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Post-Growth, In Situ Adhesion of Carbon Nanotubes to a Substrate for Robust CNT Cathodes

This technology can be used down-hole in oil wells, and in high-temperature, high-pressure, corrosive environments in the automotive industry. The field emission electron sources using carbon nanotubes (CNTs) are being targeted for low-power vacuum microelectronic applications for harshenvironment operation (high temperature, pressure, and corrosive atmosphere). While CNTs have demonstrated excellent properties in terms of low threshold field, low-power operation, and high current densities, one problem with vacuum electronic applications is poor adhesion of CNTs to the substrate on which they are synthesized. The chemical vapor deposition (CVD) process used to grow CNTs on silicon or other metallic substrates using an iron catalyst with a thin oxide diffusion barrier layer has consistently provided reproducible growth. The CNTs are only surface- adhering in these cases, and are easily removed from the surface with the application of minor forces — typically pressures of 20 to 60 kPa. This causes catastrophic failures of CNT field emitters since the applied field could exceed the adhesion strength of CNTs to the substrate.

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Thermal Mechanical Preparation of Glass Spheres

The forming process allows a very wide variety of material to be processed into spheres. Samples of lunar regolith have included small glass spheres. Most literature has suggested the small spheres were formed by meteorite impacts. The resulting transformation of kinetic energy to thermal energy caused the lunar surface to melt. The process yielded glass spheres. Recreating a meteorite impact that yields glass spheres is very challenging. Furthermore, the melting temperature of certain minerals on the Moon precludes the use of standard thermal techniques.

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Development of a Precision Thermal Doubler for Deep Space

A copper thermal doubler is used to spread the thermal loads. Thermal requirements and a need for a very flat mechanical interface led to the development of a copper doubler for the titanium vault on the Juno Spacecraft. The vault is designed to contain the science instruments on the spacecraft, protecting them from damage due to the extreme radiation environment of Jupiter. The titanium used in the vault creates unwanted thermal effects due to the poor thermal conductivity of titanium. To remove heat from the telecommunication equipment mounted to the interior of the vault, a copper thermal doubler was used to spread the thermal loads over the entire area of the radiator (located on the outside of the vault), which decreased the effective thermal resistance through the vault wall. A method of bonding a copper doubler to the titanium preserves the mounting interface flatness to less than 0.005 in. (0.13 mm) while providing a superior thermal path to the radiators, which are fitted with thermal control louvers. The precisely controlled titanium surface, and that of the milled copper doubler with integral spacing features, provides the mechanical interface flatness, structural integrity, and thermal performance required by the telecommunications subsystem.

Posted in: Briefs, TSP

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Improving Friction Stir Welds Using Laser Peening

This technique can be used in any application of friction stir welding, including automotive, railroad, and maritime industries. Friction stir welding (FSW) has emerged as a promising solid-state process with encouraging results, particularly when used on high-strength aerospace aluminum alloys that are generally difficult to weld. Laser peening has been applied to the mechanical and fatigue properties of welded joints. Laser peening introduces a compressive residual stress at the surface that can extend several millimeters or deeper into the material. These residual stresses resulting from laser peening can be significantly higher and deeper than for conventional shot peening, resulting in superior mechanical and fatigue properties in FSW.

Posted in: Briefs, TSP

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Methodology of Evaluating Margins of Safety in Critical Brazed Joints

This methodology provides a guide consisting of design, testing, and structural analysis steps developed to assure positive strength margins of safety (MS) in critical brazed joints used for assembly of flight and non-flight structures.

Posted in: Briefs, TSP

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Additive Manufacturing of Ti-6Al-4V Alloy Components for Spacecraft Applications

Additive manufacturing is a viable and affordable process to manufacture complex parts for aerospace, medical, and automotive applications. In the past two decades, there have been significant advancements in the field of additive manufacturing (AM) of titanium alloy (Ti-6Al-4V) and other metallic components for aerospace applications.

Posted in: Manufacturing & Prototyping, Briefs

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Hermetic Seal Designs for Sample Return Sample Tubes

Prototype sample tube seals prevent material loss and maintain sample integrity. Prototypes have been developed of potential hermetic sample sealing techniques for encapsulating samples in a ≈1-cm-diameter thin-walled sample tube that are compatible with IMSAH (Integrated Mars Sample Acquisition and Handling) architecture. Techniques include a heat-activated, finned, shape memory alloy plug; a contracting shape memory alloy activated cap; an expanding shape memory alloy plug; and an expanding torque plug.

Posted in: Manufacturing & Prototyping, Briefs, TSP

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