Geometric Modeling of Inflatable Structures for Lunar Base

A modular inflatable structure consisting of thin, composite membranes is presented for use in a lunar base. Results from a linear elastic analysis of the structure indicate that it is feasible in the lunar environment. Further analysis requires solving nonlinear equations and accurately specifying the geometries of the structural members. A computerized geometric modeling technique, using bicubic Bezier surfaces to generate the geometries of the inflatable structure, was conducted. Simulated results are used to create three‐dimensional wire frames and solid renderings of the individual components of the inflatable structure. The component geometries are connected into modules, which are then assembled based upon the desired architecture of the structure.     

Coupling among Pitch Motion, Axial Vibration, and Orbital Motion of Large Space Structures

The parameter dependency of large space structures on the coupling among attitude motion, structural vibration, and orbital motion has been investigated, particularly for structures such as tethered satellite systems. Tethered satellites are noticed for their possible applications. From space solar power systems to deorbit system, the applications of tethered satellites spread out over various fields. In this paper, we investigate planar motion of a satellite model, which consists of two tip particles and a massless spring. For such a space structure, the characteristics of the planar motion are shown to be determined by the mass ratio of tip particles, the natural frequency ratio of axial vibration to orbital motion, and the axial length ratio of the spring to the orbital radius. Among these three parameters, the natural frequency ratio has the greatest influence on the coupling phenomenon. Furthermore, the parameter range over which the coupling phenomenon occurs is specified.     

Mechanical Equipment Requirements for Inflatable Lunar Structures

Inflatable structures have been proposed by a number of authors. Several structural forms have been conceptually designed, including spherical, pillow‐shaped, semicylindrical, and domed saucer. Regardless of structural form, all inflatables require mechanical equipment to initiate and maintain inflation. This paper identifies the mechanical equipment and operations required to support an inflatable structure. A previously proposed semicylindrical structure is selected for this study, but the principal results are applicable to all inflatable structures. The results indicate that air for inflatable structures should be transported to the moon in a liquid (cryogenic) state. The liquefied air can be evaporated and heated to the proper temperature using solar energy and a conventional pumping system. Removing the air from the facility is an entirely different problem and requires different equipment. There are two alternatives: (1) Discharge the air to the moon; and (2) reclaim the air for reuse. The first alternative is not likely to be cost‐effective and might well be scientifically unacceptable. The second alternative presents numerous technical problems but appears technically feasible.     

Hierarchical High-Fidelity Analysis Methodology for Buckling Critical Structures

A hierarchical high-fidelity analysis methodology for predicting the critical buckling load of compression-loaded thin-walled isotropic shells is described. This hierarchical procedure includes three levels of fidelity for the analysis. Level 1 assumes that the buckling load can be predicted by the classical shell solution with simply supported boundary condition, and with a linear membrane prebuckling solution. Level 2 includes the effects of a nonlinear prebuckling solution and the effects of traditional clamped or simply supported boundary conditions. Level 3 includes the nonlinear interaction between nearly simultaneous buckling modes and the effects of boundary imperfections and general boundary conditions. Various deterministic and probabilistic approaches are used to account for the degrading effects of unavoidable shell-wall geometric imperfections. The results from the three solution levels are compared with experimental results, and the effects of the assumptions and approximations used for the three solution levels are discussed. This hierarchical analysis approach can be used in the design process to converge rapidly to an accurate prediction of the expected buckling load of a thin-shell design problem.     

Modeling the Hinge Moment of Skew-Mounted Tape Spring Folds

Tape springs, defined as thin metallic strips with an initially curved cross section, are an attractive structural solution and hinge mechanism for small satellite deployable structures due to their low mass, low cost, and general simplicity. When mounted at skewed angles to the hinge line, the tapes can be subjected to complex folds involving both bending and twisting of the tape. These folds have been experimentally investigated and theories have been developed to model the resulting opening moment. However, the opening moments of these theories are not equivalent to the opening moment about the hinge line, which is the parameter required in satellite deployment applications. This paper derives a method to determine the hinge moment from the previous theories and compares the theoretical predictions with experimental and finite element results. It uses this model to investigate the predicted hinge moment trends for full deployments of 180°. The model is then applied to a practical spacecraft hinge application.     

Motion Control of Space Structures

A new area of civil engineering is emerging as we begin to establish a permanent presence in space. The new area of civil engineering is the motion control of space structures. This paper describes why the motion control of space structures is fundamentally a civil engineering problem.     

Feasibility of Rigidified Inflatable Structures for Housing

Rigidified inflatable structures (RIS) are thin, flexible membrane structures that are pneumatically deployed. After deployment, these structures harden because of chemical or physical change of the membrane. Because of this change, or rigidification, these structures no longer require pneumatic pressure to maintain their shape. With the aim of reducing the cost and examining the feasibility of RIS structures, a new material is proposed, developed, and evaluated. This material involves the formation of a semi-interpenetrating polymer network based on polyvinyl chloride and an acrylate-based reactive plasticizer. The economical and environmental performances of RIS using this new material are assessed by means of a case study. In this study, the performance of RIS technology is compared with that of a typical wood light-frame structure in the application of a small single-family house. The study indicates that the cost of ownership in present day value for the RIS is approximately 35% less than the cost of a comparable wood light-frame structure. The study also indicates that significant environmental benefits exist with the use of RIS. These structures use significantly less in terms of resources than do wood frame structures: approximately 2 times less in materials originating from nonrenewable fossil resources, approximately 2 times less in material originating from trees, and approximately 19 times less in materials originating from inorganic resources. The study concludes by delineating various means available to further increase the economical and environmental performance of RIS technology.     

Technical Requirements for Lunar Structures

The moon has recently regained the interest of many of the world’s space agencies. Lunar missions are the first steps in expanding manned and unmanned exploration inside our solar system. The moon represents various options; it can be used as a laboratory in low gravity, it is the closest and most accessible planetary object from the Earth, and it possesses many resources that humans could potentially exploit. This paper has two objectives: to review the current status of the knowledge of lunar environmental requirements for future lunar structures, and to attempt to classify different future lunar structures based on the current knowledge of the subject. The paper divides lunar development into three phases. The first phase is building shelters for equipment only; in the second phase, small temporary habitats will be built, and finally in the third phase, habitable lunar bases will be built with observatories, laboratories, or production plants. Initially, the main aspects of the lunar environment that will cause concerns will be lunar dust and meteoroids, and later will include effects due to the vacuum environment, lunar gravity, radiation, a rapid change of temperature, and the length of the lunar day. This paper presents a classification of technical requirements based on the current knowledge of these factors, and their importance in each of the phases of construction. It gives recommendations for future research in relation to the development of conceptual plans for lunar structures, and for the evolution of a lunar construction code to direct these structural designs. Some examples are presented along with the current status of the bibliography of the subject.     

Cable Structures and Lunar Environment

Lunar environmental characteristics, such as the lack of atmosphere, the smaller gravitational acceleration, and the weaker regolith, place different requirements on structural systems than the earth environment does. Some of these requirements are the internal pressurization of structures, emphasis on details, and careful design of foundation systems. Popular structural systems on the Earth environment, such as steel and reinforced concrete frames and trusses with traditional rigid connections may be inefficient for the lunar environment. Cable structures can be shown to meet the different and sometimes conflicting requirements of the lunar environment. The behavior of three different groups of cable structures in the lunar environment (differentiated by their small, medium and long spans) are studied in this paper. The structural systems can be designed to meet the main requirements in an efficient way. Foundation uplift problem is of particular interest, especially in the early lunar colonization stage. It was shown that with a slight modification in the cable system, the uplift problem can be solved, thus saving manpower and costs, while improving the overall system behavior.     

A Civil Engineer's View from Space

From the perspective of a 250‐nautical‐mile orbit aboard the Space Shuttle, the author has had the opportunity to observe the effects of man on the earth, to reflect on his future in space, and to examine the role civil engineers may have in building our future. In the decades to come, civil engineers will require skills that are not currently provided by universities and which are not adequately represented in professional societies. All disciplines of the civil engineering profession will need to examine their strategies to enable them to establish a significant place on the team. From launch pads to remote sensing satellites, from space stations to lunar bases, civil engineers can and should play a significant role in design requirements, engineering, testing, assembly, and operation. The Aerospace Division of the ASCE should take the lead to insure that civil engineers are prepared to meet the challenge.     

Z-Pin Composites: Aerospace Structural Design Considerations

Z-pins are increasingly used to enhance the delamination toughness and impact damage tolerance of composite aircraft structures. An important consideration in the design of z-pinned structures is the deterioration of the in-plane mechanical properties of the composite material because of the pins. Experimental property data presented in this paper reveal that large improvements to the delamination toughness of carbon-epoxy composite gained with z-pins also result in an unavoidable reduction to the in-plane tension, compression, bending, interlaminar shear, and fatigue properties. The data show that increasing the volume fraction of z-pins in carbon-epoxy to increase the delamination resistance causes a corresponding deterioration to the in-plane properties, and this is a key consideration in the design of z-pinned aircraft structures for damage tolerance. The data reveal that the reduction to the in-plane mechanical properties caused by z-pins is usually modest (typically less than 5–15%) compared to the very large improvements in delamination toughness (up to nearly 500%).     

Femtotechnology: Design of the Strongest AB Matter for Aerospace

Aerospace, aviation particularly, need, in any era, the strongest and most thermostable materials available, often at nearly any price. The space elevator, space ships (especially during atmospheric reentry), rocket combustion chambers, thermally challenged engine surfaces, hypersonic aircraft materials are better now than any available, with undreamed performance as the reward if obtained. As shown in this research, the offered new material allows to greatly improve all characteristics of space ships, rockets, engines, and aircraft, and design new types space, propulsion, and aviation systems. At present the term “nanotechnology” is well known—in its ideal form, the flawless and completely controlled design of conventional molecular matter from molecules or atoms. Such power over nature would offer routine achievement of remarkable properties in conventional matter, and creation of metamaterials where the structure not the composition brings forth new powers of matter. But even this yet unachieved goal is not the end in material science possibilities. The writer herein offers the idea of design of new forms of nuclear matter from nucleons (neutrons, protons), electrons, and other nuclear particles. He shows this new “AB Matter” has extraordinary properties (for example, tensile strength, stiffness, hardness, critical temperature, superconductivity, supertransparency, zero friction, etc.), which are up to millions of times better than corresponding properties of conventional molecular matter. He shows concepts of design for space ships, rockets, aircraft, sea ships, transportation, thermonuclear reactors, constructions, and so on from nuclear matter. These vehicles will have unbelievable possibilities (e.g., invisibility, ghostlike penetration through any walls and armor, protection from nuclear bomb explosions and any radiation flux, etc.). People may think this as fantasy. But 15 years ago most people and many scientists thought nanotechnology was fantasy. Now many groups and industrial laboratories, even start-ups, spend hundreds of millions of dollars for development of nanotechnological-range products (precise chemistry, patterned atoms, catalysts, metamaterials, etc.) and we have nanotubes (a new material which does not exist in nature) and other achievements are beginning to come out of the pipeline in prospect. Nanotubes are stronger than steel by a hundred times—surely an amazement to a 19th century observer if he could behold them. Nanotechnology, in near term prospect, operates with objects (molecules and atoms) having the size in nanometer (10?9?m). The writer here outlines perhaps more distant operations with objects (nuclei) having the size in the femtometer range (10?15?m, millions of times smaller than the nanometer scale). The name of this new technology is femtotechnology.     

Application of Optical Measurement Techniques to Supersonic and Hypersonic Aerospace Flows

Experimental investigation is essential to improve the understanding of aerospace flows. During the last years, effort has been put on the development of optical diagnostics capable of imaging or yielding data from the flow in a nonintrusive way. The application of some of these techniques to supersonic and hypersonic flows can be highly challenging due to the high velocity, strong gradients, and restricted optical access generally encountered. Widely used qualitative and semiquantitative optical flow diagnostics are shadowgraph, schlieren, and interferometry. Laser-based techniques such as laser Doppler anemometry and particle image velocimetry are well established for investigation of supersonic flows, but as yet their use in hypersonic flows has been limited. Other relevant measurement techniques include particle tracking velocimetry, Doppler global velocimetry, laser-two-focus anemometry, background oriented schlieren and laser induced fluorescence methods. This paper reviews the development of these and further optical measurement techniques and their application to supersonic and hypersonic aerospace flows in recent years.     

Analysis of Rim Supports for Off‐Axis Inflatable Reflectors. II: Deformations

A structural analysis is performed for the rim support of a pressurized off‐axis paraboloidal membrane, serving as a space‐based solar concentrator. The function of the rim support is to take up the tensile forces created by the stretched membrane. This paper analyzes the deformations in the rim support, based on an earlier evaluation of the internal forces and moments resulting from the load applied by the membrane. The deformations are calculated in the x‐ and y‐directions at all points along the rim. They are shown to depend on the rim geometry, the applied loads, and a dimensionless rigidity parameter comprising the inflation pressure, the major axis of the elliptical rim, the modulus of elasticity of the rim support material, and its moment of inertia. The angular deformation at each point is also evaluated. A simplified solution for small deformations shows them to be approximately proportional to the rigidity parameter.     

Soft Computing Algorithm to Data Validation in Aerospace Systems Using Parity Space Approach

This paper deals with the problem of data validation of an instrumentation system applied in the aerospace area. The fault diagnosis method used for the validation is based on the principle of the parity space approach. Residuals are generated thanks to the analytical redundancy relations given by the model and the important number of sensors. Indeed, we propose a procedure, which permits us to compute systematically all the redundancy equations for the residual generation phase. The additional concept, called residuals structuration, is necessary to isolate the detected faults. Finally, the data validation task consists in isolating the failing data and in sending only the valid information to a control system. An application to an aerospace system illustrates the proposed algorithm.     

Projectile Shape and Material Effects in Hypervelocity Impact Response of Dual‐Wall Structures

All large spacecraft are susceptible to impacts by meteoroids and pieces of orbiting space debris. These impacts occur at extremely high speeds and can damage flight‐critical systems, which can in turn lead to catastrophic failure of the spacecraft. A long‐duration spacecraft developed for a mission into this environment must include adequate protection against perforation of pressurized components by such impacts. This paper presents the results of an investigation into the effects of projectile shape and material on the perforation of aluminum dual‐wall structural systems. Impact damage is characterized according to the extent of perforation, crater, and spall damage in the structural systems as a result of hypervelocity projectile impact loadings. Analysis of the damage data shows that there are distinct differences in impact damage from cylindrical and sherical projectiles. Projectile density is also found to affect the type and extent of damage sustained by dual‐wall structural systems.     

Analysis of Rim Supports for Off‐Axis Inflatable Reflectors. I: Loads

A structural analysis is performed for the rim support of a pressurized off‐axis paraboloidal membrane, serving as a space‐based solar concentrator. The function of the rim support is to take up the tensile forces created by the stretched membrane. This paper deals with the load analysis. The tensile forces transmitted by the membrane to the rim support are calculated, and are proportional to pb, where p is the inflation pressure and b is one‐half the major axis of the elliptical rim. Next, the internal forces and moments generated in the rim support by the membrane forces are calculated. The compression forces are considerably larger, at any point, than the shear forces; both are proportional to pb2. The bending moments are proportional to pb3. The critical point is found to be at the top of the rim, where both the bending moment and compression force are at their maximum.     

Graph‐Theory Approach to Eigenvalue Problem of Large Space Structures

The dynamic analysis and control system design of large space structures involve the solution of the large‐dimensional generalized matrix eigenvalue problem. The computational effort involved is proportional to the third power of the dimension of the matrices involved. To minimize the computational time a graph‐theory approach to reduce a matrix to lower‐ordered submatrices is proposed. The matrix‐reduction algorithm uses the Boolean matrices corresponding to the original numerical matrices and, thus, the computational effort to reduce the original matrix is nominal. The computational savings directly depend upon the number of submatrices into which the original matrix is reduced. A free‐free square plate is considered as an example to illustrate the technique. In this example a matrix of 16th order is reduced to three scalars corresponding to three rigid‐body modes, and three matrices of order three and one matrix of order four.     

Space Structures: Issues in Dynamics and Control

A selective technical overview is presented on the vibration and control of large space structures, the analysis, design, and construction of which will require major technical contributions from the civil∕structural, mechanical, and extended engineering communities. The immediacy of the U.S. space station makes the particular emphasis placed on large space structures and their control appropriate. The space station is but one part of the space program, and includes the lunar base, which the space station is to service. This paper attempts to summarize some of the key technical issues and hence provide a starting point for further involvement. The first half of this paper provides an introduction and overview of large space structures and their dynamics; the latter half discusses structural control, including control‐system design and nonlinearities. A crucial aspect of the large space structures problem is that dynamics and control must be considered simultaneously; the problems cannot be addressed individually and coupled as an afterthought.     

Active Control of Structures in Nonlinear Response

The need to account for geometric and material nonlinearities in the active control of highly flexible, large, space structures is emphasized herein. The performance index of the control problem is minimized subject to equations of state and costate using a variable metric algorithm. Unlike the conventional techniques for active control, the present algorithm is able to exploit the sparsity and symmetry of the mass and stiffness matrices of the finite element models of structures. The algorithm thus has the potential of being able to control moderately large‐scale, finite element models of highly flexible, large, space structures in a cost‐effective manner. The proposed algorithm is validated in suppressing the nonlinear vibrations of an impulsively loaded, highly flexible beam, and the need for inclusion of nonlinearities is demonstrated.