The US Air Force has set plans to begin the competitive phase of a plan to develop a dual mode ramjet for a new class of missiles and aircraft with top speeds over Mach 3.

Two contract awards worth a total of $10 million for design and testing of a dual mode ramjet are now anticipated, the USAF’s Air Force Research Laboratory says in a notice dated 8 June.

The acquisition will begin with the signing of initial task orders worth up to $200,000 each, the AFRL says.

It’s part of the AFRL’s Enabling Technologies for High-speed Operable Systems (ETHOS) programme.

SR-72 640 article

Image courtesy of Lockheed Martin

AFRL unveiled the purpose of the ETHOS programme in 2016. Its goal is to complete the design of a dual mode ramjet, build a test article and perform wind tunnel and free-jet testing, the acquisition notice says.

“The overall objective is to identify, develop, mature, and demonstrate technologies that enable refurbishable high speed (M>3) capability for intelligence/surveillance/reconnaissance (ISR) and strike platforms by 2028, and for quick-turn fully reusable systems by 2035,” the AFRL stated in 2016.

“It is envisioned that the earlier demonstration systems will be air-launched utilising rocket-boost to reach hypersonic cruise speeds, and later employing combined cycle engines that permit runway operations,” the AFRL says.

Such a runway-based, combined-cycle propulsion system also forms the heart of the SR-72, a concept proposed by Lockheed Martin in 2014 for a M6.0-class, unmanned reconnaissance aircraft.

It would use a gas turbine to takeoff and accelerate the vehicle to faster than M2.0. At that point, the propulsion system would transition thrust to a dual mode ramjet. In the first mode, the aircraft is flying over M3.0, but airflow entering the engine intake is slowed to subsonic speed. As the aircraft accelerates beyond Mach 5.0, the flow entering the ram-air engine becomes supersonic.