Northrop Grumman’s Next-Generation Scramjet Delivers Hypersonic Propulsion That Weighs Less to Pack More Punch
By Kenneth Kesner
Speed and stealth are key in the all-domain battlespace. A hypersonic pace – five or more times the speed of sound – can put a missile on target before enemy defense systems can respond effectively. Having long range hypersonic systems allows pilots to prosecute targets without having to put themselves within range of air defense systems.
Dependent on the mission need, scramjet propulsion systems are capable of achieving hypersonic speeds in an optimized package for a long range, time-critical strike capability. The need for extended ranges while maintaining magazine depth really plays to the strengths of hypersonic air-breathing propulsion. Air-breathing engines leverage the oxygen in the atmosphere and minimal moving parts to deliver a high speed weapon systems in a tactical form factor. The result is a great number of weapons on the platform which gives our warfighters the flexibility and operational utility they need in a near-peer fight.
What military strategists want is a missile that combines speed, range, high load out, and affordability.
Game, set, match. Northrop Grumman’s next-generation scramjet engine helps solve those challenges. It has already propelled a Hypersonic Air-breathing Weapons Concept (HAWC) missile through milestone flight tests for the Defense Advanced Research Projects Agency and the U.S. Air Force (USAF), most recently in summer of 2022, with more tests to come. HAWC was developed by Raytheon Missiles & Defense, a Raytheon Technologies business, in partnership with Northrop Grumman. The partnership team was recently selected to develop the USAF’s Hypersonic Attack Cruise Missile (HACM) – a first-of-its-kind weapon being developed in conjunction with the Southern Cross Integrated Flight Research Experiment (SCIFiRE), a U.S. and Australia project arrangement.
Scramjets have been studied since the late 1950s, with few sustained flight successes. They are essentially supersonic ramjet engines and require high vehicle speed – provided by a rocket booster or supersonic aircraft – to compress air through an inlet into a combustion chamber. That’s where oxygen combines with fuel and is ignited, creating the tremendous thrust that enables sustained hypersonic flight.
“It’s more complicated than a typical solid rocket motor, but much less than the turbine engines on some cruise missiles and jets,” said Jim Philpott, a Northrop Grumman Fellow whose specialty is high-speed air-breathing propulsion systems.
He’s been working on scramjet technology for more than a decade. “There are almost no moving parts inside the engine. It’s all about the design to manage the aerodynamic forces involved.”
Northrop Grumman’s scramjet propulsion solution is a major step forward. It integrates recent breakthroughs in Computational Fluid Dynamics and digital design techniques, and couples them with advanced additive manufacturing (AM) and materials expertise. The scramjet engine’s design leverages new analysis methods that enable engineers to create holistic, systemic solutions to solve complex thermal and structure problems that vexed engineers for decades.
“We committed early to advanced and additive manufacturing, and it opened a new world of design. Seams, welds and joints are both cost drivers and points of weaknesses. With AM, you can design features inside the combustor that are never touched by a tool,” Philpott said. “It allowed a clean, elegant and effective solution to thermal management that is integral in our design and manufacturing.”
Chris Gettinger, Northrop Grumman director of Advanced Propulsion and Systems, emphasized this scramjet is not just another experiment. It has, from the beginning, been designed to be built. Affordability, safe handling, availability of materials and long-term storage reliability were among the factors considered and balanced along with the technical challenges.
And the team was able to tap expertise and resources in laboratories and test facilities across the company, including Northrop Grumman’s hypersonics hub under construction in Elkton, Maryland. The company is growing its future advanced propulsion capabilities with the construction of its Hypersonics Capability Center, a new facility dedicated to support the design, development and production of hypersonic weapons.
“We were able to bring a system mindset to bear on this project, modeling the engine and dynamics in the digital realm, then using advanced manufacturing for true prototyping of hardware, not just research and development models,” Gettinger said. “Our ability to go straight to flight-weight hardware can quickly turn engine ideas into reality.”
As a result, the scramjet engine used in the flight test is much closer to an Engineering & Manufacturing Development (EMD) production phase than usual at this point in a program.
“It was really exciting,” said Philpott, who attended the tests. He and the room cheered as instruments indicated the missile’s smooth transition to sustained hypersonic flight following ignition of the scramjet.
“It did exactly what we asked it to do, what we designed it to do,” he said. “Can’t ask for more than that.”