted starting in 2023. The SR-72 flight testing follows the planned timeline for the hypersonic High Speed Strike Weapon. The SR-72 is to be similar in size to the SR-71 at over 100 ft long and have the same range, with entry into service by 2030. The SR-72 follows the US Air Force's hypersonic road map for developing a hypersonic strike weapon by 2020, and a penetrating ISR aircraft by 2030. At the time of the concept's unveiling, Lockheed Martin had engaged in talks with government officials, but has not secured funding for the demonstrator or engine.

On 13 November 2013, Air Force Chief of Staff General Mark Welsh revealed that the Air Force was interested in the SR-72's hypersonic capabilities, but had not spoken with Lockheed about the aircraft. Its high speed appeals to the service to reduce the time an adversary would have to react to an operation. They are pursuing hypersonic technology, but don't yet have the material ability to construct a full-size plane like the unmanned SR-72. The SR-72 was unveiled in the midst of sequestration budget cuts that have forced the Air Force to prioritize acquisition projects and sacrifice mission readiness. By the mid-2020s, it is believed that foreign countries will produce and export advanced aerial technologies that could end up in battlespaces against the United States. This drives the Air Force to further develop new systems, including hypersonic, to replace legacy systems that would be outclassed in those situations.