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At least 973 records · Page 54

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Dynamic Stability Finite Element Analysis of Multiple Potential Large Space Telescope Structural Designs

One of the driving structural requirements of the Habitable Exo-Planet telescope is to maintain line of sight stability between the primary and secondary mirror of ≤ 5 milli-arc seconds. Dynamic analyses of two configurations of a proposed Habitable Exo-Planet 4 meter off-axis telescope structure were performed to predict effects of a vibration input on primary/secondary mirror alignment. The dynamic disturbance used as the forcing function was the James Webb Space Telescope reaction wheel assembly vibration emission specification level. The objective of these analyses was to predict order-of-magnitude performance for various structural configurations which contribute to efforts in defining the Habitable Exo-Planet structural design’s global architecture. Two variations of the basic architectural design were analyzed. Relative motion between the PM and the SM for each design configuration are reported.

jitter↗

NASA NTRS2002

Photogrammetry Methodology Development for Gossamer Spacecraft Structures

Photogrammetry--the science of calculating 3D object coordinates from images--is a flexible and robust approach for measuring the static and dynamic characteristics of future ultra-lightweight and inflatable space structures (a.k.a., Gossamer structures), such as large membrane reflectors, solar sails, and thin-film solar arrays. Shape and dynamic measurements are required to validate new structural modeling techniques and corresponding analytical models for these unconventional systems. This paper summarizes experiences at NASA Langley Research Center over the past three years to develop or adapt photogrammetry methods for the specific problem of measuring Gossamer space structures. Turnkey industrial photogrammetry systems were not considered a cost-effective choice for this basic research effort because of their high purchase and maintenance costs. Instead, this research uses mainly off-the-shelf digital-camera and software technologies that are affordable to most organizations and provide acceptable accuracy.

Pappa, Richard S.↗

NASA NTRS1992

Modal Test/Analysis Correlation of Space Station Structures Using Nonlinear Sensitivity

The modal correlation problem is formulated as a constrained optimization problem for validation of finite element models (FEM's). For large-scale structural applications, a pragmatic procedure for substructuring, model verification, and system integration is described to achieve effective modal correlation. The space station substructure FEM's are reduced using Lanczos vectors and integrated into a system FEM using Craig-Bampton component modal synthesis. The optimization code is interfaced with MSC/NASTRAN to solve the problem of modal test/analysis correlation; that is, the problem of validating FEM's for launch and on-orbit coupled loads analysis against experimentally observed frequencies and mode shapes. An iterative perturbation algorithm is derived and implemented to update nonlinear sensitivity (derivatives of eigenvalues and eigenvectors) during optimizer iterations, which reduced the number of finite element analyses.

Gupta, Viney K.↗

NASA NTRS1992

Modal test/analysis correlation of Space Station structures using nonlinear sensitivity

The modal correlation problem is formulated as a constrained optimization problem for validation of finite element models (FEM's). For large-scale structural applications, a pragmatic procedure for substructuring, model verification, and system integration is described to achieve effective modal correlations. The space station substructure FEM's are reduced using Lanczos vectors and integrated into a system FEM using Craig-Bampton component modal synthesis. The optimization code is interfaced with MSC/NASTRAN to solve the problem of modal test/analysis correlation; that is, the problem of validating FEM's for launch and on-orbit coupled loads analysis against experimentally observed frequencies and mode shapes. An iterative perturbation algorithm is derived and implemented to update nonlinear sensitivity (derivatives of eigenvalues and eigenvectors) during optimizer iterations, which reduced the number of finite element analyses.

Gupta, Viney K.↗

NASA NTRS1981

The 15th Aerospace Mechanisms Symposium

The purpose of the symposium was to provide a forum for the interchange of information among those active in the field of mechanism technology. To that end, 27 papers were presented on aeronautics and space flight, with special emphasis on actuators and aerospace applications for pointing systems, latches, connectors, and other mechanisms for large space structures. The papers were authored by engineers from a broad aerospace spectrum including the U. S. aerospace industry, NASA, and several European participants. Technological areas covered include: aerospace propulsion; aerodynamic devices; crew safety; space vehicle control; spacecraft deployment, positioning, and pointing; deployable antennas/reflectors; and large space structures. Devices for payload deployment, payload retention, and crew extravehicular activities on the space shuttle orbiter are also described.

Actuators↗

NASA NTRS1991

Composite load spectra for select space propulsion structural components

The objective of this program is to develop generic load models with multiple levels of progressive sophistication to simulate the composite load spectra that are induced in space propulsion system components, representative of Space Shuttle Main Engines (SSME), such as transfer ducts, turbine blades, and liquid oxygen (LOX) posts and system ducting. These models will be developed using two independent approaches. The first approach consists of using state-of-the-art probabilistic methods to describe the individual loading conditions and combinations of these loading conditions to synthesize the composite load spectra simulation. The methodology required to combine the various individual load simulation models (hot-gas dynamic, vibrations, instantaneous position, centrifugal field, etc.) into composite load spectra simulation models will be developed under this program. A computer code incorporating the various individual and composite load spectra models will be developed to construct the specific load model desired. The second approach, which is covered under the options portion of the contract, will consist of developing coupled models for composite load spectra simulation which combine the (deterministic) models for composite load dynamic, acoustic, high-pressure and high rotational speed, etc., load simulation using statistically varying coefficients. These coefficients will then be determined using advanced probabilistic simulation methods with and without strategically selected experimental data. This report covers the efforts of the third year of the contract. The overall program status is that the turbine blade loads have been completed and implemented. The transfer duct loads are defined and are being implemented. The thermal loads for all components are defined and coding is being developed. A dynamic pressure load model is under development. The parallel work on the probabilistic methodology is essentially completed. The overall effort is being integrated in an expert system code specifically developed for this project.

Newell, J. F.↗

DOE OSTI2011

On relaxation and transport in gyrokinetic drift wave turbulence with zonal flow

We present a theory for relaxation and transport in phase space for gyrokinetic drift wave turbulence with zonal flow. The interaction between phase space eddys and zonal flows is considered in two different limits, namely for K>>1 and K{approx_equal} 1 where K is the Kubo number. For K>>1, the growth of an isolated coherent phase space structure is calculated, including the associated zonal flow dynamics. For K{approx_equal} 1, mean field relaxation dynamics is considered in the presence of phase space granulations and zonal flows. In both limits, it is shown that the evolution equations for phase space structures are structurally similar to a corresponding Charney-Drazin theorem for zonal momentum balance in a potential vorticity conserving, quasi-geostrophic system. The transport flux in phase space is calculated in the presence of phase space density granulations and zonal flows. The zonal flow exerts a dynamical friction on ion phase space density evolution, which is a fundamentally new zonal flow effect.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1978

Space Spider - A concept for fabrication of large structures

The Space Spider concept for the automated fabrication of large space structures involves a specialized machine which roll-forms thin gauge material such as aluminum and develops continuous spiral structures with radial struts to sizes of 600-1,000 feet in diameter by 15 feet deep. This concept allows the machine and raw material to be integrated using the Orbiter capabilities, then boosting the rigid system to geosynchronous equatorial orbit (GEO) without high sensitivity to acceleration forces. As a teleoperator controlled device having repetitive operations, the fabrication process can be monitored and verified from a ground-based station without astronaut involvement in GEO. The resultant structure will be useful as an intermediate size platform or as a structural element to be used with other elements such as the space-fabricated beams or composite nested tubes.

Britton, W. R.↗

NASA NTRS1991

Composite load spectra for select space propulsion structural components

The objective of this program is to develop generic load models with multiple levels of progressive sophistication to simulate the composite (combined) load spectra that are induced in space propulsion system components, representative of Space Shuttle Main Engines (SSME), such as transfer ducts, turbine blades, and liquid oxygen posts and system ducting. The first approach will consist of using state of the art probabilistic methods to describe the individual loading conditions and combinations of these loading conditions to synthesize the composite load spectra simulation. The second approach will consist of developing coupled models for composite load spectra simulation which combine the deterministic models for composite load dynamic, acoustic, high pressure, and high rotational speed, etc., load simulation using statistically varying coefficients. These coefficients will then be determined using advanced probabilistic simulation methods with and without strategically selected experimental data.

Newell, J. F.↗

NASA NTRS1971

Preliminary criteria for the fracture control of space shuttle structures

The complex and multidisciplinary factors are presented which relate to the prevention of structural failure due to the initiation or propagation of cracks or crack-like defects. The fracture control criteria are applicable to space shuttle components which are: (1) susceptible to cracking or fracture on the basis of anticipated loads and environment, and (2) critical to either crew safety or system performance. The criteria define the design, fabrication, environmental control, inspection, maintenance, repair, and verification procedures required for adequate fracture control.

Source record↗

NASA NTRS2002

A Biologically Inspired Cooperative Multi-Robot Control Architecture

A prototype cooperative multi-robot control architecture suitable for the eventual construction of large space structures has been developed. In nature, there are numerous examples of complex architectures constructed by relatively simple insects, such as termites and wasps, which cooperatively assemble their nests. The prototype control architecture emulates this biological model. Actions of each of the autonomous robotic construction agents are only indirectly coordinated, thus mimicking the distributed construction processes of various social insects. The robotic construction agents perform their primary duties stigmergically i.e., without direct inter-agent communication and without a preprogrammed global blueprint of the final design. Communication and coordination between individual agents occurs indirectly through the sensed modifications that each agent makes to the structure. The global stigmergic building algorithm prototyped during the initial research assumes that the robotic builders only perceive the current state of the structure under construction. Simulation studies have established that an idealized form of the proposed architecture was indeed capable of producing representative large space structures with autonomous robots. This paper will explore the construction simulations in order to illustrate the multi-robot control architecture.

Howsman, Tom↗

NASA NTRS2004

A Stigmergic Cooperative Multi-Robot Control Architecture

In nature, there are numerous examples of complex architectures constructed by relatively simple insects, such as termites and wasps, which cooperatively assemble their nests. A prototype cooperative multi-robot control architecture which may be suitable for the eventual construction of large space structures has been developed which emulates this biological model. Actions of each of the autonomous robotic construction agents are only indirectly coordinated, thus mimicking the distributed construction processes of various social insects. The robotic construction agents perform their primary duties stigmergically, i.e., without direct inter-agent communication and without a preprogrammed global blueprint of the final design. Communication and coordination between individual agents occurs indirectly through the sensed modifications that each agent makes to the structure. The global stigmergic building algorithm prototyped during the initial research assumes that the robotic builders only perceive the current state of the structure under construction. Simulation studies have established that an idealized form of the proposed architecture was indeed capable of producing representative large space structures with autonomous robots. This paper will explore the construction simulations in order to illustrate the multi-robot control architecture.

Howsman, Thomas G.↗

NASA NTRS1986

Composite load spectra for select space propulsion structural components

A multiyear program is performed with the objective to develop generic load models with multiple levels of progressive sophistication to simulate the composite (combined) load spectra that are induced in space propulsion system components, representative of Space Shuttle Main Engines (SSME), such as transfer ducts, turbine blades, and liquid oxygen (LOX) posts. Progress of the first year's effort includes completion of a sufficient portion of each task -- probabilistic models, code development, validation, and an initial operational code. This code has from its inception an expert system philosophy that could be added to throughout the program and in the future. The initial operational code is only applicable to turbine blade type loadings. The probabilistic model included in the operational code has fitting routines for loads that utilize a modified Discrete Probabilistic Distribution termed RASCAL, a barrier crossing method and a Monte Carlo method. An initial load model was developed by Battelle that is currently used for the slowly varying duty cycle type loading. The intent is to use the model and related codes essentially in the current form for all loads that are based on measured or calculated data that have followed a slowly varying profile.

Newell, J. F.↗

NASA NTRS2022

Research Campaign: Advanced Manufacturing in Space: Properties, Structure and Simulations to Pioneer New Applications

This topic underpins synthesis of, and in many cases manufacturing of, value-added materials via liquid phase processing. Materials and processes range from cast metals and optical glasses through exploration-relevant technologies such as additive manufacturing, casting and in-situ resource utilization to support human space exploration. A recurring theme is the need for accurate thermophysical property and atomic structure data for relevant materials and the exploitation of reduced convection/sedimentation in microgravity to enhance the quality of data and to develop new and transformative technologies for materials processing.

Michael SanSoucie↗

NASA NTRS1985

MSFC Data Analysis of the SAFE/DAE Experiment

The Solar Array Flight Experiment (SAFE) on-orbit experiment for measurement of large structures dynamics consists of a dynamic sensing system designed to record and analyze the dynamic characteristics of the SAFE. The early availability of the SAFE and its basic large space structure characteristics made it a logical candidate for verification of the sensing system and evaluation technique. The characteristics of the solar array which place it well within the generic class of large space structures are: (1) Large size; (2) Low natural frequencies; (3) Mechanical complexity of its extendable/retractable mast; and (4) The inability to dynamic test in Earth atmosphere and one g.

Schock, R. W.↗

NASA NTRS1981

Composite beam builder

The building block approach to large space structures is discussed, and the progress made in constructing aluminum beams is noted. It is pointed out that composites will also be required in space structures because they provide minimal distortion characteristics during thermal transients. A composite beam builder currently under development is discussed, with attention given to cap forming and the fastening of cross-braces. The various composite materials being considered are listed, along with certain of their properties. The need to develop continuous forming stock up to 300 m long is stressed.

Poveromo, L. M.↗

NASA NTRS1986

Correcting for Supports in Structual Dynamic Testing

Testing under variety of support conditions combined with computer analysis to update mathematical models to match test data. Report suggests dynamic characteristics of large space structures predicted, without full-scale testing, by method that combines experiment and analysis. Method, multiple-boundary-condition testing, developed for such large space structures as dish antennas, towers, and solar-cell arrays.

Wada, B. K.↗

NASA NTRS1988

ACES program - Lessons learned

The ACES Program involved the experimental evaluation of three LSS (large space structures) control design techniques at the LSS GTF (ground test facility) at NASA/MSFC. The three techniques were developed under the ACOSS (active control of space structures) Program specifically for application to LSS. The techniques included FAMESS (filter accommodated model error sensitivity suppression), HAC/LAC (high authority control/low authority control), and positivity. Some of the lessons that have been learned during the course of the ACES program are examined.

Jones, Victoria L.↗