The Road to Hypersonics - Key Challenges, Advantages and Disadvantages Dr. David Hunn Director Technology and Senior Fellow Emeritus Lockheed Martin Missiles and Fire Control 2 What Do We Mean By “Hypersonics”? •In this context, controlled and precise flight within the atmosphere with speeds in excess of Mach 5/3800 mph/6100 kph •Maneuvers may occur in all phases of flight •Comprised of air-breathing systems and boosted “glide bodies” •Aerodynamic environment not fully understood (hypersonic boundary layers, leading edge physics, unsteady flow…..) •Structural heating rates significant, especially at the leading edges (thousands degrees Celsius) •Extreme heating in novel propulsion systems Hypersonics 2 What Hypersonics Offer • Survivability: Offset air defenses • Weapon survival as it seeks the target • Afford global target access: • Mach 5+ missile goes 1,000 nm in <20 min • Provide “4th dimension” effects … Time warfare: • Compresses a foe’s decision-making window, effectively enabling the hypersonic attacker to get inside an adversary’s Command, Control, Battle Management, and Communications (C2BMC) • Afford unprecedented rapid reach: • Shrink the “time to target” window • 6X swifter than a conventional cruise missile • Demands a more effective intel & targeting cycle The Economist Hypersonics 3 Air Vehicle Iso-Survivability “High” Survivability “Medium” Survivability “Low” Survivability Conceptual simulations showing speed & observability combinations that yield iso-survivability against 2018 threat AF Studies Board, NRC, 2006 Hypersonics 4 “Atmospheric hypersonic flight is only three years away…and always will be.” Hypersonics 5 Renewed interest in hypersonics has significantly increased in the past decade, 202X ARRW entering a new paradigm* 201X Tactical Boost Glide 2010 Falcon Hypersonic Test Vehicle-2 Future Reusable Hypersonic Vehicle 2007 CKEM 1980s-2000s Shuttle 2010 X-51 1951 X-7 202X LRHW 1950s 1960s 1970s 1980s 1990s 2000s 2010s 2020s 202X HCSW 1959 X-15 1980-1990 National Aero-Space Plane 2004 X-43 2012 HiFire ARRW: Air-launched Rapid Response Weapon 202X HAWC HCSW: Hypersonic Conventional Strike Weapon HAWC: Hypersonic Air-breathing Weapon Concept IR-CPS: Intermediate Range-Conventional Prompt Strike *”It was the best of times, it was the worst of times.” 202X IR-CPS LRHW: Long Range Hypersonic Weapon Hypersonics 6 Hypersonics Challenges: Physics, Aero, Engineering Hypersonics 7 Developing a Relevant Hypersonic System “Ain’t Easy”* • Air can no longer be assumed to be “air”, and the constituents change across the flow field • Leading Edge “bluntness” drives drag • Boundary layer transition from laminar to turbulent flow affects drag, heating, and stability; aerodynamic coupling in all axes likely • Pressure rises across shocks are similar to a “detonation” and can interact with the boundary layer • Propulsion systems need to compress, dissemble, mix, react, and exert thrust in only a few milliseconds • The engine needs to keep the ignition process going similar to “keeping a match lit in a hurricane” • Everything happens quickly (heat transfer, controls, navigation, etc.) *Uttered by anonymous Lockheed • Ground testing at the correct conditions is almost impossible Chief Engineer in Dallas ~1997 Hypersonics 8 Hypersonics Siren Song: Speed Matters! “Speed is imperative for effective action [and] safety against enemy counter-measures.” Theodore von Kármán, Science: Key to Air Supremacy, 1946. “Hypersonics promises most favorable access- to-space” US Science Advisory Board, 2000 “Imagine flying from Dallas to London in less time than it takes to drive from London to Heathrow..that’s just cool” Hunn, 2019 Hypersonics 9 Hypersonics Siren Song: Speed Matters! “Speed is imperative for effective action [and] safety against enemy counter-measures.” Theodore von Kármán, Science: Key to Air Supremacy, 1946. “Hypersonics promises most favorable access- to-space” US Science Advisory Board, 2000 “Imagine flying from Dallas to London in less time than it takes to drive from London to Heathrow..that’s just cool” Hunn, 2019 Hypersonics 10 The Hypersonic “Extreme Challenges” 1. Sustained Hypersonic Flight Limited by Materials • Extraordinarily high heat flux over a small area • Very high surface temperatures, oxidation, catalysis effects • Changing material properties during flight • High temperature gradients, high thermal shock • Limited options for sensor and communication apertures/antennas Photo credit: NASA 2. Dramatically Changing Flow Physics with Mach Number • Non linear aerodynamics, unstable boundary layers, varying shock locations • Desired high aerodynamic efficiency drives very sharp and noneroding wing leading edges • Guidance and control complicated by unsteady aerodynamics • Navigation and communication complicated by plasma effects 3. Development of Highly Integrated Flight Architectures • Minimisation of subsystem size/weight/power required, complicating internal thermal management • Coupled optimisation of propulsion, airframe, and control surfaces necessary • Validation and verification of performance very difficult Hypersonics 11 The Hypersonic “Extreme Challenges” 1. Sustained Hypersonic Flight Limited by Materials • Extraordinarily high heat flux over a small area • Very high surface temperatures, oxidation, catalysis effects • Changing material properties during flight • High temperature gradients, high thermal shock • Limited options for sensor and communication apertures/antennas Photo credit: NASA 2. Dramatically Changing Flow Physics with Mach Number • Non linear aerodynamics, unstable boundary layers, varying shock locations • Desired high aerodynamic efficiency drives very sharp and noneroding wing leading edges • Guidance and control complicated by unsteady aerodynamics • Navigation and communication complicated by plasma effects 3. Development of Highly Integrated Flight Architectures • Minimisation of subsystem size/weight/power required, complicating internal thermal management • Coupled optimisation of propulsion, airframe, and control surfaces necessary • Validation and verification of performance very difficult Hypersonics 12 The Hypersonic “Extreme Challenges” 1. Sustained Hypersonic Flight Limited by Materials • Extraordinarily high heat flux over a small area • Very high surface temperatures, oxidation, catalysis effects • Changing material properties during flight • High temperature gradients, high thermal shock • Limited options for sensor and communication apertures/antennas Photo credit: NASA 2. Dramatically Changing Flow Physics with Mach Number • Non linear aerodynamics, unstable boundary layers, varying shock locations • Desired high aerodynamic efficiency drives very sharp and noneroding wing leading edges • Guidance and control complicated by unsteady aerodynamics • Navigation and communication complicated by plasma effects 3. Development of Highly Integrated Flight Architectures • Minimisation of subsystem size/weight/power required, complicating internal thermal management • Coupled optimisation of propulsion, airframe, and control surfaces necessary • Validation and verification of performance very difficult Hypersonics 13 The Hypersonic Materials Challenge Recovery (adiabatic wall) temperature for a turbulent boundary layer (recovery factor r = 0.9) Leading edge temperatures expected to exceed 2000 °C at hypersonic speeds in the atmosphere “Missile Design and System Engineering” , E. Fleeman, ISBN 978-1-60086-908-2 Hypersonics 14 Hypersonics: Hot Stuff Hypersonics 15 Approaches to Handle the Heat • Radiation Cooled Structure – also known as “Hot Structure” Depends upon the conduction and radiation of the thermal energy away from the structure to maintain a balance with the thermal input; passive and shape stable • Insulated Structure – also known as a Thermal Protection System (TPS) The primary structural elements are protected from the direct effect of the hot environment by a “shield”. The TPS can be passive, ablative, or semi- active. • Internally Cooled Structure The structural system employs a coolant which circulates through the structure and is either recovered or jettisoned after use. Hypersonics 16 Approaches to Handle the Heat • Radiation Cooled Structure – also known as “Hot Structure” Depends upon the conduction and radiation of the thermal energy away from the structure to maintain a balance with the thermal input; passive and shape stable • Insulated Structure – also known as a Thermal Protection System (TPS) The primary structural elements are protected from the direct effect of the hot environment by a “shield”. The TPS can be passive, active, or ablative. • Internally Cooled Structure The structural system employs a coolant which circulates through the structure and is either recovered or jettisoned after use. Hypersonics 17 The Hypersonic Materials Challenge Unless actively cooled, metals aren’t the answer Leading edge temperatures expected to exceed 2000 °C at hypersonic speeds in the atmosphere Hypersonics 18 What Materials Might Be the Answer? From “Materials Selection in Mechanical Design”, Ashby, ISBN 0-08-041907-0, 1992 Hypersonics 19 Materials To Consider For >1600°C….Limited From “Materials Selection in Mechanical Design”, Ashby, ISBN 0-08-041907-0, 1992 Hypersonics 20 Materials To Consider For >1600°C….Limited High temp hypersonic materials likely composed of some combination of these From “Materials Selection in Mechanical Design”, Ashby, ISBN 0-08-041907-0, 1992 Hypersonics 21 Materials To Consider For >1600°C….Limited High temp hypersonic