The first unconfirmed reports about the SR-72 appeared in 2007, when various sources disclosed that Lockheed Martin was developing an airplane able to fly six times the speed of sound or Mach6 (4,000mph; 6,400km/h; 3,500kn) for the Air Force.[4][5] Lockheed Martin Skunk Works' development work on the SR-72 was first published by Aviation Week & Space Technology on 1 November 2013.[6][2] Public attention to the news was large enough to overwhelm the Aviation Week servers.[7]
To attain its design speeds, Lockheed Martin had been collaborating with Aerojet Rocketdyne since 2006 on an appropriate engine. The company has been developing the system from the scramjet-powered HTV-3X, which was canceled in 2008. The SR-72 is envisioned with an air-breathing hypersonic propulsion system that has the ability to accelerate from standstill to Mach6 using the same engine, making it about twice as fast as the SR-71.[6] The challenge was to design an engine to handle the flight regimes of subsonic, supersonic, and hypersonic speeds. Using turbine compression, turbojet engines can work at zero speed and usually perform best up to Mach 2.2.[8]Ramjets, using aerodynamic compression with subsonic combustion, perform poorly under Mach 0.5, are most efficient around Mach 3, and can go up to around Mach 6. 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. Finally, scramjets with supersonic combustion cover the range of high supersonic to hypersonic speeds. The SR-72 was to use a turbine-based combined cycle (TBCC) system to use a turbine engine at low speeds and a scramjet engine at high speeds.[2] The turbine and ramjet engines share common inlet and nozzle, but with separate airflow paths.[9][10]
At speeds of Mach 5 and above, aerodynamic heating creates temperatures hot enough to melt conventional metallic airframes, so engineers are considering composites such as high-performance carbon, ceramic, and metal mixes, for fabrication of critical components. Such composites have been used in intercontinental ballistic missiles and the retired Space Shuttle.
As of May2015[update], the SR-72 was envisioned as an ISR and strike platform, but no payloads were specified, likely because current payloads would be insufficient on an aircraft flying at Mach 6 up to 80,000 feet (24,400m) high requiring hundreds of miles to turn. New sensors and weapons would likely have to be created specifically to operate at such speeds.[11]
In November 2013, construction of an optionally piloted scaled demonstrator was planned to start in 2018. The demonstrator was to be about 60ft (18m) long, about the size of a Lockheed Martin F-22 Raptor, and powered by one full-scale engine to fly for several minutes at Mach 6.[6][2] SR-72 flight testing was planned to follow the timeline for the hypersonic High Speed Strike Weapon.
The SR-72 would be similar in size to the SR-71 at over 100ft (30m) long and have the same range, with entry into service by 2030. It follows the U.S. 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.[6][2]
On 13 November 2013, Air Force Chief of Staff General Mark Welsh revealed that the service was interested in the SR-72's hypersonic capabilities, but had not spoken with Lockheed Martin about the aircraft. Its high speed appeals to the service to reduce the time an adversary would have to react to an operation. They were pursuing hypersonic technology, but do not yet have the material ability to construct a full-size plane like the uncrewed SR-72. The SR-72 was unveiled amid sequestration budget cuts that required the Air Force to balance capability, capacity, and mission readiness. By the mid-2020s, it was believed, foreign countries will produce and export advanced aerial technologies that could end up in battle spaces against the U.S. This drives the Air Force to further develop new systems, including hypersonic, to replace outclassed existing systems.[12]
In 2013, it was reported that the Air Force would decline to fund the SR-72 program, choosing instead to develop the Northrop Grumman RQ-180 stealth UAV to perform the task of conducting ISR missions in contested airspace. The RQ-180 was expected to be cheaper, faster, and less complex to design and manufacture.[13]
2014 NASA contracts
In December 2014, NASA awarded Lockheed Martin a contract to study the feasibility of building the SR-72's propulsion system using existing turbine engine technologies, The $892,292 (~$1.13million in 2023) contract funds a design study to determine the viability of a TBCC propulsion system by combining one of several current turbine engines, with a very low Mach ignition Dual Mode Ramjet (DMRJ). NASA previously funded a Lockheed Martin study that found speeds up to Mach 7 could be achieved with a dual-mode engine combining turbine and ramjet technologies. The problem with hypersonic propulsion has always been the gap between the highest speed capabilities of a turbojet, from around Mach 2.2 to the lowest speed of a scramjet at Mach 4. Typical turbine engines cannot achieve high enough speeds for a scramjet to take over and continue accelerating. The NASA-Lockheed Martin study is looking at the possibility of a higher-speed turbine engine or a scramjet that can function in a turbine engine's slower flight envelope; the DARPA HTV-3X had demonstrated a low-speed ramjet (Dual Mode Ramjet) that could operate below Mach 3. Existing turbofan engines powering jet fighters and other experimental designs are being considered for modification. If the study is successful, NASA will fund a demonstrator to test the DMRJ in a flight research vehicle.[14]Aerojet Rocketdyne was awarded a $1,099,916 contract by NASA's Glenn Research Center on 15 December 2014 during mode transition.[10] The two firms were reported to be collaborating on turbine-based combined cycle (TBCC) propulsion system, with plans to begin developing the SR-72 hypersonic demonstrator in 2018, with the first flight expected in 2023.[15]
In March 2016, Lockheed Martin CEO Hewson said that the company was on the verge of a technological breakthrough that would allow its conceptual SR-72 hypersonic plane to reach Mach6. She said a hypersonic demonstrator aircraft the size of an F-22 stealth fighter could be built for less than $1 billion.[16][17][18][19]
2017 to present
In June 2017, Lockheed Martin announced that the SR-72 would be in development by the early 2020s, with top speed in excess of Mach 6. Executive Vice President Rob Weiss said, "We've been saying hypersonics [are] two years away for the last 20 years, but all I can say is the technology is mature and we, along with DARPA and the services, are working hard to get that capability into the hands of our warfighters as soon as possible."[20]
In January 2018, Lockheed Vice President Jack O'Banion gave a presentation that credited the advancements in additive manufacturing and computer modeling, stating that it would not have been possible to make the airplane five years ago and that 3D printing allowed a cooling system to be embedded in the engine.[21][22]
In February 2018, Orlando Carvalho, executive vice president of aeronautics at Lockheed Martin, pushed back on reports of the SR-72's development, saying that no SR-72 had been produced. He also said that hypersonic research is fueling weapons development. "Eventually as that technology is matured, it could ultimately enable the development of a reusable vehicle. Prior to this we may have referred to it as a 'like an SR-72', but now the terminology of choice is 'reusable vehicle'", he said.[22]
In November 2018, Lockheed Martin said that a prototype of the SR-72 was scheduled to fly by 2025. In addition the company stated that the aircraft is to be equipped to fire hypersonic missiles.[23] The SR-72 could enter service in the 2030s.[24]
A ramjet is a form of airbreathing jet engine that requires forward motion of the engine to provide air for combustion. Ramjets work most efficiently at supersonic speeds around Mach 3 and can operate up to Mach 6.
The Lockheed SR-71 "Blackbird" is a retired long-range, high-altitude, Mach 3+ strategic reconnaissance aircraft developed and manufactured by the American aerospace company Lockheed Corporation. The SR-71 has several nicknames, including "Blackbird" and "Habu".
A supersonic transport (SST) or a supersonic airliner is a civilian supersonic aircraft designed to transport passengers at speeds greater than the speed of sound. To date, the only SSTs to see regular service have been Concorde and the Tupolev Tu-144. The last passenger flight of the Tu-144 was in June 1978 and it was last flown in 1999 by NASA. Concorde's last commercial flight was in October 2003, with a November 26, 2003 ferry flight being its last airborne operation. Following the permanent cessation of flying by Concorde, there are no remaining SSTs in commercial service. Several companies have each proposed a supersonic business jet, which may bring supersonic transport back again.
A scramjet is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow. As in ramjets, a scramjet relies on high vehicle speed to compress the incoming air forcefully before combustion, but where as a ramjet decelerates the air to subsonic velocities before combustion using shock cones, a scramjet has no shock cone and slows the airflow using shockwaves produced by its ignition source in place of a shock cone. This allows the scramjet to operate efficiently at extremely high speeds.
The NASA X-43 was an experimental unmanned hypersonic aircraft with multiple planned scale variations meant to test various aspects of hypersonic flight. It was part of the X-plane series and specifically of NASA's Hyper-X program developed in the late 1990s. It set several airspeed records for jet aircraft. The X-43 is the fastest jet-powered aircraft on record at approximately Mach 9.6.
Black project is an informal term used to describe a highly classified, top-secret military or defense project that is not publicly acknowledged by government, military personnel, or contractors.
The US Air Force's Aerospaceplane was a basic research project led by Weldon Worth at the Wright-Patterson AFB concerning the design of future recoverable spaceplanes. The effort was started in 1957 as a result of the USAF official SR-89774 for a reusable spaceplane. By 1959 this work was more known as the Recoverable Orbital Launch System (ROLS). It encompassed a variety of concepts, designs and research projects from 1958, but was cancelled as impractical in 1963.
A supersonic aircraft is an aircraft capable of supersonic flight, that is, flying faster than the speed of sound. Supersonic aircraft were developed in the second half of the twentieth century. Supersonic aircraft have been used for research and military purposes, but only two supersonic aircraft, the Tupolev Tu-144 and the Concorde, ever entered service for civil use as airliners. Fighter jets are the most common example of supersonic aircraft.
The DARPA FALCON Project was a two-part joint project between the Defense Advanced Research Projects Agency (DARPA) and the United States Air Force (USAF) and is part of Prompt Global Strike. The first part of the project aimed to develop a Small Launch System (SLS) capable of accelerating hypersonic gliding weapons as well as launching small satellites into Earth orbit. The second part of the project aimed to develop Hypersonic Weapon Systems (HWS): a short term high performance hypersonic gliding weapon previously named the X-41 Common Aero Vehicle (CAV) that could be launched from Expendable Launch Vehicles (ELV), Reusable Launch Vehicles (RLVs), Hypersonic Cruise Vehicles (HCV), or Space Maneuvering Vehicles (SMP), and a long term hypersonic cruise aircraft named the Hypersonic Cruise Vehicle (HCV). This two-part program was announced in 2003 and continued into 2006.
The General Electric YF120, internally designated as GE37, was a variable cycle afterburning turbofan engine designed by General Electric Aircraft Engines in the late 1980s and early 1990s for the United States Air Force's Advanced Tactical Fighter (ATF) program. It was designed to produce maximum thrust in the 35,000 lbf (156 kN) class. Prototype engines were installed in the two competing technology demonstrator aircraft, the Lockheed YF-22 and Northrop YF-23.
Scramjet programs refers to research and testing programs for the development of supersonic combustion ramjets, known as scramjets. This list provides a short overview of national and international collaborations, and civilian and military programs. The USA, Russia, India, and China (2014), have succeeded at developing scramjet technologies.
Lockheed L-301 was an experimental air-breathing hypersonic aircraft project. It was developed by the NASA and United States Air Force (USAF) organization National Hypersonic Flight Research Facility, with Skunk Works as the prime contractor. In January 1977, the program was "tentatively scheduled to operate two vehicles for eight years and to conduct 100 flights per vehicle." NASA discontinued work on L-301 and NHRF in September 1977 due to budget constraints and lack of need.
The Tupolev Tu-2000 was a planned hypersonic flight experimental aircraft designed by the Tupolev design bureau. It was intended to test technologies for a single-stage-to-orbit aerospaceplane and also the Tupolev Tu-360 intercontinental bomber.
Hypersonic flight is flight through the atmosphere below altitudes of about 90 km at speeds greater than Mach 5, a speed where dissociation of air begins to become significant and high heat loads exist. Speeds over Mach 25 have been achieved below the thermosphere as of 2020.
The Ayaks is a hypersonic waverider aircraft program started in the Soviet Union and currently under development by the Hypersonic Systems Research Institute (HSRI) of Leninets Holding Company in Saint Petersburg, Russia.
Frederick Stucky Billig was an American aerospace engineer who was a pioneer in the development of scramjet propulsion.
An airbreathing jet engine is a jet engine in which the exhaust gas which supplies jet propulsion is atmospheric air, which is taken in, compressed, heated, and expanded back to atmospheric pressure through a propelling nozzle. Compression may be provided by a gas turbine, as in the original turbojet and newer turbofan, or arise solely from the ram pressure of the vehicle's velocity, as with the ramjet and pulsejet.
The Northrop Grumman RQ-180 is an American stealth unmanned aerial vehicle (UAV) surveillance aircraft intended for contested airspace. As of 2019, there had been no images or statements released, but growing evidence points to the existence of the RQ-180 and its use in regular front-line service. The use of the nickname "White Bat" in a 2021 video released by the US Air Force Profession of Arms Center of Excellence (PACE) suggests that the military may be preparing to release information on the RQ-180.
A hypersonic weapon is a weapon capable of travelling at hypersonic speed, defined as between 5 and 25 times the speed of sound or about 1 to 5 miles per second.
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