Search NASA⌕ Search

SEARCH · Search NASA

Results for “In Space Manufacturing”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17

Advancement of Novel Additively Manufactured Alloys for Space Applications

NASA has been involved in the development and maturation of metal additive manufacturing (AM) for space applications since the late 2000’s. Several efforts have focused on the understanding of AM processes through material characterization and testing, standards development, component fabrication, and infusion into development and flight applications. While many common aerospace alloys have been and continue to be a focus of ongoing development, the need for custom-alloy developments for high performance applications enabled by AM processes has been realized. The applications being targeted are liquid rocket engines with high heat fluxes, high pressure, and that utilize propellants such as hydrogen, which can degrade the alloy. NASA has recently focused on the development and advancement of novel alloy advancement using AM for use in these harsh environments, such as GRCop-42, GRCop-84, NASA HR-1, and JBK-75. These alloys have been evaluated using the laser powder bed fusion (L-PBF) and laser powder directed energy deposition (LP-DED) processes. The results from these processes have demonstrated that AM can enable rapid development of new alloy systems that can yield higher performances. These alloys have undergone the fundamental metallurgical evaluations, heat treatment study, and microstructure characterization and mechanical testing campaign. This, combined with direct application-specific component fabrication and hot-fire testing, enabled the increase of the Technology Readiness Level (TRL). This presentation will provide a background and overview of these AM-enabled novel alloys, AM processing development including metallurgical and mechanical property studies. It will also cover the latest advancement in the parallel component development and testing and future developments. The goal of these alloy development is to allow for technology infusion into NASA and commercial spaceflight missions as well as to establish and sustain the needed commercial AM supply chain.

Additive Manufacturing↗

America's Next Great Ship: Space Launch System Core Stage Transitioning from Design to Manufacturing

The Space Launch System (SLS) Program is essential to achieving the Nation's and NASA's goal of human exploration and scientific investigation of the solar system. As a multi-element program with emphasis on safety, affordability, and sustainability, SLS is becoming America's next great ship of exploration. The SLS Core Stage includes avionics, main propulsion system, pressure vessels, thrust vector control, and structures. Boeing manufactures and assembles the SLS core stage at the Michoud Assembly Facility (MAF) in New Orleans, LA, a historical production center for Saturn V and Space Shuttle programs. As the transition from design to manufacturing progresses, the importance of a well-executed manufacturing, assembly, and operation (MA&O) plan is crucial to meeting performance objectives. Boeing employs classic techniques such as critical path analysis and facility requirements definition as well as innovative approaches such as Constraint Based Scheduling (CBS) and Cirtical Chain Project Management (CCPM) theory to provide a comprehensive suite of project management tools to manage the health of the baseline plan on both a macro (overall project) and micro level (factory areas). These tools coordinate data from multiple business systems and provide a robust network to support Material & Capacity Requirements Planning (MRP/CRP) and priorities. Coupled with these tools and a highly skilled workforce, Boeing is orchestrating the parallel buildup of five major sub assemblies throughout the factory. Boeing and NASA are transforming MAF to host state of the art processes, equipment and tooling, the most prominent of which is the Vertical Assembly Center (VAC), the largest weld tool in the world. In concert, a global supply chain is delivering a range of structural elements and component parts necessary to enable an on-time delivery of the integrated Core Stage. SLS is on plan to launch humanity into the next phase of space exploration.

Birkenstock, Benjamin↗

New Era Towards Autonomous Additive Manufacturing: A Review of Recent Trends and Future Perspectives

Abstract The Additive Manufacturing (AM) landscape has significantly transformed in alignment with Industry 4.0 principles, primarily driven by the integration of Artificial Intelligence (AI) and Digital Twin (DT). However, current Intelligent Additive Manufacturing (IAM) systems face limitations such as fragmented AI tool usage and suboptimal human-machine interaction (HMI). This paper reviews existing IAM solutions, emphasizing control, monitoring, process autonomy, and end-to-end integration, and identifies key limitations, such as the absence of a high-level controller for global decision-making. To address these gaps, we propose a transition from IAM to Autonomous Additive Manufacturing (AAM), featuring a hierarchical framework with four integrated layers: knowledge, generative solution, operational, and cognitive. In the cognitive layer, AI agents notably enable machines to independently observe, analyze, plan, and execute operations that traditionally require human intervention. These capabilities streamline production processes and expand the possibilities for innovation, particularly in sectors like in-space manufacturing (ISM). Additionally, this paper discusses the role of AI in self-optimization and lifelong learning, positing that the future of AM will be characterized by a symbiotic relationship between human expertise and advanced autonomy, fostering a more adaptive, resilient manufacturing ecosystem.

Fan, Haolin↗

Macroeconomic Benefits of Low-Cost Reusable Launch Vehicles

The National Aeronautics and Space Administration (NASA) initiated its Reusable Launch Vehicle (RLV) Technology Program to provide information on the technical and commercial feasibility of single-stage to orbit (SSTO), fully-reusable launchers. Because RLVs would not depend on expendable hardware to achieve orbit, they could take better advantage of economies of scale than expendable launch vehicles (ELVs) that discard costly hardware on ascent. The X-33 experimental vehicle, a sub-orbital, 60%-scale prototype of Lockheed Martin's VentureStar SSTO RLV concept, is being built by Skunk Works for a 1999 first flight. If RLVs achieve prices to low-earth orbit of less than $1000 US per pound, they could hold promise for eliciting an elastic response from the launch services market. As opposed to the capture of existing market, this elastic market would represent new space-based industry businesses. These new opportunities would be created from the next tier of business concepts, such as space manufacturing and satellite servicing, that cannot earn a profit at today's launch prices but could when enabled by lower launch costs. New business creation contributes benefits to the US Government (USG) and the US economy through increases in tax revenues and employment. Assumptions about the costs and revenues of these new ventures, based on existing space-based and aeronautics sector businesses, can be used to estimate the macroeconomic benefits provided by new businesses. This paper examines these benefits and the flight prices and rates that may be required to enable these new space industries.

Shaw, Eric J.↗

Current NASA In-Situ Resource Utilization (ISRU) Strategic Vision

Perform development to TRL 5/6 through ground demonstration in relevant environment. Perform component/subscale subsystem flight demonstrations on small/mid-size landers. Assess and characterize water in volatiles in lunar polar shadowed regions and craters. Reduce risk of ISRU for mission critical consumables through Integrated End-to-End Flight Demonstrations (pilot scale). Establish initial Human Mission Scale production capability to promote sustainable operations and as anchor for commercial involvement. Identify and characterize polar region environment and resources/volatiles for Science and future Exploration/Commercial applications. Provide ground-truth physical, mineral, and water/volatile resource characteristic information at multiple locations to provide geological context for science-focused theories of volatile placement and initial mining assessments.Test technologies and processes to reduce risk of future extraction/mining systems. Quantify concentration and lateral/vertical distribution of resources/volatiles. Utilize ISRU capabilities to Extend and Enhance Human Lunar Exploration Missions. Provide oxygen (and fuel) to enable reusable human lunar lander (10+ MT/yr O2)Process carbon-based crew waste/trash into gases and propellants; can reduce logistics while minimizing public perception issues (alternative is conversion to radiation shielding). Scavenge unused propellants and hardware from spent landers. Metal extraction from regolith as feedstock for in situ and in space manufacturing demonstrations. Civil engineering and construction aimed at future outpost/infrastructure build-up. Develop and Demonstrate ISRU for Human Mars Missions. ISRU for propellant production (10-15 MT/yr); Liquefy, store, transfer, and refuel ascent vehicle. Use Moon for operational experience and mission validation for Mars: Pre-deployment & remote activation and operation without crew. Storing and transferring mission consumables Landing crew with empty tanks with ISRU propellants already made and waiting. Support/Promote Commercialization of Space. Large scale polar ice mining (100+ MT/yr water)O2/H2 propulsion for landers/cis-lunar transportation with surface and in space depots. In situ construction and energy expansion at mining and human outpost site(s). ISRU Ground Development. Develop and advance ISRU technologies to enable acquisition of resources and processing into mission consumables. Utilize Multi-center collaboration with a portfolio that includes internal NASA work, external contracts, and collaborative agreements/partnerships. Where appropriate, develop lunar ISRU components and subsystems with a Mars-forward application. Engage industry through public-private partnerships to lay the foundation for long-term lunar and space economic development. Spin-in/spin-out technologies for terrestrial applications and industry (mining, oil & gas, alternative energy, construction). Flight Demonstration Path to Operational ISRU. Utilize small demonstrations with near off-the-shelf hardware to obtain critical information quickly on lunar resources and operations. Demonstrate critical technologies and processes that interact with lunar materials and environments. Perform 'pilot plant' demonstrations at architecture relevant scales and durations to reduce the risk for ISRU-provided products for critical human mission applications.

In-situ Resource Utilization↗

Spline-locking screw fastening strategy

A fastener was developed by NASA Goddard for efficiently performing assembly, maintenance, and equipment replacement functions in space using either robotics or astronaut means. This fastener, the 'Spline Locking Screw' (SLS) would also have significant commercial value in advanced space manufacturing. Commercial (or DoD) products could be manufactured in such a way that their prime subassemblies would be assembled using SLS fasteners. This would permit machines and robots to disconnect and replace these modules/parts with ease, greatly reducing life cycle costs of the products and greatly enhancing the quality, timeliness, and consistency of repairs, upgrades, and remanufacturing. The operation of the basic SLS fastener is detailed, including hardware and test results. Its extension into a comprehensive fastening strategy for NASA use in space is also outlined. Following this, the discussion turns toward potential commercial and government applications and the potential market significance of same.

Vranish, John M.↗

New space processing experiments for the Skylab missions.

The M512 Materials Processing Facility, which is the main item of equipment for the Skylab space manufacturing experiments is described. It is basically an electron-beam welding apparatus, consisting of a battery power supply, a 20-kV electron beam source, and a spherical 40-cm-diam vacuum chamber. It will be used to perform the M551 Metals Melting Experiment, the M552 Exothermic Brazing Experiment, the M553 Sphere Forming Experiment, the M554 Composite Casting Experiment, the M555 Gallium Arsenide Crystal Growth Experiment, the M561 Whisker-Reinforced Composites Experiment, the M562 Indium Antimonide Crystal Growth, Experiment, the M563 Mixed III-V Crystal Growth Experiment, the M564 Alkali Halide Eutectics Experiment, the M565 Silver Grids Melted in Space Experiment, and the M566 Copper-Aluminum Eutectic Experiment. Three apparatus systems designed to broaden the technical scope of the experiments and to gain experience with new experimental techniques are described. These are an electrophoretic separator, an electromagnetic levitation system, and a versatile electric furnace with an electronic control system.

Bredt, J. H.↗

Computationally Guided Design of Polymer-Coated Microparticles as Reusable Materials

Long-duration space exploration missions and sustained lunar or Martian surface operations present greater demands for multifunctional and reusable materials. By scaling down the amount of material to be launched from Earth, both mission cost and risk can be reduced. In this regard, leveraging in-space manufacturing capabilities with reusable feedstock materials is an attractive option, as it will allow for articles to be generated on demand, utilized, and then recycled for additional use. NASA’s Enabling Sustained Presence Using Recyclables (ESPUR) project aims to develop reusable materials using polymer-coated microparticles that are bonded via reversible Diels-Alder reactions, where only modest heat is needed to trigger the reverse reaction and enable reuse. For proof-of-concept demonstration, research is currently focused on the fabrication of epoxy microparticles that contain a copoly(carbonate urethane) coating with maleimide and furan functionalities. Here, we discuss the integration of computational materials modeling approaches to help navigate the large design space in this development effort. We perform molecular dynamics (MD) simulations with atomistic and coarse-grained models of the copolymer, which allow us to evaluate the effects of design parameters like the molecular weight and composition on the molecular interactions and chain dynamics. We show how the properties change with the reversible bonds. We also leverage discrete element method (DEM) simulations to assess how microparticle design parameters like the size ratio and volume fraction can be tuned to increase the packing density and number of microparticle contacts to improve the mechanical properties. Our results demonstrate how computational tools can be used in close collaboration with experimental efforts to accelerate material design.

reusable materials↗

Supportability Challenges, Metrics, and Key Decisions for Future Human Spaceflight

Future crewed missions beyond Low Earth Orbit (LEO) represent a logistical challenge that is unprecedented in human space flight. Astronauts will travel farther and stay in space for longer than any previous mission, far from timely abort or resupply from Earth. Under these conditions, supportability { defined as the set of system characteristics that influence the logistics and support required to enable safe and effective operations of systems { will be a much more significant driver of space system lifecycle properties than it has been in the past. This paper presents an overview of supportability for future human space flight. The particular challenges of future missions are discussed, with the differences between past, present, and future missions highlighted. The relationship between supportability metrics and mission cost, performance, schedule, and risk is also discussed. A set of pro- posed strategies for managing supportability is presented (including reliability growth, uncertainty reduction, level of repair, commonality, redundancy, In-Space Manufacturing (ISM) (including the use of material recycling and In-Situ Resource Utilization (ISRU) for spares and maintenance items), reduced complexity, and spares inventory decisions such as the use of predeployed or cached spares - along with a discussion of the potential impacts of each of those strategies. References are provided to various sources that describe these supportability metrics and strategies, as well as associated modeling and optimization techniques, in greater detail. Overall, supportability is an emergent system characteristic and a holistic challenge for future system development. System designers and mission planners must carefully consider and balance the supportability metrics and decisions described in this paper in order to enable safe and effective beyond-LEO human space flight.

Owens, Andrew C.↗

Input Waste Stream Modeling for Trash Management, Recycling, and Manufacturing Processes

Astronaut waste is an important aspect of the planning and execution of long-term crewed missions, especially to the Moon and Mars. However, as new technologies arise and mission planning evolves, the projected composition of the waste similarly evolves. This poses a problem for researchers who are investigating various approaches to mitigating crew waste, since the investigation of each new waste-mitigation technology typically uses a static waste composition that is based on a simulant developed at the time of the research; several such waste simulants have been developed over recent years. To mitigate the ‘moving target’ aspect of crew waste composition and use, researchers at NASA KSC have developed a computational tool wherein researchers can adjust the composition of the crew waste, as well as other important parameters such as crew size, mission duration, and waste mitigation method (e.g., incineration, compaction, jettison, etc.). The computational tool then returns important mission metrics such as waste-related mass reduction, power consumed, water produced or consumed, elemental mass balance, and available feedstock for in-space manufacturing (ISM) applications. This tool can then be used to adjust aspects of a waste model (e.g., removal of metal aluminum (Al) for ISM applications) and determine an associated set of metrics in order to inform mission planning.

Ray Pitts↗

Low-Earth Orbit Flight Test of an Inflatable Decelerator (LOFTID) Mission Overview, Science Return, and Future Applications of This Technology

The Low-Earth Orbit (LEO) Flight Test of an Inflatable Decelerator (LOFTID) mission was the culmination of two decades of research and development for Hyper-sonic Inflatable Aerodynamic Decelerator (HIAD) technology. LOFTID was a project overseen by the Technology Demonstration Mission (TDM) program within NASA’s Space Technology Mission Directorate. The success of the LOFTID mission could enable new NASA missions to Mars, Venus, and most solar-system destinations with atmospheres, as well as cost-effective payload returns to Earth, including in-space manufactured materials and launch vehicle asset recovery. LOFTID, with its unique inflatable heat shield, was the first-of-a-kind orbital reentry flight, and the largest blunt body atmospheric entry of any kind. On November 10, 2022, just over 10 years since the previous flight test of the smaller sub-orbital Inflatable Reentry Vehicle Experiment-3 (IRVE-3) [1], NASA Langley Research Center, with partner United Launch Alliance (ULA), successfully launched and achieved reentry and recovery of the LOFTID Reentry Vehicle (RV), further demonstrating the viability of the HIAD technology for large-diameter, inflatable heat shields to safely and accurately deliver large payloads through an atmosphere via a controlled descent and landing. Launching as a secondary payload with the Joint Polar Satellite System 2 (JPSS-2) from Vandenberg Space Force Base, California, stowed inside an ex-tended payload adapter of the Atlas V 401 launch vehicle, the LOFTID mission officially began after the JPSS-2 payload was delivered to its orbit by the Centaur second stage. The LOFTID RV was flying solo on its spin-stabilized ballistic reentry trajectory about one hour after launch, and the flight ended approximately one hour later with a gentle splashdown under parachute in the Pacific Ocean off the east coast of Hawaii, where the RV was recovered and later shipped back to NASA Langley. LOFTID endured the harsh environments of atmospheric reentry while demonstrating stable aerodynamics through the entire spectrum of hypersonic, supersonic, transonic, and subsonic flight. The LOFTID RV was exposed to an aeroheating environment representative of many Mars and LEO HIAD applications, while successfully demonstrating the ability of the heat-affected inflatable structure to with-stand aerodynamic forces that exceeded those expected at Mars. This flight demonstration of a 6m diameter HIAD confirmed the technology structural and thermal performance as it protected the 1100kg RV entering Earth’s atmosphere at 8 km/s, reaching Mach 30, and experiencing 9g deceleration before deploying parachutes and splashing down in the Pacific Ocean. HIAD technology involves an aeroshell that can be hard packed into a small volume for launch and then deployed prior to atmospheric entry for a controlled deceleration through the atmosphere. Large deployable heat shields enable spacecraft to carry bigger, heavier payloads, including scientific instruments and human support systems for planetary landing and exploration. Much larger than traditional fixed diameter aeroshells that are constrained by the size of launch vehicle shrouds, inflatable decelerators create more drag and start the deceleration process in the upper reaches of the atmosphere with greater efficiency and stability. LOFTID’s successful demonstration of the HIAD technology has greatly expanded NASA’s options for future planetary missions and opened new commercial opportunities for lower-cost mission pay-load recovery including recovery of launch vehicle assets, or as a delivery system to return cargo from the International Space Station or cislunar space. The developments for some of these applications are al-ready underway. While LOFTID was indeed a first-of-a-kind flight for an inflatable heatshield, the largest blunt-body entry ever, its remarkable performance assured that it will not be the last of its kind.

John DiNonno↗

FLUTE: Fluidic Telescope

The future of space-based UV/optical/IR astronomy requires ever larger telescopes. The highest priority astrophysics targets (including Earth-like exoplanets, first generation stars, and early galaxies) are all extremely faint, which presents an ongoing challenge for current missions and is the opportunity space for next generation telescopes: larger telescopes are the primary way to address this issue. The FLUTE project aims to revolutionize space astronomy (and in-space manufacturing of high-precision optics for a variety of other applications) by leveraging the physics of wetting and hydrostatic phenomena in microgravity. The approach being developed by the team uses surface tension to shape a liquid into a desired optical form with sub-nanometer surface quality. A liquid with appropriate optical properties is brought into contact with a high affinity bounding frame, resulting in pinning of the liquid to the frame. In microgravity, the shape of the free surface is dictated solely by surface tension, thus assuming the shape of a spherical cap. Further dynamic control over the shape is possible through changing the liquid volume, the frame geometry, and — if desired — with the addition of external forces (e.g., electromagnetic forces). The approach is scale-invariant and is expected to enable space telescopes with optical apertures measuring in tens or even hundreds of meters, allowing, for instance, direct imaging of extra-solar planets. Both refractive and reflective optical components can be created using this approach. If the liquid’s properties enable solidification (e.g., a liquid metal), the resulting component can then become an optical-grade solid object, without post-processing steps. The approach has been successfully validated in a laboratory neutral buoyancy environment, in parabolic microgravity flights, and in experiments aboard the International Space Station (ISS). FLUTE is a collaboration between NASA Ames Research Center, NASA Goddard Space Flight Center, and Technion – Israel Institute of Technology. More on information on FLUTE can be found at https://www.nasa.gov/science-research/astrophysics/what-is-the-fluidic-telescope/. This presentation provides an update on the project's accomplishments to-date and discusses next steps.

Space observatory↗

Composites Materials and Manufacturing Technologies for Space Applications

Composite materials offer significant advantages in space applications. Weight reduction is imperative for deep space systems. However, the pathway to deployment of composites alternatives is problematic. Improvements in the materials and processes are needed, and extensive testing is required to validate the performance, qualify the materials and processes, and certify components. Addressing these challenges could lead to the confident adoption of composites in space applications and provide spin-off technical capabilities for the aerospace and other industries. To address the issues associated with composites applications in space systems, NASA sponsored a Technical Interchange Meeting (TIM) entitled, "Composites Materials and Manufacturing Technologies for Space Applications," the proceedings of which are summarized in this Conference Publication. The NASA Space Technology Mission Directorate and the Game Changing Program chartered the meeting. The meeting was hosted by the National Center for Advanced Manufacturing (NCAM)-a public/private partnership between NASA, the State of Louisiana, Louisiana State University, industry, and academia, in association with the American Composites Manufacturers Association. The Louisiana Center for Manufacturing Sciences served as the coordinator for the TIM.

Vickers, J. H.↗

Analysis of Historical International Space Station Logistical Mass Delivery

Crewed space exploration missions are extremely logistics dependent, as cargo requirements shape numerous program elements such as vehicle and habitat size. Logistics mass is the mass of items like food and clothing that are not a part of the vehicle or habitat, yet are required by the crew to complete the mission. Numerous studies, such as the Human Exploration Research Analog (HERA) and the Human Exploration Spacecraft Testbed for Integration and Advancement (HESTIA) 20-foot chamber analog, have been conceived to research the rates at which crews consume logistics mass. These analogs can simulate many aspects of life in space, including confinement, isolation, limited supplies, and, in certain experiments, the habitat pressure. However, some aspects of space exploration, such as the effects of low gravity and the use of space-based amenities, cannot currently be tested on the ground. In this paper, International Space Station (ISS) manifest data obtained through the National Aeronautics and Space Administration’s (NASA’s) Mission Integration Database Application System (MIDAS) portal is used as a precursor to space-based analogs. The objective of the analysis is determining the breakdown of logistics mass used in space exploration. This identifies potential areas of improvement and highlights the rates at which significant items are supplied, aiding in the weighing of alternative options such as utilizing in space manufacturing for supplies vs. manifesting spares, or cleaning clothing in flight vs. discarding it. Official flight manifests ranging a span of 878 days, just short of the three-year length of a potential human mission to Mars, were analyzed to find the rates at which astronauts consumed various logistics supplies. From this analysis we have found that contrary to our own hypothesis, ‘food’ was not the largest portion of the supplied mass. Instead, ‘Environmental Control and Life Support Systems’ (ECLSS) contributed 34% of the overall supplied mass, followed by ‘Science and Outfitting,’ which contributed 29%. Food totaled less than a quarter (21% of the resupplied mass, while other items of focus in mass reduction efforts such as ‘Hygiene’ (6%), ‘Clothing’ (3%), and ‘Operational Supplies’ (4%) each contributed less than a tenth of the supplied mass. This data suggests that by categorizing and analyzing the data based on an alternative taxonomy and analyzing the full supply manifests rather than handpicked items, we have revealed unexpectedly significant items which had not been previously tracked by exploration logistics efforts. For example, toilet hardware made up 4% of ECLSS mass, and laptop hardware and multi-tools each made up 10% of operational supplies mass. Additionally, the ‘Specialized Clothing’ subcategory containing fire protective equipment, coveralls, and penguin suits made up 15% of the overall clothing mass. By identifying these newly found significant items, we can create more realistic mass estimates for exploration missions and direct mass reduction efforts to new areas, potentially leading to lower future mission masses.

Logistics↗

Study of single crystals of metal solid solutions

The growth of single crystals of relatively high melting point metals such as silver, copper, gold, and their alloys was investigated. The purpose was to develop background information necessary to support a space flight experiment and to generate ground based data for comparison. The ground based data, when compared to the data from space grown crystals, are intended to identify any effects which zero-gravity might have on the basic process of single crystal growth of these metals. The ultimate purposes of the complete investigation are to: (1) determine specific metals and alloys to be investigated; (2) grow single metal crystals in a terrestrial laboratory; (3) determine crystal characteristics, properties, and growth parameters that will be effected by zero-gravity; (4) evaluate terrestrially grown crystals; (5) grow single metal crystals in a space laboratory such as Skylab; (6) evaluate the space grown crystals; (7) compare for zero-gravity effects of crystal characteristics, properties, and parameters; and (8) make a recommendation as to production of these crystals as a routine space manufacturing proceses.

Doty, J. P.↗

Acoustical levitation for space processing

It is pointed out that many space-manufacturing processes will require the manipulation of weightless molten material within a container in such a way that the material does not touch the container wall. A description is given of an acoustical method which can be used for the positioning and shaping of any molten material including nonconductors such as glasses. The new approach makes use of an acoustical standing wave which is excited within an enclosure or resonator.

Wang, T. G.↗