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NASA NTRS1980

Large space structures - Fantasies and facts

A review of large space structures activities from 1973 to 1979 is presented. Long-range studies of space colonies, gigantic solar power stations and projected earth applications revived interest in space activities. Studies suggest opportunities for advanced antenna and platform applications. Matching low-thrust propulsion to large flexible vehicles will be a key technology. Current structures technology investigations include deployable and erectable structures and assembly techniques. Based on orbited structures experience, deployment reliability is a critical issue for deployable structures. For erectable structures, concepts for earth-fabricated and space-fabricated memb

Card, M. F.↗

NASA NTRS1982

Solution Accounts for Structural Damping

New analytical technique determines dynamic response of damped structures dominated by internal structural damping mechanisms. Though structural damping is often negligible compared with damping due to air friction and friction in joints, structural damping can be of major importance in structures having heavy damping treatments or in outer-space structures. Finite-element model includes nonlinear, nonviscous internal damping.

Roussos, L. A.↗

NASA NTRS1980

Recent advances in structural technology for large deployable and erectable spacecraft

Ultra-low mass deployable and erectable truss structure designs for spacecraft are identified using computerized structural sizing techniques. Extremely slender strut proportions are shown to characterize minimum mass spacecraft which are designed for shuttle transport to orbit. Discrete element effects using a recently developed buckling theory for periodic lattice type structures are presented. An analysis of fabrication imperfection effects on the surface accuracy of four different antenna reflector structures is summarized. The tetrahedral truss has the greatest potential of the structures examined for application to accurate or large reflectors. A deployable module which can be efficiently transported is identified and shown to have significant potential for application to future antenna requirements. Investigations of erectable structure assembly are reviewed.

Bush, H. G.↗

NASA NTRS1980

Recent advances in structural technology for large deployable and erectable spacecraft

Ultra-low mass deployable and erectable truss structure designs for spacecraft are identified using computerized structural sizing techniques. Extremely slender strut proportions are shown to characterize minimum mass spacecraft which are designed for Shuttle transport to orbit. Analytical results are presented which demonstrate discrete element effects using a recently developed buckling theory for periodic lattice type structures. An analysis of fabrication imperfection effects on the surface accuracy of four different antenna reflector structures is summarized. This study shows the tetrahedral truss to have the greatest potential of the structures examined for application to accurate or large reflectors. A deployable module which can be efficiently transported is identified and shown to have significant potential for application to future antenna requirements. Recent investigations of erectable structure assembly are reviewed. Initial experiments simulating astronaut assembly by extra-vehicular activity (EVA) show that a pair of astronauts can achieve assembly times of 2-5 min/strut. Studies indicate that an automated assembler can achieve times of less than 1 min/strut on an around-the-clock basis.

Bush, H. G.↗

NASA NTRS1981

Integrated analysis of engine structures

The need for light, durable, fuel efficient, cost effective aircraft requires the development of engine structures which are flexible, made from advaced materials (including composites), resist higher temperatures, maintain tighter clearances and have lower maintenance costs. The formal quantification of any or several of these requires integrated computer programs (multilevel and/or interdisciplinary analysis programs interconnected) for engine structural analysis/design. Several integrated analysis computer prorams are under development at Lewis Reseach Center. These programs include: (1) COBSTRAN-Composite Blade Structural Analysis, (2) CODSTRAN-Composite Durability Structural Analysis, (3) CISTRAN-Composite Impact Structural Analysis, (4) STAEBL-StruTailoring of Engine Blades, and (5) ESMOSS-Engine Structures Modeling Software System. Three other related programs, developed under Lewis sponsorship, are described.

Chamis, C. C.↗

NASA NTRS1982

Structural Assembly Demonstration Experiment (SADE) experiment design

The Structural Assembly Demonstration Experiment concept is to erect a hybrid deployed/assembled structure as an early space experiment in large space structures technology. The basic objectives can be broken down into three generic areas: (1) by performing assembly tasks both in space and in neutral buoyancy simulation, a mathematical basis will be found for the validity conditions of neutral buoyancy, thus enhancing the utility of water as a medium for simulation of weightlessness; (2) a data base will be established describing the capabilities and limitations of EVA crewmembers, including effects of such things as hardware size and crew restraints; and (3) experience of the M.I.T. Space Systems Lab in neutral buoyancy simulation of large space structures assembly indicates that the assembly procedure may create the largest loads that a structure will experience during its lifetime. Data obtained from the experiment will help establish an accurate loading model to aid designers of future space structures.

Akin, D. L.↗

NASA NTRS1980

Satellite power systems structures: A 1980 technology status review

The classes of major structural components and constructions utilized were considered. A review of the current (SPS) structure technology status was made. The major issues considered pertinent to SPS structures are: Cost effective construction, construction materials, structural design requirements, stress and dimensional integrity of as-built structures, and predictability of strength and dynamic behavior. The feasibility of passive figure control approach to MPTS flatness, of structure stiffness compatible with MPTS pointing, of passive control through damping, and the feasibility of space fabrication of ultra-large reflector surfaces are also considered. Qualification, model verification, inspection are considered of vital concern.

Greenberg, H. S.↗

NASA NTRS1982

Dynamics of bi-periodic structures

In order to gain insight into the dynamics of biperiodic aerospace structures, a variety of one- and two-dimensional biperiodic structures are considered. It is shown that bands in which natural frequencies lie for periodic structures are further subdivided as a consequence of the biperiodicity. Analytical solutions for the modes and frequencies of finite-length one-dimensional biperiodic structures are obtained for general boundary conditions. A transmission method is developed to simplify the application of boundary conditions. Some modes are found to occur at frequencies outside the frequency bands predicted for biperiodic structures. Two-dimensional biperiodic crossed beam grillage and truss structures are considered in the present study.

Mcdaniel, T. J.↗

NASA NTRS1983

Advances in structural concepts

A number of different structural concepts are currently under development as a means of placing large structures in orbit. Three commonly considered concepts are described. The radial rib structure and the hoop-column structure have undergone considerable early development because of their seeming potential for providing a reliably deployable reflector surface. In the present paper, attention is focused on truss structures which historically have been widely used in ground based structures because of their inherent simplicity, versatility, and high stiffness.

Mikulas, M. M., Jr.↗

NASA NTRS1983

Long Duration Exposure Facility (LDEF) structural verification test report

Structural load tests on the Long Duration Exposure Facility's (LDEF) primary structure were conducted. These tests had three purposes: (1) demonstrate structural adequacy of the assembled LDEF primary structure when subjected to anticipated flight loads; (2) verify analytical models and methods used in loads and stress analysis; and (3) perform tests to comply with the Space Transportation System (STS) requirements. Test loads were based on predicted limit loads which consider all flight events. Good agreement is shown between predicted and observed load, strain, and deflection data. Test data show that the LDEF structure was subjected to 1.2 times limit load to meet the STS requirements. The structural adequacy of the LDEF is demonstrated.

Jones, T. C.↗

NASA NTRS1983

Structural concepts for future space transportation orbiters

Two structural concepts for a fully reusable STS orbiter are compared with respect to weight and the ability to satisfy structural goals. The cryogenic propellant tanks for both concepts use welded, blade-stiffened aluminum skins for leak-free containment and compatibility with LOX and LH2. The tanks are sized primarily by pressure, although some areas are sized by bending and fracture mechanics considerations. The tank concept is regarded as state-of-the-art, even though it requires a closed cell foam insulation with a dry air purge to prevent air liquefaction and ice formation. It is noted that the foam will require testing to verify its design life for use in the STS. One concept has nonintegral tanks suspended inside an insulated aluminum airframe and thrust structure. Here, a durable thermal protection system external insulation is mechanically attached to the airframe, allowing a buckled skin design. The other concept uses a novel structural arrangement consisting of a separate tank/thrust structure that supports a hot advanced-carbon-carbon aeroshell structure.

Taylor, A. H.↗

NASA NTRS1983

An analytical investigation of shape control of large space structures by applied temperatures

An analytical procedure for the static shape control of flexible space structures subjected to thermal distortions is developed which is based on prescribing temperatures in control elements having much higher coefficients of thermal expansion than the main structure. The temperatures at the control elements are defined so as to minimize the overall thermal distortion of the structure from its ideal shape, and a matrix equation is obtained which can be solved for the set of optimum control temperatures. A formulation of the procedure for continuous structures governed by differential equations and a formulation for discrete (finite element modeled) structures governed by matrix equations are presented. The equations from the continuous formulation are employed for the shape control of a simple beam distorted by nonuniform heating, and the discrete formulation is applied in a general purpose finite-element structural analysis computer program for the shape control of a 750 m radiometer antenna reflector dish subjected to orbital heating. A reduction in thermal distortion by a factor of nearly 50 was obtained with the use of only seven control elements. Results for four different sets of control locations for the antenna are presented in which reductions in distortion of up to a factor of four were obtained.

Haftka, R. T.↗

NASA NTRS1984

Mathematical synthesization of complex structures

A mathematical synthesization approach for rapidly modeling and analyzing complex structures comprised of hundreds or thousands of repeating individual structural members, interconnecting hardware, and other components was described. The techniques are applicable to any structure with repeating structural members. The capabilities are embodied within the Interactive Design and Evaluation of Advanced Spacecraft (IDEAS) computer-aided design system. IDEAS has a full range of integrated spacecraft modeling, design, analysis, performance, and cost estimating capabilities which include about 40 technical program and executive, data base, and file management systems. With IDEAS, a single user at an interactive terminal can create, design, analyze, and conduct parametric studies of Earth orbiting spacecraft in a timely, cost-efficient manner. The system is particularly useful in the conceptual design phases of advanced space missions when a multiplicity of concepts must be evaluated. The IDEAS interactive finite-element modeling capabilities are discussed. The mathematical synthesization programs were structured not only to provide a detailed finite-element model of the structure but also to automatically perform the many auxiliary computations needed to analyze the spacecraft in its orbital operational environment.

Garrett, L. B.↗

NASA NTRS1984

Development and support structures for high-power solar arrays

A number of structurally efficient configurations for wing-type solar arrays are developed by a combination of deepening the planform of the blanket and structure and by partitioning the blanket with battens and frequent attachments to the support structure. This technique reduces the tension required to avoid a low natural frequency for the blanket, and the load reduction results in a lighter structure. The use of three different structures are investigated: the Astromast, the Extendible Support Structure (ESS), and a new beam called the STACBEAM (Stacking Triangular Articulated Compact Beam) and their relative performances are compared. The investigation of the STACBEAM is emphasized because its sequential deployment is more reliable for very long systems, and its linear deployment facilitates local attachments to the blanket and the development of a low mass deployer.

Knapp, K.↗

NASA NTRS1984

Natural large-scale structures in the axisymmetric mixing layer

The present study is concerned with the optimization of conditional sampling techniques for eduction of naturally occurring large-scale structures in an axisymmetric mixing layer, and a comparison of the natural structure with that induced by means of controlled excitation. Questions regarding the sensitivity of the educed structure to the excitation amplitude are also explored. Aspects regarding the eduction with the high-speed-side reference signal are considered, taking into account structure identification, the smearing effect and a comparison with the structure under excitation, the effects of the threshold level, and the effect of a trigger-level window. Attention is given to structure characteristics and their dependence on Reynolds number and initial condition.

Zaman, K. B. M. Q.↗

NASA NTRS1984

Structure and evolution of the large scale solar and heliospheric magnetic fields

Structure and evolution of large scale photospheric and coronal magnetic fields in the interval 1976-1983 were studied using observations from the Stanford Solar Observatory and a potential field model. The solar wind in the heliosphere is organized into large regions in which the magnetic field has a componenet either toward or away from the sun. The model predicts the location of the current sheet separating these regions. Near solar minimum, in 1976, the current sheet lay within a few degrees of the solar equator having two extensions north and south of the equator. Soon after minimum the latitudinal extent began to increase. The sheet reached to at least 50 deg from 1978 through 1983. The complex structure near maximum occasionally included multiple current sheets. Large scale structures persist for up to two years during the entire interval. To minimize errors in determining the structure of the heliospheric field particular attention was paid to decreasing the distorting effects of rapid field evolution, finding the optimum source surface radius, determining the correction to the sun's polar field, and handling missing data. The predicted structure agrees with direct interplanetary field measurements taken near the ecliptic and with coronameter and interplanetary scintillation measurements which infer the three dimensional interplanetary magnetic structure. During most of the solar cycle the heliospheric field cannot be adequately described as a dipole.

Hoeksema, J. T.↗

NASA NTRS1985

A computer analysis program for interfacing thermal and structural codes

A software package has been developed to transfer three-dimensional transient thermal information accurately, efficiently, and automatically from a heat transfer analysis code to a structural analysis code. The code is called three-dimensional TRansfer ANalysis Code to Interface Thermal and Structural codes, or 3D TRANCITS. TRANCITS has the capability to couple finite difference and finite element heat transfer analysis codes to linear and nonlinear finite element structural analysis codes. TRANCITS currently supports the output of SINDA and MARC heat transfer codes directly. It will also format the thermal data output directly so that it is compatible with the input requirements of the NASTRAN and MARC structural analysis codes. Other thermal and structural codes can be interfaced using the transfer module with the neutral heat transfer input file and the neutral temperature output file. The transfer module can handle different elemental mesh densities for the heat transfer analysis and the structural analysis.

Thompson, R. L.↗

NASA NTRS1985

Optimization of Controlled Structures

A formulation is presented for the coupled optimal design of a structural system and its control by defining a composite objective function as a linear combination of two components: a structural objective and a control objective. For the case when the structural objective is a function of the structural design variables only, and when the control objective is represented by the quadratic functional of the response and control energy, one can analytically express the optimal control in terms of any set of admissible structural design variables. The expression for the optimal control is used recursively in an iterative Newton-Raphson search scheme, the goal of which is to determine a corresponding optimal set of structural design variables that minimize the composite objective function. A numerical example is given to illustrate the computational procedure.

Salama, M.↗

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