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NASA NTRS2011

Electrically Conductive, Optically Transparent Polymer/Carbon Nanotube Composites and Process for Preparation Thereof

The present invention is directed to the effective dispersion of carbon nanotubes (CNTs) into polymer matrices. The nanocomposites are prepared using polymer matrices and exhibit a unique combination of properties, most notably, high retention of optical transparency in the visible range (i.e., 400-800 nm), electrical conductivity, and high thermal stability. By appropriate selection of the matrix resin, additional properties such as vacuum ultraviolet radiation resistance, atomic oxygen resistance, high glass transition (T.sub.g) temperatures, and excellent toughness can be attained. The resulting nanocomposites can be used to fabricate or formulate a variety of articles such as coatings on a variety of substrates, films, foams, fibers, threads, adhesives and fiber coated prepreg. The properties of the nanocomposites can be adjusted by selection of the polymer matrix and CNT to fabricate articles that possess high optical transparency and antistatic behavior.

Connell, John W.↗

NASA NTRS2010

The Software Correlator of the Chinese VLBI Network

The software correlator of the Chinese VLBI Network (CVN) has played an irreplaceable role in the CVN routine data processing, e.g., in the Chinese lunar exploration project. This correlator will be upgraded to process geodetic and astronomical observation data. In the future, with several new stations joining the network, CVN will carry out crustal movement observations, quick UT1 measurements, astrophysical observations, and deep space exploration activities. For the geodetic or astronomical observations, we need a wide-band 10-station correlator. For spacecraft tracking, a realtime and highly reliable correlator is essential. To meet the scientific and navigation requirements of CVN, two parallel software correlators in the multiprocessor environments are under development. A high speed, 10-station prototype correlator using the mixed Pthreads and MPI (Massage Passing Interface) parallel algorithm on a computer cluster platform is being developed. Another real-time software correlator for spacecraft tracking adopts the thread-parallel technology, and it runs on the SMP (Symmetric Multiple Processor) servers. Both correlators have the characteristic of flexible structure and scalability.

Zheng, Weimin↗

NASA NTRS2011

Health Monitor for Multitasking, Safety-Critical, Real-Time Software

Health Manager can detect Bad Health prior to a failure occurring by periodically monitoring the application software by looking for code corruption errors, and sanity-checking each critical data value prior to use. A processor s memory can fail and corrupt the software, or the software can accidentally write to the wrong address and overwrite the executing software. This innovation will continuously calculate a checksum of the software load to detect corrupted code. This will allow a system to detect a failure before it happens. This innovation monitors each software task (thread) so that if any task reports "bad health," or does not report to the Health Manager, the system is declared bad. The Health Manager reports overall system health to the outside world by outputting a square wave signal. If the square wave stops, this indicates that system health is bad or hung and cannot report. Either way, "bad health" can be detected, whether caused by an error, corrupted data, or a hung processor. A separate Health Monitor Task is started and run periodically in a loop that starts and stops pending on a semaphore. Each monitored task registers with the Health Manager, which maintains a count for the task. The registering task must indicate if it will run more or less often than the Health Manager. If the task runs more often than the Health Manager, the monitored task calls a health function that increments the count and verifies it did not go over max-count. When the periodic Health Manager runs, it verifies that the count did not go over the max-count and zeroes it. If the task runs less often than the Health Manager, the periodic Health Manager will increment the count. The monitored task zeroes the count, and both the Health Manager and monitored task verify that the count did not go over the max-count.

Zoerner, Roger↗

NASA NTRS2006

Tool for Coupling a Torque Wrench to a Round Cable Connector

A tool makes it possible to couple a torque wrench to an externally knurled, internally threaded, round cable connector. The purpose served by the tool is to facilitate the tightening of multiple such connectors (or the repeated tightening of the same connector) to repeatable torques. The design of a prior cable-connector/ torque-wrench coupling tool provided for application of the torque-wrench jaws to a location laterally offset from the axis of rotation of the cable connector, making it necessary to correct the torque reading for the offset. Unlike the design of the prior tool, the design of the present tool provides for application of the torque-wrench jaws to a location on the axis of rotation, obviating correction of the torque reading for offset. The present tool (see figure) consists of a split collet containing a slot that provides clearance for inserting and bending the cable, a collet-locking sleeve, a collet-locking nut, and a torque-wrench adaptor that is press-fit onto the collet. Once the collet is positioned on the cable connector, the collet-locking nut is turned to force the collet-locking sleeve over the collet, compressing the collet through engagement of tapered surfaces on the outside of the collet and the inside of the locking sleeve. Because the collet is split and therefore somewhat flexible, this compression forces the collet inward to grip the connector securely. The torque wrench is then applied to the torque-wrench adaptor in the usual manner for torquing a nut or a bolt.

Hacker, Scott C.↗

NASA NTRS2006

Spectral Analysis Tool 6.2 for Windows

Spectral Analysis Tool 6.2 is the latest version of a computer program that assists in analysis of interference between radio signals of the types most commonly used in Earth/spacecraft radio communications. [An earlier version was reported in Software for Analyzing Earth/Spacecraft Radio Interference (NPO-20422), NASA Tech Briefs, Vol. 25, No. 4 (April 2001), page 52.] SAT 6.2 calculates signal spectra, bandwidths, and interference effects for several families of modulation schemes. Several types of filters can be modeled, and the program calculates and displays signal spectra after filtering by any of the modeled filters. The program accommodates two simultaneous signals: a desired signal and an interferer. The interference-to-signal power ratio can be calculated for the filtered desired and interfering signals. Bandwidth-occupancy and link-budget calculators are included for the user s convenience. SAT 6.2 has a new software structure and provides a new user interface that is both intuitive and convenient. SAT 6.2 incorporates multi-tasking, multi-threaded execution, virtual memory management, and a dynamic link library. SAT 6.2 is designed for use on 32- bit computers employing Microsoft Windows operating systems.

Morgan, Feiming↗

NASA NTRS2007

NavP: Structured and Multithreaded Distributed Parallel Programming

We present Navigational Programming (NavP) -- a distributed parallel programming methodology based on the principles of migrating computations and multithreading. The four major steps of NavP are: (1) Distribute the data using the data communication pattern in a given algorithm; (2) Insert navigational commands for the computation to migrate and follow large-sized distributed data; (3) Cut the sequential migrating thread and construct a mobile pipeline; and (4) Loop back for refinement. NavP is significantly different from the current prevailing Message Passing (MP) approach. The advantages of NavP include: (1) NavP is structured distributed programming and it does not change the code structure of an original algorithm. This is in sharp contrast to MP as MP implementations in general do not resemble the original sequential code; (2) NavP implementations are always competitive with the best MPI implementations in terms of performance. Approaches such as DSM or HPF have failed to deliver satisfying performance as of today in contrast, even if they are relatively easy to use compared to MP; (3) NavP provides incremental parallelization, which is beyond the reach of MP; and (4) NavP is a unifying approach that allows us to exploit both fine- (multithreading on shared memory) and coarse- (pipelined tasks on distributed memory) grained parallelism. This is in contrast to the currently popular hybrid use of MP+OpenMP, which is known to be complex to use. We present experimental results that demonstrate the effectiveness of NavP.

navigational programming (NavP)↗

NASA NTRS2011

Prominences: The Key to Understanding Solar Activity

Prominences are spectacular manifestations of both quiescent and eruptive solar activity. The largest examples can be seen with the naked eye during eclipses, making prominences among the first solar features to be described and catalogued. Steady improvements in temporal and spatial resolution from both ground- and space-based instruments have led us to recognize how complex and dynamic these majestic structures really are. Their distinguishing characteristics - cool knots and threads suspended in the hot corona, alignment along inversion lines in the photospheric magnetic field within highly sheared filament channels, and a tendency to disappear through eruption - offer vital clues as to their origin and dynamic evolution. Interpreting these clues has proven to be contentious, however, leading to fundamentally different models that address the basic questions: What is the magnetic structure supporting prominences, and how does so much cool, dense plasma appear in the corona? Despite centuries of increasingly detailed observations, the magnetic and plasma structures in prominences are poorly known. Routine measurements of the vector magnetic field in and around prominences have become possible only recently, while long-term monitoring of the underlying filament-channel formation process also remains scarce. The process responsible for prominence mass is equally difficult to establish, although we have long known that the chromosphere is the only plausible source. As I will discuss, however, the motions and locations of prominence material can be used to trace the coronal field, thus defining the magnetic origins of solar eruptions. A combination of observations, theory, and numerical modeling must be used to determine whether any of the competing theories accurately represents the physics of prominences. I will discuss the criteria for a successful prominence model, compare the leading models, and present in detail one promising, comprehensive scenario for prominence formation and evolution that could answer the two questions posed above.

Karpen, Judy T.↗

NASA NTRS2011

3D Reconstruction of a Rotating Erupting Prominence

A bright prominence associated with a coronal mass ejection (CME) was seen erupting from the Sun on 9 April 2008. This prominence was tracked by both the Solar Terrestrial Relations Observatory (STEREO) EUVI and COR1 telescopes, and was seen to rotate about the line of sight as it erupted; therefore, the event has been nicknamed the "Cartwheel CME." The threads of the prominence in the core of the CME quite clearly indicate the structure of a weakly to moderately twisted flux rope throughout the field of view, up to heliocentric heights of 4 solar radii. Although the STEREO separation was 48 deg, it was possible to match some sharp features in the later part of the eruption as seen in the 304 Angstrom line in EUVI and in the H alpha-sensitive bandpass of COR1 by both STEREO Ahead and Behind. These features could then be traced out in three dimensional space, and reprojected into a view in which the eruption is directed towards the observer. The reconstructed view shows that the alignment of the prominence to the vertical axis rotates as it rises up to a leading-edge height of approximately equals 2.5 solar radii, and then remains approximately constant. The alignment at 2.5 solar radii differs by about 115 deg. from the original filament orientation inferred from H alpha and EUV data, and the height profile of the rotation, obtained here for the first time, shows that two thirds of the total rotation is reached within approximately equals 0.5 solar radii above the photosphere. These features are well reproduced by numerical simulations of an unstable moderately twisted flux rope embedded in external flux with a relatively strong shear field component.

Thompson, W. T.↗

NASA NTRS2006

Promoted-Combustion Chamber with Induction Heating Coil

An improved promoted-combustion system has been developed for studying the effects of elevated temperatures on the flammability of metals in pure oxygen. In prior promoted-combustion chambers, initial temperatures of metal specimens in experiments have been limited to the temperatures of gas supplies, usually near room temperature. Although limited elevated temperature promoted-combustion chambers have been developed using water-cooled induction coils for preheating specimens, these designs have been limited to low-pressure operation due to the hollow induction coil. In contrast, the improved promoted-combustion chamber can sustain a pressure up to 10 kpsi (69 MPa) and, through utilization of a solid induction coil, is capable of preheating a metal specimen up to its melting point [potentially in excess of 2,000 F (approximately equal to 1,100 C)]. Hence, the improved promoted combustion chamber makes a greater range of physical conditions and material properties accessible for experimentation. The chamber consists of a vertical cylindrical housing with an inner diameter of 8 in. (20.32 cm) and an inner height of 20.4 in. (51.81 cm). A threaded, sealing cover at one end of the housing can be unscrewed to gain access for installing a specimen. Inlet and outlet ports for gases are provided. Six openings arranged in a helical pattern in the chamber wall contain sealed sapphire windows for viewing an experiment in progress. The base of the chamber contains pressure-sealed electrical connectors for supplying power to the induction coil. The connectors feature a unique design that prevents induction heating of the housing and the pressure sealing surfaces; this is important because if such spurious induction heating were allowed to occur, chamber pressure could be lost. The induction coil is 10 in. (25.4 cm) long and is fitted with a specimen holder at its upper end. At its lower end, the induction coil is mounted on a ceramic base, which affords thermal insulation to prevent heating of the base of the chamber during use. A sapphire cylinder protects the coil against slag generated during an experiment. The induction coil is energized by a 6-kW water-cooled power supply operating at a frequency of 400 kHz. The induction coil is part of a parallel-tuned circuit, the tuning of which is used to adjust the coupling of power to the specimen. The chamber is mounted on a test stand along with pumps, valves, and plumbing for transferring pressurized gas into and out of the chamber. In addition to multiple video cameras aimed through the windows encircling the chamber, the chamber is instrumented with gauges for monitoring the progress of an experiment. One of the gauges is a dual-frequency infrared temperature transducer aimed at the specimen through one window. Chamber operation is achieved via a console that contains a computer running apparatus-specific software, a video recorder, and real-time video monitors. For safety, a blast wall separates the console from the test stand.

Richardson, Erin↗

NASA NTRS2006

Variable-Tension-Cord Suspension/Vibration-Isolation System

A system for mechanical suspension and vibration isolation of a machine or instrument is based on the use of Kevlar (or equivalent aromatic polyamide) cord held in variable tension between the machine or instrument and a surrounding frame. The basic concept of such a tensioned-cord suspension system (including one in which the cords are made of aromatic polyamide fibers) is not new by itself; what is new here is the additional provision for adjusting the tension during operation to optimize vibration- isolation properties. In the original application for which this system was conceived, the objective is to suspend a reciprocating cryocooler aboard a space shuttle and to prevent both (1) transmission of launch vibrations to the cryocooler and (2) transmission of vibrations from the cryocooler to samples in a chamber cooled by the cryocooler. The basic mechanical principle of this system can also be expected to be applicable to a variety of other systems in which there are requirements for cord suspension and vibration isolation. The reciprocating cryocooler of the original application is a generally axisymmetric object, and the surrounding frame is a generally axisymmetric object with windows (see figure). Two cords are threaded into a spoke-like pattern between attachment rings on the cryocooler, holes in the cage, and cord-tension- adjusting assemblies. Initially, the cord tensions are adjusted to at least the level necessary to suspend the cryocooler against gravitation. Accelerometers for measuring vibrations are mounted (1) on the cold tip of the cryocooler and (2) adjacent to the cage, on a structure that supports the cage. During operation, a technician observes the accelerometer outputs on an oscilloscope while manually adjusting the cord tensions in an effort to minimize the amount of vibration transmitted to and/or from the cryocooler. A contemplated future version of the system would include a microprocessor-based control subsystem that would include cord-tension actuators. This control subsystem would continually adjust the cord tension in response to accelerometer feedback to optimize vibration-isolation properties as required for various operating conditions. The control system could also adjust cord tensions (including setting the two cords to different tensions) to suppress resonances. Other future enhancements could include optimizing the cord material, thickness, and braid; optimizing the spoke patterns; and adding longitudinal cords for applications in which longitudinal stiffness and vibration suppression are required.

Villemarette, Mark L.↗

NASA NTRS2011

Electrically conductive, optically transparent polymer/carbon nanotube composites

Connell, John W.↗

NASA NTRS2005

Stable Polyimides for Terrestrial and Space Uses

Polyimides of a recently developed type have an attractive combination of properties, including low solar absorptivity (manifested as low color) when cast into thin films, resistance to atomic oxygen and ultraviolet radiation, solubility in organic solvents, high glass-transition temperatures, and high thermal stability. The focus of the development work was on polymers that can endure the space environment and that have specific combinations of properties for use on Gossamer spacecraft. Because of their unique combination of properties, these polymers are also expected to find use in a variety of other applications on Earth as well as in space. Examples of other space applications include membranes on antennas, second-surface mirrors, thermal optical coatings, and multilayer thermal insulation. For both terrestrial and space applications, these polyimides can be processed into various forms, including films, fibers, foams, threads, adhesives, and coatings.

Connell, John W.↗

NASA NTRS2011

Fabric circuits and method of manufacturing fabric circuits

A flexible, fabric-based circuit comprises a non-conductive flexible layer of fabric and a conductive flexible layer of fabric adjacent thereto. A non-conductive thread, an adhesive, and/or other means may be used for attaching the conductive layer to the non-conductive layer. In some embodiments, the layers are attached by a computer-driven embroidery machine at pre-determined portions or locations in accordance with a pre-determined attachment layout before automated cutting. In some other embodiments, an automated milling machine or a computer-driven laser using a pre-designed circuit trace as a template cuts the conductive layer so as to separate an undesired portion of the conductive layer from a desired portion of the conductive layer. Additional layers of conductive fabric may be attached in some embodiments to form a multi-layer construct.

Chu, Andrew W.↗

NASA NTRS2005

Deployable Wide-Aperture Array Antennas

Inexpensive, lightweight array antennas on flexible substrates are under development to satisfy a need for large-aperture antennas that can be stored compactly during transport and deployed to full size in the field. Conceived for use aboard spacecraft, antennas of this type also have potential terrestrial uses . most likely, as means to extend the ranges of cellular telephones in rural settings. Several simple deployment mechanisms are envisioned. One example is shown in the figure, where the deployment mechanism, a springlike material contained in a sleeve around the perimeter of a flexible membrane, is based on a common automobile window shade. The array can be formed of antenna elements that are printed on small sections of semi-flexible laminates, or preferably, elements that are constructed of conducting fabric. Likewise, a distribution network connecting the elements can be created from conventional technologies such as lightweight, flexible coaxial cable and a surface mount power divider, or preferably, from elements formed from conductive fabrics. Conventional technologies may be stitched onto a supporting flexible membrane or contained within pockets that are stitched onto a flexible membrane. Components created from conductive fabrics may be attached by stitching conductive strips to a nonconductive membrane, embroidering conductive threads into a nonconductive membrane, or weaving predetermined patterns directly into the membrane. The deployable antenna may comprise multiple types of antenna elements. For example, thin profile antenna elements above a ground plane, both attached to the supporting flexible membrane, can be used to create a unidirectional boresight radiation pattern. Or, antenna elements without a ground plane, such as bow-tie dipoles, can be attached to the membrane to create a bidirectional array such as that shown in the figure. For either type of antenna element, the dual configuration, i.e., elements formed of slots in a conductive membrane, can also be used. Finally, wide bandwidth antennas or arrays can be formed in which the principal direction of radiation is in the plane of the membrane. For this embodiment, the set of elements on the membrane is arranged to form one or more traveling wave antennas. In this case, a nonconductive form of the perimeter springlike material is required to provide the deploying force.

Fink, Patrick W.↗

NASA NTRS2005

Bonding-Compatible Corrosion Inhibitor for Rinsing Metals

A corrosion-inhibiting mixture of compounds has been developed for addition to the water used to rinse metal parts that have been cleaned with aqueous solutions in preparation for adhesive bonding of the metals to rubber and rubber-like materials. Prior to the development of this corrosion inhibitor, the parts (made, variously, of D6AC steel and 7075-T73 aluminum) were rinsed by deionized water, which caused corrosion in some places on the steel parts especially in such occluded places as sealing surfaces and threaded blind holes. An integral part of the particular cleaning process is the deposition of a thin layer of silicates and silane primers that increase the strength of the adhesive bond. The corrosion inhibitor is formulated, not only to inhibit corrosion of both D6AC steel and 7075- T73 aluminum, but also to either increase or at least not reduce the strength of the adhesive bond to be formed subsequently. The corrosion inhibitor is a mixture of sodium silicate and sodium tetraborate. The sodium silicate functions as both a corrosion inhibitor and a bond-strength promoter in association with the silane primers. The sodium tetraborate buffers the rinse solution at the optimum pH and functions as a secondary corrosion inhibitor for the steel. For a given application, the concentrations of sodium silicate and sodium tetraborate must be chosen in a compromise among the needs to inhibit corrosion of steel, inhibit corrosion of aluminum, and minimize cosmetic staining of both steel and aluminum. Concentrations of sodium silicate in excess of 150 parts of silicon per million parts of solution (ppm Si) have been determined to enhance inhibition of corrosion; unfortunately, because of the alkalinity of sodium silicate, even a small concentration can raise the pH of the rinse solution to such a level that aluminum becomes corroded despite the inhibiting effect. The pH of a solution that contains a high concentration of sodium silicate can be decreased by adding sodium tetraborate. On the other hand, the addition of sodium tetraborate increases the concentration of dissolved solids to such a high level that cosmetic staining becomes an issue.

Saunders, C. R.↗

NASA NTRS2005

Data-Analysis System for Entry, Descent, and Landing

A report describes the Entry Descent Landing Data Analysis (EDA), which is a system of signal-processing software and computer hardware for acquiring status data conveyed by multiple-frequency-shift-keying tone signals transmitted by a spacecraft during descent to the surface of a remote planet. The design of the EDA meets the challenge of processing weak, fluctuating signals that are Doppler-shifted by amounts that are only partly predictable. The software supports both real-time and post processing. The software performs fast-Fourier-transform integration, parallel frequency tracking with prediction, and mapping of detected tones to specific events. The use of backtrack and refinement parallel-processing threads helps to minimize data gaps. The design affords flexibility to enable division of a descent track into segments, within each of which the EDA is configured optimally for processing in the face of signal conditions and uncertainties. A dynamic-lock-state feature enables the detection of signals using minimum required computing power less when signals are steadily detected, more when signals fluctuate. At present, the hardware comprises eight dual-processor personal-computer modules and a server. The hardware is modular, making it possible to increase computing power by adding computers.

Pham, Timothy↗

NASA NTRS2004

Mechanism for Self-Reacted Friction Stir Welding

A mechanism has been designed to apply the loads (the stirring and the resection forces and torques) in self-reacted friction stir welding. This mechanism differs somewhat from mechanisms used in conventional friction stir welding, as described below. The tooling needed to apply the large reaction loads in conventional friction stir welding can be complex. Self-reacted friction stir welding has become popular in the solid-state welding community as a means of reducing the complexity of tooling and to reduce costs. The main problems inherent in self-reacted friction stir welding originate in the high stresses encountered by the pin-and-shoulder assembly that produces the weld. The design of the present mechanism solves the problems. The mechanism includes a redesigned pin-and-shoulder assembly. The welding torque is transmitted into the welding pin by a square pin that fits into a square bushing with set-screws. The opposite or back shoulder is held in place by a Woodruff key and high-strength nut on a threaded shaft. The Woodruff key reacts the torque, while the nut reacts the tensile load on the shaft.

Venable, Richard↗

NASA NTRS2004

Framework for Development of Object-Oriented Software

The Real-Time Control (RTC) Application Framework is a high-level software framework written in C++ that supports the rapid design and implementation of object-oriented application programs. This framework provides built-in functionality that solves common software development problems within distributed client-server, multi-threaded, and embedded programming environments. When using the RTC Framework to develop software for a specific domain, designers and implementers can focus entirely on the details of the domain-specific software rather than on creating custom solutions, utilities, and frameworks for the complexities of the programming environment. The RTC Framework was originally developed as part of a Space Shuttle Launch Processing System (LPS) replacement project called Checkout and Launch Control System (CLCS). As a result of the framework s development, CLCS software development time was reduced by 66 percent. The framework is generic enough for developing applications outside of the launch-processing system domain. Other applicable high-level domains include command and control systems and simulation/ training systems.

Perez-Poveda, Gus↗