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The Aerospace Mechanisms Symposium (AMS) provides a unique forum for those active in the design, production, and use of aerospace mechanisms. A major focus is the reporting of problems and solutions associated with the development, and flight certification of new mechanisms.
The development of plant growth systems with high yields and low maintenance for food production is a key focus area for NASA. One of the remaining technical challenges is keeping the plant watering systems clean without affecting plant growth, requiring consumables, or demanding crew time. Plant watering systems, such as the one onboard the International Space Station (ISS), provide a nutrient rich environment for biofilm formation. Frequent maintenance is necessary to prevent biofouling, which currently requires crew time and a mechanical means of cleaning. Better solutions are needed. The current ISS practices for biofilm mitigation in the water recovery and distribution system include the use of biocides (silver ion or iodine) along with regular maintenance (e.g. flushing, filter replacement). These biocide-based strategies could be problematic for plant watering systems, such as in Ohalo, the Exploration Garden, and the APH, due to incompatibilities of the biocides with plants. We propose the application of AgXX, a novel antifouling surface treatment that meets the above requirements. This paper will report on an initial study that was completed to determine whether AgXX would be effective in a plant nutrient solution, and whether it would negatively impact plant growth in a hydroponics-type system.
The Aerospace Mechanisms Symposium (AMS) provides a unique forum for those active in the design, production and use of aerospace mechanisms. A major focus is the reporting of problems and solutions associated with the development and flight certification of new mechanisms. Sponsored and organized by the Mechanisms Education Association, responsibility for hosting the AMS is shared by the National Aeronautics and Space Administration and Lockheed Martin Space. The 47th AMS was held in Virginia Beach, Virginia from May 15 to May 17. These proceedings are published to provide these lessons learned and mechanism design information to the mechanism community. Topics included instrument mechanisms, gimbals, release devices, tribology, materials issues, deployment, on-orbit performance, actuators and cubesat mechanisms. The high quality of this symposium is a result of the work of many people, and their efforts are gratefully acknowledged. This extends to the voluntary members of the symposium organizing committee representing the eight NASA field centers, Lockheed Martin Space, and the European Space Agency. Appreciation is also extended to the session chairs, the authors, and particularly the personnel at NASA Langley responsible for the symposium arrangements and the publication of these proceedings. A sincere thank you also goes to the symposium executive committee who is responsible for the year-to-year management of the AMS, including paper processing. The use of trade names of manufacturers in this publication does not constitute an official endorsement of such products or manufacturers, either expressed or implied, by the National Aeronautics and Space Administration.
This report compiles a list of commercial and developmental niobium-based alloys developed during the Space Age (late 1950s through mid-1970s) for extreme-temperature applications, including rocket engine thrust chambers, hypersonic re-entry thermal protection systems, and space fission reactor loops. Niobium (Nb) was widely pursued because it provided the lowest density (~8.6 g/cc) among the primary refractory metals, a high melting temperature (~2470°C), exceptional low-temperature ductility, good formability, and compatibility with liquid alkali metals. An evaluation of physical metallurgy mechanisms, focusing on solid-solution strengthening via heavy refractory solutes (W, Mo, Ta), dual-purpose reactive solutes (Hf, Zr, Ti), and dispersion strengthening using carbides, nitrides, and oxides is presented. Additionally, the report compares Western and Soviet Union metallurgical approaches, explaining how supply chain factors and manufacturing infrastructure influenced element selection, interstitial chemistry, and alloy identification/naming conventions. Cataloging these historical alloy chemical compositions serves as a foundational reference for modern alloy additive manufacturing, thermodynamic CALPHAD modeling, and machine-learning discovery pipelines for next-generation extreme-environment niobium-based alloys.
The linkage between science and human exploration is close. Currently, proponents of science and human presence themes identified by the Synthesis Group as the most important themes of Mars exploration, tend to have reservations about the other camp. Mechanisms that integrate the program themes are essential, to gain the advocacies of the exploration communities and find optimal solutions to the technical problems. Without such mechanisms, it will be difficult to gain widespread acceptance of the SEI as the strategic horizon for the U.S. civilian space program.
A user-oriented subroutine package is built around a highly stable explicit integration algorithm for solution of large order systems of ordinary differential equations, as result from discretization of initial-boundary value problems in continuum mechanics. Fast and accurate solutions, for problems in laminar and turbulent, two and three-dimensional viscous flow fields and multi-dimensional transient heat transfer, are presented using this algorithm, as embodied within a general purpose finite element computer program.
The effects of cavitating flow on the polymeric additives used in functional fluids are described. A comparison of thermal and mechanical stability tests for these polymer solutions show distinct differences in the machanism of the polymer degradation. The thermal degradation tests appear to cause an unzippering or depolymerization type of reaction in which there is no particular selectivity based on molecular weight. The mechanical degradation of these fluids appears to be based on molecular weight. Measurements of molecular weight distributions during mechanical degradation show that for a given level of intensity only molecules above a certain minimum size are degraded. The effects of ultrasonic radiation on polymer degradation are reported. Tests were conducted to demonstrate the mechanism of mechanical polymer degradiation in an orifice. A more severe test than the orifice test in which two tapered roller bearings loaded against each other produce the mechanical breakdown is discussed.
The compressive properties of near <001> and <111> oriented NiAl-2Cr single crystals and near <011> oriented NiAl-6Cr samples have been measured between 1100 and 1500 K. The 2Cr addition produced significant solid solution strengthening in NiAl, and the <111> and <001> single crystals possessed similar strengths. The 6Cr crystals were not stronger than the 2Cr versions. At 1100 and 1200 K plastic flow in all three Cr-modified materials was highly dependent on stress with exponents > 10. The <011> oriented 6Cr alloy exhibited a stress exponent of about 8 at 1400 and 1500 K; whereas both <001> and <111> NiAl-2Cr crystals possessed stress exponents near 3 which is indicative of a viscous dislocation glide creep mechanism. While the Cottrell-Jaswon solute drag model predicted creep rates within a factor of 3 at 1500 K for <001>-oriented NiAl-2Cr; this mechanism greatly over predicted creep rates for other orientations and at 1400 K for <001> crystals.
Interpretations of the quasi-periodic outbursts of dwarf novae in terms of a thermal-viscous limit cycle mechanism operating in the accretion disk are discussed. Numerical solutions to vertical equilibrium equations are used to show that the limit cycle mechanism should occur in supermassive disks. The mechanism acts as a gate that modulates the rate of accretion reaching small radii, where most of the luminosity is produced. Formulas are derived for the period and outburst luminosity in terms of the black hole mass and the radius at which the unstable zone occurs.
A superalloy based on Udimet 700, in which all of the cobalt was replaced by nickel, was prepared from hot isostatically pressed prealloyed powders. This material was given various heat treatments consisting of partial solutioning and aging in a sequence of four different temperatures. Comparisons were made of microstructures and mechanical properties. Best results were obtained by partially solutioning at 1145 deg C and aging through a sequence of 870, 1030, 650 and 760 deg C. This heat treatment also provided significantly improved properties for wrought material of the same composition. The results suggest that cobalt free Udimet 700 should be considered as a substitute for Udimet 700 with the standard 17 percent cobalt content.
A superalloy based on Udimet 700, in which all of the cobalt was replaced by nickel, was prepared from hot isostatically pressed prealloyed powders. This material was given various heat treatments consisting of partial solutioning and aging in a sequence of four different temperatures. Comparisons were made of microstructures and mechanical properties. Best results were obtained by partially solutioning at 1145 deg C and aging through a sequence of 870, 1030, 650 and 760 deg C. This heat treatment also provided significantly improved properties for wrought material of the same composition. The results suggest that cobalt free Udimet 700 should be considered as a substitute for Udimet 700 with the standard 17 percent cobalt content.
Intensity and lifetime quenching of the polystyrene monomer and excimer fluorescence emission by a pendant quencher have been studied in the solid state and in solution for a series of copolymers of styrene and 2-(2-prime-hydroxy-5-prime-vinylphenyl)-2H-benzotriazole. Two mechanisms of quenching have been identified. One involves interception of the migrating monomer excitation by the quencher, and the other involves a single-step Foerster energy-transfer process from the excimer traps to a quencher. The relative efficiencies of these two quenching mechanisms in the solid state and in solution have been compared and related to the efficiency of electronic energy migration. An estimate of the excimer trap concentration in solid polystyrene is also reported.
A comparison of the finite element method (FEM) and boundary element method (BEM) for the solution of two-dimensional plane strain problems in fracture mechanics is presented in this paper. Stress intensity factors (SIF's) were calculated using both methods for elastic plates with either a single-edge crack or an inclined-edge crack. In particular, two currently available programs, ANSYS for finite element analysis and BEASY for boundary element analysis, were used.
Advanced turbine engine configurations using higher temperature combustor and airfoil concepts require compressor and turbine disks that can withstand temperatures higher than the 650 C typical of current engines. This requires disk alloy and processing improvements. A versatile disk alloy was needed that could be given either fine grain heat treatments for high strength and fatigue and creep resistance up to 704 C or given coarse grain heat treatments for high strength and creep and dwell crack-growth resistance at higher temperatures. This alloy could produce disks with uniform microstructures and properties, as well as with varied, optimized microstructures at disk bore and rim sections. A series of experimental disk alloys were designed and processed to give subscale disks about 13 cm in diameter and 4 cm thick. These alloys had varying levels of key elements to affect mechanical properties and change the "solvus" solution heat-treatment temperature necessary to produce coarse grain microstructures. Disks were given coarse grain heat treatments followed by rapid oil quenching and slower fan air quenching. These heat treatments were intended to simulate the cooling paths of rapidly cooled full-scale disks at the outermost rim and interior bore locations, respectively. Preliminary quench tests of tensile specimens and coin-size minidisks had indicated that alloys having high solvus temperatures were more prone to cracking during rapid quenching from coarse grain heat treatments. These findings were confirmed in the subscale disks, where such alloys did form undesirable quench cracks. Mechanical tests were performed on specimens from subscale disks given these coarse grain heat treatments, as well as on specimens given a fine grain heat treatment. Tensile, creep, and crack growth tests were performed at 704 C and higher temperatures. A versatile alloy was identified that had a low solvus temperature for resistance to quench cracking as well as an optimal combination of high levels of strengthening refractory elements that produced balanced high mechanical properties for both fine grain and coarse grain microstructures. This low-solvus, high-refractory (LSHR) alloy has been scaled-up to produce prototype full-scale turbine disks typical of regional jet turbofan engines. Disks were successfully heat treated to give uniform coarse grain and uniform fine grain microstructures. Additional disks were given a NASA dual microstructure heat treatment (DMHT) that intentionally varied the solution heat-treatment temperatures between the disk rim and bore (re f. 1). The disk rim was heated to a high enough temperature to produce a coarse grain microstructure, while the bore was maintained at a lower temperature to produce a fine grain microstructure (see the figure). This DMHT can produce optimal high strength, fatigue, and creep resistance up to 704 C in the cooler running disk bore, and high strength, creep resistance, and dwell crack growth resistance at higher temperatures for the hotter disk rim. Extensive mechanical testing is being initiated to compare the mechanical properties of the uniform and DMHT disks.
The mechanical properties of chromium, molybdenum, and tungsten alloys are reviewed with particular emphasis on high-temperature strength and low-temperature ductility. Precipitate strengthening is highly effective at 0.4 to 0.8 times the melting temperature in these metals, with HfC being most effective in tungsten and molybdenum, and Ta(B,C) most effective in chromium. Low-temperature ductility can be improved by alloying to promote rhenium ductilizing or solution softening. The low-temperature mechanical properties of these alloys appear related to electronic interactions rather than to the usual metallurgical considerations.
This paper describes the requirements, design, assembly and testing of the linear Scan Mechanism (SM) of the Composite Infrared Spectrometer (CIRS) Instrument. The mechanism consists of an over constrained flexible structure, an innovative moving magnet actuator, passive eddy current dampers, a Differential Eddy Current (DEC) sensor, Optical Limit Sensors (OLS), and a launch lock. Although all the components of the mechanism are discussed, the flexible structure and the magnetic components are the primary focus. Several problems encountered and solutions implemented during the development of the scan mechanism are also described.
Compact scheme formulation was used in the treatment of boundary conditions for a system of coupled diffusion and Poisson equations. Models and practical solutions of specific engineering problems arising in solid mechanics, chemical engineering, heat transfer and fuid mechanics are described and analyzed for efficiency and accuracy. Only 2-D cases are discussed and a new method of numerical treatment of boundary conditions common in the fundamental problems of mechanics of continua is presented.
Newton's method for nonlinear mechanics problems replaces the governing nonlinear equations by an iterative sequence of linear equations. When the linear equations are linear differential equations, the equations are usually solved by numerical methods. The iterative sequence in Newton's method can exhibit poor convergence properties when the nonlinear problem has multiple solutions for a fixed set of parameters, unless the iterative sequences are aimed at solving for each solution separately. The theory of the linear differential operators is often a better guide for solution strategies in applying Newton's method than the theory of linear algebra associated with the numerical analogs of the differential operators. In fact, the theory for the differential operators can suggest the choice of numerical linear operators. In this paper the method of variation of parameters from the theory of linear ordinary differential equations is examined in detail in the context of Newton's method to demonstrate how it might be used as a guide for numerical solutions.