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NASA NTRS1992

Thermal control surfaces experiment flight system performance

The Thermal Control Surfaces Experiment (TCSE) is the most complex system retrieved after long term space exposure. The TCSE is a microcosm of complex electro-optical payloads being developed and flown. The objective of the TCSE on the LDEF was to determine the effects of the near-Earth orbital environment and the LDEF induced environment on spacecraft thermal control surfaces. The TCSE was a comprehensive experiment that combined in-space measurements with extensive post-flight analyses of thermal control surfaces to determine the effects of exposure to the low Earth orbit space environment. The TCSE was the first space experiment to measure the optical properties of thermal control surfaces the way they are routinely measured in the lab. The performance of the TCSE flight system on the LDEF was excellent.

Wilkes, Donald R.↗

NASA NTRS1993

A comparison of spectral mixture analysis an NDVI for ascertaining ecological variables

In this study, we compare the performance of spectral mixture analysis to the Normalized Difference Vegetation Index (NDVI) in detecting change in a grassland across topographically-induced nutrient gradients and different management schemes. The Konza Prairie Research Natural Area, Kansas, is a relatively homogeneous tallgrass prairie in which change in vegetation productivity occurs with respect to topographic positions in each watershed. The area is the site of long-term studies of the influence of fire and grazing on tallgrass production and was the site of the First ISLSCP (International Satellite Land Surface Climatology Project) Field Experiment (FIFE) from 1987 to 1989. Vegetation indices such as NDVI are commonly used with imagery collected in few (less than 10) spectral bands. However, the use of only two bands (e.g. NDVI) does not adequately account for the complex of signals making up most surface reflectance. Influences from background spectral variation and spatial heterogeneity may confound the direct relationship with biological or biophysical variables. High dimensional multispectral data allows for the application position of techniques such as derivative analysis and spectral curve fitting, thereby increasing the probability of successfully modeling the reflectance from mixed surfaces. The higher number of bands permits unmixing of a greater number of surface components, separating the vegetation signal for further analyses relevant to biological variables.

Wessman, Carol A.↗

NASA NTRS1988

Applications of surface analysis and surface theory in tribology

Tribology, the study of adhesion, friction and wear of materials is a complex field which requires a knowledge of solid state physics, surface physics, chemistry, material science and mechanical engineering. It has been dominated, however, by the more practical need to make equipment work. With the advent of surface analysis and advances in surface and solid state theory, a new dimension has been added to the analysis of interactions at tribological interfaces. In this paper the applications of tribological studies and their limitations are presented. Examples from research at the NASA Lewis Research Center are given. Emphasis is on fundamental studies involving the effects of monolayer coverage and thick films on friction and wear. A summary of the current status of theoretical calculations of defect energetics is presented. In addition, some new theoretical techniques which enable simplified quantitative calculations of adhesion, fracture and friction are discussed.

Ferrante, John↗

NASA NTRS1989

Applications of surface analysis and surface theory in tribology

Tribology, the study of adhesion, friction and wear of materials, is a complex field which requires a knowledge of solid state physics, surface physics, chemistry, material science, and mechanical engineering. It has been dominated, however, by the more practical need to make equipment work. With the advent of surface analysis and advances in surface and solid-state theory, a new dimension has been added to the analysis of interactions at tribological interfaces. In this paper the applications of tribological studies and their limitations are presented. Examples from research at the NASA Lewis Research Center are given. Emphasis is on fundamental studies involving the effects of monolayer coverage and thick films on friction and wear. A summary of the current status of theoretical calculations of defect energetics is presented. In addition, some new theoretical techniques which enable simplified quantitative calculations of adhesion, fracture, and friction are discussed.

Ferrante, John↗

NASA NTRS1984

Transonic analysis of canted winglets

A computational method developed to provide a transonic analysis for upper/lower surface wing-tip mounted winglets is described. Winglets with arbitrary planform, cant and toe angle, and airfoil section can be modeled. The embedded grid approach provides high flow field resolution and the required geometric flexibility. In particular, coupled Cartesian/cylindrical grid systems are used to model the complex geometry presented by canted upper/lower surface winglets. A new rotated difference scheme is introduced in order to maintain the stability of the small-disturbance formulation in the presence of large spanwise velocities. Wing and winglet viscous effects are modeled using a two-dimensional 'strip' boundary layer analysis. Correlations with wind tunnel and flight test data for three transport configurations are included.

Rosen, B. S.↗

NASA NTRS1999

Surface Segregation in Multicomponent Systems: Modeling of Surface Alloys and Alloy Surfaces

The study of surface segregation, although of great technological importance, has been largely restricted to experimental work due to limitations associated with theoretical methods. However, recent improvements in both first-particle and semi-empirical methods are opening, the doors to an array of new possibilities for surface scientists. We apply one of these techniques, the Bozzolo, Ferrante and Smith (BFS) method for alloys, which is particularly suitable for complex systems, to several aspects of the computational modeling of surfaces and segregation, including alloy surface segregation, structure and composition of alloy surfaces, and the formation of surface alloys. We conclude with the study of complex NiAl-based binary, ternary and quaternary thin films (with Ti, Cr and Cu additions to NiAl). Differences and similarities between bulk and surface compositions are discussed, illustrated by the results of Monte Carlo simulations. For some binary and ternary cases, the theoretical predictions are compared to experimental results, highlighting the accuracy and value of this developing theoretical tool.

Bozzolo, Guillermo↗

NASA NTRS1972

Scanning electron microscopy, non-dispersive X-ray analysis and electron microprobe studies of lunar soil, rocks and microbreccia

Silicate glass of composition similar to brown lunar glass was reduced with carbon and hydrogen. The typical complex iron sulfide and metallic iron mound formed by reduction with carbon is zoned. Its interior is metallic iron or a mixture of iron sulfide and metallic iron. The outer layer is pure metallic iron which is generally discontinuous, but the surface of the mound next to the silicate host is iron sulfide. This type of mound commonly has a waist of metallic iron and a void beneath it. The silicate surface of the void is covered with droplets or stringers of iron sulfide. The complex iron sulfide and metallic iron mounds formed by reduction with hydrogen generally are zoned. The outer layer is iron sulfide or a mixture of iron sulfide and metallic iron but the interior is metallic iron and iron sulfide, and the mound material next to the silicate host is iron sulfide. On the surface of some complex mounds, globules of silicate material are present. In one example, the globules consist of particles of aluminum oxide surrounded by silicate material. In turn, the margin of the globules is surrounded by iron sulfide. Dimples are present and surface of the dimples is covered by dendritic sheaths of iron sulfide and isolated metallic iron globules.

Carter, J. L.↗

NASA NTRS1991

Thermal modeling of comet Kopff: Implications for the CRAF mission

A thermal model of periodic comet Kopff was developed to aid in planning for the Comet Rendezvous Asteroid Flyby mission. The model is based on the comet nucleus model, which estimates the surface temperature distribution and sublimation rates on a rotating icy sphere in heliocentric orbit. The model results are compared with the observed gas production rates from Kopff in 1983. It is found that approximately 15 percent of the sunlit nucleus surface is active, a relatively high fraction for a typical short-period comet. This suggests that the actual nucleus radius may be larger than the model value. The slope of the observed gas production curve with heliocentric distance is steeper than that predicted by the thermal model. This may indicate the existence of a more complex process than direct sublimation of surface ices, such as gas diffusion through a nonvolatile insulating crust.

Weissman, Paul↗

NASA NTRS1985

Some observations on the occurrence of striation heating

Various wind tunnel flow visualization techniques have revealed the presence of striations on the surface of both simple geometries and complex winged entry configurations over a wide range of test conditions. The striations are attributed to streamwise vortices embedded in the boundary layer which produce locally enhanced heating levels. Mechanisms for such vortex formation are suggested based on observation of their occurrence on the simple configurations. These mechanisms are then related to striations observed in the wind tunnel on windward surfaces, swept wing leading edges and on the side fuselage of winged entry bodies. Flight data obtained on the side fuselage of ASSET and Shuttle support the conclusions derived from wind tunnel results. Quantitative criteria for the appearance of striations resulting from some of these mechanisms are presented. It is shown that the presence of embedded vorticity may be a consideration in the design of thermal protection systems for advanced winged entry vehicles.

Kipp, H. W.↗

NASA NTRS1992

Multidisciplinary design optimization using response surface analysis

Aerospace conceptual vehicle design is a complex process which involves multidisciplinary studies of configuration and technology options considering many parameters at many values. NASA Langley's Vehicle Analysis Branch (VAB) has detailed computerized analysis capabilities in most of the key disciplines required by advanced vehicle design. Given a configuration, the capability exists to quickly determine its performance and lifecycle cost. The next step in vehicle design is to determine the best settings of design parameters that optimize the performance characteristics. Typical approach to design optimization is experience based, trial and error variation of many parameters one at a time where possible combinations usually number in the thousands. However, this approach can either lead to a very long and expensive design process or to a premature termination of the design process due to budget and/or schedule pressures. Furthermore, one variable at a time approach can not account for the interactions that occur among parts of systems and among disciplines. As a result, vehicle design may be far from optimal. Advanced multidisciplinary design optimization (MDO) methods are needed to direct the search in an efficient and intelligent manner in order to drastically reduce the number of candidate designs to be evaluated. The payoffs in terms of enhanced performance and reduced cost are significant. A literature review yields two such advanced MDO methods used in aerospace design optimization; Taguchi methods and response surface methods. Taguchi methods provide a systematic and efficient method for design optimization for performance and cost. However, response surface method (RSM) leads to a better, more accurate exploration of the parameter space and to estimated optimum conditions with a small expenditure on experimental data. These two methods are described.

Unal, Resit↗

NASA NTRS2001

Automatic Overset Grid Generation with Heuristic Feedback Control

An advancing front grid generation system for structured Overset grids is presented which automatically modifies Overset structured surface grids and control lines until user-specified grid qualities are achieved. The system is demonstrated on two examples: the first refines a space shuttle fuselage control line until global truncation error is achieved; the second advances, from control lines, the space shuttle orbiter fuselage top and fuselage side surface grids until proper overlap is achieved. Surface grids are generated in minutes for complex geometries. The system is implemented as a heuristic feedback control (HFC) expert system which iteratively modifies the input specifications for Overset control line and surface grids. It is developed as an extension of modern control theory, production rules systems and subsumption architectures. The methodology provides benefits over the full knowledge lifecycle of an expert system for knowledge acquisition, knowledge representation, and knowledge execution. The vector/matrix framework of modern control theory systematically acquires and represents expert system knowledge. Missing matrix elements imply missing expert knowledge. The execution of the expert system knowledge is performed through symbolic execution of the matrix algebra equations of modern control theory. The dot product operation of matrix algebra is generalized for heuristic symbolic terms. Constant time execution is guaranteed.

Robinson, Peter I.↗

NASA NTRS2011

Single Piezo-Actuator Rotary-Hammering Drill

This innovation comprises a compact drill that uses low-axial preload, via vibrations, that fractures the rock under the bit kerf, and rotates the bit to remove the powdered cuttings while augmenting the rock fracture via shear forces. The vibrations fluidize the powered cuttings inside the flutes around the bit, reducing the friction with the auger surface. These combined actions reduce the consumed power and the heating of the drilled medium, helping to preserve the pristine content of the produced samples. The drill consists of an actuator that simultaneously impacts and rotates the bit by applying force and torque via a single piezoelectric stack actuator without the need for a gearbox or lever mechanism. This reduces the development/fabrication cost and complexity. The piezoelectric actuator impacts the surface and generates shear forces, fragmenting the drilled medium directly under the bit kerf by exceeding the tensile and/or shear strength of the struck surface. The percussive impact action of the actuator leads to penetration of the medium by producing a zone of finely crushed rock directly underneath the struck location. This fracturing process is highly enhanced by the shear forces from the rotation and twisting action. To remove the formed cuttings, the bit is constructed with an auger on its internal or external surface. One of the problems with pure hammering is that, as the teeth become embedded in the sample, the drilling efficiency drops unless the teeth are moved away from the specific footprint location. By rotating the teeth, they are moved to areas that were not fragmented, and thus the rock fracturing is enhanced via shear forces. The shear motion creates ripping or chiseling action to produce larger fragments to increase the drilling efficiency, and to reduce the required power. The actuator of the drill consists of a piezoelectric stack that vibrates the horn. The stack is compressed by a bolt between the backing and the horn in order to prevent it from being subjected to tensile stress that will cause it to fail. The backing is intended to transfer the generated mechanical vibrations towards the horn. In order to cause rotation, the horn is configured asymmetrically with helical segments and, upon impacting the bit, it introduces longitudinal along the axis of the actuator and tangential force causing twisting action that rotates the bit. The longitudinal component of the vibrations of the stack introduces percussion impulses between the bit and the rock to fracture it when the ultimate strain is exceeded under the bit.

Sherrit, Stewart↗

NASA NTRSDate not supplied

Understanding the Response of Common Spacecraft Shields to Hypervelocity Impacts of Meteorite and Other Terrestrial Analog Materials

Micrometeoroid and orbital debris (MMOD) populations can vary significantly in composition, density, and homogeneity. Hypervelocity testing campaigns intended to design and optimize MMOD shields for spacecraft are recognizing the need to investigate shield response from different types of impactors that span the range of densities observed in the MMOD population, such as nylon, Al, Al 2 O 3 , steel, and Cu. These tests, however, still pre-dominantly employ spherical and homogenous projectiles. Adding any compositional or mineralogical complexity to the impactor, such as what would be expected from a polymineralic micrometeoroid, for ex-ample, will be concomitant with a more complex shockwave structure in the projectile after it impacts the outer surface of any type of MMOD shield. The magnitude of these complexities will depend on how varied the mineralogy of the projectile is, but in the case of a metal-bearing chondrite, the disparate shock impendence between adjacent metal and silicate grains will potentially create localized areas of shock focusing (local increase in nominal shock pressure), or shock shadowing (local decrease in nominal shock pressure). The response of a MMOD shield is generally predicted using a ballistic limit equation – a semiempirical curve, derived from hypervelocity testing data, that denotes a particle diameter (for a given set of impact conditions such as projectile density and impact angle) when a shield will fail as a function of impact speed. These curves exhibit inflection points as a function of impact speed that represent when the projectile experiences sufficient pressure to fragment, melt, or vaporize. The introduction of shock focusing and shadowing in a heterogenous projectile will add uncertainty to the predicted pressures needed to go through each transition, leading to increased uncertainty in the expected performance of the MMOD shield. Therefore, it is necessary to explore the performance of MMOD shields in hypervelocity tests against more complex, natural projectile materials. To this end we have conducted a comparative test series to begin investigating the impact damage caused by meteoritic and terrestrial-analog projectiles, to that of spherical Al projectiles of similar mass.

Impact testing↗

NASA NTRS1987

Chemical processes in Triton's atmosphere and surface

The Neptune moon Triton may have an appreciable atmosphere; the preliminary calculations of Delitsky (1983) have suggested that there should be a significant resultant chemistry in a possible N2 ocean with dissolved CH4, given charged-particle radiolysis of gaseous mixtures and gamma radiolysis of N2-CH4 solutions. The latter will yield substantial quantities of organic products which will be partially soluble in any N2-CH4 liquid present. Attention is presently given to the energy sources available for Triton, in order to estimate rates of synthesis and ascertain the possible history of such simple and complex organic products on Triton's surface.

Delitsky, M. L.↗

NASA NTRS1991

RWF rotor-wake-fuselage code software reference guide

The RWF (Rotor-Wake-Fuselage) code was developed from first principles to compute the aerodynamics associated with the complex flow field of helicopter configurations. The code is sized for a single, multi-bladed main rotor and any configuration of non-lifting fuselage. The mathematical model for the RWF code is based on the integration of the momentum equations and Green's theorem. The unknowns in the problem are the strengths of prescribed singularity distributions on the boundaries of the flow. For the body (fuselage) a surface of constant strength source panels is used. For the rotor blades and rotor wake a surface of constant strength doublet panels is used. The mean camber line of the rotor airfoil is partitioned into surface panels. The no-flow boundary condition at the panel centroids is modified at each azimuthal step to account for rotor blade cyclic pitch variation. The geometry of the rotor wake is computers at each time step of the solution. The code produces rotor and fuselage surface pressures, as well as the complex geometry of the evolving rotor wake.

Berry, John D.↗

NASA NTRS1977

Mars - Photodesorption from mineral surfaces and its effects on atmospheric stability

Kinetic constraints are employed to identify the reactive chemisorbed complexes, to describe the mechanism of UV-accelerated desorption from Fe (+2) on mineral surfaces, and to estimate the photodesorption rate on Mars. In particular, it is proposed that gases such as O2, CO2, CO, H2O and N2 undergo an adsorption-desorption process at octahedrally coordinated Fe (+2) surface sites to produce seven-coordinate transition-state complexes. The ligand field stabilization energy acquired by these complexes lies between 16 and 18 kcal per mole. Published photocatalysis data are used to assess the role of photodesorption in Martian atmospheric chemistry and stability.

Huguenin, R. L.↗

NASA NTRS1999

Vortex-Body Interactions: A Critical Assessment. Coupled Gap-Wake Instabilities/Turbulence: A Source of Noise

This program has involved, first of all, a critical state-of-the-art assessment of vortex-body interactions. Then, efforts were focused on experimental investigation on coupled-wake instabilities and turbulence occurring in a two-cylinder system. An extensive review was undertaken on the effect of incident vortices on various types of bodies. These incident vortices have a length scale of the same order of magnitude as the scale of the body. The body can take on various forms, including, for example, a circular cylinder, a blade or a wing. The classes of vortex-body interaction that were critically assessed include: (1) Periodic distortion of the incident (primary) vortex and shedding of secondary vorticity from the surface of the body. (2) Modulated vortex distortion and shedding at a leading-edge or surface due to incidence of a complex system of vortices. (3) Vortex distortion and shedding in presence of body oscillation. (4) Three-dimensional vortex interaction and shedding. For all of these classes of vortex-body interaction, quantitative topologies of the vorticity distributions and streamline patterns were found to be central to a unified description of mechanisms of vortex distortion and shedding. In most cases, it was possible to define relationships between vortex interactions and unsteady loading at the body surface. This phase of the program was an experimental investigation of a two-cylinder system, which simulated a central aspect of a four-wheel bogie on a large-scale commercial aircraft. The overall aim of this experimental research program was to determine the crucial elements of the unsteadiness in the gap and near-wake regions as a function of time using cinema-based techniques. During the research program, various image evaluation techniques were employed. They involved assessment of instantaneous velocity fields, streamline topology and patterns of vorticity. Experiments were performed in a large-scale water channel using a high-resolution version of digital particle image velocimetry. The program has focused on acquisition of images of velocity and vorticity for varying gap widths between the two-cylinder system. As a result of analysis of a relatively large number of images, it is demonstrated that low frequency instabilities can occur in the gap region between the cylinder. These low frequency instabilities are hypothesized to influence the near-wake structure of the entire two-cylinder system. The nature of the unstable shear layers in the gap region involves generation of small-scale Kelvin-Helmholtz instabilities. These unsteady shear layers then impinge upon the upper and lower surfaces of the cylinders, thereby influencing both the unsteady structure and the time-averaged patterns of the near-wake. Initial efforts have focused on characterization of the patterns of instantaneous and averaged streamlines using topological concepts. The end result of this investigation is a series of documented instantaneous images. They will serve as a basis for various types of post-processing, which will lead to a fuller understanding of the instantaneous and time-averaged unstable-turbulent fields in the gap region and downstream of the two-cylinder system. This further assessment is the focus of a subsequent program.

Rockwell, Donald↗

NASA NTRS2021

Assessing Relay Communications for Mars Sample Return Surface Mission Concepts

The Mars Sample Return (MSR) Campaign would be a 3-mission campaign concept supported by NASA and ESA to return samples from the Mars surface. MSR would, for the first time ever, present a need to communicate with multiple surface assets that are co-located on Mars in a coordinated effort to accomplish the unified objective of fetching, transporting, and returning samples from Mars. Currently, Mars surface assets relay data to and from Earth using a number of orbiters in what’s known as the Mars Relay Network (MRN). This network is characterized by a small number of surface assets distributed across the Martian globe and a larger number of orbiters to provide relay services. As of June 2020, there are two surface assets for which five orbiters are providing relay. During the MSR Campaign, there would be two rovers and a lander that all would require relay communication from a small number of Mars orbiters to meet the aggressive MSR timeline. The inversion of the current MRN paradigm, a system of many surface assets requiring relay and few orbiters to provide relay, necessitates the unique challenge of optimally allocating relay passes to maximize the operational capability of all assets. The allocation must consider a large number of trade variables including Mars asset operational requirements and Earth ground system constraints, including staffing schedules, operations planning across time zones, and more. To address these telecommunication challenges, the Mars Asset Relay Mission Link Allocation Design Environment (MARMLADE) tool was developed. It is a MATLAB-based tool to assign orbiter passes or Direct-From-Earth (DFE) links to each of the three surface assets and quantify the operational efficiency of each surface asset.MARMLADE uses a data set of simulated Mars relay orbiter geometry and telecommunication capabilities provided by JPL’s Telecom Orbit Analysis and Simulation Tool (TOAST) software to compute which asset should get each pass based on a series of heuristics and predictions of all assets’ states. Within MARMLADE, the user can provide inputs including the option for time-based pass splitting, fixed FWD data rate capabilities, DFE communication capabilities, and link parameters allowing for the assessment of complex operations and hardware trades using surface mission operational efficiency as a primary figure of merit. As the MSR mission concepts continue to mature, MARMLADE is being used to assess ability of all MSR elements to meet the surface mission timeline requirements and to provide relay link allocations to each of the MSR surface assets.This paper will describe the motivation and design of the MARMLADE tool and how it is being used to perform campaign and mission level trades, generate requirements, and support development of the MSR surface mission scenarios.

Lee, Charles↗