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NASA NTRS2004

Highlights of the ASPE 2004 Winter Topical Meeting on Free-Form Optics: Design, Fabrication, Metrology, Assembly

We present highlights from the American Society for Precision Engineering's 2004 winter topical meeting entitled Free-Form Optics: Design, Fabrication, Metrology, Assembly. We emphasize those papers that are most relevant to astronomical optics. Optical surfaces that transcend the bounds of rotational symmetry have been implemented in novel optical systems with fantastic results since the release of Polaroid's first instant camera. Despite these successes, free-form optics have found only a few niche applications and have yet to enter the mainstream. The purpose of this meeting is to identify the state of the art of free-form optics design, fabrication, metrology and assembly and to identify the technical and logistical challenges that inhibit their widespread use. Issues that will be addressed include: What are free-form optics? How can optical systems be made better with free-form optics? How can designers use free-form optics? How can free-form optics be fabricated? How can they be measured? How are free-form optical systems assembled? Control of multi-axis systems.

Ohl, Raymond G.↗

NASA NTRS2004

Large-Scale Fabrication of Carbon Nanotube Probe Tips For Atomic Force Microscopy Critical Dimension Imaging Applications

Carbon nanotube (CNT) probe tips for atomic force microscopy (AFM) offer several advantages over Si/Si3N4 probe tips, including improved resolution, shape, and mechanical properties. This viewgraph presentation discusses these advantages, and the drawbacks of existing methods for fabricating CNT probe tips for AFM. The presentation introduces a bottom up wafer scale fabrication method for CNT probe tips which integrates catalyst nanopatterning and nanomaterials synthesis with traditional silicon cantilever microfabrication technology. This method makes mass production of CNT AFM probe tips feasible, and can be applied to the fabrication of other nanodevices with CNT elements.

Ye, Qi Laura↗

NASA NTRS2003

Thermoelectric microdevice fabricated by a MEMS-like electrochemical process

Microelectromechanical systems (MEMS) are the basis of many rapidly growing technologies, because they combine miniature sensors and actuators with communications and electronics at low cost. Commercial MEMS fabrication processes are limited to silicon-based materials or two-dimensional structures. Here we show an inexpensive, electrochemical technique to build MEMS-like structures that contain several different metals and semiconductors with three-dimensional bridging structures. We demonstrate this technique by building a working microthermoelectric device. Using repeated exposure and development of multiple photoresist layers, several different metals and thermoelectric materials are fabricated in a three-dimensional structure. A device containing 126 n-type and p-type (Bi, Sb)2Te3 thermoelectric elements, 20 microm tall and 60 microm in diameter with bridging metal interconnects, was fabricated and cooling demonstrated. Such a device should be of technological importance for precise thermal control when operating as a cooler, and for portable power when operating as a micro power generator.

Evaluation Studies↗

NASA NTRS2004

Wave Propagation in 2-D Granular Matrix and Dust Mitigation of Fabrics for Space Exploration Mission

Wave Propagation study is essential to exploring the soil on Mars or Moon and Dust Mitigation is a necessity in terms of crew's health in exploration missions. The study of Dust Mitigation has a significant impact on the crew s health when astronauts track dust back into their living space after exploration trips. We are trying to use piezoelectric fiber to create waves and vibrations at certain critical frequencies and amplitudes so that we can shake the particles off from the astronaut s fabrics. By shaking off the dust and removing it, the astronauts no longer have to worry about breathing in small and possibly hazardous materials, when they are back in their living quarters. The Wave Propagation in 2-D Granular Matrix studies how the individual particles interact with each other when a pressure wave travels through the matrix. This experiment allows us to understand how wave propagates through soils and other materials. By knowing the details about the interactions of particles when they act as a medium for waves, we can better understand how wave propagates through soils and other materials. With this experiment, we can study how less gravity effects the wave propagation and hence device a way to study soils in space and on Moon or Mars. Some scientists treat the medium that waves travel through as a "black box", they did not pay much attention to how individual particles act as wave travels through them. With this data, I believe that we can use it to model ways to measure the properties of different materials such as density and composition. In order to study how the particles interact with each other, I have continued Juan Agui's experiment of the effects of impacts on a 2-D matrix. By controlling the inputs and measuring the outputs of the system, I will be able to study now the particles in that system interact with each other. I will also try to model this with the software called PFC2D in order to obtain theoretical data to compare with the experiment. PFC2D is a program that allows the user to control the number of particle's characteristic, and the environment of the particle. With this I can run simulations that mimic the impulse test. This software uses a language called FISH, probably created by the creator of the software. This means that in order to model anything, one must use the command terminal instead of GUI's. I will also use this program to simulate the Moon/Mars simulate adhering to the fabric for the Dust Mitigation project. My goals for this summer are just to complete preliminary studies of the feasibility of the Shaking Fabric, learn the PFC-2D program, and to complete building and testing the wave propagation experiment.

Thanh, Phi Hung X.↗

NASA NTRS2004

Fabrication of a novel gigabit/second free-space optical interconnect - photodetector characterization and testing and system development

The time when computing power is limited by the copper wire inherent in the computer system and not the speed of the microprocessor is rapidly approaching. With constant advances in computer technology, many researchers believe that in only a few years, optical interconnects will begin to replace copper wires in your Central Processing Unit (CPU). On a more macroscopic scale, the telecommunications industry has already made the switch to optical data transmission as, to date, fiber optic technology is the only reasonable method of reliable, long range data transmission. Within the span of a decade, we will see optical technologies move from the macroscopic world of the telecommunications industry to the microscopic world of the computer chip. Already, the communications industry is marketing commercially available optical links to connect two personal computers, thereby eliminating the need for standard and comparatively slow wired and wireless Ethernet transfers and greatly increasing the distance the computers can be separated. As processing demands continue to increase, the realm of optical communications will continue to move closer to the microprocessor and quite possibly onto the microprocessor itself. A day may come when copper connections are used only to supply power, not transfer data. This summer s work marks some of the beginning stages of a 5 to 10 year, long-term research project to create and study a free-space, 1 Gigabit/sec optical interconnect. The research will result in a novel fabricated, chip-to-chip interconnect consisting of a Vertical Cavity Surface Emitting Laser (VCSEL) Diode linked through free space to a Metal- Semiconductor-Metal (MSM) Photodetector with the possible integration of microlenses for signal focusing and Micro-Electromechanical Systems (MEMS) devices for optical signal steering. The advantages, disadvantages, and practicality of incorporating flip-chip mounting technologies will also be addressed. My work began with the design and construction of a test setup for the experiment and then appropriate characterization of the test system. Specifically, I am involved in the characterization of a commercially available 1550nm wavelength, 5mW diode laser and a study of its modulation bandwidth. Commercially produced photodetectors as well as the incorporation of microwave technology, in the form of RF input and output, are used in the characterization procedure. The next stage involves the use of a probe station and network analyzer to characterize and test a series of photodetectors fabricated on a 2 inch, Indium Gallium Arsenide (InGaAs) wafer in the Branch s microlithography lab. Other project responsibilities include, but are not limited to the incorporation of a transimpedance amplifier to the photodetector circuit; a study of VCSEL technology; bit error rate analysis of an optical interconnect system; and analysis of free space divergence of the VCSEL, optical path length of the interconnect; and any other pertinent optical properties of the one gigabit per second interconnect for fabrication and testing.

Savich, Gregory R.↗

NASA NTRS2004

Subscale Testing of a Ceramic Composite Cooled Panel Led to Its Design and Fabrication for Scramjet Engine Testing

In a partnership between the NASA Glenn Research Center and Pratt & Whitney, a ceramic heat exchanger panel intended for use along the hot-flow-path walls of future reusable launch vehicles was designed, fabricated, and tested. These regeneratively cooled ceramic matrix composite (CMC) panels offer lighter weight, higher operating temperatures, and reduced coolant requirements in comparison to their more traditional metallic counterparts. A maintainable approach to the design was adopted which allowed the panel components to be assembled with high-temperature fasteners rather than by permanent bonding methods. With this approach, the CMC hot face sheet, the coolant containment system, and backside structure were all fabricated separately and could be replaced individually as the need occurred during use. This maintainable design leads to both ease of fabrication and reduced cost.

Jaskowiak, Martha H.↗

NASA NTRS2000

Chemical Fabrication Used to Produce Thin-Film Materials for High Power-to- Weight-Ratio Space Photovoltaic Arrays

The key to achieving high specific power (watts per kilogram) space solar arrays is the development of a high-efficiency, thin-film solar cell that can be fabricated directly on a flexible, lightweight, space-qualified durable substrate such as Kapton (DuPont) or other polyimide or suitable polymer film. Cell efficiencies approaching 20 percent at AM0 (air mass zero) are required. Current thin-film cell fabrication approaches are limited by either (1) the ultimate efficiency that can be achieved with the device material and structure or (2) the requirement for high-temperature deposition processes that are incompatible with all presently known flexible polyimide or other polymer substrate materials. Cell fabrication processes must be developed that will produce high-efficiency cells at temperatures below 400 degrees Celsius, and preferably below 300 degress Celsius to minimize the problems associated with the difference between the coefficients of thermal expansion of the substrate and thin-film solar cell and/or the decomposition of the substrate.

Hepp, Aloysius F.↗

NASA NTRS2004

Thin-Film Ceramic Thermocouples Fabricated and Tested

The Sensors and Electronics Technology Branch of the NASA Glenn Research Center is developing thin-film-based sensors for surface measurement in propulsion system research. Thin-film sensors do not require special machining of the components on which they are mounted, and they are considerably thinner than wire- or foil-based sensors. One type of sensor being advanced is the thin-film thermocouple, specifically for applications in high-temperature combustion environments. Ceramics are being demonstrated as having the potential to meet the demands of thin-film thermocouples in advanced aerospace environments. The maximum-use temperature of noble metal thin-film thermocouples, 1500 C (2700 F), may not be adequate for components used in the increasingly harsh conditions of advanced aircraft and next-generation launch vehicles. Ceramic-based thermocouples are known for their high stability and robustness at temperatures exceeding 1500 C, but are typically in the form of bulky rods or probes. As part of ASTP, Glenn's Sensors and Electronics Technology Branch is leading an in-house effort to apply ceramics as thin-film thermocouples for extremely high-temperature applications as part of ASTP. Since the purity of the ceramics is crucial for the stability of the thermocouples, Glenn's Ceramics Branch and Case Western Reserve University are developing high-purity ceramic sputtering targets for fabricating high-temperature sensors. Glenn's Microsystems Fabrication Laboratory, supported by the Akima Corporation, is using these targets to fabricate thermocouple samples for testing. The first of the materials used were chromium silicide (CrSi) and tantalum carbide (TaC). These refractory materials are expected to survive temperatures in excess of 1500 C. Preliminary results indicate that the thermoelectric voltage output of a thin-film CrSi versus TaC thermocouple is 15 times that of the standard type R (platinum-rhodium versus platinum) thermocouple, producing 20 mV with a 200 C temperature gradient. The photograph on the left shows the CrSi-TaC thermocouple in a test fixture at Glenn, and the resulting output signal is shown on the right. The temperature differential across the sample, from the center of the sample inside the oven to the sample mount outside the oven, is measured using a type R thermocouple on the sample.

Wrbanek, John D.↗

NASA NTRS2002

High-Strength Composite Fabric Tested at Structural Benchmark Test Facility

Large sheets of ultrahigh strength fabric were put to the test at NASA Glenn Research Center's Structural Benchmark Test Facility. The material was stretched like a snare drum head until the last ounce of strength was reached, when it burst with a cacophonous release of tension. Along the way, the 3-ft square samples were also pulled, warped, tweaked, pinched, and yanked to predict the material's physical reactions to the many loads that it will experience during its proposed use. The material tested was a unique multi-ply composite fabric, reinforced with fibers that had a tensile strength eight times that of common carbon steel. The fiber plies were oriented at 0 and 90 to provide great membrane stiffness, as well as oriented at 45 to provide an unusually high resistance to shear distortion. The fabric's heritage is in astronaut space suits and other NASA programs.

Krause, David L.↗

NASA NTRS2003

Fabrication And Evaluation Of Sic/Sic Tubes With Various Fiber Architectures

SiC/SiC composites are excellent material candidates for high temperature applications where the performance requirements are high strength, high creep-rupture resistance, high environmental durability, and high thermal conductivity. In the past, the NASA UEET program has demonstrated fabrication of high-performance SiC/SiC flat panels reinforced by Sylramic-iBN SiC fibers. Currently NASA UEET is scaling up this SiC/SiC system by fabrication of more complex shaped components using the same fiber type. This paper reports the effects of various fiber architectures on the processing, mechanical, and durability behavior of small-diameter 0.5" ID SiC/SiC tubes, which are potential sub-elements for leading edges and cooling channels in turbine vanes and blades. Nine different fiber architectures were utilized for construction of seamless tube preforms, from simple 2D jelly-rolling to complex braiding, pin-weaving, filament-winding and 3D orthogonal weaving with approximately 5% fibers in the thru-thickness direction. Using the BN interphase and Sic matrix processing steps established for the flat panels, SiC/SiC tubes were fabricated with wall thicknesses of approximately 60 mils and total fiber fractions of approximately 35%. The "D" split ring tests for hoop tensile properties, micro-structural examinations for relationship between fiber architecture formation and matrix infiltration, and the low-pressure burner rig tests for the high temperature durability under thru-thickness thermal gradient were conducted. The better matrix infiltration and higher hoop strength were achieved using the tri-axial braided and the three-float pin woven SiC/SiC tubes. In general, it needs not only higher hoop direction fibers but also axial direction fibers for the higher hoop strength and the better infiltration, respectively. These results are analyzed to offer general guidelines for selecting fiber pre-form architectures and SiC/SiC processes that maximize tube hoop strength, thru-thickness thermal conductivity, and burner-rig durability under a high thermal gradient.

Yun, H. M.↗

NASA NTRS2003

Advanced Packaging Technology Used in Fabricating a High-Temperature Silicon Carbide Pressure Sensor

The development of new aircraft engines requires the measurement of pressures in hot areas such as the combustor and the final stages of the compressor. The needs of the aircraft engine industry are not fully met by commercially available high-temperature pressure sensors, which are fabricated using silicon. Kulite Semiconductor Products and the NASA Glenn Research Center have been working together to develop silicon carbide (SiC) pressure sensors for use at high temperatures. At temperatures above 850 F, silicon begins to lose its nearly ideal elastic properties, so the output of a silicon pressure sensor will drift. SiC, however, maintains its nearly ideal mechanical properties to extremely high temperatures. Given a suitable sensor material, a key to the development of a practical high-temperature pressure sensor is the package. A SiC pressure sensor capable of operating at 930 F was fabricated using a newly developed package. The durability of this sensor was demonstrated in an on-engine test. The SiC pressure sensor uses a SiC diaphragm, which is fabricated using deep reactive ion etching. SiC strain gauges on the surface of the diaphragm sense the pressure difference across the diaphragm. Conventionally, the SiC chip is mounted to the package with the strain gauges outward, which exposes the sensitive metal contacts on the chip to the hostile measurement environment. In the new Kulite leadless package, the SiC chip is flipped over so that the metal contacts are protected from oxidation by a hermetic seal around the perimeter of the chip. In the leadless package, a conductive glass provides the electrical connection between the pins of the package and the chip, which eliminates the fragile gold wires used previously. The durability of the leadless SiC pressure sensor was demonstrated when two 930 F sensors were tested in the combustor of a Pratt & Whitney PW4000 series engine. Since the gas temperatures in these locations reach 1200 to 1300 F, the sensors were installed in water-cooled jackets, as shown. This was a severe test because the pressure-sensing chips were exposed to the hot combustion gases. Prior to the installation of the SiC pressure sensors, two high-temperature silicon sensors, installed in the same locations, did not survive a single engine run. The durability of the leadless SiC pressure sensor was demonstrated when both SiC sensors operated properly throughout the two runs that were conducted.

Beheim, Glenn M.↗

NASA NTRS2005

In Situ Fabrication Technologies: Meeting the Challenge for Exploration

A viewgraph presentation on Lunar and Martian in situ fabrication technologies meeting the challenges for exploration is shown. The topics include: 1) Exploration Vision; 2) Vision Requirements Early in the Program; 3) Vision Requirements Today; 4) Why is ISFR Technology Needed? 5) ISFR and In Situ Resource Utilization (ISRU); 6) Fabrication Feedstock Considerations; 7) Planetary Resource Primer; 8) Average Chemical Element Abundances in Lunar Soil; 9) Chemical Elements in Aerospace Engineering Materials; 10) Schematic of Raw Regolith Processing into Constituent Components; 11) Iron, Aluminum, and Basalt Processing from Separated Elements and Compounds; 12) Space Power Systems; 13) Power Source Applicability; 14) Fabrication Systems Technologies; 15) Repair and Nondestructive Evaluation (NDE); and 16) Habitat Structures. A development overview of Lunar and Martian repair and nondestructive evaluation is also presented.

Howard, Richard W.↗

NASA NTRS2005

Fabrication of GRCop-84 Rocket Thrust Chambers

GRCop-84, a copper alloy, Cu-8 at% Cr-4 at% Nb developed at NASA Glenn Research Center for regeneratively cooled rocket engine liners has excellent combinations of elevated temperature strength, creep resistance, thermal conductivity and low cycle fatigue. GRCop-84 is produced from prealloyed atomized powder and has been fabricated into plate, sheet and tube forms as well as near net shapes. Fabrication processes to produce demonstration rocket combustion chambers will be presented and includes powder production, extruding, rolling, forming, friction stir welding, and metal spinning. GRCop-84 has excellent workability and can be readily fabricated into complex components using conventional powder and wrought metallurgy processes. Rolling was examined in detail for process sensitivity at various levels of total reduction, rolling speed and rolling temperature representing extremes of commercial processing conditions. Results indicate that process conditions can range over reasonable levels without any negative impact to properties.

Loewenthal, William S.↗

NASA NTRS2002

Nano-fabricated size exclusion chromatograph

This paper describes the development of a nano-fabricated size exclusion chromatograph (nSEC) based on the principle that molecules traveling through amicrocolumn containing nano-fabricated features will have characteristic elution times that directly correlate to molecular weight. Compared to conventional size exclusion chromatography, the nSEC offers greater control over the size exclusion process; mass fabrication; integration of the separation column with associated valves, pumps, and detectors; and dramatic reductions in instrument mass and power requirements.

nanofluids lab-on-a-chip chromatograph separation↗

NASA NTRS2006

Metallurgical Mechanisms Controlling Mechanical Properties of Aluminum Alloy 2219 Produced by Electron Beam Freeform Fabrication

The electron beam freeform fabrication (EBF3) layer-additive manufacturing process has been developed to directly fabricate complex geometry components. EBF3 introduces metal wire into a molten pool created on the surface of a substrate by a focused electron beam. Part geometry is achieved by translating the substrate with respect to the beam to build the part one layer at a time. Tensile properties demonstrated for electron beam deposited aluminum and titanium alloys are comparable to wrought products, although the microstructures of the deposits exhibit cast features. Understanding the metallurgical mechanisms controlling mechanical properties is essential to maximizing application of the EBF3 process. Tensile mechanical properties and microstructures were examined for aluminum alloy 2219 fabricated over a range of EBF3 process variables. Unique microstructures were observed within the deposited layers and at interlayer boundaries, which varied within the deposit height due to microstructural evolution associated with the complex thermal history experienced during subsequent layer deposition. Microstructures exhibited irregularly shaped grains with interior dendritic structures, described based on overall grain size, morphology, distribution, and dendrite spacing, and were correlated with deposition parameters. Fracture features were compared with microstructural elements to define fracture paths and aid in definition of basic processing-microstructure-property correlations.

Domack, Marcia S.↗

NASA NTRS2006

Fabrication of GRCop-84 Rocket Thrust Chambers

GRCop-84, a copper alloy, Cu-8 at% Cr-4 at% Nb developed at NASA Glenn Research Center for regenerative1y cooled rocket engine liners has excellent combinations of elevated temperature strength, creep resistance, thermal conductivity and low cycle fatigue. GRCop-84 is produced from pre-alloyed atomized powder and has been fabricated into plate, sheet and tube forms as well as near net shapes. Fabrication processes to produce demonstration rocket combustion chambers will be presented and includes powder production, extruding, rolling, forming, friction stir welding, and metal spinning. GRCop-84 has excellent workability and can be readily fabricated into complex components using conventional powder and wrought metallurgy processes. Rolling was examined in detail for process sensitivity at various levels of total reduction, rolling speed and rolling temperature representing extremes of commercial processing conditions. Results indicate that process conditions can range over reasonable levels without any negative impact to properties.

Loewenthal, William↗

NASA NTRS2007

Electron Beam Freeform Fabrication in the Space Environment

The influence of reduced gravitational forces (in space and on the lunar or Martian surfaces) on manufacturing processes must be understood for effective fabrication and repair of structures and replacement parts during long duration space missions. The electron beam freeform fabrication (EBF3) process uses an electron beam and wire to fabricate metallic structures. The process efficiencies of the electron beam and the solid wire feedstock make the EBF3 process attractive for use in-space. This paper will describe the suitability of the EBF3 process in the space environment and will highlight preliminary testing of the EBF3 process in a zero-gravity environment.

Hafley, Robert A.↗

NASA NTRS2007

Design and Fabrication Highlights Enabling a 2 mm, 128 Element Bolometer Array for GISMO

The Backshort-Under-Grid (BUG) superconducting bolometer array architecture is intended to be highly versatile, operating in a large range of wavelengths and background conditions. We have undertaken a three-year program to develop key technologies and processes required to build kilopixel arrays. To validate the basic array design and to demonstrate its applicability for future kilopixel arrays, we have chosen to demonstrate a 128 element bolometer array optimized for 2 mm wavelength using a newly built Goddard instrument, GISMO (Goddard /RAM Superconducting 2-millimeter Observer). The arrays are fabricated using batch wafer processing developed and optimized for high pixel yield, low noise, and high uniformity. The molybdenum-gold superconducting transition edge sensors are fabricated using batch sputter deposition and are patterned using dry etch techniques developed at Goddard. With a detector pitch of 2 mm 8x16 array for GISMO occupies nearly one half of the processing area of a 100 mm silicon-on-insulator starting wafer. Two such arrays are produced from a single wafer along with witness samples for process characterization. To provide thermal isolation for the detector elements, at the end of the process over 90% of the silicon must be removed using deep reactive ion etching techniques. The electrical connections for each bolometer element are patterned on the top edge of the square grid supporting the array. The design considerations unique to GISMO, key fabrication challenges, and laboratory experimental results will be presented.

Allen, Christine↗