Tech Briefs

Oriented Nanofibers Embedded in a Polymer Matrix

Lyndon B. Johnson Space Center, Houston, Texas A method of forming a composite of embedded nanofibers in a polymer matrix with a high degree of alignment has been created using a nanofiber continuous fiber (NCF) system. This innovation incorporates nanofibers in a plastic matrix forming agglomerates, and then uniformly distributes them by exposing the agglomerates to hydrodynamic stresses that force the agglomerates to break apart. In combination, or additionally, elongational flow is used to achieve small diameters and alignment.

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Low-Scatter Starshade Edges

This technology has applications in flexible optical masks, apertures, and encoders where sharp edges and material robustness are important. NASA’s Jet Propulsion Laboratory, Pasadena, California A starshade occulter is a large space structure whose shape is specially designed to produce a diffraction pattern in starlight that can aid a telescope in direct imaging of exoplanets. The diffraction pattern produces extremely high-contrast dark regions in the starshade’s shadow on the order of 10-9 or 10-10. To do so, the edge shape of the structure must be held to extremely tight tolerances. In addition, potentially obscuring glint light from the Sun must be minimized to prevent loss of contrast.

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Method to Improve the Synthesis Process of High-Purity Bulk Multi-Element Compounds

Marshall Space Flight Center, Alabama Multi-element compounds have been used ubiquitously in various applications, including electronics, optics, opto-electronics, thermoelectrics, superconductivity, and the recently developed application of spintronics. Besides being the main components of some of these devices, the bulk form of these compounds is needed as a standard for fundamental property characterizations as well as the starting materials for thin-film deposition. Hence, the chemical purity and crystalline quality of these bulk compounds are critical for the applications.

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Laser Subdivision of the Genesis Concentrator Target Sample 60000

Lyndon B. Johnson Space Center, Houston, Texas A need arose for approximately 1 cm2 of a diamond-like-carbon (DLC) concentrator target for the analysis of solar wind nitrogen isotopes. The original target was a circular quadrant with a radius of 3.1 cm; however, the piece did not survive intact when the spacecraft suffered an anomalous landing upon returning to Earth. An estimated 75% of the DLC target was recovered in at least 18 fragments. The largest fragment, Genesis sample 60000, was designated for this allocation, and is the first sample to be subdivided using a laser scribing system. Laser subdivision has associated risks, including thermal diffusion of the implant if heating occurs, and unintended breakage during cleavage. In order to minimize the possibility of unintended breakage of the actual target wafer during subdivision, a careful detailed study involving numerous laser scribing plans was undertaken. The innovation described here involves the results of this study that yielded a cutting plan essentially guaranteeing ~100% cleaving success of this precious space-exposed wafer.

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Fabrication of an Integrated Photonic Waveguide Joint in Micromachined Silicon

This technology could be used in any MEMS or micromachined structure that requires multiple levels of topography. Goddard Space Flight Center, Greenbelt, Maryland High-aspect-ratio silicon structures are necessary components in many MEMS (microelectromechanical systems). Aspect ratio is defined as the ratio of the height of the structure to its lateral width. The structures are typically fabricated through bulk micromachining steps such as deep reactive ion etching. In some cases, multiple levels of high-aspect-ratio structures are required. For instance, one may want to etch completely through a silicon wafer to thermally isolate a bolometer or provide waveguide coupling to an antenna defined on an insulating membrane, and at the same time have integrated high-topology structures required for microwave coupling or filtering. Definition of the structures typically uses photolithographic technology. But for high-aspect-ratio structures, spin cast resist becomes difficult to incorporate due to the non-uniform thickness of the resist around tall structures. One can cast very thick layers of photoresist, but this limits the minimum feature size, and additionally, very thick layers of photoresist are difficult to work with due to solvent release and moisture that can cause the resist to crack or swell. For electromagnetic reasons, the structures would preferably be made from conductive material such as metal or degeneratively doped silicon. The objective of this work was to incorporate multiple levels of conductive high-aspectratio structures with standard micromachining processes.

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Very Large Inflatable Antenna Structures

This methodology enables production of very large, but lightweight, structures in space. Langley Research Center, Hampton, Virginia Future space exploration past Earth orbit has a significant need for manufacturing in space beyond simple assembly of prefabricated parts. The next generation of very large aperture antennas will exceed the size achievable with conventional folding mesh technologies and new concepts are needed to support football-field-size structures. Technologies to address the problem have been developed using the formation of polyurethanes in a vacuum environment. Large inflatable structures can be stabilized by the formation of polyurethane foams of controlled density. For use in a vacuum environment, the availability of oligomeric precursors is important. Low-molecular-weight components would immediately evaporate, changing the stoichiometry of the reaction and potentially contaminate a space environment, but high-molecular-weight precursors have a much more limited range of properties.

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Constraint Force Equation (CFE) Solver for Multi-Body Dynamics and its Implementation in POST2

Langley Research Center, Hampton, Virginia Existing aerospace flight trajectory programs simulate the motion of aerospace vehicles by modeling external forces and moments acting on each body, but lack provisions for determining reaction forces and moments exerted by one body on another through a connecting joint. These reaction forces and moments are also known as constraint forces and moments because they permit specified motion of one body relative to another, and, at the same time, prohibit all other relative motions. In other words, a joint imposes certain constraints on relative motion.

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