Non-Intrusive Aerodynamic State Sensing for Hypersonic Flight Control

Navy STTR 23.A - Topic N23A-T029
ONR - Office of Naval Research
Pre-release 1/11/23   Opens to accept proposals 2/08/23   Closes 3/08/23 12:00pm ET

N23A-T029   TITLE: Non-Intrusive Aerodynamic State Sensing for Hypersonic Flight Control

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Hypersonics;Microelectronics

OBJECTIVE: We will develop the flow theory, measurement technology, and estimation algorithms to enable non-intrusive aerodynamic state sensing for hypersonic flight control. The flow theory will describe measurable flow phenomena and their correlation to a weapon�s aerodynamic state. The measurement technology will sense the flow phenomena and produce correlated signals without devices that protrude into the flow around the weapon. The estimation algorithms will process the signal data to produce accurate and precise estimates of the weapon�s aerodynamic state. Collectively, the flow theory, measurement technology and estimation algorithms will be the foundation of a non-intrusive air data system that can operate in sustained hypersonic flight conditions. The system will produce aerodynamic state estimates at a rate sufficient for flight control.

DESCRIPTION: Hypersonic flight conditions drive phenomena, e.g., chemical dissociation, material ablation, etc., that are generally not encountered in other flight regimes. Recent hypersonic flight experiments seek to understand phenomena such as boundary layer transition and its impact on heat transfer [Ref 1]. Ground-based hypersonic research has spurred successful investigations for non-intrusive flow measurement in a wind tunnel [Refs 2, 3]. Researchers have long recognized air data�s critical importance to controlled hypersonic flight. Driven by the promise of hypersonic flight sustained by air breathing propulsion, researchers investigated air data systems needed for highly coupled flight and propulsion control systems [Ref 4]. Despite the lack of an air-breathing engine, successful hypersonic flights with the X-15 rocket plane provided useful information on air data challenges. Even a sensor with 1% accuracy is not sufficient for control under the extreme pressures and temperatures associated with hypersonic flight. Researchers investigated a broad array of technologies ranging from pressure transducers to gas fluorescence with laser excitation as they worked to solve the air data problem for hypersonic flight [Ref 5]. Thus far, researchers have not identified a single technology capable of producing sufficient accuracy, precision, and bandwidth across the entire flight envelope of a hypersonic weapon, especially for weapons that cover subsonic, supersonic, and hypersonic conditions in a single flight. This raises the importance of state estimation algorithms that will need to fuse data from varying sensors over a broad range of conditions and aerodynamic phenomena. As flow diagnostic science and technology advanced for hypersonic wind tunnel experiments, researchers began to investigate these approaches for flight experiments. Researchers investigated electron beam fluorescence as a tool for non-intrusive flow diagnostics of the boundary layer in a hypersonic vehicle [Ref 6]. Researchers have also proposed using Raleigh Lidar to measure upstream density in concert with electron beam fluorescence to measure density and temperature of gas species within the boundary layer [Ref 7]. Given the potential and historical significance of using surface pressure measurements to estimate a vehicle�s aerodynamic state, researchers developed algorithms and an array of flush-mounted pressure sensors to estimate the aerodynamic state of an uncontrolled hypersonic flight experiment [Refs 8, 9]. A more recent flow visualization method that researchers have proven in the wind tunnel is Femtosecond Laser Electronic Excitation Tagging (FLEET), and they investigated FLEET as a measurement solution for a hypersonic air data system [Ref 10]. Researchers have demonstrated flow-imaging rates of 100 kHz using FLEET [Ref 11]. Given the extremely high speed of hypersonic vehicles, one might reasonable consider using only the inertial velocity vector to estimate the aerodynamic state. However, hypersonic vehicles go through large speed ranges as they accelerate to hypersonic speeds and decelerate while maneuvering. The difference between Earth-relative and Air-relative velocities can become non-trivial, and this large flight envelope ultimately requires hypersonic air data systems that also work below hypersonic speeds. Researchers addressed this challenge by investigating air data solutions built primarily on more complex algorithms rather than more complex sensors [Ref 12].

Continuing these scientific and technological developments, the objective is to develop the flow theory, measurement technology and estimation algorithms to enable non-intrusive aerodynamic state sensing for hypersonic flight control. Researchers have investigated and demonstrated numerous methods for hypersonic flow visualization in a wind tunnel, and they have made some headway towards translated these methods to flight vehicles. Successful performers will prototype a flight-representative, non-intrusive air data system with performance sufficient for flight control from subsonic through hypersonic conditions. Detailed modeling and analysis of the air data system, rigorous testing and model validation of subcomponents are critical first steps. Key system parameters and outputs are:

� Air data measurement accuracy & precision

� Air data measurement rate

� Air data measurement time delay

� Air speed

� Aerodynamic angles

� Air density and temperature

� Robustness to hypersonic conditions, e.g., ablation, temperature, plasma, shocks, etc.

� Robustness to weather and environmental conditions

� Measurement range from subsonic through hypersonic


Proposers must explicitly answer all of the Heilmeier questions to be considered for an award.

PHASE I: The performer will work with Government and Industrial partners to establish a range of flight conditions for aerodynamic state sensing. Once the flight envelope is established, the performer will focus on evaluating current air data technology as well as investigating potential new approaches. New approaches may be driven by recent advancements in measurement techniques for flow diagnostics, modelling techniques for flow/structure interaction, high temperature materials for sensors, or any other technology that can produce a signal with a reliable correlation to a vehicle�s aerodynamic state.

The performer will deliver the theory, modelling, and analysis of an air data system that functions from subsonic to hypersonic flight conditions. The theory will include a detailed explanation of the working principles behind the system, from flow dynamics to sensor dynamics. Modelling will include first order dynamics of the vehicle flow and sensors as well as algorithms for estimating a vehicle�s aerodynamic state. Analysis will include simulation results and predicted performance of the system based on the first order models. These deliverables will be in addition to the Navy�s standard Phase I deliverables listed in a contract award. A milestone for continuing to Phase II will be conceptual design calculations indicating that the proposed solution meets the established performance criteria.

PHASE II: The performer will refine the theory of operation, increase model fidelity, and conduct higher order analysis to support the detailed air data system design. The performer will complete the engineering and detailed design for the concept developed in Phase I. Design details include physical and electrical interfaces, materials & devices, fabrication & assembly methods, signal conditioning electronics, embedded software, processors, power supply, cooling, etc. The analytical model developed in Phase I will be updated to include component models with sufficient complexity to predict the prototype system�s performance. The detailed explanation of the working principles behind the system will be updated to include implementation considerations such as quantization, sensor noise, sampling delays, filter dynamics, data fusion, etc. The model will be used to justify component requirements and predict the prototype system�s accuracy. The Phase II base scope will also produce a detailed test plan to validate both the system and the dynamic model. The test plan will cover everything from component level testing, ground testing, and flight testing. Ideally, flight testing would include hypersonic flight, but testing may be limited to supersonic flight. Test and validation for critical components will be included in the Phase II base period. Milestones required for the Phase II Option, if exercised, will be a detailed prototype design, validated test results for critical components, a detailed system model predicting acceptable performance, and an approved test plan. The Phase II Option will continue with any necessary component testing and fabrication of the prototype air data system. The milestone required for any Subsequent Phase II funding will be successful ground testing to demonstrate agreement between predicted and measured sensor dynamics. Subsequent Phase II awards will complete the test plan through flight test.

PHASE III DUAL USE APPLICATIONS: Phase III will consist of four parts:

Phase IIIa will refine the prototype design to ensure compliance with production requirements for vibration, shock, electromagnet interference, security, electrical & mechanical interfaces, etc. Three serialized production representative air data systems will be produced in collaboration with an airframe manufacturer. Calibration data will be collected and archived for all of the systems. System Serial Number 0 (SN0) will be subjected to environmental testing necessary to qualify for flight.

Two milestones required for Phase IIIb funding are acceptable calibration data for all sensors and environmental test data to demonstrate that the production design meets requirements. Phase IIIb will integrate the system SN1 into a supersonic air vehicle in collaboration with an airframe manufacturer. System SN2 will be maintained as a spare. Flight test instrumentation will be installed to gather high rate sensor data as well as truth data from conventional sensors. A ground test plan will be developed, and ground testing will be conducted to ensure proper mechanical and electrical interfacing with the host vehicle as well as functionality of the air data system and flight-test instrumentation. The performer will develop a Flight Test Plan (FTP) for testing and evaluating the system. The FTP will include prescribed maneuvers, predicted responses, and pass/fail criteria for each test case. Highly dynamic maneuvers and variable atmospheric conditions will be included. Where possible, the FTP will include experiments to simulate phenomena present in hypersonic flight, e.g., ablative particulates, high temperatures, chemical dissociation, etc. The FTP will also specify equipment, team members and training requirements. A Flight Test Readiness Review (FTRR) will be conducted to get approval to execute the FTP.

The milestone required for Phase IIIc funding is a successful FTRR. Phase IIIc will execute flight tests following the FTP. The flight experiments should produce data suitable for documenting the air data system�s accuracy and precision in an operational environment. The performer will assess the results and estimate the impact of hypersonic flight conditions on the system performance. The performer will draft a Flight Test Plan for conducting a hypersonic flight test of the air data system.

The two milestones required for Phase IIId funding will be successful supersonic flight experiments with simulated hypersonic flight phenomena and an approved FTP for a hypersonic flight test. Phase IIId will execute the hypersonic FTP. The FTP will include vehicle integration, flight test instrumentation, telemetry, ground testing, training, and execution of the flight experiment. The milestone for a successful Phase IIId will be hypersonic flight data demonstrating the efficacy of the air data system as a flight control sensor for precise, accurate, and high rate measurements of a hypersonic vehicle�s aerodynamic state.


1.       Leyva, I. "Introduction to the Special Section on the Boundary Layer Transition (BOLT) Flight Experiment". Journal of Spacecraft and Rockets. Vol. 58, No. 1, Jan � Feb 2021

2.       Boutier, A. (Ed.). (2012). New trends in instrumentation for hypersonic research (Vol. 224). Springer Science & Business Media.

3.       Brooks, J. M., Gupta, A. K., Smith, M., Marineau, E. C. "Development of Non-Intrusive Velocity Measurement Capabilities at AEDC Tunnel 9". AIAA 2014-1239. 52nd Aerospace Sciences Meeting. 13-17 January 2014. National Harbor, Maryland.

4.       Kang, B. H. Air data and surface pressure measurement for hypersonic vehicles. Master of Science Thesis, Massachusetts Institute of Technology, 1989

5.       Hattis, Philip. "Hypersonic Vehicle Air Data Collection: Assessing the Relationship Between the Sensor and Guidance and Control System Requirements". 1990 American Control Conference [ACC 1990], May 23, 1990 - May 25, 1990, San Diego, CA, United States

6.       Cattolica, R., Schmitt, R., Palmer, R. "Feasibility of non-intrusive optical diagnostic measurements in hypersonic boundary layers for flight experiments". AIAA 28th Aerospace Sciences Meeting. 1990, January, p. 627

7.       Mohamed, A. K., Bonnet, J. "Advanced Concept for Air Data System using EBF and Lidar". Flight Experiments for Hypersonic Vehicle Development, pp. 16-1 - 16-32. 2007. Educational Notes RTO-EN-AVT-130, Paper 16. Neuilly-sur-Seine, France.

8.       Bode, C., Eggers, T., Smart, M. "Numerical Generation of a Flush Air Data System for the Hypersonic Flight Experiment HIFiRE 7". New Results in Numerical and Experimental Fluid Mechanics VIII. Notes on Numerical Fluid Mechanics and Multidisciplinary Design. Vol 121. Springer, Berlin, Heidelberg. 2010.

9.       Razzaqi, S. A., Bode, C., Eggers, T., Smart, M. K. "Development of functional relationships for air-data estimation using numerical simulations". 18th Australasian Fluid Mechanics Conference. Launceston, Australia. 3-7 December 2012.

10.   DeLuca, N. J. "Femtosecond laser electronic excitation tagging (FLEET) for a hypersonic optical air data system". M.S.E. Thesis, Princeton University, Department of Mechanical & Aerospace Engineering, June 2014.

11.   DeLuca, N. J., Miles, R. B., Jiang, N., Kulatilaka, W. D., Patnaik, A. K., & Gord, J. R., "FLEET velocimetry for combustion and flow diagnostics". Applied Optics, 56(31), 8632-8638. 2017.

12.   Nebula, F., Ariola, M. "A Hypersonic Application of the Fully Sensor-Less Virtual Air Data Algorithm". AIAA 2018-1350. 2018 AIAA Guidance, Navigation, and Control Conference. January 2018.


KEYWORDS: Hypersonic flight; flight control; air data; aerodynamic state estimation; conformal sensors; high temperature sensors; in situ hypersonic flow measurement


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