Tech Briefs

Arrays of Bundles of Carbon Nanotubes as Field Emitters

Area-averaged current densities exceed those of arrays of single nanotubes.

Experiments have shown that with suitable choices of critical dimensions, planar arrays of bundles of carbon nanotubes (see figure) can serve as high-current-density field emitter (cold-cathode) electron sources. Whereas some hot-cathode electron sources must be operated at supply potentials of thousands of volts, these cold-cathode sources generate comparable current densities when operated at tens of volts. Consequently, arrays of bundles of carbon nanotubes might prove useful as cold-cathode sources in miniature, lightweight electron-beam devices (e.g., nanoklystrons) soon to be developed.

Posted in: Briefs, TSP, Physical Sciences, Materials properties, Nanomaterials, Test procedures

Staggering Inflation To Stabilize Attitude of a Solar Sail

A document presents computational simulation studies of a concept for stabilizing the attitude of a spacecraft during deployment of such structures as a solar sail or other structures supported by inflatable booms. Specifically, the solar sail considered in this paper is a square sail with inflatable booms and attitude control vanes at the corners. The sail inflates from its stowed configuration into a square sail with four segments and four vanes at the tips. Basically, the concept is one of controlling the rates of inflation of the booms to utilize in mass distribution properties to effect changes in the system’s angular momentum.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Simulation and modeling, Solar energy, Spacecraft

Bare Conductive Tether for Decelerating a Spacecraft

A document describes a prototype of electrically conductive tethers to be used primarily to decelerate spacecraft and/or generate electric power for the spacecraft. Like prior such tethers, this tether is designed so that when it is deployed from a spacecraft in orbit, its motion across the terrestrial magnetic field induces an electric current. The Lorentz force on the current decelerates the spacecraft. Optionally, the current can be exploited to convert some orbital kinetic energy to electric energy for spacecraft systems. Whereas the conductive portions of prior such tethers are covered with electrical insulation except for end electrodes that make contact with the ionosphere, this tether includes a conductive portion that is insulated along part of its length but deliberately left bare along a substantial remaining portion of its length to make contact with the ionosphere. The conductive portions of the tether are made of coated thin aluminum wires wrapped around strong, lightweight aromatic polyamide braids. The main advantages of the present partly-bare-tether design over the prior all-insulated-tether design include greater resistance to degradation by the impact of monatomic oxygen at orbital altitude and speed and greater efficiency in collecting electrons from the ionosphere.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Electric power, Conductivity, Spacecraft

Flexible Skins Containing Integrated Sensors and Circuitry

Densely arrayed tactile sensors measure multiple, spatially registered physical quantities simultaneously.

Artificial sensor skins modeled partly in imitation of biological sensor skins are undergoing development. These sensor skins comprise flexible polymer substrates that contain and/or support dense one- and two-dimensional arrays of microscopic sensors and associated microelectronic circuits. They afford multiple tactile sensing modalities for measuring physical phenomena that can include contact forces; hardnesses, temperatures, and thermal conductivities of objects with which they are in contact; and pressures, shear stresses, and flow velocities in fluids. The sensor skins are mechanically robust, and, because of their flexibility, they can be readily attached to curved and possibly moving and flexing surfaces of robots, wind-tunnel models, and other objects that one might seek to equip for tactile sensing.

Posted in: Briefs, Physical Sciences, Integrated circuits, Sensors and actuators, Fabrics, Polymers, Test equipment and instrumentation

Artificial Hair Cells for Sensing Flows

Small, robust sensors can be fabricated on a variety of substrates.

The purpose of this article is to present additional information about the flow-velocity sensors described briefly in the immediately preceding article. As noted therein, these sensors can be characterized as artificial hair cells that implement an approximation of the sensory principle of flow-sensing cilia of fish: A cilium is bent by an amount proportional to the flow to which it is exposed. A nerve cell at the base of the cilium senses the flow by sensing the bending of the cilium. In an artificial hair cell, the artificial cilium is a microscopic cantilever beam, and the bending of an artificial cilium is measured by means of a strain gauge at its base (see Figure 1).

Posted in: Briefs, Manufacturing & Prototyping, Sensors and actuators, Biological sciences

Optoelectronic Nose Senses Vapors Associated with Hazmat and Security Scenarios

Using multiple principles of olfactory system function and libraries of broadly responding sensors enable devices to be tailored to different odor-detection problems.

Since 9/11, we are increasingly threatened by terrorist plots — the release of noxious substances into crowded public places or on airplanes, in crowded buildings, and in sports arenas. Anxieties about these rare events are mostly unrealized, but such events have occurred frequently enough — such as in Madrid, London, or Delhi — that protective measures that will reassure the public are needed. To be effective, sensors and screening devices must be deployed widely, be inexpensive, support high-volume throughput (respond rapidly), and be available for a wide range of threats (i.e., flexible and adaptable to different or new scenarios).

Posted in: Briefs, Electronics & Computers, Optics, Sensors and actuators, Bacteria, Disaster and emergency management, Emergency management, Gases, Hazardous materials

Video Guidance Sensor and Time-of-Flight Rangefinder

A prior VGS would be modified to incorporate the rangefinder function.

A proposed video guidance sensor (VGS) would be based mostly on the hardware and software of a prior Advanced VGS (AVGS), with some additions to enable it to function as a time-offlight rangefinder (in contradistinction to a triangulation or image-processing rangefinder). It would typically be used at distances of the order of 2 or 3 kilometers, where a typical target would appear in a video image as a single blob, making it possible to extract the direction to the target (but not the orientation of the target or the distance to the target) from a video image of light reflected from the target.

Posted in: Briefs, Electronics & Computers, Flight guidance systems, Imaging and visualization, Sensors and actuators

Optical Beam-Shear Sensors

Simple sensors measure radiant fluxes in beam quadrants.

A technique for measuring optical beam shear is based on collecting light from the four quadrants of the beam and comparing the optical power collected from each quadrant with that from the other three quadrants. As used here, “shear” signifies lateral displacement of a beam of light from a nominal optical axis.

Posted in: Briefs, TSP, Physical Sciences, Optics, Sensors and actuators

The PICWidget

The Plug-in Image Component Widget (PICWidget) is a software component for building digital imaging applications. The component is part of a methodology described in “GIS Methodology for Planning Planetary-Rover Operations” (NPO-41812), which appears elsewhere in this issue of NASA Tech Briefs. Planetary rover missions return a large number and wide variety of image data products that vary in complexity in many ways. Supported by a powerful, flexible image-data-processing pipeline, the PICWidget can process and render many types of imagery, including (but not limited to) thumbnail, subframed, downsampled, stereoscopic, and mosaic images; images coregistred with orbital data; and synthetic red/green/blue images. The PICWidget is capable of efficiently rendering images from data representing many more pixels than are available at a computer workstation where the images are to be displayed. The PICWidget is implemented as an Eclipse plug-in using the Standard Widget Toolkit, which provides a straightforward interface for re-use of the PICWidget in any number of application programs built upon the Eclipse application framework. Because the PICWidget is tile-based and performs aggressive tile caching, it has flexibility to perform faster or slower, depending whether more or less memory is available.

Posted in: Briefs, TSP, Software, Computer software and hardware, Imaging and visualization

Fusing Symbolic and Numerical Diagnostic Computations

“X-2000 Anomaly Detection Language” denotes a developmental computing language, and the software that establishes and utilizes the language, for fusing two diagnostic computer programs, one implementing a numerical analysis method, the other implementing a symbolic analysis method into a unified eventbased decision analysis software system for real-time detection of events (e.g., failures) in a spacecraft, aircraft, or other complex engineering system. The numerical analysis method is performed by beacon- based exception analysis for multimissions (BEAMs), which has been discussed in several previous NASA Tech Briefs articles. The symbolic analysis method is, more specifically, an artificial-intelligence method of the knowledge-based, inference engine type, and its implementation is exemplified by the Spacecraft Health Inference Engine (SHINE) software. The goal in developing the capability to fuse numerical and symbolic diagnostic components is to increase the depth of analysis beyond that previously attainable, thereby increasing the degree of confidence in the computed results. In practical terms, the sought improvement is to enable detection of all or most events, with no or few false alarms.

Posted in: Briefs, TSP, Software, Mathematical analysis, Artificial intelligence, Computer software and hardware, On-board diagnostics, On-board diagnostics (OBD), Vehicle health management

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