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July 07, 2012

DARPA continues investments in extreme hypersonics

Hypersonic technologies have the potential to provide the dominance once afforded by stealth to support a range of varied future national security missions.

Extreme hypersonic flight at Mach 20 (i.e., 20 times the speed of sound)—which would enable the department of Defence to get anywhere in the world in under an hour—is an area of research where significant scientific advancements have eluded researchers for decades. Thanks to programs by DARPA, the Army, and the Air Force in recent years, however, more information has been obtained about this challenging subject.

DoD’s hypersonic technology efforts have made significant advancements in our technical understanding of several critical areas including aerodynamics; aerothermal effects; and guidance, navigation and control,” said Acting DARPA Director, Kaigham J. Gabriel. “but additional unknowns exist.”

The IH program is designed to address technical challenges and improve understanding of long-range hypersonic flight through an initial full-scale baseline test of an existing hypersonic test vehicle, followed by a series of subscale flight tests, innovative ground-based testing, expanded modeling and simulation, and advanced analytic methods, culminating in a test flight of a full-scale hypersonic X-plane (HX) in 2016. HX is envisioned as a recoverable next-generation configuration augmented with a rocket-based propulsion capability that will enable and reduce risk for highly maneuverable, long-range hypersonic platforms.




DARPA and DoD’s Strategic Warfare Office are jointly pursuing advancements in global range hypersonic technologies through the Integrated Hypersonics (IH) program. The goal of the IH program is to develop, mature, and test next- generation technologies needed for global-range, maneuverable, hypersonic flight at Mach 20 and above for missions ranging from space access to survivable, time-critical transport to conventional prompt global strike.
“We do not yet have a complete hypersonic system solution,” said Gregory Hulcher, director of Strategic Warfare, Office of the Under Secretary of Defense for Acquisition, Technology and Logistics. “Programs like Integrated Hypersonics will leverage previous investments in this field and continue to reduce risk, inform development, and advance capabilities.”

The IH program expands hypersonic technology research to include five primary technical areas: thermal protection system and hot structures; aerodynamics; guidance, navigation, and control (GNC); range/instrumentation; and propulsion.

At Mach 20, vehicles flying inside the atmosphere experience intense heat, exceeding 3,500 degrees Fahrenheit, which is hotter than a blast furnace capable of melting steel, as well as extreme pressure on the aeroshell. The thermal protection materials and hot structures technology area aims to advance understanding of high-temperature material characteristics to withstand both high thermal and structural loads. Another goal is to optimize structural designs and manufacturing processes to enable faster production of high-mach aeroshells.

The aerodynamics technology area focuses on future vehicle designs for different missions and addresses the effects of adding vertical and horizontal stabilizers or other control surfaces for enhanced aero-control of the vehicle. Aerodynamics seeks technology solutions to ensure the vehicle effectively manages energy to be able to glide to its destination. Desired technical advances in the GNC technology area include advances in software to enable the vehicle to make real-time, in-flight adjustments to changing parameters, such as high-altitude wind gusts, to stay on an optimal flight trajectory.

The range/instrumentation area seeks advanced technologies to embed data measurement sensors into the structure that can withstand the thermal and structural loads to provide real-time thermal and structural parameters, such as temperature, heat transfer, and how the aeroshell skin recedes due to heat. Embedding instrumentation that can provide real-time air data measurements on the vehicle during flight is also desired. Unlike subsonic aircraft that have external probes measuring air density, temperature and pressure of surrounding air, vehicles traveling Mach 20 can’t take external probe measurements. Vehicle concepts that make use of new collection and measurement assets are also being sought.

The propulsion technology area is developing a single, integrated launch vehicle designed to precisely insert a hypersonic glide vehicle into its desired trajectory, rather than adapting a booster designed for space missions. The propulsion area also addresses integrated rocket propulsion technology onboard vehicles to enable a vehicle to give itself an in-flight rocket boost to extend its glide range.

The goal of the IH program is to develop, test, and mature next generation hypersonic technologies to enable rapid global national security missions (transportation, x-plane, conventional prompt global strike, long-range hypersonic cruise) in excess of 20,000 nautical miles with advanced maneuverability. Innovative hypersonic technology improvements for long range HGVs, TAVs, and hypersonic X-planes is envisioned in five primary technology areas: aero-configurations; TPS and hot structures; GNC; range / recovery / instrumentation; and propulsion. The aero-configurations technology area will develop and test next generation aerodynamic configurations which retain or improve upon the high L/D performance tested under the Falcon program, gain robust aerodynamic control and utilize aerothermodynamic and energy management capabilities. The TPS and hot structures technology area will mature and test high temperature material characteristics, and optimize structural design and manufacturing approaches. GNC will develop adaptive reconfigurable control, robust real time trajectory optimization, and precision navigation. Range activities are anticipated to develop and demonstrate space based range for telemetry collection for greater testing efficiency and flexibility. The area of recovery will explore concepts to recover or capture the vehicle at the end of its flight in order to maximize flight data collection. The instrumentation technology development area will develop instrumentation approaches to address critical data collection deficiencies, especially aeroshell thermal and recession and vehicle air data measurements. Finally, the propulsion area will leverage integrated rocket propulsion technology onboard vehicles to enable extended glide range, optimal insertion and trajectory shaping.

51 page DARPA - Draft Integerated Hypersonics Broad Agency Announcement (BAA)

Design Reference Mission

The IH program design reference mission was created with the intent of enabling TAV, hypersonic X-plane, or long range hypersonic glide concepts and includes the following for consideration:

• Aero/thermal hypersonic flight capability of 2 hours
• Enhanced aerodynamic maneuvering: Global down range  greater than 20,000 nm with cross range capability greater than 10,000 nm (as counted by either a single maneuver or the total of multiple mid-course, near terminal and terminal maneuvers)
• Ground or air launch
• Small to medium launch vehicle weight class • High G-load capability (to explore the trade space for terminal evasive maneuvers)
• Propulsion system concepts (non-airbreathing) to extend range (endo- and/or exo-atmospheric) and/or assist mid-course cross range maneuvers, and/or assist aggressive near terminal/terminal maneuvers
• Air Recoverable to afford the opportunity for post-flight vehicle data analysis

Technology Areas

The following technology areas are solicited in this BAA:

Technology Area 1: Aero-Configuration

The overall objective of the aero-configuration technology area is to address vehicle configurations, aerodynamics and aerothermodynamics applicable to development and demonstration of next generation vehicle concepts/configurations which retain or improve upon the high L/D performance tested under the Falcon program and gain robust aerodynamic control and energy management capabilities. These aero advancements are intended to expand the flight envelope (short-mid-long range, wider altitude - velocity corridor) and enable more robust energy management capabilities.

Current generation hypersonic demonstrators have sought to show large improvements in hypersonic lift to drag ratio by aerodynamic tailoring of lifting body shapes or demonstrate robust flight control for less aerodynamically efficient “axisymmetric” -type shapes. These approaches while useful for technology development and testing purposes fall short of the desired end state for prompt global reach concepts. The desired end state is a vehicle concept that delivers both high aerodynamic (L/D) performance for global range flight as well as robust control for maneuvering and energy management. Aero-configuration work will require close integration with the material/thermal protection technology area the GNC technology area and the propulsion technology area.

Technology Area 2: Thermal Protection Systems (TPS) and Hot Structures

The overall objective of the Thermal Protection Systems (TPS) and Hot Structures technical area is to develop and test improved design and analysis techniques for TPS and/or hot structures, improved manufacturing techniques for TPS and/or hot structures, and improved material or structural capability or performance. These TPS and/or hot structure improvements are intended to provide more robust designs (increased margin and/or reduced weight), more accurate thermal-structural analyses, reduced cost and/or time for manufacturing, and improved system performance or capability relative to the current state of the art.

Current generation hypersonic demonstrators have sought to test increased performance through high temperature capability and high specific strength (high strength and low density) materials and structures. The desired end state is a vehicle that can survive the severe environment of long range flight, while manufactured within cost and schedule constraints consistent with an operational system. High performance vehicle configurations necessitate sharp leading edges, thermally and structurally efficient TPS and hot structures contributing to thin vehicle cross sections, and smooth continuous aerodynamic surfaces. This requirement places severe demands on the TPS and hot structures. As a result of these vehicle integration issues, this technology area will consider and have close integration with the aero-configuration, the GNC, and the propulsion technology areas.

TPS and Hot Structures Sub-elements:
TPS and hot structures technology development and testing proposals are desired that will support the development of vehicles with the attributes described above and that address the Design Reference Mission. Technology sub-elements of interest include, but are not limited to, the following:
• Innovative processes required for the rapid manufacture of low cost aeroshell TPS and/or hot structures
• Improved ablation models to accurately predict recession that may occur over the course of long duration flight in the atmosphere due to oxidation of the TPS and/or hot structure
• Stochastic finite element modeling (SFEM) for evaluating the behavior of TPS and/or hot structures due to non-deterministic inputs (such as material properties, geometry, and/or applied loads), including use of uncertainties
• Development of an automated adaptive remeshing tool for accurately modeling a receding surface which could be integrated within commercial finite element analysis codes
• Development of optimal structural design processes for high load concepts
• Aeroshell hot structures with improved interlaminar properties Improved high-temperature, light-weight, non-load bearing thermal insulation
• Improved high-temperature structural insulators
• Improved mechanical attachment techniques for hot structures
• Non- or low-recession sharp leading edges, nose tips, and acreage material that produce negligible communication signal attenuation
• Characterization and ground qualification of next generation nose tip material
• Innovative techniques to survive short term, high heat flux environments on TPS and/or hot structures
• Durable material treatment for c/c to reduce oxidation rates
• Innovative concepts for critical components such as leading edges, embedded antenna windows, and control surfaces

Technology Area 3: Guidance, Navigation and Control (GNC)
The overall objective of the GNC technology area is to develop and test next generation robust and/or adaptive GNC, rapid mission planning and energy management capabilities. These GNC advancements are intended to expand the flight envelope and enable more robust energy management capabilities. Additionally new navigation capabilities are desired for precise operation under non-optimal conditions.
The goal is to enable GNC technologies to provide robust mission planning and flight over the majority of the footprint represented by the Design Reference Mission. This capability places demands not only on the guidance navigation and control system but also on the aerodynamic shape and the vehicle control concept and thermal protection. It is likely that the realization of a wide flight envelope will require balancing the energy management requirements between the launch system (initial energy provided to the flight vehicle) and the flight vehicle (management of the kinetic and potential energy during the flight). Consequently the GNC work will require close integration with the material/thermal protection, the aero-configuration and the propulsion technology areas.

Technology Area 4: Range / Recovery / Instrumentation
The overall objective of the Range, Recovery, and Instrumentation technology area is to enhance the data collection scheme to allow for more robust in-flight and post-flight data analysis. This technology area seeks to define a range architecture that can utilize existing space based resources to collect telemetry data during flight which would allow for a longer, broader test range

Technology Area 5: Propulsion
The overall objective of the propulsion area is to develop and test next generation vehicle concepts/configurations which can augment high L/D performance and gain robust aerodynamic control and energy management capabilities with a capability to insert into their relatively low, equilibrium glide conditions, or provide integrated booster system augmentation to enable a global atmospheric flight range capability without going into orbit. These propulsion advancements are intended to expand the flight time to up 2 hours capability.

Current launch systems are designed for ICBM missions, utilizing high acceleration, short burn motors for exo-atmospheric ballistic trajectories to target at relatively high flight path angles. HGV insertion conditions at low-altitude, long-range horizontal flight path at the edge of the Earth’s atmosphere, provide all the energy available to the HGV to meet mission requirements relying on considerable in-flight energy management. Current rocket systems need to be modified, or augmented by new stages that have added flexibility to accommodate the challenging insertion requirements for next-generation gliding hypersonic vehicles. Among the physical challenges that will be encountered are increased heating at the interface, shock-shock interaction, aggressive stage steering and relatively high dynamic pressure conditions for payload fairing, stage and payload separation. Capabilities required include flexibility to tailor ascent profiles to meet variable insertion state vectors.

For HX concepts, an integrated or attached propulsion system needs to be considered beyond the initial rocket insertion. The augmenting propulsion system can be used initially to maintain high Mach velocity to increase range, intermittently burn throughout the glide to augment turns or at mid-course to re-boost back to high Mach and separate after a completion of initial glide. Extended range, mission planning flexibility, and augmented pull-out or turns are some of the advantages of an integrated rocket capability.

Among the physical challenges that will be encountered for integrated propulsion systems are high heat environment, packaging, jet interaction, heating in vicinity of nozzle, stable flight with a moving center of gravity and multiple firing capability, and for a separable propulsion system one challenge is achieving stable flight after separation. The ultimate goal is to provide global reach but relief to the ground launched rocket and glide vehicle energy management systems and more robust mission planning. Phase 1 will address identification and design of key methodologies and technologies needed for propulsion concepts to meet these new mission conditions. In Phase 2, a combination ground facility and/or subscale flight tests to validate designs from Phase 1. Propulsion work will require close integration with the material/thermal protection technology area, the Guidance and Control technology area and the aero-configurations area.

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