The first grand challenge, aerodynamics and flight mechanics, spans both fundamental and applied research that underpins every futuristic aerospace system. Engineers are working to combine theoretical, experimental, and computational studies of multidisciplinary nature to advance environmentally responsible aerodynamic technologies. The topics include the aerodynamics of streamlined and bluff bodies, the stability of free and wall shear flows, laminar, transitional, turbulent, and separated flows, jets, wakes, and shear flows in general. Passive, active, and re-active flow control, using open and closed loop schemes with novel actuators and sensors, promises to reshape how air vehicles manage drag and lift. Reduced-order modeling and flow control, fluid-structure interaction, and aeroelastic analysis and control are also central, alongside flight mechanics innovations such as nonlinear six-degree-of-freedom flight simulation, coupled lateral and longitudinal aircraft motions, and flight control design for all categories of aircraft.

Computational fluid dynamics sits at the heart of this challenge. Turbulence and transition modeling and validation remain stubborn problems, and researchers are pushing Large Eddy Simulation and Direct Numerical Simulations to resolve flows that simpler models cannot capture. Machine learning and artificial intelligence are increasingly applied to aerodynamics, enhancing computational fluid dynamics with data-driven methods. High-lift systems, which allow large commercial aircraft to fly safely at low speeds during takeoff and landing, are another active frontier, as are applications to aircraft, rotorcraft, and other air vehicles, and even the aerodynamics of ground and marine vehicles.

The second grand challenge concerns materials and structures, where demand from the aircraft and aerospace industries has increased dramatically. High-strength, lightweight, non-corrosive, recyclable, ultra-violet and impact resistant properties are key factors for materials for new types of flying vehicles. Advanced manufacturing processes, including additive manufacturing, digital manufacturing, and virtual-twin technologies, provide new solutions for space structures subject to harsh environments. Nanotechnology supports fundamental changes in the mechanical properties of metal and polymer-based composites, adding better electrical, thermal, and multifunctional properties at extreme temperature conditions. The electromagnetic shielding properties of polymer-based composites could be altered by nanofillers for space re-entry vehicles.

For small space structures such as cube satellites, metamaterials, deployable and morphing structures are of intense interest. The development of fully electric-driven and hydrogen-electric hybrid eVTOL and eSTOL vehicles requires new materials to compensate for the weight penalty of batteries. Meanwhile, the ambient conditions of flying vehicles at high altitude and in space, with low temperature, low pressure, and radiation attacks, may deteriorate material properties. Space debris and natural meteoroids moving at hypervelocity can damage satellites and space stations easily due to accumulated impact energy, and nano-structural design may be promising to dissipate energy and prevent catastrophic damage. Carbon-based materials driving high-temperature resistant composites, energy composites including supercapacitors, cryogenic fuel tanks, and radiation-resistant coatings also fall within this specialty.

The third grand challenge, aerospace propulsion and energetics, may be the most consequential for sustainability. Conventional aircraft propulsion relies predominantly on fossil aviation fuels and has considerable environmental impact through greenhouse gas emissions, air pollutants, and contrails. In response, research is ongoing on fully electric, hybrid-electric, and hydrogen-fueled propulsion systems, alongside bio-derived and synthetic fuels. These multidisciplinary efforts involve bio-chemically engineered fuels, fuel cells for efficient conversion of chemical energy to electricity, next-generation batteries, and new hybrid and electric concepts for distributed and embedded propulsion units that allow air vehicle geometries to be re-envisioned and optimized.

Air-breathing hypersonic propulsion has been pursued for decades but remains in the research and development phase, owing to the inherent difficulty of designing robust systems capable of supersonic combustion and surviving hypersonic aerothermodynamic environments. Scramjet engines operating on hydrogen or liquid fuels must be sufficiently compact and robust to integrate into an air vehicle and operate for minutes to hours rather than seconds. Current research challenges include supersonic fuel-air mixing, combustion stabilization, materials and cooling systems for thermal management, and the development of ground-based experimental facilities to test hypersonic concepts. Electric space propulsion, including Hall, ion, and electrothermal thrusters, has grown rapidly, and new concepts under development include electrospray arrays, radio-frequency and microwave systems coupled with magnetic nozzles, pulsed inductive thrusters, magneto-plasma-dynamic and nuclear thermal propulsion systems. Green monopropellants and additively manufactured energetic materials with reduced environmental impact round out the challenge.

The fourth grand challenge, guidance, navigation, and control, is receiving increased attention as unmanned systems play an irreplaceable role in civil and military aviation. Without navigation and control, an unmanned system would have no autonomy. Researchers are advancing dynamic modeling, fault management, reconfigurable and fault-tolerant flight control, multi-sensor data fusion, sensor and actuator fault monitoring and diagnosis, and the detection and mitigation of anomalous events and threats. Upset recovery and management of loss of control in-flight, safe flight envelope prediction and protection, and intelligent functionalities for trustworthy and evolvable autonomy for next-generation unmanned systems, including satellites, unmanned aerial vehicles, and unmanned underwater vehicles, are all active frontiers. As individual systems evolve and operate with greater autonomy within networked and distributed cyber-physical environments, the challenges continue to grow.

The fifth grand challenge, intelligent aerospace systems, describes a major paradigm shift driven by artificial intelligence coupled with increasingly autonomous aerospace systems. Advanced air mobility alone has an estimated global market value of 1.9 trillion US dollars over the next 25 years, and recent demonstrations by the civilian space industry have opened avenues such as space tourism while investments in long-term deep space missions grow. Autonomy is a key enabler and must be trustworthy, synergizing with human operators to augment performance and assure safety. Topics include responsible, trustworthy, transparent, and certifiable AI, explainable AI, assured autonomy for non-deterministic systems, cyber-attack resilience, real-time learning and adaptation, AI-driven prognostics and health management, human-AI teaming, and AI-enabled augmented and virtual reality for training and concept of operations development.

The sixth grand challenge, aircraft engineering and design, confronts safety, long-haul flights, sustainability, and capacity. Modern designs have long been driven by a higher, faster, and farther doctrine, with continuous performance improvements accompanied by continuous increases in complexity and cost, a paradigm no longer acceptable to suppliers or customers. The requirement now is performance improvement with lower cost. Lean aircraft engineering concepts, integrated product and process development, and systems engineering, a holistic approach spanning customer specifications, conceptual design, risk analysis, functional and physical architecture, trade studies, manufacturing, testing, and life cycle cost management, have become the state-of-the-art methodology for organizing aerospace production. The traditional three-step design process of conceptual, preliminary, and production design resulted in long cycle times, high risk, and high cost; the way forward is an integrated approach that simultaneously considers design, manufacturing, and support, using modeling and simulation tools to conduct cost-performance trade-offs early. Together, these six grand challenges define the research agenda that will determine whether the next century of flight is as transformative as the last.

Subject of Research: Aerospace Engineering Faces Six Grand Challenges That Will Define Flight's Next Century

Article Title: Grand challenges in aerospace engineering

Article References: Agarwal, R. K. (2024). Grand challenges in aerospace engineering. Frontiers in Aerospace Engineering, 3, Article 1383934. https://doi.org/10.3389/fpace.2024.1383934

Image Credits: AI Generated

DOI: 10.3389/fpace.2024.1383934

Keywords: aerospace engineering, aerodynamics, propulsion, hydrogen aircraft, hypersonics, artificial intelligence, materials science, aircraft design, sustainable aviation, autonomy, Grand, challenges