Al Balushi 2
Al Balushi 20
Al Balushi 4
Major Challenges Associated with Hypersonic Air Travel
for
Mr. Timothy Chapman
Technical Communication Instructor
Western Michigan University
by
Saud Al Balushi
IEE 1030 Student
Submitted December 7, 2021
Table of Contents
Abstract 3
Introduction 4
Research Question 5
Scope and Feasibility 5
Problem Statement 6
Purpose and Audience 6
Data Sources 7
Working Definitions (optional) 7
Limitations 8
Collected Data 8
The Heating Problem in Hypersonic Air Travel 8
Heat, Materials and Structure 9
Challenges of Producing the Hypersonic Test Environment 10
Measurement Techniques and Facilities’ Characteristics 11
Possible Suggestions/Solutions in Literature 15
Catalysts 16
Conclusion 17
Summary of Findings 17
Comprehensive Interpretation of Findings. 18
Recommendations 19
References 20
Abstract
Hypersonic Air travel is not a new concept on the planet, but rather an old concept being worked upon to develop an aircraft that can operate within half the time of an ordinary craft, based on principles of the Concorde. However, despite having been worked upon since 1960s, the principles of chemistry and physics have hardly been put into physicality with assurance due to challenges being identified herein. Accordingly, the results of the study show that challenges within the research and development of hypersonic air travel are heat, material changes, universality and maneuverability as well as communication deficiencies. Findings indicate that heat is a leading concern within the field because; at hypersonic velocities, friction and air resistance are able to create outstanding levels of heat that may not be controllable within a given testing facility based on its characteristics. For instance, testing facilities differ in capabilities and limitations and choosing one provides only one advantage yet the other is also necessary; reflected shock and expansion tunnels despite their ability to accommodate high enthalpy conditions and detailed measurements and yet, continuous running and blow-down test facilities can accommodate detailed measurements and excellent running times and free-stream properties but limited by their intolerance of high enthalpy. This comes with limited variety of measurement techniques and short test times for facilities. Conclusively, the study suggests application of the zeolite catalysts and thermal protection systems (TPS) with a touch of intense collaboration among the different scientists, countries and hence facilitations.
Introduction
Hypersonic Air travel is a dream come true for the air manufacturing industry after the Concord, which operated between 1976 and 2008. A journey can take only half the time a basic airplane flight would take (Nicholls, 2018). For instance, the proposed travel planes would take under two hours for a sampled journey of Los Angeles to Tokyo in less than two hours with speeds of up to Mach-8, which is about 5,400 miles per hour and able to reach altitudes approximated to 98,000ft as compared to conventional planes (Baggaley, 2019). Following the changes in the economic market that challenged the operation of the Concorde, such as very high maintenance costs and low market for travel, hypersonic air travel was paused as the Concorde went out of operation (Nicholls, 2018). This historical trial shows that flying faster than Mach5 has been an idea orchestrated right from the 1950s in which vehicles with the hypersonic ability only experimented. Yet, there has been a resurgence of creating these in the unfolding decades (Sampson, 2021). Hypersonic travel within this technological era, compared to the former, has higher chances of improving manufacturing, considering that technology is greatly evolving. Moreover, the benefits of the hypersonic developments are immense in terms of security, business/commercial travel, and access to greater research channels in the aerospace field.
Therefore, looking into the challenges of the Concorde brings to mind the challenges currently facing the developments of the hypersonic air travel industry, especially within manufacturing. In response, the hypersonic regime and ground testing have taken up the mantle in establishing more standardized (chemical and physics-related) qualities of supersonic air travel mechanisms (Marren, 2017). However, research has been slowed by challenges in the ground test facilities and, therefore abilities. These challenges include a limited variety of measurement techniques and short test times for facilities such as the reflected shock and expansion tunnels despite their ability to accommodate high enthalpy conditions and detailed measurements and yet, continuous running and blow-down test facilities can accommodate detailed measurements and excellent running times and free-stream properties but limited by their intolerance of high enthalpy (Gu & Oliver, 2020, Jiang, Hu, Wang, & Han, 2020).
Additionally, challenges have escalated and taken time to resolve because most researchers are not well acquainted with experience in hypersonic travel, according to Baggaley (2019). This recalls the significance of this study as it seeks to enlighten on research in this area. With these technological challenges, the manufacturing industry of hypersonic planes is forecasted to improve and reach its goals approximately by 2035, taking another decade to actualize (Baggaley, 2019). This study delves into challenges in the hypersonic air travel industry’s developmental testing processes. It mainly focuses on the test durations and restricted measurement methods available at test sites considering different testing facilities such as expansion tunnels.
Research Question
The research question is: What major challenges are inhibiting the technological developments of hypersonic air travel?
Scope and Feasibility
The study will focus on major, and not all, challenges inhibiting the developments in the hypersonic air travel industry. These will mainly be testing time and the limited variety of measurement methods of the test facilities. This scope is very important because other challenges are attached to distinct characteristics such as geographical location. Such general research would be less feasible than focusing on these points. As such, the solutions recommended herein are applicable and feasible within this scope and therefore increase accuracy. The report is therefore formatted to avail information on the challenges from major hypersonic travel grey literature sources and structured as; introduction, collected data and Conclusion with important sub-sections such as problem statement in the introduction, Catalysts.
Testing limitations, Measurement techniques and challenges in data collection and finally presenting a discussion with recommendations based on relevant literature in conclusion. The study made use of research articles that were selected to inform the challenges in hypersonic air travel.
Problem Statement
The world’s challenge with hypersonic air travel is the test duration and restricted measurement methods available at test sites. Expansion tunnels, for example, have test times in the tens of milliseconds (Jewell et al., 2017). The short test period permits shock waves to collide with a continuous surface, lengthening the time required for various processes to occur in the shock tubes (Rodriguez et al., 2009). As a result, when a shock wave interacts with the contact surface, a transmitted wave shock is likely to develop. The inability to assess a full-scale flight vehicle throughout a wide range of flight conditions is one of the limitations of reflected shock tunnel measurement approaches.
Purpose and Audience
This research investigates the difficulties in the hypersonic air travel industry’s developmental testing processes, emphasizing the short test duration and a limited number of evaluation methods available at testing facilities, taking into account various research facilities such as expansion tunnels. Furthermore, the study aims to enlighten academics, scientists, and engineers working on hypersonic flight advancement. The study benefits companies such as Boom Supersonic, aircraft builder Hermeus, United Airlines and other manufacturing affiliates in identifying solutions to challenges faced in the technological development of hypersonic aircraft.
Data Sources
Considering the nature of the study (engineering-based), particular databases such as Science Direct, availing journals such as Chinese Journal of Aeronautics, the z-library and U-M library for more articles. Moreover, the study used scientific specific literature from other academic sources/technological sources such as aerospace testing international, Airforce magazines, IEEE Explore for more information in the specified field.
Working Definitions (optional)
Hypersonic regime: a physics- and chemistry-based characterization of high-speed flight in the sensible environment at which certain physics- and chemistry-based manifestations that are defining features of atmospheric flight at speeds greater than five times the speed of sound (Mach 5) get to be highly significant to vehicular development and production
Ground testing: a way of determining the efficacy/evaluation of theoretical assertions about hypersonic flight using flight testing and computer technologies.
Wind Tunnel Testing: Evaluation methods in which wind tunnels are used to test proposed aircraft and engine components models. During a test, the model is placed in the test section of the tunnel and air is made to flow past the model.
Limitations
Considering the current remote status of education and research, the study took up a more secondary research aspect than experimental research used for scientific studies. Following this designation, the discussion of the study is limited to particular challenges within testing facilities irrespective of other factors such as geographical settings and differences that may not be considered. Moreover, the discussion will focus on three articles selected and assessed for validity and reliability based on the topic, informed by literature availed in background information.
Collected Data
Hypersonic vehicles travel at speeds greater than five times the speed of sound, enabling a new class of aircraft vehicles that can provide faster access to space, long-range military reaction, and commercial air travel. The main problem (from which most other problems hail) is the management of “HEAT”; the heat produced by pressure drag and shock waves caused by travelling faster than the speed of sound. The temperatures encountered by a hypersonic vehicle are so extreme that ordinary materials cannot resist them while maintaining their strength.
The Heating Problem in Hypersonic Air Travel
Given that hypersonic air travel mainly travels through the air, a fluid, forces such as drag are to be expected and therefore controlled. However, drag can easily be controlled by making the craft’s body slender and finer regarding the physical shape. However, the reduction of drag, among other processes, is a cause of structural heating, and for this reason, the shape of the aircraft has been designed with a blunt nose. For instance, the heating of the nose (stagnation point) is inversely related to the radius of the nose. This whole basic system shows that the design and product of hypersonic air travel manufacturing is heat but not drag-driven. As such, hypersonic flight’s heating has become a major problem (Dickeson et al., 2009). However, heating varies cubically with velocity in the hypersonic realm, drag changes as a quadratic function.
Heat, Materials and Structure
Heat starts being caused by friction, which most of the materials cannot withstand under such thermal stress. Moreover, materials that can handle this stress are often heavy, costly or both, and the use of the material avails one of two of the advantages (Theon, 2021). Meanwhile, Sampson (2021) notes that while the heating problem continues to reduce due to increasing technologies in many tests on materials, the problem has become a threat in certain flights in which the instrumentation systems are 80% smaller than they were two decades ago because high heat dissipation becomes a concern with increased operation data rate. The heating problem is further identified in thermo and elastic propulsion of the aircraft. The designers have to choose; to either have a very light vehicle (within a permissible pay-load size) or high thermal protection. Hypersonic air crafts are built in a way that makes them unstable (with an engine at the rear and long front body) and therefore requires a low control bandwidth to increase stability (Dickeson et al., 2009). However, achieving this is limited by structural (flexibility), actuator, uncertain high-frequency dynamics, and varying limitations such as controlled saturation levels.
Moreover, higher Mach numbers (which are desirable) cause outstanding heating and flexing levels; for instance, a front body flex induced by such heat can cause a bow shock wave and engine in-let oscillations, which impede aircraft performance in terms of momentum, stability and overall performance (Dickeson et al., 2009). This fails and becomes a controlling system error where the craft is open, unstable, and too light/flexible. The airframe becomes a structural problem and challenges propulsion because shape varies with speed and range.
Research further indicates that the hypersonic flights’ heating problems are attenuated by their impacts; bow shocks caused by front body heat flexing increase the heating impact, destroying structural modifications (Dickeson et al., 2009). It is noteworthy that heat issues are consistently expected at almost all points of the hypersonic air travel flights challenges. For instance, the stability of the hypersonic boundary layer as some of the core challenges is related to heat control; the occurrence of a series of instability modes known as the Mack modes is a unique feature of a hypersonic boundary layer. There is just one destabilization mode in a low-speed boundary layer, Tollmien–Schlichting (T–S) waves. However, there are higher unstable modes in a hypersonic boundary layer, including first-mode instability, equivalent to T–S waves in the low-speed boundary layer (Lee & Chen, 2018). The linear unstable modes make up the so-called Mack modes. They also contribute to the transition by generating large variations. As a result, low-speed trends differ from hypersonic trends, such as the effect of surface temperature (Lee & Chen, 2018).
Challenges of Producing the Hypersonic Test Environment
The hypersonic test capabilities of major developments have been challenged with a shortage of testing facilities which, according to Sampson (2021), have slowed down hypersonic concepts and technologies. Moreover, the study shows that while the majority of the studies have taken up the desire to delve into the new technology, they have remained at the R&D (research and design) phase only due to this challenge (Sampson, 2021). The challenges of the hypersonic air travel environment can be classified into different spheres; heat, material advancements, maneuverability and communication within the field to cause significant changes (Hunn, 2020, Martin, Ambrose, & Greene, 2021). Given the complexity of the environment, communication and connection is required, both technologically and technically to involve the quality of signals in such an extreme environment in which waves continuously interact and technically as a requirement to work in teams. Following the challenges of the environment in which the experiments are made, turbulences (developed and on-set turbulence) are great challenges in experimentation especially calling for attention to the hypersonic boundary layer (Lee & Chen, 2018). Even more challenging is the absence of a perfect measuring and quiet wind tunnel for experimentation.
Measurement Techniques and Facilities’ Characteristics
Different modes of experimental testing present different limitations and abilities that may be used to decide on the better method to use. However, major techniques are; Ground simulation methodology (experiment the different hypersonic Aerodynamic flow fields over the vehicles) and Air-breathing propulsion testing used for scramjets. According to studies and experiments by Jewell, Parziale, Leyva, and Shepherd (2017), the experimental field of the hypersonic air travel vehicles is complex and the results therein are dictated by a variety of situations that make the environment hard to completely create; first all the required measurements have to be made in limited number of facilities and for this case, shock waves could only be measured from a free-piston-driven reflected-shock tunnel which is only one location and also, the measurement of various changes within the wind tunnel is dependent on different transition tunnel parameters that could be almost immeasurable in a repeatable way/manner. This condition reflects one in which the available measuring techniques are unable to measure a full vehicle range of different parameters and flight conditions for two reasons, limited measurement techniques and minimal facilities to accommodate full vehicle research. Flow tunnels require some of the lowest noise that can be compared to a real flight and yet, the transitional number (Reynolds Number) used for the prediction of the flow transitions within the tunnels as would be required is directly related to the heating effect, causing heating evaluation and assessment, or even management to become a critical issue in the development of the air crafts (Lee & Chen, 2018). In this light, other challenges come into play; firstly, given the high pressures, temperatures, and disturbance frequencies in hypersonic flow, developing a transducer for monitoring disturbance is difficult. Secondly, the primary source of noise is acoustic waves scattered from the nozzle walls. The fundamental goal of silent tunnel design is to reduce noise levels. Finally, matching experimental procedures is extremely challenging and requires independent development (Lee & Chen, 2018).
Testing facilities include Shock tunnels and expansion tunnels, Blowdown tunnels, Ludwieg tubes, hotshots, and gun tunnels. For assessments and evaluation in particular conditions, unique testing facilities can be used. For instance, the blowdown tunnels and gun tunnels are applied in cases of low enthalpies (lower than 2 MJ/kg), reflected/shock tunnels used for high enthalpy environments (approximately 2–7 km/s) and an expansion tube in very high enthalpy environments, among others.
Figure 1 Blowdown Wind Tunnel
Figure 2 Gun Tunnel
Figure 3 Reflected Tunnel
Source: Gu & Oliver (2020)
Besides the experimental environment being complicated to re-create and standardize, Gu & Oliver (2020) add that the different testing facilities for the measurements have very varying capabilities and limitations that influence the measurements; Shock tunnels and expansion tunnels can create situations with extremely high velocities, but their test times are extremely short. Figure4 presents that the test time for expansion tubes is in the tens of microseconds range. Blowdown tunnels, Ludwieg tubes, hotshots, and gun tunnels, on the other hand, have extensive test times but can only provide low velocity conditions. Figure 1 shows that the test times for gun tunnels and hotshots are in the tens of milliseconds, while the test times for blowdown tunnels are in the seconds, yet only hotshots can produce cumulative temperatures as high to 6000 K (Gu & Oliver, 2020).
Figure 4 Unique Characteristics of Available Facilities
Source: Gu & Oliver (2020)
In comparison to some of the other capabilities, reflected shock tunnels feature medium duration test times and medium efficiency capabilities, with test times in the order of a few milliseconds. The nozzle exit velocity of reflected shock tunnels is typically limited to roughly 7 km/s, the total enthalpy is 25 MJ/kg, the total temperature is 10000 K, and the total pressure is 200 MPa. However, driver capabilities, which have the ability to support faster acceleration and total pressure circumstances, are usually not the primary factor to this performance constraint. The existing material limits are primarily to blame for the performance limitations of reflected shock tunnels. The high-pressure loss damages the structure, while the high stagnation temperatures damage the material. In the case of the T3 and T5 reflected shock tunnels, the influence of premature arrival of driving gas at the test section rises with increasing shock velocity, culminating in essentially no test time beyond 7 km/s (25 MJ/kg) (Gu & Oliver, 2020). Furthermore, reflected shock tunnels are inefficient facilities for creating very high enthalpy flows due to considerable radiation losses by the nozzle reservoir above total enthalpies as low as 10 MJ/kg. However, testing in as large a facility as possible is not always desired. Smaller facilities have the benefits of being more cost-effective to operate. For instance, shock tubes are not utilized to generate flows around test models, unlike the other facilities. The moving shock wave in the shock tube, on the other hand, is being researched. While there is an obvious disadvantage in that the variety of experiments available in shock tubes is limited, shock tube experiments have various advantages (Gu & Oliver, 2020). To begin with, the shock tube’s core flow is restricted to one dimension, allowing thermochemical kinetics and radiation to be examined in a straightforward gasdynamic setting. In fact, at low and medium enthalpy conditions, a wholly stalled condition at the shock tube’s end can be forced to establish a zero-dimensional gasdynamic environment, totally isolating the thermochemical kinetics and radiation phenomena. In some cases, such as scramjet testing, it is also not necessary to create extremely high velocity conditions. Likewise, for the investigation of thermo – chemical kinetics, extensive test times may have not been required.
Possible Suggestions/Solutions in Literature
According to Dickeson et al. (2009) who agree with Glass (2008), a thermal protection system (TPS) is recommended to reduce impacts of thermal flexing in the aircrafts and clear decision and choice on structural preferences assessed to ensure that all options and expected changes are understood. Moreover, to withstand structural destruction caused by excessive heating, further research suggests the use of high density and strength ceramics such as ceramic matrix composites (CMCs) to provide for more tolerant material in manufacturing. Glass, 2008 argues that the shift from rocket-based aircrafts to air-breathing crafts requires the technology to also shift away from insulation of the aircrafts to different types of thermal protection systems such as leading edges, control surfaces and acreage TPS. However, the same can be argued as environmentally un-friendly and less durable despite having solution to the heating problem, an area that provides opportunity for further research, in such a case. Also, further advancements in the development of accuracy of Parabolised Navier-Stokes (PNS) flow solvers can be applied in predictions and therefore preventions of over-heating in hypersonic air travel. Studies by Mifsud, Estruch-Samper, MacManus, Chaplin, & Stollery (2012) suggest the use of this technology following an assessment of the significant impacts of the Spalart-Allmaras and Baldwin-Lomax turbulent models on the heat transfer exchanges. This study found significant relationship between the PNS predictions, measurements and empirical methods for the front-body of the vessel.
Catalysts
The heating problem has been a bottleneck to the development of hypersonic air travel for a very long time that developments in this area cannot be overlooked. Ultimately, Azeez (2021) identifies that the use of catalysts can solve this issue with further research. Catalysts are chemicals that are added to chemical reactions to accelerate reaction times without changing the reaction itself. The catalysts can be shaped into the most effective shapes to interact with the fuel burning and cooling process by 3D printing them. A 3D printer is used to generate the catalysts, which are made of metal alloys and covered with synthetic minerals called zeolites (Azeez, 2021). The zeolites react with the metal when it is heated. The researchers tested their idea in a controlled lab setting, simulating the severe heat and pressures encountered by the fuel at hypersonic speeds.
Conclusion
Summary of Findings
Collectively, thermal control and management within the experimentation and assessment of the hypersonic air travel environment comes up as some of the most important concerns in the developments within this field. Hypersonic systems are built to operate in hostile conditions and must be able to overcome a variety of obstacles. As a direct result of having a specific fuel (FER) margin (additional fuel required for thermal choking to occur or for or stoichiometric fuel-to-air ratio to be reached), thermal limits are imposed on control system design (Dickeson et al., 2009).
In unison, the findings indicate major challenges include heat flux that directly causes limitations in the nature of materials used, dramatically changing physics dynamics with Mach number and highly limited architectural designs based on other challenges. Starting with issues in architecture, leading edge bluntness drives drag because in hypersonic air travel, air cannot simply be considered as air due to the change of the constituents across the flow field, boundary layer transition from laminar to turbulent flow also impacts the drag, heating, stabilities, and aerodynamic coupling at different axes (Lee & Chen, 2018). The control of size, weight, power required and coupling this with the optimization of propulsion, air frame and control surfaces with the overall requirement of quality performance is almost un-achievable and remains one of the greatest challenges (Sampson, 2021, Dickeson et al., 2009).
Considering the nature of materials as some of the greatest experimental concerns dealing with hypersonic air travel, the research indicates that outstanding heat influx over small areas coupled with continuous changes in very high temperatures, oxidation and catalytic effects are further attenuated with changing material properties on flights and high temperature gradients making the flights prone to thermal shock (Hunn, 2020). Moreover, this becomes a bigger problem when encountered by limited number and options of sensors and communication antennas (Martin, Ambrose, & Greene, 2021).
Comprehensive Interpretation of Findings
The major problems that are being faced within the research and development of hypersonic air travel are heat, material changes, universality, and maneuverability as well as communication deficiencies. Findings indicate that heat is a leading concern within the field because; at hypersonic velocities, friction and air resistance are able to create outstanding levels of heat that may not be controllable within a given testing facility based on its characteristics. Heat must therefore be managed through, often tough and yet light weight shields and protection systems that can be used at these conditions in which the flight is to travel. Managing extreme heat levels comes with a task to take on changes and qualities of materials that are either unavailable or scarce to the industry and as such, the industry is then tasked to look into the creation, innovation and development of new solutions of materials that can handle the operating temperatures of the hypersonic air travel (Martin, Ambrose, & Greene, 2021). Extreme environments further pose challenges in the industry through the possibility of causing structural impairments as exemplified in the presented data by heat induced flexing in the aircrafts. Certainly, these induce limitations of the nature of structural designs and therefore reduce the scope that can be experimented within the industry. Furthermore, the microenvironment is so hostile that pressure surges across the shocks resemble a “detonation,” and they can engage with both the boundary layer (Lee & Chen, 2018). Within just a few moments, propulsion systems must compress, disassemble, mix, react, and generate thrust. Ground testing under ideal conditions is extremely difficult since the engine must keep the formation of single phase continuing like “keeping a match lighted in a thunderstorm.”
Flexibility and durability of the created flights through extreme environments is greatly contested and challenging because the experimentation of these crafts is created in uncertain conditions and environments. In this regard, research indicates that there is a gap in the availability and quality of testing facilities across the globe which ultimately shows that the products therefore are almost not trustworthy. Moreover, this is where communication in the field becomes quite important even as various institutions become competitive in creating the very first successes of their time even after existence of the Concorde. Communication translates into the unification of knowledge to overcome these challenges and coming together as researchers, not rivals, to solve existing problems as designers that seek a similar solution.
Recommendations
Collaboration presents some of the most important development possibilities in the research field and begins with; sharing of information and development opportunities to overcome the technological and technical challenges through finding solutions to increasing the range of testing facilities and their quality. Moreover, collaboration can be done through joint acquisitions, internal team works (as a state or industry partnering) and multiple domain action on operations to create a network among the hypersonics.
The study also finds that the possible use of catalysts and zeolites can be suggested based on on-going experiments to reduce the heating problem in the development of hypersonics.
References
Azeez, W. (2021). Have researchers found a way to power hypersonic jets from London to New York in 90 minutes? EURO NEWS. Retrieved from https://www.euronews.com/next/2021/09/09/could-3d-printed-catalysts-power-hypersonic-flights-from-london-to-new-york-in-90-minutes
Baggaley, K. (2019). This hypersonic airliner would take you from Los Angeles to Tokyo in under two hours. NBC News. Retrieved from https://www.nbcnews.com/mach/science/hypersonic-airliner-would-take-you-los-angeles-tokyo-under-two-ncna1045986
Dickeson, J., Rodriguez, A., Sridharan, S., Soloway, D., Korad, A., Khatri, J., … Vogel, J. (2009). Control-relevant modeling, analysis, and design for scramjet-powered hypersonic vehicles. 16th AIAA/DLR/DGLR International Space Planes and Hypersonic Systems and Technologies Conference. doi:10.2514/6.2009-7287
Glass, D. (2008). Ceramic matrix composite (CMC) thermal protection systems (TPS) and hot structures for hypersonic vehicles. 15th AIAA International Space Planes and Hypersonic Systems and Technologies Conference. doi:10.2514/6.2008-2682
Gu, s., & Oliver, H. (2020). Capabilities and limitations of existing hypersonic facilities. Progress in Aerospace Sciences. Retrieved from https://www.researchgate.net/publication/339683395_Capabilities_and_limitations_of_existing_hypersonic_facilities
Hunn, D. D. (2020). The Road to Hypersonics – Key Challenges, Advantages and Disadvantages. Lockheed Martin Missiles and Fire Control. Retrieved from https://www.aerosociety.com/media/12849/2-david-hunn.pdf
Jewell, J. S., Parziale, N. J., Leyva, I. A., & Shepherd, J. E. (2017). Effects of shock-tube cleanliness on hypersonic boundary layer transition at high enthalpy. AIAA Journal, 55(1), 332-338. doi:10.2514/1.j054897
JIANG, Z., HU, Z., WANG, Y., & HAN, G. (2020). Advances in critical technologies for hypersonic and high-enthalpy wind tunnel. Chinese Journal of Aeronautics, 33(12), 3027-3038. doi:10.1016/j.cja.2020.04.003
Lee, C., & Chen, S. (2018). Recent progress in the study of transition in the hypersonic boundary layer. National Science Review, 6(1), 155-170. doi:10.1093/nsr/nwy052
Marren, M. E. (2017). Hypersonic flight regime and ground testing. The Science Authority. Retrieved from https://www.accessscience.com/content/YB160013
Martin, L., Ambrose, R., & Greene, S. (2021). Four Challenges to Hypersonics. LOCKHEED MARTIN. Retrieved from https://www.lockheedmartin.com/en-us/capabilities/space/executive-blog-rick-ambrose-scott-greene-lmiq.html
Mifsud, M., Estruch-Samper, D., MacManus, D., Chaplin, R., & Stollery, J. (2012). A case study on the aerodynamic heating of a hypersonic vehicle. The Aeronautical Journal, 116(1183), 873-893. doi:10.1017/s0001924000007338
Nicholls, S. (2018). Life after Concorde: Bringing back supersonic air travel. Neuro News. Retrieved from https://www.euronews.com/2018/07/19/life-after-concorde-bringing-back-supersonic-air-travel
Sampson, B. (2021). How engineers test and develop hypersonic aircraft and weapons. AERO-SPACE ENGINEERING INTERNATIONAL. Retrieved from https://www.aerospacetestinginternational.com/features/how-engineers-test-and-develop-hypersonic-aircraft-and-weapons.html
Theon, R. (2021). Hypersonics: Developing And Defending Against Missiles Far Faster Than Sound. BREAKING MEDIA. Retrieved from https://breakingdefense.com/2021/09/hypersonics-developing-and-defending-against-missiles-far-faster-than-sound/
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