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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.

Posted in: Briefs

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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.

Posted in: Briefs

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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.

Posted in: Briefs

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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.

Posted in: Briefs

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Vacuum-Jacketed Cryogenic Flex-Through

John F. Kennedy Space Center, Florida A vacuum-jacketed, cryogenic flex hose was designed with an integrated flange to be able to pass through a vacuum chamber wall. This design increases the quality of the cryogenic fluid at the exit of the hose (i.e., more liquid, less vapor) by extending the hose vacuum-jacket through the chamber wall, where usually a non-insulated fluid fitting would be required.

Posted in: Briefs

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Normally-Closed Zero-Leak Valve with a Magnetostrictive Actuator

The valve can be used wherever normally closed valves are required. Goddard Space Flight Center, Greenbelt, Maryland A hermetically sealed, normally closed (NC) zero-leak valve has been developed. Prior to actuation, the valve isolates the working fluid in the upstream volume from the downstream volume with a parent metal seal. The valve utilizes the magnetostrictive alloy Terfenol-D for actuation. This alloy experiences a phenomenon known as magnetostriction, i.e., a gross elongation, when exposed to a magnetic field. This elongation fractures the seal within the wetted volume of the valve, opening the valve permanently and establishing fluid flow. The required magnetic field is generated by redundant coils concentric to the Terfenol, but isolated from the working fluid. The response time for this phenomenon to occur and subsequently for actuation is on the order of milliseconds. The wetted volume consists of entirely parent-metal 6Al-4V titanium, compatible with all storable propellants, helium, nitrogen, argon, isopropyl alcohol, and argon. When coupled with the parent metal seal, this design gives the valve internal and external leak rates of zero.

Posted in: Briefs

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Wideband, GaN MMIC, Distributed Amplifier-Based Microwave Power Module

The solid-state module operates as a radar, communication, or navigation system. John H. Glenn Research Center, Cleveland, Ohio Historically, the term microwave power module (MPM) has been associated with a small, fully integrated, self-contained radio frequency (RF) amplifier that combines both solid-state and microwave vacuum electronics technologies. Typically, the output power of these MPMs is on the order of about 100 Watts CW over an octave bandwidth. The MPMs require both a solid-state amplifier at the front end and a microwave vacuum electronics amplifier at the back end. However, such MPMs cannot be utilized for communications because the MPMs are not optimized for linearity or efficiency. Also, the MPMs can be very expensive to manufacture, particularly when modules are produced in very small quantities for space applications. Also, a kilovolt (kV) class power supply is required to power the traveling-wave tube amplifier, which is a part of the microwave vacuum electronics.

Posted in: Briefs, Power Management

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