Hypersonic Spy Plane In Works For Lockheed Martin, Aerojet

About 15 years ago, the United States military retired the SR-71 Blackbird, a spy plane capable of reaching speeds up to Mach 3.5 and flying from New York to London in less than two hours. Recently, Lockheed Martin has announced plans for the aircraft's successor. With the help of Aerojet Rocketdyne, the SR-72 will not only shatter the limits established by the Blackbird, but also not require the control of an on-board pilot. [1][2]

A concept drawing of the SR-72, projected for flight in 2030. [3]

The SR-72 is under development by Lockheed Martin's Advanced Development Programs (ADP), also known as Skunk Works. Its main innovation will be its unprecedented speed, with the plane expected to reach speeds up to Mach 6, or 7,350 kilometers per hour (4,567 mph). This level of speed would be enough to traverse a continent in around an hour, with a trip around the Earth clocking in at only 6 hours. This speed would make the plane an incredible reconnaissance weapon for the United States, allowing them to observe or attack any location around the world in mere hours. In addition, the SR-72 will operate at an altitude of 24,300 meters (80,000 feet), making it very difficult for enemies to knock it out of the sky. Though the development plan includes an option for a pilot to fly the aircraft, the ultimate goal is for the SR-72 to be completely unmanned. Its speed would allow it to carry weapons such as missiles without boosters, which would significantly reduce weight. Not only that, the plane's speed would allow it to strike before a target can find it and sufficiently react. [2][4][5]

There is but one problem for this project: the technology to reach speeds of Mach 6 has not yet been developed. Turbofan engines that are found in typical airliners can only efficiently operate up to Mach 2.5, while ramjet engines can only reach Mach 4, and not efficiently.  However, Lockheed believes they have found a solution by joining forces with Aerojet Rocketdyne. The idea is to create a turbine/supersonic combustion ramjet (scramjet) hybrid engine of sorts. The scramjet, as the name implies, uses super-compressed air with fuel to propel aircraft at supersonic speeds. The only drawback is that at lower speeds, the engine won't receive the compressed air it needs to operate. This is where the conventional turbine engine would come in. The turbine jet engine, which operates at speeds from zero to Mach 3, would share the inlet and nozzle with the scramjet and handle the initial ignition and acceleration. Once the aircraft reaches the upper limit of the turbine engine and the compressed air is created, some sort of mechanical device would switch the airflow to the scramjet, which would propel the plane to the desired hypersonic speed. [2][4]

A diagram and explanation of the proposed hybrid engine that would power the SR-72 to speeds of Mach 6. [6]

Though Lockheed Martin has confirmed that development of the SR-72 has begun, the project is still only in the concept stages and hasn't even received funding yet. Thus, we are years away from seeing even a physical prototype. A piloted scale version is expected to be constructed in 2018 and flight tested by 2023. If all goes according to schedule, the SR-72 will be completely built, tested, and approved for military use by 2030. Though it will be almost 20 years before the project sees real use, if it succeeds and the hybrid engine can indeed propel the aircraft to speeds of Mach 6, the SR-72 can be a real intelligence weapon in the future for the United States.[2]

Sources:
[1] Broge, Jean L. "SR-72 Flies into 21st Century at Mach 6." SAE International. SAE International, 24 Nov. 2013. <http://articles.sae.org/12619/>.
[2] Anthony, Sebastian. "Lockheed Unveils SR-72 Hypersonic Mach 6 Scramjet Spy Plane." ExtremeTech. N.p., 6 Nov. 2013.<http://www.extremetech.com/extreme/170463-lockheed-unveils-sr-72-hypersonic-mach-6-scramjet-spy-plane>.
[3] <http://www.extremetech.com/wp-content/uploads/2013/11/SR-72-640x353.jpg>
[4] Atherton, Kelsey D. "Lockheed Martin Is Developing A Hypersonic Spy Plane." Popular Science. Popular Science, 4 Nov. 2013. <http://www.popsci.com/article/technology/lockheed-martin-developing-hypersonic-spy-plane>.
[5] Norris, Guy. "Exclusive: Skunk Works Reveals SR-71 Successor Plan." Exclusive: Skunk Works Reveals SR-71 Successor Plan. Aviation Week, 1 Nov. 2013. <http://www.aviationweek.com/Article.aspx?id=/article-xml/awx_11_01_2013_p0-632731.xml>.
[6] <http://www.extremetech.com/wp-content/uploads/2013/11/sr72_big-640x452.jpg>