Journal of Aerospace Engineering

Published by American Society of Civil Engineers
Online ISSN: 0893-1321
Publications
Article
The space program is aiming towards the permanent use of space; to build and establish an orbital space station, a Moon base and depart to Mars and beyond. We must look after the total independency from the Earth's natural resources and work in the design of a modular space base in which each module is capable of duplicating one natural process, and that all these modules in combination take us to conceive a space base capable of sustaining life. Every area of human knowledge must be involved. This modular concept will let us see other space goals as extensions of the primary project. The basic technology has to be defined, then relatively minor adjustments will let us reach new objectives such as a first approach for a lunar base and for a Mars manned mission. This concept aims towards an open technology in which standards and recommendations will be created to assemble huge space bases and spaceships from specific modules that perform certain functions, that in combination will let us reach the status of permanent use and exploration of space.
 
Article
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.
 
Article
Space Biospheres and Ventures, a private, for-profit firm, has undertaken a major research and development project in the study of biospheres, with the objective of creating and producing biospheres. Biosphere II-scheduled for completion in March 1991-will be essentially isolated from the existing biosphere by a closed structure, composed of components derived from the existing biosphere. Like the biosphere of the Earth, Biosphere II will be essentially closed to exchanges of material or living organisms with the surrounding environment and open to energy and information exchanges. Also, like the biosphere of the Earth, Biosphere II will contain five kingdoms of life, a variety of ecosystems, plus humankind, culture, and technics. The system is designed to be complex, stable and evolving throughout its intended 100-year lifespan, rather than static. Biosphere II will cover approximately 1.3 hectare and contain 200,000 m3 in volume, with seven major biomes: tropical rainforest, tropical savannah, marsh, marine, desert, intensive agriculture, and human habitat. An interdisciplinary team of leading scientific, ecological, management, architectural, and engineering consultants have been contracted by Space Biospheres Ventures for the project. Potential applications for biospheric systems include scientific and ecological management research, refuges for endangered species, and life habitats for manned stations on spacecraft or other planets.
 
Article
This paper highlights technology development for space exploration. It draws on the proceedings of Space 88, Engineering, Construction, and Operations in Space, which includes 125 papers providing in-depth discussions of space policy, extraterrestrial basing, space stations and orbiting structures. In the space station and orbiting structures (orbital facilities) section, papers discuss the engineering, construction, and operations of orbiting space systems. Papers in the extraterrestrial basing section deal with the engineering, construction, and operations challenges faced in development of bases and operations on extraterrestrial bodies. The special interest (interacting disciplines) section provides a discussion of challenges facing us in meeting needs for space power, life support, human factors, astronomy, education, and management.
 
Article
The simultaneous design of a structure/active control system is addressed in which the mass of the actuators required to implement the active control is considered. An algorithm for estimating the required actuator mass given the control law and the desired maneuver is presented. A nonlinear optimization algorithm is used to direct the design process. Results are given for the design of a L shaped structure where it is desired to minimize the line of sight pointing error after a worst case slew maneuver.
 
Article
A NASA R&D program, the Large Deployable Antenna program, was initiated to investigate and demonstrate the availability of critical technologies for passive microwave imagers. The science objectives, current state-of-the-art, a number of electromagnetic configurations under consideration, and the mechanical systems development effort are presented. The program team conducted a detailed technology review, evaluated the feasibility and technology readiness for a large dual-reflector radiometer, and developed a system concept for a 25-meter deployable radiometer. The study approach involved determining basic operational parameters and configurations for a geosynchronous wide-scanning radiometer from which specific structural requirements were utilized as goals (rather than specifications) with which specific technologies could be evaluated.
 
-MATERIAL PROPERTIES FOR POLYMER MATRIX MATERIALS
Article
A previously developed analytical formulation has been modified in order to more accurately account for the effects of hydrostatic stresses on the nonlinear, strain rate dependent deformation of polymer matrix composites. State variable constitutive equations originally developed for metals have been modified in order to model the nonlinear, strain rate dependent deformation of polymeric materials. To account for the effects of hydrostatic stresses, which are significant in polymers, the classical J2 plasticity theory definitions of effective stress and effective inelastic strain, along with the equations used to compute the components of the inelastic strain rate tensor, are appropriately modified. To verify the revised formulation, the shear and tensile deformation of two representative polymers are computed across a wide range of strain rates. Results computed using the developed constitutive equations correlate well with experimental data. The polymer constitutive equations are implemented within a strength of materials based micromechanics method to predict the nonlinear, strain rate dependent deformation of polymer matrix composites. The composite mechanics are verified by analyzing the deformation of a representative polymer matrix composite for several fiber orientation angles across a variety of strain rates. The computed values compare well to experimentally obtained results.
 
Article
The best location in the inner solar system for the grand observatories of the 21st century may be the moon. A multidisciplinary team including university students and faculty in engineering, astronomy, physics, and geology, and engineers from industry is investigating the moon as a site for astronomical observatories and is doing conceptual and preliminary designs for these future observatories. Studies encompass lunar facilities for radio astronomy and astronomy at optical, ultraviolet, and infrared wavelengths of the electromagnetic spectrum. Although there are significant engineering challenges in design and construction on the moon, the rewards for astronomy can be great, such as detection and study of earth-like planets orbiting nearby stars, and the task for engineers promises to stimulate advances in analysis and design, materials and structures, automation and robotics, foundations, and controls. Fabricating structures in the reduced-gravity environment of the moon will be easier than in the zero-gravity environment of earth orbit, as Apollo and space-shuttle missions have revealed. Construction of observatories on the moon can be adapted from techniques developed on the earth, with the advantage that the moon's weaker gravitational pull makes it possible to build larger devices than are practical on earth.
 
Article
Impact tests using a soft gelatin projectile were performed to identify failure modes that occur at high strain energy density during impact loading. Failure modes were identified for aluminum plates and for composites plates and half-rings made from triaxial carbon fiber braid having a 0/+/-60degrees architecture. For aluminum plates, a large hole formed as a result of crack propagation from the initiation site at the center of the plate. For composite plates, fiber tensile failure occurred in the back ply at the center of the plate. Cracks then propagated from this site along the +/-60degrees fiber directions until triangular flaps opened to form a hole. For composite half-rings fabricated with 0degrees fibers aligned circumferentially, fiber tensile failure also occurred in the back ply. Cracks first propagated from this site perpendicular the 0degrees fibers. The cracks then turned to follow the 60degrees fibers and 0degrees fibers until rectangular flaps opened to form a hole. Damage in the composites was localized near the impact site, while cracks in the aluminum extended to the boundaries.
 
Article
Impact tests using a soft gelatin projectile were performed to identify failure modes that occur at high strain energy density during impact loading. Failure modes were identified for aluminum plates and for composites plates and half-rings made from triaxial carbon fiber braid having a 0/+/- 60deg architecture. For aluminum plates, a large hole formed as a result of crack propagation from the initiation site at the center of the plate. For composite plates, fiber tensile failure occurred in the back ply at the center of the plate. Cracks then propagated from this site along the +/-60deg fiber directions until triangular flaps opened to form a hole. For composite half-rings fabricated with 0deg fibers aligned circumferentially, fiber tensile failure also occurred in the back ply. Cracks first propagated from this site perpendicular the 0deg fibers. The cracks then turned to follow the +/-60deg fibers and 0deg fibers until rectangular flaps opened to form a hole. Damage in the composites was localized near the impact site, while cracks in the aluminum extended to the boundaries.
 
Article
A process for evaluating lunar-base construction equipment and methods concepts is presented. The process is driven by the need for more quantitative, systematic, and logical methods for assessing further research and development requirements in an area where uncertainties are high, dependence upon terrestrial heuristics is questionable, and quantitative methods are seldom applied. Decision theory concepts are used in determining the value of accurate information and the process is structured as a construction-equipment-and-methods selection methodology. Total construction-related, earth-launch mass is the measure of merit chosen for mathematical modeling purposes. The work is based upon the scope of the lunar base as described in the National Aeronautics and Space Administration's Office of Exploration's 'Exploration Studies Technical Report, FY 1989 Status'. Nine sets of conceptually designed construction equipment are selected as alternative concepts. It is concluded that the evaluation process is well suited for assisting in the establishment of research agendas in an approach that is first broad, with a low level of detail, followed by more-detailed investigations into areas that are identified as critical due to high degrees of uncertainty and sensitivity.
 
Article
A simple truss-beam method for determining the dynamic characteristics of the space structures intended to perform various tasks in orbit is presented. Algorithms are provided to determine the flexibility matrix of the truss beam for use in the equation of motion. The natural frequencies obtained through this method are compared with those obtained through the finite element method. An experimental procedure for verifying the theoretical results is described. It is concluded that the truss-beam method is a simple analysis technique that yields reasonably accurate results with a minimum of computational effort, especially for the critical lower bending modes of flexible structures. The method takes less computer time than more conventional methods and can be programed in both BASIC and FORTRAN for use in micro- and mainframe computers.
 
Article
The feasibility of using piezoelectric actuators to control the flexural oscillations of large structures in space is investigated. Piezoelectric actuators have the advantage of exerting localized bending moments. In this way, vibration is controlled without exciting rigid body modes in the structure. The actuators are used in collocated sensor/driver pairs to form a feedback control system. The sensor produces a voltage that is proportional to the dynamic stress at the sensor location, and the driver produces a force that is proportional to the voltage applied to it. The analog control system amplifies and phase shifts the sensor signal to produce the voltage signal that drives the driver piezoelectric. The feedback control system is demonstrated to increase the first mode damping in a cantilever beam by up to 85%, depending on the amplifier gain. An analytical model of the control system is developed. The estimated and measured vibration control compare favorably. A simulated free-free beam is fabricated and instrumented with a distribution of piezoelectric sensor/driver pairs. The purpose is to evaluate the damping efficiency of the control system when the piezoelectrics are not optimally positioned at points of high stress in the beam. The control system is found to reduce the overall vibration response to impact by a factor of two.
 
Article
The analysis aspects of the 23,000-line FORTRAN program VIPASA with constraints and optimization (VICONOPT) are described. Overall stiffness matrices assembled from the earlier exact vibration and instability of plate assemblies including shear and anisotropy (VIPASA) flat plate stiffnesses are optionally coupled by Langrangian multipliers to find critical buckling loads, or natural frequencies of undamped vibration, of prismatic assemblies of anisotropic flat plates with arbitrarily located point supports or simple transverse supporting frames. The longitudunal continuity of typical wing and fuselage panels is closely approximated because the solutions are for the infinitely long structure obtained by repeating a bay and its supports longitudinally. Any longitudinally invariant in-plane plate stresses are permitted, and very rapid solutions are guaranteed by numerous refinements, including multilevel substructuring and a method for repetitive cross sections that is exact for regular polygons used to represent cylinders. Modal displacements and stresses in or between plies of laminated plates are calculated and plotted, with values being recovered at all nodes of substructures. Comparison with usual approximate finite-element methods confirms that, for comparably converged solutions, VICONOPT is typically between 100 and 10(exp 4) times faster.
 
Article
The objectives of this study are to create a lunar simulant locally from a basaltic rock and to design and develop a vacuum triaxial test device that can permit testing of compacted lunar simulant under cyclic loading with different levels of initial vacuum. Triaxial testing is performed in the device itself without removing the compacted specimen. Preliminary constrained compression and triaxial shear tests are performed to identify effects of initial confinements and vacuums. The results are used to define deformation and strength parameters. At this time, vacuum levels up to 0.0001 are possible. The research can aid in the development of compacted materials for various construction applications.
 
Article
A significant numerical simulation capability now exists for studying the various phenomena associated with the response, failure, and performance of multilayered composite panels and shells subjected to combined pressure, mechanical, and thermal loads. The phenomena involved cover a wide range of length scales from local to global structural response. The modeling approaches used for multilayered panels include micromechanical models, three-dimensional continuum models, quasi-three-dimensional models, and two-dimensional plate and shell models. Within each category a number of models with several levels of sophistication has evolved. The four categories are described in review papers. Despite the extensive literature cited in the afore-mentioned references, only a few studies have been reported on the effects of stiffness discontinuities, such as those associated with an abrupt stiffener termination or dropped plies, on the response of composite panel. Stiffener termination is often necessary in composite aerospace structures to satisfy detailed design requirements, and therefore an understanding and a prediction of its effect on the response and failure of composite panels are desirable. Such a prediction must take into account the fact that current measurement technology does not allow the accurate determination of the material parameters that are used in the analytical models.
 
Article
The feasibility of pneumatic transfer for the movement of regolith at a lunar base is evaluated. Operation of pneumatic conveying systems at partial (lunar and Mars) gravity on NASA's KC-135 aircraft allowed the determination of some key parameters necessary for the design of an operable system. Both horizontal and vertical transfer is studied. In the vertical experiment, the choking velocity for 150-micron glass spheres was determined to be 1/2 to 1/3 the velocity required at 1 g. Pressure drops were reduced by roughly the same amount. Determination of the saltation velocity in the horizontal run was problematic, but qualitatively similar results were obtained. Comparison of the partial g results to 1-g behavior and theoretical analysis is made.
 
Article
The erosion of lunar soil by rocket exhaust plumes is investigated experimentally. This has identified the diffusion-driven flow in the bulk of the sand as an important but previously unrecognized mechanism for erosion dynamics. It has also shown that slow regime cratering is governed by the recirculation of sand in the widening geometry of the crater. Scaling relationships and erosion mechanisms have been characterized in detail for the slow regime. The diffusion-driven flow occurs in both slow and fast regime cratering. Because diffusion-driven flow had been omitted from the lunar erosion theory and from the pressure cratering theory of the Apollo and Viking era, those theories cannot be entirely correct. Comment: 13 pages, link to published version: http://cedb.asce.org/cgi/WWWdisplay.cgi?0900004
 
Article
A methodology has been developed and embodied in two computer codes for quantitatively characterizing the material strength degradation of aerospace propulsion system structural components that are subjected to various random effects over the course of their service lives. The codes, PROMISS and PROMISC, constitute a material-resistance model that is used in the NESSUS aerospace structural-reliability program. NESSUS addresses the service life-reducing effects of high temperature, mechanical fatigue, and creep.
 
Article
To halt erosion and desertification, it is necessary to quantify resources that are affected. Necessary information includes inventory of croplands and desert areas as they change over time. Several studies indicate the value of remote sensor data as input to inventories. In this study, the radiometric modeling of spectral characteristics of soil and vegetation provides the theoretical basis for the remote sensing approach. Use of Landsat Thematic Mapper images allows measurement of croplands in Saudi Arabia, demonstrating the capability of the approach. The inventory techniques and remote sensing approach presented are potentially useful in developing countries.
 
Article
Cooperative missions in earth orbit can be facilitated by developing a strategy to regulate the manner in which vehicles interact in orbit. One means of implementing such a strategy is to utilize a control zones technique that assigns different types of orbital operations to specific regions of space surrounding a vehicle. Considered here are issues associated with developing a control zones technique to regulate the interactions of spacecraft in proximity to a manned vehicle. Technical and planning issues, flight hardware and software issues, mission management parameter, and other constraints are discussed. Also covered are manned and unmanned vehicle operations, and manual versus automated flight control. A review of the strategies utilized by the Apollo Soyuz Test Project and the Space Station Freedom Program is also presented.
 
Article
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 spherical projectiles. Projectile density is also found to affect the type and extent of damage sustained by dual-wall structural systems.
 
Article
Graph theory is used to obtain numerical solutions to eigenvalue problems of large space structures (LSS) characterized by a state vector of large dimensions. The LSS are considered as large, flexible systems requiring both orientation and surface shape control. Graphic interpretation of the determinant of a matrix is employed to reduce a higher dimensional matrix into combinations of smaller dimensional sub-matrices. The reduction is implemented by means of a Boolean equivalent of the original matrices formulated to obtain smaller dimensional equivalents of the original numerical matrix. Computation time becomes less and more accurate solutions are possible. An example is provided in the form of a free-free square plate. Linearized system equations and numerical values of a stiffness matrix are presented, featuring a state vector with 16 components.
 
Article
A telescope on the Moon is needed for astronomy and can be constructed in this decade or early in the next century. Design for this telescope will be fundamentally different from the design of free-flying telescopes. Its design will be more like the new Keck telescope being completed on a mountaintop in Hawaii than the Hubble Space Telescope, in low Earth orbit. Success of the lunar-based telescope will depend on an appropriately engineered structure, a suitable interface (foundation) in the lunar soil, and a carefully thought out construction process. Participation of engineers in identifying and resolving issues for this extraterrestrial engineering and construction project is a natural extension of the traditional engineering role, and will prepare the engineering and construction communities for the subsequent greater challenges associated with basing on the Moon. These communities need to document now the types of data and information that NASA should obtain in the next early lunar missions so that construction on the Moon will be facilitated.
 
Article
Physical structures are often sufficiently complicated to preclude constructing an accurate mathematical model of the system dynamics from simple analysis using the laws of physics. Consequently, determination of an accurate model requires utilization of (generally noisy) output measurements from dynamic tests. In this paper, a robust method for constructing accurate, structural-dynamic models from discrete time-domain measurements is presented. The method processes the measurements in order to determine the number of modes present, the damping and frequency of each mode, and the mode shape. The structure may be highly damped. Although the mode-shape identification is more sensitive to measurement noise than the order, frequency, and damping identification, the method is considerably less sensitive to noise than other leading methods. Accurate detection of the modal parameters and mode shapes is demonstrated for modes with damping ratios exceeding 15 percent.
 
Article
The mechanical response of E-862 and PR-520 resins is investigated in tensile and shear loadings. At both types of loading the resins are tested at strain rates of about 5x10(exp 5), 2, and 450 to 700 /s. In addition, dynamic shear modulus tests are carried out at various frequencies and temperatures, and tensile stress relaxation tests are conducted at room temperature. The results show that the toughened PR-520 resin can carry higher stresses than the untoughened E-862 resin. Strain rate has a significant effect on the response of both resins. In shear both resins show a ductile response with maximum stress that is increasing with strain rate. In tension a ductile response is observed at low strain rate (approx. 5x10(exp 5) /s), and brittle response is observed at the medium and high strain rates (2, and 700 /s). The hydrostatic component of the stress in the tensile tests causes premature failure in the E-862 resin. Localized deformation develops in the PR-520 resin when loaded in shear. An internal state variable constitutive model is proposed for modeling the response of the resins. The model includes a state variable that accounts for the effect of the hydrostatic component of the stress on the deformation.
 
Article
Human exploration of the solar system can be said to have begun with the Apollo landings on the Moon. The Apollo Project was publicly funded with the narrow technical objective of landing human beings on the Moon. The transportation and life support systems were specialized technical designs, developed in a project management environment tailored to that objective. Most scenarios for future human exploration assume a similar long-term commitment of public funds to a narrowly focused project managed by a large, monolithic organization. Advocates of human exploration of space have not yet been successful in generating the political momentum required to initiate such a project to go to the Moon or to Mars. Alternative scenarios of exploration may relax some or all of the parameters of organizational complexity, great expense, narrow technical focus, required public funding, and control by a single organization. Development of the Moon using private investment is quite possibly a necessary condition for alternative scenarios to succeed.
 
Article
The present digital processing of 18 accelerograms associated with Space Shuttle liftoffs splits each of the accelerograms into three time-slices, respectively representing (1) SSME thrust buildup, (2) the period immediately following the SRBs' ignition, and (3) the subsequent period of intense acoustical activity due to the exhaust plume's interactions with the launch pad. The spectral treatment of these data involve the use of autoregressive and autoregressive-moving-average filters that furnish analytical representations of the spectra for all three time-slices in terms of a set of coefficients; these coefficients are applicable to the synthesis of artificial acceleration time-histories.
 
Article
The analysis of earthquake fault lineament patterns within the alluvial valley of west Tennessee, which is often made difficult by the presence of unconsolidated sediments, is presently undertaken through a synergistic use of Landsat satellite images in conjunction with gravity anomaly data, which were quantitatively analyzed and compared by means of two-dimensional histograms and rose diagrams. The northeastern trend revealed for the lineaments corresponds to faults and is in keeping with reactivation of the Reelfoot rift near the Mississippi River; this suggests that deeper features, perhaps at earthquake focal depth, may extend to the land surface as Landsat-detectable lineaments.
 
Article
A thermoviscoplastic finite element method employing the Bodner-Partom constitutve model is used to investigate the response of simplified thermal-structural models to intense local heating. The computational method formulates the problem in rate and advances the solution in time by numerical integration. The thermoviscoplastic response of simplified structures with prescribed temperatures is investigated. With rapid rises of temperature, the nickel alloy structures display initially higher yield stresses due to strain rate effects. As temperatures approach elevated values, yield stress and stiffness degrade rapidly and pronounced plastic deformation occurs.
 
Article
The system identification process presently discussed for the case of large space structures uses the observed input to a system and its observed response, or output, to derive an analytical model of the system which can then be used to predict its response to future inputs. Due to their size and complexity, as well as the intrinsic difficulty of identifying the environment in which they function, large space structures will require vast amounts of information, encompassing both experimental and analytical data for identification. A status evaluation is made of the structural system identification literature to date.
 
Article
A method and facilities for delivering payload and people into outer space are presented. This method uses, in general, engines located on a planetary surface. The installation consists of a space apparatus, power drive stations, which include a flywheel accumulator (for storage) of energy, a variable reducer, a powerful homopolar electric generator and electric rails. The drive stations accelerate the apparatus up to hypersonic speed. The estimations and computations show the possibility of making this project a reality in a short period of time (for payloads which can tolerate high g-forces). The launch will be very cheap at a projected cost of 3 - 5 dollars per pound. The authors developed a theory of this type of the launcher.
 
Article
High frequency Space Shuttle liftoff data are treated by autoregressive (AR) and autoregressive-moving-average (ARMA) digital algorithms. These algorithms provide useful information on the spectral densities of the data. Further, they yield spectral models, which lend themeselves to incorporation into the concept of the random response spectrum. This concept yields a reasonably smooth power spectrum for the design of structural and mechanical systems when the available data bank is limited. Due to the nonstationary of the liftoff event, the pertinent data are split into three slices. Each of the slices is associated with a rather distinguished phase of the liftoff event, in which stationarity can be expected. The presented results are preliminary in nature; they aim to call attention to the availability of the discussed concepts and to the need to augment the Space Shuttle data bank as more flights are completed.
 
Article
A recent trend towards greater automation of earthmoving machines, such as backhoes, loaders, and dozers, reflects a larger movement in the construction industry to improve productivity, efficiency and safety. This document reviews related work in various disciplines drawn upon by researchers--- soil mechanics, computer graphics, kinematic and dynamical modeling, optimization, control and decision theory. A taxonomy is suggested into which various automated systems reported in the literature, can be classified. Key Words: automation, earthmoving, excavation, soil-tool interaction, kinematic and dynamical modeling, tactical and strategic planning, tele-operation, trajectory control. In ASCE Journal of Aerospace Engineering, Vol 10, # 4, October 1997 ASCE 1 1 Introduction Industries such as mining and construction in which earthmoving plays a fundamental role are constantly under pressure to improve productivity (amount of work done), efficiency (cost of work done in terms of labor ...
 
Article
: Hydraulic machines used in mining and excavation applications are non-linear systems. Besides the nonlinearity due to the dynamic coupling between the different links there are significant actuator non-linearities due to the inherent properties of the hydraulic system. Optimal motion planning for these machines, i.e. planning motions that optimize a user-selectable combination of criteria such as time, energy etc., would help the designers of such machines, besides aiding the development of more productive robotic machines. Optimal motion planning in turn requires fast (computationally efficient) machine models in order to be practically usable. This work proposes a method for constructing hydraulic machine models using memory-based learning. We demonstrate the approach by constructing a machine model of a 25-ton hydraulic excavator with a 10m maximum reach. The learning method is used to construct the hydraulic actuator model, and is used in conjunction with a linkage dynamic model ...
 
Article
. Serpentine robots offer advantages over traditional mobile robots and robot arms because they have enhanced flexibility and reachability, especially in convoluted environments. These robots are well suited to inspect large space-fairing truss structures such as the future space station and can also be used to inspect the Space Shuttle cargo bay before launch. Serpentine mechanisms offer unique capabilities on Earth to applications such as bridge inspection, search and rescue, surface coating, and minimally invasive surgery. The work, described in this paper, will exploit a geometric structure, termed a roadmap, to guide the motions of a serpentine robot in highly convoluted spaces. This approach offers advantages over previous work with serpentine robots because it provides a general mathematical structure that is not mechanism specific, thereby having applications to a large class of problems. 1 INTRODUCTION We present some preliminary experimental results in the area of global s...
 
Article
This paper describes the validation of a Lagrange-Rayleigh-Ritz technique for the mathematical modeling of mass loaded panels for active control studies. The validation has been carried out by comparing the results produced by a Lagrange-Rayleigh-Ritz model with the results produced by a finite-element model and experimental data. Attention was focussed on a simply supported panel with a lumped mass constrained to its surface to simulate the presence of equipment mounted on the panel and twin piezoelectric patches bonded to the panel, working as sensors and actuators. The design of the experimental rig is described in detail, and a test campaign was carried out to obtain a set of transfer functions characteristic of this plant. The experimental data are then used to validate the predictions of the mathematical model. In particular, it was demonstrated that the Lagrange-Rayleigh-Ritz model was able to reproduce accurately the dynamics of the plant requiring a relatively small number of degrees of freedom.
 
Article
Space-borne imaging sensors onboard remote sensing satellites capture images of specific interest to the mission. These images contain tremendous volumes of data. Storage capacity onboard the satellite is limited and downlink channels have limited bandwidth capacity. Moreover, most remote sensing satellites are visible to their ground stations for only short periods of time during the day. Therefore, there is significant delay between image capture and terrestrial analysis. Hence, onboard image compression is essential to deliver captured data to the ground in a timely fashion. Smart and efficient onboard image compression using reconfigurable computing technology such as field programmable gate arrays (FPGAs) represents a unique solution that significantly increases the mission effectiveness. The High Performance Computing (HPC-I) payload on the Australian scientific mission satellite FedSat is a demonstration of reconfigurable computing technology in space for a variety of applications including image compression. In this paper, we present the design and implementation on HPC-I of the Satellite Adaptive Image Compression System (SAICS) for space missions. The system concept is based on an FPGA implementation of the adaptive JPEG-LS algorithm. The SAICS is a low complexity, high speed adaptive compression system that uses lossless and near lossless techniques depending on local image statistics, Performance evaluation indicates that satisfactory compression results can only be achieved through a careful trade-off between design complexity and efficiency.
 
Article
In this paper, we describe a new modeling approach to tackle the challenging problem of in-flight icing prediction. In this approach, termed morphogenetic modeling, we predict the structural details of aircraft ice accretion by emulating the behavior of individual fluid elements. A two-dimensional morphogenetic model is used here to predict the ice accretion shape forming on a National Advisory Committee For Aeronautics 0012 airfoil under various atmospheric conditions. The influence of the surface heat transfer formulation on the ice accretion shape is examined. We complement the numerical simulation with an analytical model for airfoil icing that is based on a simple form of the mass and heat conservation equations. This analytical investigation allows us to identify a significant new dimensionless ratio, the runback factor, defined as the ratio of the impinging water mass flux to the freezing mass flux at the stagnation line. An increasing runback factor leads to a quantifiable downstream displacement of the accretion mass. We also use the analytical model to verify the morphogenetic model during the early stages of icing, and find that there is reasonable agreement between the two models in terms of ice accretion shape. A comparison with experimental data and other models shows that even simple morphogenetic modeling is competitive with existing models. Further improvements will take advantage of the model's unique ability to simulate discontinuous ice accretions in complex geometries, leading to a considerable advancement in the simulation of in-flight icing.
 
Article
Some of the important types of information on the geotechnical characterization of potential lunar sites are outlined, and some of the more promising strategies which might be used to obtain such information in the lunar environment are identified. Some of the most important geotechnical information for planning and site development pertains to construction in the lunar soil. Several techniques for geotechnical investigation that may provide very useful information in an expedient manner are described. Geophysical methods include seismic and electromagnetic methods, including seismic surveys that use surface waves. Electromagnetic methods such as ground-penetrating radar are fast, efficient methods for mapping the subsurface, although these techniques do not measure soil characteristics that can readily be correlated with engineering properties. In situ physical testing is to include penetration testing for direct physical measurement of lunar soil behavior.
 
Article
A gradient-based optimization scheme has been developed for obtaining the maximum coupling in thin-walled composite beams subject to hygrothermal and frequency constraints. The stacking sequences for producing the maximum extension-twist and bending-twist coupling in two designs of single-celled beams have been determined. The sensitivity of the optimum lay-ups to variations in material properties and ply angles has been investigated. Nine beams have been manufactured and tested to verify the optimality of the predicted solutions.
 
Case 1-2 design curves for α 15 AE 30 AE & 45 AE with skew-transverse edges elastically restrained against rotation and longitudinal edges simply supported.  
Case 2-2 design curves for α 15 AE 30 AE & 45 AE with all edges elastically restrained against rotation.  
Relative increase in buckling strength arising from skew plates: (a) skew-transverse edges (Case 1-3) and; (b) all four edges (Case 3-3).  
Article
Buckling strength predictions are presented for a wide range of thin isotropic skew plates. The key studied parameters include the aspect ratio, skew angle, and rotational restraint stiffness on the different edges of the plate. The buckling strengths are evaluated both for isolated plates and for plates that are continuous with other parts of the structure. The assumed loading is uniform, uniaxial compression. The buckling predictions are presented in the form of dimensionless buckling curves, which permit a ready adoption into the "data sheets" commonly used in current design. The buckling predictions demonstrate the effect of introducing symmetrical combinations of elastic restraints against rotation on the edges of isolated skew plates. Further, they are presented in a manner that allows the benefits of continuity over skew bays to be evaluated. The curves also illustrate the complex character of the buckling mode changes that take place with a change in aspect ratio in skew plate structures. In addition, these mode changes lead to well defined local optima, which the designer can exploit if he has control over the aspect ratio of a skew plate.
 
Article
The establishment of an efficient transportation system is key to any human development on Earth or in space. Different technologies for transporting humans and goods have been developed, the diversity of which indicates that individual concepts have specific strengths and weaknesses. So far, transportation on the Moon has utilized a wheel-based vehicle, the lunar rover. Present concepts for transporting goods and people in a lunar base of the future are generally based on using wheels and traction. While such systems have many advantages for a variety of applications, the hauling of heavy goods will require the preparation of stable and trafficable roadways, a challenging and potentially expensive undertaking. This paper presents an alternative based on using one of the fundamental means to move objects, namely ropes and cables. Because of their inherent characteristics, ropes have been used to lift and haul heavy loads for long distances with high levels of reliability. This mature and constantly perfected technology, not well known in this car-oriented society, has been investigated for its use as a true alternative to the traditional wheel-based transportation systems. As will be shown, innovative applications of cable-based technologies may in effect provide many opportunities to leverage the differences between the Earth and the Moon for the purpose of creating efficient engineering products.
 
Article
The cold expansion technique is often used to introduce beneficial compressive stress at fastener holes, and can be used for remedial work where cracks already exist. In this paper, results are presented showing the effect of preexisting cracks on the residual stress field produced by cold expanding a fastener hole, and on subsequent fatigue crack growth. The effect on the residual stresses was experimentally evaluated in two ways: indirectly, in terms of retained expansion and directly, by measurement of the stresses using the X-ray and neutron diffraction techniques. The retained expansion ratio showed that cold expansion is more sensitive to the existence of precracks at lower levels of applied interference, and the inlet and outlet faces have different behavior. The stress measurements showed that preexisting cracks reduce the compressive residual stresses more on the mandrel inlet face than on the outlet face and in the middle of the specimen. The effect on fatigue crack growth rates was modeled using a linear-elastic fracture mechanics approach. It was found that cold expansion of a hole containing a preexisting crack longer than I rum introduces little benefit for subsequent fatigue crack growth behavior.
 
Article
The exploration of Mars has generated a lot of interest in recent years. With the completion of the Pathfinder Mission and the commencement of detailed mapping by Mars Global Surveyor, the possibility of an inhabited outpost on the planet is becoming more realistic. In spite of the upbeat mood, human exploration of Mars is still many years in the future. Additionally, the earliest return of any martian soil samples will probably not be until 2008. So why the discussion about martian soil mechanics when there are no returned soil samples on hand to examine? In view of the lack of samples, the basis of this or any discussion at this time must necessarily be one that involves conjecture, but not without the advantage of our knowledge of regolith mechanics of the Moon and soil mechanics on Earth. The objective of this presentation/discussion is fourfold: (1) Review some basic engineering-related information about Mars that may be of interest to engineers, and scientists - including characteristics of water and C02 at low temperature; (2) review and bring together principles of soil mechanics pertinent to studying and predicting how martian soil may behave, including the morphology and physical characteristics of coarse-grained and fine-grained soils (including clays), the characteristics of collapsing soils, potentials and factors that affect migration of water in unfrozen and freezing/frozen soils, and the strength and stiffness characteristics of soils at cold temperatures; (3) discuss some preliminary results of engineering experiments performed with frozen lunar soil simulants, JSC-1, in the laboratory that show the response to temperature change with and without water, effects of water on the strength and stiffness at ambient and at below freezing temperatures; and (4) discuss engineering studies that could be performed prior to human exploration and engineering research to be performed alongside future scientific missions to that planet.
 
Article
Whereas only a few years ago the United States and Russia were competitors in the space race, joint participation is now being encouraged in the form of international conferences and technical cooperation. In response to the free flow of information, this paper presents a discussion of technical and operating data for Russian water-recovery and air-revitalization systems, and examines their operating parameters in relation to U.S. system constraints. The advantages of studying existing hardware are numerous, including the availability of flight data, alternative technologies for research and design at reasonable costs and time frames, and joint interactions for a new generation of life-support systems with maximum closure capabilities. The paper introduces operational characteristics, design flow rates, and power requirements of six environmental control systems. The analysis of flow rates and power consumption demonstrates that the hardware developed and tested in Russia can be used for future joint space missions. In addition, the hardware has performed safely under flight conditions with little maintenance required.
 
Article
The conceptual design of a self-deployable structure with flexible joints is presented in this paper. Joints store elastic energy in the folded, prestressed position and allow deployment until they are stopped by tendons. A study on a wire rope joint is first presented to determine its mechanical behavior with experimental, theoretical, and numerical approaches. An analysis is then performed on a bidimensional structure to propose the specific modeling of introducing prestress to the joints. The method is applied to a spatial system in an analysis that uses static equilibrium and kinematic deployment simulations. The results show good concordance among the different approaches. DOI: 10.1061/(ASCE)AS.1943-5525.0000075. (C) 2011 American Society of Civil Engineers.
 
Article
This paper draws attention to the importance of readiness time (i.e., the time it takes to develop the necessary supporting infrastructure on the moon for the structure to be ready for use) of a lunar structure. It illustrates a rational process of determining readiness time using an example the pressurized self-supporting membrane structure, a concept proposed in 1989. To assess manpower requirement for construction, it is necessary to assess the productivity of a construction crew on the moon, taking into consideration the hazardous conditions they confront, and the encumbrances due to the use of space suits and other protective systems. These handicaps can be compensated to some extent by making maximum use of mechanical and automatic equipment. The procedure adopted here is to determine the manpower requirement for a similar construction on earth, then adjust it to the conditions on the moon. Once the productivity factor relative to earth is determined, the manpower requirement for lunar construction can be assessed.
 
Article
Deployable structures can be stored in a compact, folded configuration and are easily deployed into load-bearing, open forms. Hence, they are suitable for applications where speed and ease of erection and reusability are desired. The structures investigated here are prefabricated space frames made of so called scissor-like elements, sets of two straight bars connected to each other by a pivot. These structures are stress-free and self-standing in both their folded and deployed configurations, thus overcoming major disadvantages of previous designs. This study deals with deployable structures that are flat and subjected to normal loads in their deployed configuration. Although the behavior for that loading case is linear, the availability of an equivalent continuum model for stiffness prediction is desirable because it can significantly reduce the computational effort during preliminary design. The derivation of such a model is not straightforward because of the unorthodox geometry and the rotations allowed by the hinged and pivotal connections. This problem is addressed by first applying the direct stiffness method within a symbolic manipulation framework to transform the lattice structure to an equivalent single-layer grid, and then using existing expressions to obtain the desired equivalent plate. The model exhibits good accuracy and convergence characteristics for uniform loads.
 
Article
A major benefit of utilizing local planetary resources is that it reduces the need and cost of lifting materials from the Earth`s surface into Earth orbit. The location of the moon makes it an ideal site for harvesting the materials needed to assist space activities. Here, lunar excavation will take place in the dynamic unstructured lunar environment, in which conditions are highly variable and unpredictable. Autonomous mining (excavation) machines are necessary to remove human operators from this hazardous environment. This machine must use a control system structure that can identify, plan, sense, and control real-time dynamic machine movements in the lunar environment. The solution is a vision-based hierarchical control structure. However, excavation tasks require force/torque sensor feedback to control the excavation tool after it has penetrated the surface. A fuzzy logic controller (FLC) is used to interpret the forces and torques gathered from a bucket mounted force/torque sensor during excavation. Experimental results from several excavation tests using the FLC are presented here. These results represent the first step toward an integrated sensing and control system for a lunar mining system. 29 refs.
 
Top-cited authors
Chee Kiong Soh
  • Nanyang Technological University
Robert K. Goldberg
W. K. Binienda
  • University of Akron
Suresh Bhalla
  • Indian Institute of Technology Delhi
Tasawar Hayat