Aerospace

The Lynn Booth and Kent Kresa Department of Aerospace, founded in 1926 as the Guggenheim Aeronautical Laboratory, aims to maintain its long-held position as a premier department in aerospace education and research, by attracting the best minds, students, and faculty, and providing the best facilities for aerospace research. Since its founding, our department has been committed to fundamental science and to the education of new generations of aerospace science and technology leaders. Our goal is to enable reliable, sustainable, and affordable systems for air and space. The department is also the home of the Center for Autonomous Systems and Technologies (CAST), which includes a state-of-the art wind-shaper fan-wall, a drone arena, and a space robotics laboratory, and also of the Space Structures Laboratory that develops, builds and tests ultralight deployable structures for the Space Solar Power Project (SSPP).

Aerospace has evolved at Caltech from a field of basic research and engineering, primarily related to the development of the airplane, into a discipline encompassing a broad spectrum of basic as well as applied problems in fluid dynamics, mechanics of solids and materials and design and control of autonomous systems. Educational and research thrusts include the application of mechanics to various aspects of space exploration and to the study of biosystems and bio-propulsion. Research at the Booth-Kresa Department of Aerospace has traditionally pioneered exploration of areas that have led to subsequent significant technological achievements. This tradition places a high premium on in-depth understanding of fields both closely and remotely related to the behavior of fluids, solids, combustion, materials, and structures, such as physics, applied and computational mathematics, dynamical systems, earthquake physics, atmospheric studies, materials science, micro- and optoelectronics, microfluidics, bioinspired design, biomedical devices, and even astrophysics. Aerospace students are known and sought-after for the breadth and depth of their education and for their ability to deal with new and challenging problems.

Major areas of experimental, theoretical, and numerical research currently pursued by aerospace students at Caltech are briefly described below.

• Mechanics of Lightweight Space Structures. Current efforts in the field of next-generation deployable space structures aim to increase reliability and lower fabrication and assembly costs by moving toward structures that consist of only a small number of separate pieces able to undergo large elastic deformations. These elastic–stored-energy structures return to their original, unstressed configuration when they are released in orbit. The design of these structures requires accurate structural models that incorporate geometry change and contact effects in sufficient detail to capture the actual behavior that is observed in ground tests. Local and global instabilities are often observed during folding/deployment, and their effects can also be important. Ultimately, validation against space-based experiments will be pursued for a selected number of structural configurations. In parallel to these studies, thermomechanical constitutive models for ultrathin composite materials for these novel deployable space structures are being developed. Extensive studies of the deployment, elastic, and viscoelastic stability of stratospheric balloons are also being conducted.
• Physics of Fluids. Physics of fluids refers to research in areas closer to applied physics than to direct technical applications. Present active research includes studies in
  • gas dynamics and hypervelocity flows,
  • diffraction and focusing of shock waves and detonation waves,
  • shock-induced inertial instabilities,
  • transient supersonic jets,
  • laser-scattering diagnostic techniques for fluid-flow measurements,
  • coherent structures and their role in transition and turbulence,
  • two-phase flows and turbulent mixing,
  • chemically reacting flows, and
  • experimental manipulation and control of wall-bounded flows for improved flow characteristics, such as reduction of drag, noise, and structural loading.
• Physics of Solids and Mechanics of Materials. Mechanics of materials research involves both the quasi-static and dynamic characterization of the mechanical behavior and failure of solids. To understand materials for applications in a wide range of structures relevant to aerospace as well as other engineering disciplines, both the physical foundations of that behavior and the mathematical or numerical representation of such behavior needs to be understood. Accordingly, studies involve material response at both the macroscopic (continuum) scales and the micro- and nanoscales. Of interest are typical engineering metals, multiphase (composite) materials, polymers and ceramics, thin film materials used in microelectronic and optoelectronic applications, soft tissue mechanics of materials, and active materials used in structural actuation and controls. Other areas of active research include the study of highly nonlinear dynamics in solids, multiscale acoustic metamaterials, the analysis and design of mechanical metamaterials for the extreme conditions in air and space applications, and nondestructive evaluation (micro-tomography)/structural health monitoring of structures.
• Space Technology. Achieving the goal of industrial utilization and exploration of space requires that one addresses a wide range of engineering problems. Examples of research activities include lightweight structures for large aperture systems, in-space manufacturing, material and structural behavior in extreme temperature and radiation environments, spacecraft shielding against hypervelocity impact threats, the mechanics of sample containment for planetary protection, low-g biomechanics, biomimetics of locomotion in planetary atmospheres, hypersonic reentry into planetary atmospheres, in-space propulsion, guidance, navigation and control, and launch-vehicle performance and safety. Opportunities exist for research in collaboration with the Jet Propulsion Laboratory.
• Computational and Theoretical Fluid Dynamics. Many of the fluid dynamics phenomena studied experimentally are also being investigated via numerical simulation and theoretical analysis. Present active research areas in computational and theoretical techniques include direct numerical simulation, particle methods for flow simulation, new algorithms and development of sub-grid-scale models for compressible and incompressible flows, large-eddy simulation methods, flows with shocks and driven by shocks, analytical and computational techniques for turbulence structure diagnostics, analysis of turbulent mixing dynamics, high-explosive interactions with deformable boundaries, chemically reacting flows, and detailed chemical reaction kinetics in flames and detonations.
• Mechanics of Fracture. Active research is in progress (both experimental and theoretical) to understand mechanisms in a wide range of fracture problems, at both material and structural scale. Aspects under study include quasi-static, dynamic and fatigue crack growth phenomena in brittle and plastically deforming solids, polymers and advanced composites, and emerging solids like metamaterials and high entropy alloys. Research areas adjunct to dynamic fracture studies are those of dynamic localization in metals and of failure in frictional interfaces. These include the study of shear rupture phenomena in both coherent and incoherent interfaces. The dynamic failure of modern composite and layered materials and the phenomenon of earthquake rupture growth along geological faults have motivated these studies. Extension of continuum theories to discrete solids like metamaterials is pursued with an aim to design lightweight and damage tolerant structures.
• Micromechanics with Advanced X-ray Measurements. The goal is to develop transformative experimental tools, centered on advanced X-ray techniques, to reveal local material behavior during mechanical loading. At the core of this effort is the development of a lab scale X-ray beamline powered with the world’s brightest microfocus X-ray source, combining tomography, hyperspectral X-ray imaging, ptychography, and X-ray scattering in two separate beamlines. By extracting local stress-strain behavior across scales, this platform will generate a rich database for data-driven mechanics and enable machine learning and AI approaches for accelerated materials innovation
• Aeronautical Engineering and Propulsion. Research in the aeronautical engineering area includes studies of airplane trailing vortices and separated flows at high angles of attack. Research work in the propulsion area has centered on the fluid dynamic problems associated with combustion, solid propellant rocket motor instabilities, fluid dynamics and optimization of scramjets, and pulse detonation engines.
• Biomechanics of Fluids and Solids. The kinematics and dynamics of fluid flows in biological systems are studied in experiments, numerical simulations, and theoretical analyses. These flows are often characterized by unsteady vortex dynamics, coupled fluid interactions with flexible material surfaces, non-Newtonian fluid behavior, and, in some cases, compressibility. Areas of active research include animal swimming and flying, cardiovascular fluid dynamics and hemodynamics, the mechanics of morphing/active deformable surfaces for flow control, and biologically inspired design of engineering systems.
• Technical Fluid Mechanics. These areas are related to a variety of modern technological problems and, in addition, to the traditional aeronautical problems of drag, wing stall, and shear flow mixing. Additional areas of activity include bluff-body aerodynamics, fluid-structure interaction, turbulent combustion, laminar diffusion flames and their instabilities, explosions, hydrodynamics and two-phase flows, interaction of vorticity with free-surface, cardiac flows, swimming and flying, and active and passive control of transition and turbulence. Acoustics problems studied include jet noise, combustion noise, and instabilities such as the generation of organ pipe oscillations in large burners of electric generating plants.
• Fluid Mechanics, Control, and Materials. The effects of boundary conditions and external forcing on scaling and controllability of fluid flows, in particular turbulence are investigated using interdisciplinary methods based on developments in materials science and control techniques. Experimental manipulation of canonical and simple model flows is used to probe fundamental issues of flow physics and control.
• Autonomous Systems and Technologies. Interdisciplinary research in the expanding area of autonomous systems involves, but is not limited, to drones, robots, and spacecraft for use in science, exploration, and transportation. The research addresses sensing, control, vision, machine learning, and other emerging areas. Advanced drone research, autonomous exploration, and swarm robotics will draw research from the full range of engineering at Caltech, the geological and planetary sciences division, and JPL.

The laboratories of the Booth-Kresa Aerospace Department house a diverse set of experimental facilities in support of the programs described above. The Cann Laboratory is a teaching facility utilized for graduate and undergraduate experiments in fluid and solid mechanics. Low-speed wind tunnels include the John W. Lucas Adaptive Wall Tunnel, the Merrill Wind Tunnel, and special-purpose flow facilities. Smaller water channels and a tow tank for studies of wave motion and flow visualization are also available. For investigations of high-speed flows, there is a Ludwieg tube, a supersonic shear layer facility, a hypervelocity expansion tube, and the T5 shock tunnel for studying hypervelocity gas flows up to 7 km/s. Shock tubes and other special facilities are available for the study of extreme temperatures, shock waves, deflagrations, detonations acoustics, and combustion at variable pressure conditions.

The Center for Autonomous Systems and Technologies (CAST) contains an 85-foot track for walking robots and a wholly enclosed 75,000 cubic foot aerodrome for drone testing which is the tallest of its kind. Environmental simulation is facilitated by a 100-square-foot wall comprised of 1,296 fans capable of generating wind speeds of up to 44 mph, along with a side wall of an additional 324 fans, all of which can be individually controlled to create a nearly infinite variety of conditions.

The solid and structural mechanics laboratories contain standard as well as special testing facilities for research related to aircraft, deployable space structures, and failure/fracture behavior of materials under static and dynamic loads, including three servo-hydraulic facilities, two of which operate on a “tension/torsion’’ mode, and a nanoindenter. A range of digital and film high-speed cameras offering recording at rates up to one hundred million frames per second are available for the study of fast phenomena, such as wave propagation, hypervelocity impact, and the mechanics of static and dynamic fracture. Dynamic testing facilities include specialized electromagnetic loading devices (stored energy ~120 kJ), a drop weight tower, split Hopkinson bars (axial/torsional), and plate impact apparatus. Diagnostic devices include full-field interferometric and high-speed temperature measurements, both for static and dynamic applications. Other specialized facilities include a Class One clean room area that houses microelectronic wafer inspection metrology tools, and the Small Particle Hypervelocity Impact Range (SPHIR) jointly operated with JPL, which is capable of launching micrometeoroid surrogate particles at speeds up to 8 km/s. Facilities are available for scanning microscopy (AFM, STM) and electromechanical characterization of materials.

Other assets include state-of-the-art electronic instrumentation and computer systems for real-time control of experiments, data acquisition, processing, storage, and digital image processing. Computational facilities include powerful workstations, on-campus high-performance computing machines, and remote supercomputers such as those available at NSF, NASA, and DOE centers.