US Mayhem Spyplane Falling From Hypersonic Grace

Asia Times noted in December 2022 that the proliferation of anti-satellite and cyberwarfare capabilities may have forced the US to reconsider the necessity of manned ISR spy aircraft. However, it is not clear how it wants to use such assets.

The US Army uses its Airborne Reconnaissance and Target Exploitation Multi-Mission System (ARTEMIS) spy planes to watch China's naval forces in the Pacific and Russia's forces in Ukraine while maintaining a safe distance.

Meanwhile, the US Air Force is divesting itself of all non-stealth spy planes due to concerns about their vulnerability in a near-peer conflict.

Despite its advanced ground-sensing radars, the ARTEMIS has a limited range of operations and can only fly over friendly or permissive airspace. It can be used to scan the peripheries of China and Russia's territories but cannot safely penetrate their vast landmasses.

Developing a hypersonic spy aircraft, however, marks a significant engineering challenge, with engines being the main stumbling block.

David Axe points out in a November 2021 article for The National Interest (TNI) that the turbine-based combined cycle (TBCC) engines planned for Mayhem, which uses jet turbines to accelerate the aircraft to optimal speeds for the ramjets to kick in, present design challenges in terms of competing requirements for supersonic and hypersonic flight.

Axe says designing an air inlet that can effectively feed air to both types of engines represents a significant engineering problem. He mentions that heat during hypersonic flight requires both engines and aircraft to be made of high-temperature materials and light and durable structures.

He says that integrating engines and the airframe into one system with a comprehensive performance envelope exacerbates the design challenges.

Asia Times reported in September 2023 that a team from the University of Central Florida (UCF) is developing an experimental“aerothermodynamic” model for a shape-shifting scramjet engine, which is currently being tested.

The engine has the potential to be more efficient than current hypersonic engines, which could result in aircraft being able to travel at speeds ranging from 5 to 17 times the speed of sound. The US Naval Research Laboratory granted the UCF research team funding to create the engine to solve the challenges associated with high-speed flight.

Despite that rationale and technological advances, a hypersonic spy plane may not make military sense given the characteristics of hypersonic flight and advances in sensor and weapons technology.

In an April 2021 article for The National Interest (TNI) , Sebastien Roblin says the effectiveness of a hypersonic spy plane is questionable due to its high cost and lack of stealth characteristics.

Roblin says the heat generated by the aircraft at high speeds would make it visible to sensors and burn away its radar-absorbent coatings. He notes that adversaries could likely detect and respond to the spy plane's presence, even with little time to react.

Roblin suggests that Mayhem's emergence would likely accelerate the development of surface-to-air missiles (SAM) capable of engaging hypersonic targets. He notes that developing munitions designed for launch at hypersonic speeds would be a costly requirement for Project Mayhem.

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He also points out that a stealth drone could enter heavily defended airspace more slowly but with greater discreteness, orbiting an area of interest for extended periods and providing real-time video feeds for hours.

He suggests that the Pentagon's recent move to hire Northrop Grumman to produce stealthy, high-endurance RQ-180 drones could be interpreted as hurting the Mayhem project.

Indeed, the US may already be taking a different direction regarding deep-penetration aircraft and drones, focusing on increasing stealth rather than speed.

Asia Times reported in January 2024 that Boeing's Aurora Flight Sciences and the US Defense Advanced Research Projects Agency (DARPA) are collaborating to create an aircraft that uses active flow control (AFC) actuators that use pressurized jets of air with traditional moving control surfaces to maneuver the aircraft.

Reducing or eliminating moving control surfaces preserves the stealth shaping carefully designed to minimize radar returns. AFC may be utilized by future stealth planes such as the sixth-generation US Next Generation Air Dominance (NGAD) to take advantage of the multiple benefits provided by the technology.

The X-65 prototype is built to achieve a top speed of Mach 0.7. The innovative aircraft is expected to be ready for its maiden flight in the summer of 2025.

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