The difficulties and challenges associated with hypersonic flight are very well known, as they include a need to manage airflow, regulate heat, control guidance technology systems and sustain hypersonic speeds once they are initially achieved. 

Hypersonics are progressing amazingly well, due in large measure to a massively revved-up Pentagon and Air Force effort to fast-track the weapons, yet alongside this near-term push is a concurrent and arguably just as significant effort to break new ground with additional paradigm-changing applications of hypersonics. These include the eventual emergence of hypersonic drones, to be followed by recoverable hypersonic drones, and, maybe someday, the idea that some kind of manned aircraft could travel at hypersonic speeds. 

The U.S. Air Force Research Laboratory has been working on engineering a new kind of advanced jet engine capable of reaching hypersonic speeds. The engine, described by The Drive as a blend between traditional jet turbines and high-speed ramjets and scramjets. The report goes on to suggest that this kind of breakthrough could be intended for Lockheed Martin’s now developing SR-72 Darkstar Mach 6 bomber. 

The Air Force program is called Mayhem, and the service is now being focused by developers upon “expendable testbeds” for the new engines.  The Air Force reportedly anticipates that Mayhem will be larger than the now-developing AGM-183A Air-Launched Rapid Response Weapon hypersonic missile. The new weapon will be engineered with the ability to carry at least three separate payloads. 

“Mayhem, in its early planning stages, was described as a ‘Multi-Mission Cruiser’ due to the focus on sustained hypersonic flight capabilities independent of potential payloads,” AFRL told Aviation Week, as cited in The Drive. 

The Multi-Mission Cruiser was cited in the Air Force’s recently released 2021 budget proposal. The text of the budget documents explain that the efforts will “involve a ‘multi-cycle’ engine of some kind, potentially a reference to “a turbine-based combined cycle arrangement of a dual-mode scramjet,” 

Scramjets, as well as ramjets, generally only function properly at high speeds, requiring some kind of separate booster, typically a rocket motor, to accelerate the aircraft or missile to the appropriate velocity first. A dual-mode scramjet is one that is capable of operating efficiently in both subsonic and supersonic regimes or even hypersonic ones. 

A key advantage of this project is to develop a single air vehicle able to operate at both extended subsonic and supersonic speeds, a circumstance enabling the prospect of shifting course or making key time and targeting adjustments while in flight. 

“An aircraft with this kind of engine setup would be able to take off like any other jet, using existing infrastructure, accelerate to supersonic or hypersonic speeds for the middle portion of its flight, and then decelerate back down to land at the other end, again as normal. The ability of a military aircraft or missile to throttle between these low and high-speed regimes could also potentially help pave the way for entirely new concepts of operation, such as a low-and-slow flight to the general area followed by a high-speed, high-altitude dash to the objective itself,” the report says. 

Kris Osborn is the defense editor for the National Interest. Osborn previously served at the Pentagon as a Highly Qualified Expert with the Office of the Assistant Secretary of the Army—Acquisition, Logistics & Technology. Osborn has also worked as an anchor and on-air military specialist at national TV networks. He has appeared as a guest military expert on Fox News, MSNBC, The Military Channel, and The History Channel. He also has a Master's Degree in Comparative Literature from Columbia University.

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