Soaring at Hypersonic Speeds 2015 Status of High Speed Air Breathing Propulsion by Dora E. Musielak, Ph.D. 1 and Bayindir H. Saracoglu, Ph.D. 2 1 University of Texas at Arlington, Arlington, Texas, USA 2 von Karman Institute for Fluid Dynamics, Rhode-Saint-Genese, Belgium High Speed Strike Weapon (HSSW) - Lockheed Martin Hypersonic Missile Concept suitable for future bomber and fighter aircraft. Image Courtesy: Lockheed Martin Co. Hydrocarbon scramjet-powered propulsion, which was successfully demonstrated by the Air Force in 2013 with the X-51A WaveRider, holds the key to open new frontiers in hypersonic aero-flight. Being able to sustain flight in the atmosphere at Mach 5 or higher speeds would have many benefits for both civil and military applications. However, investment for high-speed air breathing propulsion in the U.S. is coming mainly from the military sector, guided by its need to develop fast weapon technologies, including hypersonic missiles and high-speed long-range reconnaissance transports. The High Speed Strike Weapon (HSSW) Program, a collaborative effort of DARPA, AFRL, Lockheed Martin and other contractors, include plans to develop and flight test a Mach 5+ demonstrator weapon. The HSSW Capability Program will develop and demonstrate weapon technologies that will provide effective rapid strike from a platform at safe standoff ranges in highly contested environments.
2 USAF/Lockheed Martin s High Speed Strike Weapon (HSSW) hypersonic missile. Image Credit: Lockheed Martin Co. Teams at various organizations are actively researching and developing highspeed weapon airframes, advanced guidance and precision ordnance effects for surface targets, as well as system integration to support the HSSW demonstrator. Another promising new program is DARPA s Hypersonic Air-breathing Weapon Concept (HAWC) intended to pursue flight demonstration of critical technologies for effective and affordable airlaunched hypersonic cruise missiles, including hydrocarbon scramjet-powered propulsion to enable sustained hypersonic cruise. The objective of the HAWC program, an outgrowth of the Integrated Hypersonics Program, is to develop and demonstrate technologies that will enable transformational changes in responsive, long range strike against time-critical or heavily defended targets. A joint DARPA-U.S. Air Force program, HAWC will transition critical technologies to the military after flight testing is complete. These technologies include advanced air vehicle configurations capable of efficient hypersonic flight, hydrocarbon scramjetpowered propulsion to enable sustained hypersonic cruise, thermal management approaches designed for high-temperature cruise, and affordable system designs and manufacturing approaches. HAWC technologies also extend to reusable hypersonic air platforms for other applications such as global presence and space lift. The HAWC program will leverage advances made by the previously funded Falcon, X-51, and HyFly programs. The Hypersonic Airbreathing Propulsion Branch at NASA Langley Research Center (LaRC) continued supporting several DoD programs, including the AFRL-led Medium-Scale Critical Components, the HSST-led Large-scale Scramjet Engine Test Technique, the AFRLled High Speed Strike Weapon and the DARPA-led HAWC programs. In addition to continued efforts to evaluate and understand X-51 flight data, researchers focused on three in-house projects: the development of the VULCAN CFD software suite, the new Isolator Dynamics Research Laboratory, and the Enhanced Injection and Mixing project. Dr. Richard L. Gaffney, Jr, Head of the Hypersonic Airbreathing Propulsion Branch at NASA LaRC, reported that the Arc-Heated Scramjet Test Facility is undergoing final checkout following upgrades to increase its test capability. In addition, the Direct-Connect Supersonic-Combustion Test Facility was brought back on-line in June after being dormant for several years. There is also an effort underway at LaRC to design and construct a new water-cooled Mach-6 nozzle for the 8-Ft High Temperature Tunnel. In April, the NASA Glenn Research Center (GRC)/AFRL Combined Cycle Engine- Large Scale Inlet Mode Transition Experiment (CCE-LIMX) began Phase 3 testing in the 10 x10 Supersonic Wind Tunnel. The Combined-Cycle Engine (CCE) project aims to demonstrate closed-loop control to enable smooth & stable inlet operation throughout mode transition without unstart for Turbine-Based Combined Cycle (TBCC) propulsion. NASA has demonstrated mode transition of the CCE inlets at Mach 3+, stated Paul Bartolotta. The next step is to put live propulsion into the CCE inlet hardware and test mode transition. To define CCE test parameters, GRC is investigating the feasibility of utilizing a commercial off-the-shelf (COTS) turbine for a flight demonstration vehicle. This should reduce the cost of a demo program.
3 possibly due to overheating of the voltage regulator in the telemetry system. However, data received in the early part of the flight showed that the test vehicle was functioning perfectly, the flight was proceeding on the correct trajectory, the flight control system performed flawlessly and supersonic airflow was established in the combustor. Smart stated: although the complete set of data was not received, most of the new technologies worked perfectly. Six flights have been conducted in the HIFiRE program over the past decade with scramjet engines designed by UQ. The next flight is planned to capitalize on the existing investment and the encouraging results obtained in Flight 7. Testing of the CCE-LIMX in NASA GRC s 10' 10' Supersonic Wind Tunnel. Image: NASA GRC. Researchers involved with the joint Australia-USA Hypersonic International Flight Research Experimentation (HIFiRE) Program continue investigating the fundamental science of hypersonic technology and its potential for next generation aeronautical systems. HIFiRE includes ten hypersonic flights to gather aerodynamic and scramjet data that cannot be obtained in ground tests. The HIFiRE 7 was the latest flight test, conducted at the Andøya Rocket Range in Norway. HIFiRE 7 was designed to determine how scramjet engines start up at high altitudes, and to measure how much thrust the engines produce at lower altitudes. Professor Michael Smart, Science Lead for HIFiRE 7 at the University of Queensland (UQ), reported that the scramjet stage commenced after completing a suborbital flight and re-entering the atmosphere, while the payload accelerated to over Mach 7 or 2km per second. During atmospheric re-entry, the flight data stream from the payload was lost just 15 seconds before the completion of the flight, Preparing for HIFiRE 7 flight test of the US- Australia HIFiRE Program. Image credit: University of Queensland, Australia. The HIFiRE program is a joint collaboration between the US Air Force Research Laboratories (AFRL), the Australian Defence Science and Technology Organisation (DSTO), Boeing and UQ. The HIFiRE-7 flight trial was coordinated by DSTO, which designed the flight test vehicle and control systems with rocket motors supplied by the German Aerospace Center (DLR). BAE
4 Systems contributed with ground testing of flight software. HIFiRE Researcher at UQ Lab. Image credit: University of Queensland, Australia. Global interest and investment in hypersonic technologies was manifested in the highly successful 2015 International Space Plane Hypersonic Systems and Technologies Conference held in Glasgow, Scotland. Dr. Adam Siebenhaar of Mach 7H Consulting, retired from Aerojet and conference chairman, measured success in terms of the high attendance, the 180 high quality technical papers presented, and the special sessions on current topics of interest including High Speed Transport Vehicles, Reusable Space Launch Vehicles, and Hypersonics-What Next? In September, DARPA and ONR awarded a $1.01 million Defense University Research Instrumentation Program grant to Dr. Luca Maddalena from the University of Texas at Arlington (UTA) to build the country s only university-based, arc-heated, hypersonictesting facility for thermal protection systems. UTA s facility will allow researchers to create flows with temperatures higher than 4,000 F to study and test new heat shield materials that will improve the safety and performance of hypersonic cruise and glide vehicles to withstand the intense heat generated by the interaction with the surrounding atmosphere at those speeds. Current DARPA programs consider innovative ideas for propulsion concepts appropriate for Mach 0-to-7 aircraft capable of two-stage-to-orbit or high-speed intelligence, surveillance and reconnaissance (ISR). Rotating detonation engine or turbine integrated with dual-mode ramjet are some of the concepts that could be developed. According to Dr. Siebenhaar, DARPA s HAWC and the solid booster rocket propelled Tactical Boost Glide system (TBG), both of which are heading towards flight demonstrations by 2019 or 2020, may answer the question if high speed air-breathing can overcome its nemesis, the rocket, and succeed in becoming the propulsion system of choice for long range-high speed strike weapons. Another interesting concept is the SR-72, an unmanned, Mach 6 hypersonic aircraft intended for intelligence, surveillance and reconnaissance envisioned by Lockheed Martin to succeed the retired Lockheed SR-71 Blackbird. The SR-72 vehicle is expected to be powered by a turbine-based combined cycle (TBCC) engine with the ability to accelerate from standstill to Mach 6.0, making it about twice as fast as the SR-71. Lockheed Martin expects to build an optionally-piloted scaled demonstrator. The SR-72 demonstrator will have the optional capability to strike targets. Lockheed Martin s SR-72 twin-engine TBCC aircraft designed for a Mach 6 cruise. Image Credit: Lockheed Martin Co. Europe s primary focus is on developing a Mach 5 passenger transport with 15,000 km range fueled by hydrogen to ensure better
5 thermal management, and reduced carbondioxide pollution. Non-technical concerns are also address such as take off and cruise noise, flight certification, environmental acceptance, passenger comfort and safety, and general operational concepts. These pose additional technical challenges and significant design and operational constraints. Pre-cooler technology for an air-breathing rocket is currently being developed under the ongoing Skylon-SABRE program. This is a single-stage-to-orbit (SSTO) system which has received a lot of attention. The Synergistic Air-Breathing Rocket Engine (SABRE) is an innovative air-breathing rocket. Richard Varvill, Technical Director at Reaction Engines (REL) Ltd., reported that following the successful pre-cooler and frost control demonstration in 2012, REL continues to develop the SABRE4 engine model and the design of the SSTO vehicle known as Skylon D1. This includes a number of technology programmes addressing intake and nozzle aerodynamics, long life rocket combustion chambers, and lightweight heat exchangers. In addition, REL has now began the design of a full scale engine demonstrator which will be tested before the end of this decade. In November, British defense contractor BAE Systems announced that it plans to invest roughly $31.7 million to help develop a hybrid rocket engine with REL. BAE s investment is based on the belief that SABRE will revolutionize the industry of space travel with its ability to operate not only in outer space, but within Earth s atmosphere as well. Recently it was revealed that SABRE uses a specially-engineered pre-cooler system to chill consumed air from over 1,800 F down to 240 F in under 0.01 seconds. By using a methanol injection to function as the engine s antifreeze, REL was able to overcome one of the rocket s biggest obstacles. Testing is still likely many years out. However, the new investment from BAE Systems will allow REL to expand its research and officially complete a test model. As BAE Systems and REL continue to conduct research and development on the innovative SABRE rocket, the hope is to begin groundbased testing by as early as 2020, with unmanned test flights beginning in 2025. As is the case with nearly every prototype, actual testing will likely occur later than intended. Nonetheless, the BAE-REL partnership certainly will accelerate SKYLON s development and ensure the future of commercial space travel. When asked for his personal assessment of the Skylon system, Dr. Siebenhaar stated: Regarding the validity of the Skylon claims, I am sitting somewhat on the fence. It is without any doubt a very ingenious design, but SSTO is a very tough challenge, and I am not convinced at this point that the Skylon can achieve an SSTO mission technically, reliably and economically. I seriously hope and recommend that the US Government fund NASA and DoD to further assess the Skylon design and the SSTO operational concept. If there is a shortfall, then a logical fallback could be a two-stage-to-orbit (TSTO) system. Both U.S. vehicle primes and major propulsion houses need to get involved. Ultimately the US must build an operational, reusable and economical vehicle/system for space access, or we will get upstaged by Europe. In Japan, researchers at Aoyama Gakuin University are working on fundamental detonation research to develop Rotating Detonation Engine (RDE) propulsion. They investigated a two-step reaction mechanism of JP10 fuel appropriate for RDE simulation, which agrees quite well with predictions. Simulating gaseous JP10-air RDE performance researchers obtained data for mixture-based specific impulse. Liquid JP10-air RDE simulations are in progress. Russian researchers reported that the hypersonic scramjet powered Brahmos, an antiship missile they are developing with India, will be ready to fly in 2016. They did not disclose details, but we believe that the missile may reach Mach 7. The Central Institute of Aviation Motors (CIAM) reported advances to support the project HEXAFLY-INT funded by the 7th European Framework Programme to develop a high-speed civil aircraft. CIAM researchers designed a scramjet module to power the vehicle. This module is comprised of a 3-D convergent fixed geometry inlet, an elliptical expanding 3-D combustor, a two stage fuel injection system with flame stabilizers, and an axisymmetric nozzle.
CIAM Scramjet model in assembly with power pylon (a), HEXAFLY-INT module installation in CIAM s facility.(b). Image Credit: CIAM. During a recent experiment at Mach 7.4 flight conditions, CIAM researchers measured positive aero-propulsive balance, indicating that the thrust produced by the hydrogenfueled model engine was higher than the total aerodynamic drag. CIAM also developed computational techniques for modeling of complex chemically reacting gas-dynamic flow in the inner flow path of the scramjet. Their unique facility base and module experimental data allow the verification and validation of the advanced computational methods. Although 2015 was promising, laying the ground for new hypersonic air breathing propulsion (HAP) programs, we expect more advancements in 2016. As Dr. Siebenhaar stated recently, the time has come that hypersonic fundamental research, propulsion and vehicle concept developments start to more comprehensively address actual mission and operational constraints and requirements. As of today, both the U.S. government and the global industry continue maturing the technologies for high-speed air-breathing propulsion. We believe that investment in HAP is crucial to secure the future of hypersonic civil and military transports, and to make it possible to access space with less costly launch vehicles, such as reusable spaceplanes that benefit from air-breathing propulsion. We are certain that 2016 will bring more tangible advances to get us closer to that future. Acknowledgements The authors are grateful to the following individuals for their valuable contribution: Dr. Richard L. Gaffney, Jr, Head of the NASA LaRC Hypersonic Airbreathing Propulsion Branch. Dr. Paul Bartolotta, Hypersonics Project Deputy Manager, NASA GRC. Dr. John D. Saunders, NASA GRC. Dr. Thomas J. Stueber, NASA GRC. Professor Michael Smart, Science Lead for HIFiRE 7 at the University of Queensland. Dr. Richard Varvill, Technical Director at Reaction Engines Ltd., U.K. Dr. Adam Siebenhaar, Aerojet (Retired), Mach 7H Consulting. Dr. A. Koichi Hayashi, Aoyama Gakuin University. Dr. Viacheslav Vinogradov, Central Institute of Aviation Motors, Moscow, Russia. Media Relations personnel at U.S. AFRL and at the Boeing, Company.