Details of the highly sensitive Project Mayhem were first revealed in 2021 via defense contract information posted online. The project calls for the development of hypersonic engines that can carry both strike and reconnaissance payloads. This matches Lockheed Martin’s recent proposals for the SR-72 which envision a 100-foot-long aircraft capable of reaching speeds up to Mach 6 – twice that of the SR-71 – with the use of scramjet engines. Such speeds have previously only been reached in missiles and rocket-powered test vehicles like the X-15, but never in a manned, reusable vehicle with air-breathing engines.Outside of limited details and design renders included in Lockheed Martin’s proposals, little is known about the SR-72. However, some specifications can be inferred.For example, aerodynamic heating presents a major challenge at speeds above Mach 5 which can generate temperatures hot enough to melt metal. Because of this, the construction of the SR-72 is likely to use composite materials similar to those found on spacecraft and ICBMs.