The key to performance improvements in the multicore era is for software toutilize the newly available concurrency. Consequently, programmers will have tolearn new programming techniques, and software systems will have to be able tomanage the parallelism effectively. The challenge is to do so simply, portably,and efficiently.This dissertation presents a lightweight programming framework called Gossamerthat is easy to use, enables the solution of a broad range of parallelprogramming problems, and produces efficient code. Gossamer supports task andrecursive parallelism, iterative parallelism, domain decomposition, pipelinedcomputations, and MapReduce computations. Gossamer contains (1) a set ofhigh-level annotations that one adds to a sequential program to specifyconcurrency and synchronization, (2) a source-to-source translator that producesan optimized program, and (3) a run-time system that provides efficient threadsand synchronization. The annotation-based programming model simplifies writingparallel programs by allowing the programmer to concentrate on the applicationand not the extensive bookkeeping involved with concurrency and synchronization;moreover, the annotations never reference any particulars of the underlyinghardware.

Satellite-based communication system can provide access to voice, data, video and internet transmission that is independent of terrestrial infrastructure. This is particularly important in disaster response situations and military maneuvers where mobile personnel need to maintain direct contact with each other and the central control. One of the factors that currently limits the effectiveness and practicality of these systems is portability. These systems require lightweight equipment that can be quickly and easily deployed and operated in a variety of environments. Parabolic dish antennas are the only antennas capable of providing the high gain required for direct satellite communication but their size and weight severely limit their portability and hence their use for portable direct satellite communication. Inflatable structures have been used in the space environment to overcome the limitations of launch vehicle size and weight restrictions. They are constru cted from thin film, or gossamer materials, and use internal pressure to maintain their shape. Inflatable structures are lightweight, have a low stowed volume and a high packing efficiency. It is proposed that this type of structure can be used to produce an inflatable parabolic dish antenna that can operate under terrestrial conditions to overcome the limits on portability for land-based communication. This thesis presents a design for a parabolic dish antenna and conical feed horn constructed entirely from polyester thin film. To further reduce the weight and stowed volume of the antenna the conical horn is fed by a microstrip patch. The performance of the components and their ability to operate under terrestrial conditions are assessed by comparing the results to those of an identical rigid system.

The term Gossamer is used to describe ultra-lightweight spacecraft structures that solve the aerospace challenge of obtaining maximum performance while reducing the launch costs of the spacecraft. Gossamer structures are extremely compliant, which complicates control design and ground testing in full scale. One approach is to design and construct smaller test articles and verify their computational models experimentally, so that similar computational models can be used to predict the dynamic performance of full-scale structures. Though measurement of both in-plane and out-of-plane displacements is required to characterize the dynamic response of the surface of these structures, this thesis lays the groundwork for dynamic measurement of the in-plane component. The measurement of thin films must be performed using non-contacting sensors because any contacting sensor would change the dynamics of the structure. Moreover, the thin films dealt with in this work are coated with either gold or aluminum for special applications making the film optically smooth and therefore requiring a surface pattern. A Krypton Fluoride excimer laser system was selected to fabricate patterns on thin-film mirror test articles. Parameters required for pattern fabrication were investigated. Effects of the pattern on the thin-film dynamics were studied using finite element analysis. Photogrammetry was used to study the static in-plane displacement of the thin-film mirror. This was performed to determine the feasibility of the photogrammetric approach for future dynamic tests. It was concluded that photogrammetry could be used efficiently to quantify dynamic in-plane displacement with high-resolution cameras and sub-pixel target marking.

Gossamer membranes are large, ultra light weight, highly flexible thin films. They have been proposed for use as elements in systems such as solar sails and optical apertures, whose large areas require a low-mass material that can be launched in a compact package and then deployed to operational configuration upon reaching orbit. Many of the proposed applications require that the film possess a flat, wrinkle-free surface. Surface wrinkle configuration is determined, in part, by the method used to support the film. One configuration that has not been studied in detail involves the formation of vertical wrinkles oriented along the direction of a tensile force applied at the upper and lower horizontal film supports. An experiment was designed to allow known forces to be applied to a 9 inch by 9 inch square sample of film supported at its upper and lower boundaries. Four films 7.6 m and 12.7 m thick samples of Kapton (polymide), and 12.2 m and 23.4 m thick samples of Mylar were loaded at levels of applied tensile force ranging from 1.446 to 4.388 N. The out-of-plane surface contours that resulted were measured using close-range photogrammetry, a non-contact, optical measurement technique. Experimental results indicate that both wrinkle wavelength and amplitude decrease as a function of applied force magnitude. These trends matched those obtained using numerical techniques, which also showed that lateral border strain, not measured during the experiment, may be a more important factor in determining surface wrinkle configuration. After presentation of the results, the photogrammetry technique is further considered as a tool for use in the manufacturing industry, in similar close-range applications, for the measurement of both dimensions and displacements.

Capacitive displacement sensors have many applications where non-contact, high precision measurement of a surface is required. Because of their non-contact nature they can easily measure conductive surfaces that are flexible or otherwise unable to be measured using a contact probe. Since the output of the capacitance gage is electrical, data points can be collected quickly and averaged to improve statistics. It is often necessary for capacitive displacement sensors to gage the distance from a curved (non-flat) surface. Although displacements can easily be detected, the calibration of this output can vary considerably from the flat case. Since a capacitance gage is typically factorycalibrated against a flat reference, the experimental output contains errors in both gain and linearity. A series of calibration corrections is calculated for rectifying this output. Capacitance gages are also limited in their overall displacement travel. A support stage is described that, along with control electronics, allow the properties of the capacitance gage to be combined with an interferometer to overcome this displacement limitation. Finally, an application is proposed that would make use of the capacitance sensor and support stage assembly.

This thesis introduces the analysis of a novel device which, capitalizing on recent advances in gossamer solar sail technology, offers the possibility of propellantless satellite deorbiting and attitude control. By taking advantage of aerodynamic drag effects, a lightweight sail can rapidly deorbit a satellite. At the same time, the sail provides an ideal substrate for a large area magnetic torque coil for attitude control. Through the use of orbit propagation software, the performance of an implementation of this "MagSail" on a Low Earth Orbit (LEO) small satellite is simulated. The analysis is set forth in three parts. First the orbit decay profile of the satellite under the effects of atmospheric drag is presented. The results are interpreted for various initial orbits. Next, the actual torque generation of the MagSail is analyzed. Emphasis is placed on how various design parameters change the magnetic moment of the sail. Finally, a six degree of freedom simulation, combining both orbit propagation and PD attitude control demonstrates a possible implementation of the sail's attitude control capabilities. The work presented in this thesis provides an in-depth look at the deorbiting performance of large-area, low-mass LEO satellites. This research provides a theoretical framework for the development of compact, cost-effective propellantless propulsion and space debris mitigation systems.

Increasing costs for space shuttle missions translate to smaller, lighter, and more flexible satellites that maintain or improve current dynamic requirements. This is especially true for optical systems and surfaces. Lightweight, inflatable structures, otherwise known as gossamer structures, are smaller, lighter, and more flexible than current satellite technology. Unfortunately, little research has been performed investigating cost effective and feasible methods of dynamic analysis and control of these structures due to their inherent, non-linear dynamic properties. Gossamer spacecraft have the potential of introducing lenses and membrane arrays in orbit on the order of 25 m in diameter. With such huge structures in space, imaging resolution and communication transmissibility will correspondingly increase in orders of magnitude. A daunting problem facing gossamer spacecraft is their highly flexible nature. Previous attempts at ground testing have produced only localized deformation of the structure's skin rather than excitation of the global (entire structure's) modes. Unfortunately, the global modes are necessary for model parameter verification. The motivation of this research is to find an effective and repeatable methodology for obtaining the dynamic response characteristics of a flexible, inflatable structure. By obtaining the dynamic response characteristics, a suitable control technique may be developed to effectively control the structure's vibration. Smart materials can be used for both active dynamic analysis as well as active control. In particular, piezoelectric materials, which demonstrate electro-mechanical coupling, are able to sense vibration and consequently can be integrated into a control scheme to reduce such vibration. Using smart materials to develop a vibration analysis and control algorithm for a gossamer space structure will fulfill the current requirements of space satellite systems. Smart materials will help spawn the next generation of space satellite technology. / Master of Science

Satellite antenna design requirements are driving the satellite size to proportions that cannot be launched into space using current technology. In order to reduce the launch size and mass of satellites, inflatable structures, also known as gossamer structures, are being considered. Inflatable space-based structures are susceptible to vibration disturbance due to their low stiffness and damping. This thesis discusses the structural dynamics and vibration suppression via piezoelectric actuators, using active control of an inflatable torus. A commercial finite element package, ANSYS, is used to model the inflated torus. The effect of torus aspect ratio and inflation pressure on the vibratory response of the structure is investigated. The interaction with the torus of the surface-mounted piezoelectric patches, made of PVDF, is modeled using Euler-Bernoulli beam theory. A state space representation is created of the model in modal space and modal truncation is performed. Traditional control tools are used to suppress vibration in the structure. First observer-based full state feedback is used, then direct output velocity feedback is explored. The aspect ratio of the torus is found to significantly influence the mode shapes. Toroids of small aspect ratios, skinny toroids, act like rings, but the mode shapes of toroids with large aspect ratios are much more complicated. For toroids of small aspect ratios, increasing the inflation pressure simply results in stiffening the ring, thereby increasing the natural frequencies. Increasing the pressure in toroids with large aspect ratios changes both the mode shapes and natural frequencies. The passive effect of PVDF on the dynamics of the torus is small, the mode shapes do not change and the frequencies are only slightly reduced. Active control of toroids with small aspect ratios using piezoelectric devices is effective. It may be more difficult to control toroids with large aspect ratios because the mode shapes are much more complicated than the simple ring modes found in toroids with small aspect ratios. / Master of Science

Stiff, ultra-lightweight thermal-formed polyimide panels considered in this dissertation are examples of next generation gossamer structures that resolve some of the technology barriers of previous, membrane-dominated gossamer designs while maintaining their low mass and low stowage volume characteristics. The research involved statically and dynamically characterizing and modeling several of these panels to develop validated computer models which can be used to determine the effects of changing manufacturing parameters and scalability. Static characterization showed substantial local nonlinear behavior that was replicated by new physics-based finite element models, and global linear bending behavior that was modeled using classical shell finite elements incorporating effective properties in place of bulk material properties to represent the unique stiffening structure of these panels. Dynamic characterization was performed on individual panels using standard impact hammer and accelerometer testing, enabling successful extraction of several structural natural frequencies and mode shapes. Additionally, the three dimensional time history of the surface of the panels was rendered from video data, and temporal filters were applied to the data to examine the frequency content. These data were also correlated to the shell element numerical models. Overall, the research contributes to the total knowledge base of gossamer technologies, advances stiff panel-based structures toward space qualification, and demonstrates their potential for use in apertures and other spacecraft.

High precision inflatable surfaces were introduced when NASA created the ECHO 1 Balloon in 1960. The experiment proved that inflatable structures were a feasible alternative to their rigid counterparts for high precision applications. Today inflatable structures are being used in aviation and aerospace applications and the benefits of using such structures are being recognized. Inflatable structures used in high precision structures require the inflatable surfaces to have controllable and predictable geometries. Many applications such as solar sails and radar reflectors require the surface of such structures to have a uniform surfaces as such surfaces improve the efficiency of the structure. In the study presented, tests were conducted to determine which combination of factors affect surface flatness on a triangular test article. Factors tested include, three boundary conditions, two force loadings, and two fabric orientations. In total, twelve tests were conducted and results showed that which force loading and fabric orientations used greatly affected the Root Mean Square (RMS) of the surface. It was determined that using the triangular clamp along with 00 fabric orientation and high force loading provided the best results.