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Roll soldering from continuous string of cells. Automatic, continuous process attaches interconnecting strips to series string of silicon solar cells. Manufacturing process attaches each conductor from positive side of one cell to negative side of next. For reliability, 22 contacts are soldered on each side of each cell.
Recent developments in gas foil bearing technology have led to numerous advanced high-speed rotating system concepts, many of which have become either commercial products or experimental test articles. Examples include oil-free microturbines, motors, generators and turbochargers. The driving forces for integrating gas foil bearings into these high-speed systems are the benefits promised by removing the oil lubrication system. Elimination of the oil system leads to reduced emissions, increased reliability, and decreased maintenance costs. Another benefit is reduced power plant weight. For rotorcraft applications, this would be a major advantage, as every pound removed from the propulsion system results in a payload benefit.. Implementing foil gas bearings throughout a rotorcraft gas turbine engine is an important long-term goal that requires overcoming numerous technological hurdles. Adequate thrust bearing load capacity and potentially large gearbox applied radial loads are among them. However, by replacing the turbine end, or hot section, rolling element bearing with a gas foil bearing many of the above benefits can be realized. To this end, engine manufacturers are beginning to explore the possibilities of hot section gas foil bearings in propulsion engines. This overview presents a logical follow-on activity by analyzing a conceptual rotorcraft engine to determine the feasibility of a foil bearing supported core. Using a combination of rotordynamic analyses and a load capacity model, it is shown to be reasonable to consider a gas foil bearing core section. In addition, system level foil bearing testing capabilities at NASA Glenn Research Center are presented along with analysis work being conducted under NRA Cooperative Agreements.
Recent developments in gas foil bearing technology have led to numerous advanced high-speed rotating system concepts, many of which have become either commercial products or experimental test articles. Examples include Oil-Free microturbines, motors, generators and turbochargers. The driving forces for integrating gas foil bearings into these high-speed systems are the benefits promised by removing the oil lubrication system. Elimination of the oil system leads to reduced emissions, increased reliability, and decreased maintenance costs. Another benefit is reduced power plant weight. For rotorcraft applications, this would be a major advantage, as every pound removed from the propulsion system results in a payload benefit. Implementing foil gas bearings throughout a rotorcraft gas turbine engine is an important long-term goal that requires overcoming numerous technological hurdles. Adequate thrust bearing load capacity and potentially large gearbox applied radial loads are among them. However, by replacing the turbine end, or hot section, rolling element bearing with a gas foil bearing many of the above benefits can be realized. To this end, engine manufacturers are beginning to explore the possibilities of hot section gas foil bearings in propulsion engines. This paper presents a logical follow-on activity by analyzing a conceptual rotorcraft engine to determine the feasibility of a foil bearing supported core. Using a combination of rotordynamic analyses and a load capacity model, it is shown to be reasonable to consider a gas foil bearing core section.
High hardness, high carbide powder metallurgy tools steels such as M62 enable the operation of ball bearings at extremely high load and stress levels. Operation under such conditions increases the potential for rolling contact fatigue failure attributed to ceramic particle inclusions. To address this challenge, industry has sought steel made from ever increasing levels of cleanliness but the results have been uneven owing to the random nature of the occurrence of material flaws. One common approach is to rely upon careful ingot inspections prior to bearing manufacture. By selecting the cleanest portion of an ingot, it is expected that bearings relatively free from material flaws will result. This approach is not always successful because detrimental flaws that exist deep within an ingot can pass inspection undetected potentially causing subsequent failure. Recent efforts to commercialize an intermetallic material, 60NiTi, for rolling element bearings demonstrates a pathway to produce bearing steel that is free from unwanted ceramic particle inclusions. In this paper, the process used to make bearing grade ceramic-free NiTi alloys is described and applied to steelmaking. At its core, the NiTi process differs from steel making in one key aspect. NiTi alloys are made from elementally pure starting materials that are melted, blended and processed in equipment absolutely free from exposure to oxygen and ceramics ensuring a ceramic particle-free product. In contrast, the predominant method to make bearing steel is to employ a successive series of purification steps to reduce contamination levels below required thresholds. This paper describes the processes developed and applied to high carbide tool steel, M62. The resulting material and microstructures are evaluated and compared to M62 prepared by conventional powder metallurgy techniques. It is hoped that the application of materials manufacturing techniques used for fracture sensitive ceramics and intermetallic materials like NiTi can provide a pathway to Ultra-Clean, Ceramic-Inclusion free steels for rolling element bearings and other failure critical applications.
GRCop-84 is a copper-chromium-niobium alloy developed by the Glenn Research Center for liquid rocket engine combustion chamber liners. GRCop-84 exhibits superior properties over conventional copper-base alloys in a liquid hydrogen-oxygen operating environment. The Next Generation Launch Technology program has funded a program to demonstrate scale-up production capabilities of GR-Cop 84 to levels suitable for main combustion chamber production for the prototype rocket engine. This paper describes a novel method of manufacturing the main combustion chamber liner. The process consists of several steps: extrude the GR-Cop 84 powder into billets, roll the billets into plates, bump form the plates into cylinder halves and friction stir weld the halves into a cylinder. The cylinder is then metal spun formed to near net liner dimensions followed by finish machining to the final configuration. This paper describes the friction stir weld process development including tooling and non-destructive inspection techniques, culminating in the successful production of a liner preform completed through spin forming.
Under the Intelligent Robotics System Study (IRSS) contract, a generalized robotic control architecture was developed for use with the ProtoFlight Manipulator Arm (PFMA). The controller built for the PFMA provides localized position based force control, teleoperation and advanced path recording and playback capabilities. Various hand controllers can be used with the system in conjunction with a synthetic time delay capability to provide a realistic test bed for typical satellite servicing tasks. The configuration of the IRSS system is illustrated and discussed. The PFMA has six computer controllable degrees of freedom (DOF) plus a seventh manually indexable DOF, making the manipulator a pseudo 7 DOF mechanism. Because the PFMA was not developed to operate in a gravity field, but rather in space, it is counter balanced at the shoulder, elbow and wrist and a spring counterbalance has been added near the wrist to provide additional support. Built with long slender intra-joint linkages, the PFMA has a workspace nearly 2 meters deep and possesses sufficient dexterity to perform numerous satellite servicing tasks. The manipulator is arranged in a shoulder-yaw, pitch, elbow-pitch, and wrist-pitch, yaw, roll configuration, with an indexable shoulder roll joint. Digital control of the PFMA is implemented using a variety of single board computers developed by Heurikon Corporation and other manufacturers. The IRSS controller is designed to be a multi-rate, multi-tasking system. Independent joint servos run at a 134 Hz rate and position based impedance control functions at 67 Hz. Autonomous path generation and hand controller inputs are processed at a 33 Hz.
The possibility of nanolithography of silicon and germanium surfaces with bare carbon nanotube tips of scanning probe microscopy devices is considered with large scale classical molecular dynamics (MD) simulations employing Tersoff's reactive many-body potential for heteroatomic C/Si/Ge system. Lithography plays a key role in semiconductor manufacturing, and it is expected that future molecular and quantum electronic devices will be fabricated with nanolithographic and nanodeposition techniques. Carbon nanotubes, rolled up sheets of graphene made of carbon, are excellent candidates for use in nanolithography because they are extremely strong along axial direction and yet extremely elastic along radial direction. In the simulations, the interaction of a carbon nanotube tip with silicon surfaces is explored in two regimes. In the first scenario, the nanotubes barely touch the surface, while in the second they are pushed into the surface to make "nano holes". The first - gentle scenario mimics the nanotube-surface chemical reaction induced by the vertical mechanical manipulation of the nanotube. The second -digging - scenario intends to study the indentation profiles. The following results are reported in the two cases. In the first regime, depending on the surface impact site, two major outcomes outcomes are the selective removal of either a single surface atom or a surface dimer off the silicon surface. In the second regime, the indentation of a silicon substrate by the nanotube is observed. Upon the nanotube withdrawal, several surface silicon atoms are adsorbed at the tip of the nanotube causing significant rearrangements of atoms comprising the surface layer of the silicon substrate. The results are explained in terms of relative strength of C-C, C-Si, and Si-Si bonds. The proposed method is very robust and does not require applied voltage between the nanotube tips and the surface. The implications of the reported controllable etching and hole-creating for nanolithography on silicon are discussed in detail.
Phase II Objectives: Optimize Mega-ROSA/ROSA solar array materials and structures; Characterize creep/relaxation phenomena; Perform analytical modeling; Optimize the array's manufacturing process
Micromechanics-based modeling of composite material behaviors requires an accurate assessment of the constituent properties and behaviors. For the specific case of continuous-fiber-reinforced metal matrix composites (MMC's) manufactured from a foil/fiber/foil process, much emphasis has been placed on characterizing foil-based matrix materials that have been fabricated in the same way as the composite. Such materials are believed to yield mechanical properties and behaviors that are representative of the matrix constituent within the composite (in situ matrix). Therefore, these materials are desired for micromechanics modeling input. Unfortunately, such foils are extremely expensive to fabricate and procure because of the labor-intensive rolling process needed to produce them. As a potential solution to this problem that would maintain appropriately representative in situ properties, the matrix constituent could be characterized with sheet-based materials, which are considerably less expensive to manufacture than foils, are more readily procured, and result in fewer plies to obtain a desired panel thickness. The critical question is, however, does the consolidated sheet material exhibit the same properties and behaviors as do the consolidated foils? Researchers at NASA Lewis Research Center's Life Prediction Branch completed a detailed experimental investigation to answer this question for three titanium alloys commonly used in metal matrix composite form.
Conductive polymer aluminum capacitor (PA capacitor) is an evolution of traditional wet electrolyte aluminum capacitors by replacing liquid electrolyte with a solid, highly conductive polymer. On the other hand, the cathode construction in polymer aluminum capacitors with coating of carbon and silver epoxy for terminal connection is more like a combination of the technique that solid tantalum capacitor utilizes. This evolution and combination result in the development of several competing capacitor construction technologies in manufacturing polymer aluminum capacitors. The driving force of this research on characterization of polymer aluminum capacitors is the rapid progress in IC technology. With the microprocessor speeds exceeding a gigahertz and CPU current demands of 80 amps and more, the demand for capacitors with higher peak current and faster repetition rates bring conducting polymer capacitors to the center o( focus. This is because this type of capacitors has been known for its ultra-low ESR and high capacitance. Polymer aluminum capacitors from several manufacturers with various combinations of capacitance, rated voltage, and ESR values were obtained and tested. The construction analysis of the capacitors revealed three different constructions: conventional rolled foil, the multilayer stacking V-shape, and a dual-layer sandwich structure. The capacitor structure and its impact on the electrical characteristics has been revealed and evaluated. A destructive test with massive current over stress to fail the polymer aluminum capacitors reveals that all polymer aluminum capacitors failed in a benign mode without ignition, combustion, or any other catastrophic failures. The extraordinary low ESR (as low as 3 mOMEGA), superior frequency independence reported for polymer aluminum capacitors have been confirmed. For the applications of polymer aluminum capacitors in space programs, a thermal vacuum cycle test was performed. The results, as expected, show no impact on the electrical characteristics of the capacitors. The breakdown voltage of polymer capacitors has been evaluated using a steady step surge test. Initial results show the uniform distribution in the breakdown voltage for polymer aluminum capacitors. Polymer aluminum capacitors with a combination of very high capacitance, extraordinary low ESR, excellent frequency stability, and non-ignite benign failure mode make it a niche fit in space applications for both today and future. Polymer capacitors are apparently also the best substitutes of the currently used MnO2-based tantalum capacitors in the low voltage range. However, some critical aspects are still to be addressed in the next phase of the investigation for PA capacitors. These include the long term reliability test of 125 C dry life and 85 C/85%RH humidity, the failure mechanism and de-rating, the radiation tolerance, and the high temperature performance. All of the above requires the continuous NEPP funding and support.
Production and support equipment specifications are described for the space manufacturing facility (SMF). Defined production equipment includes electromagnetic pumps for liquid metal, metal alloying furnaces, die casters, electron beam welders and cutters, glass forming for structural elements, and rolling. A cost analysis is presented which includes the development, the aquisition of all SMF elements, initial operating cost, maintenance and logistics cost, cost of terrestrial materials, and transportation cost for each major element. Computer program listings and outputs are appended.
Failure of Stirling Space Power Demonstrator Engine (SPDE) regenerator screens was investigated. After several hours of operation the SPDE was shut down for inspection and on removing the regenerator screens, debris of unknown origin was discovered along with considerable cracking of the screens in localized areas. Metallurgical analysis of the debris determined it to be cracked-off-deformed pieces of the 41 micron thickness Type 304 stainless steel wire screen. Scanning electron microscopy of the cracked screens revealed failures occurring at wire crossovers and fatigue striations on the fracture surface of the wires. Thus, the screen failure can be characterized as a fatigue failure of the wires. The crossovers were determined to contain a 30 percent reduction in wire thickness and a highly worked microstructure occurring from the manufacturing process of the wire screens. Later it was found that reduction in wire thickness occurred because the screen fabricator had subjected it to a light cold-roll process after weaving. Installation of this screen left a clearance in the regenerator allowing the screens to move. The combined effects of the reduction in wire thickness, stress concentration (caused by screen movement), and highly worked microstructure at the wire crossovers led to the fatigue failure of the screens.
Failure of Stirling Space Power Demonstrator Engine (SPDE) regenerator screens was investigated. After several hours of operation the SPDE was shut down for inspection and on removing the regenator screens, debris of unknown origin was discovered along with considerable cracking of the screens in localized areas. Metallurgical analysis of the debris determined it to be cracked-off-deformed pieces of the 41 micron thickness Type 304 stainless steel wire screen. Scanning electron microscopy of the cracked screens revealed failures occurring at wire crossovers and fatigue striations on the fracture surface of the wires. Thus, the screen failure can be characterized as a fatigue failure of the wires. The crossovers were determined to contain 30 percent reduction in wire thickness and a highly worked microstructure occurring from the manufacturing process of the wire screens. Later it was found that reduction in wire thickness occurred because the screen fabricator had subjected it to a light cold-roll process after weaving. Installation of this screen left a clearance in the regenerator allowing the screens to move. The combined effects of the reduction in wire thickness, stress concentration (caused by screen movement), and highly worked microstructure at the wire crossovers led to the fatigue failure of the screens.
Some of the specialty fasteners which are enjoying increasing usage are: thread rolling screws, self drilling and tapping screws, locking screws, tamperproof fasteners, and flanged bolts and nuts. The development of an optimum metric fastener system is recommended for future fastener manufacturing.
Tensile data were obtained from four different types of rhenium at ambient and elevated temperatures. The four types of rhenium included chemical vapor deposition (CVD) and three powder metallurgy (PM) types, i.e., rolled sheet and pressed and sintered bars, with and without hot isostatic pressure (HIP) treatment. Results revealed a wide range of values with ultimate strengths at ambient temperatures varying from 663 MPa for CVD rhenium to 943 MPa for rolled sheet. A similar spread was also obtained for material tested at 1088 K and 1644 K. The wide variance observed with the different materials indicated that the rhenium manufacturing process, material composition and prior handling strongly dictated its properties. In addition to tensile properties, CVD, pressed and sintered material and HIP rhenium successfully completed 100 cycles of low cycle fatigue. Creep data were also obtained showing that CVD and pressed and sintered rhenium could sustain five hours of testing under a tension of 27.5 MPa at 1922 K.
A set of energy conservation actions that cut across all sectors of the economy were analyzed so that all actions under consideration be analyzed systematically and as a whole. The actions considered were as follows: (1) roll back the price of newly discovered oil, (2) freeze gasoline production for 3 years at 1972 levels, (3) mandate automobile mileage improvements, (4) require industry to improve energy efficiency, (5) require manufacture of household appliances with greater efficiency, (6) force conversion of many power plants from gas and oil to coal. The results showed that considerable gas and oil would be saved by forcing switches to coal. However, the large scale switch to coal was shown to require greatly increased outputs from many other industries that in turn require more energy. It was estimated that nearly 2.5 quads of additional coal were needed to produce these additional requirements. Also, the indirect requirements would create more jobs.
The bearings used in the space shuttle main engine (SSME) high pressure oxidizer turbopump (HPOTP) do not meet the expected life goals that were set for them. In an effort to improve their performance, many solutions are being studied. New bearing materials are being developed, better manufacturing techniques are being investigated, and improved cage materials for better lubrication are being tested. The focus is on the replacement of steel balls with ones made of silicon nitride in 57-mm HPOTP bearings. The bearings were then installed in a test rig and run at near turbopump operating conditions. The results from this test series are encouraging, with silicon nitride showing good wear resistance and thermal stability.
America has begun the development of a new heavy lift rocket which will enable humans to return to the moon and reach even farther destinations. Five decades ago, the National Aeronautics and Space Administration designed a system (called Saturn/Apollo) to carry men to the moon and back; the rocket which boosted them to the moon was the Saturn V. Saturn V was huge relative to contemporary rockets and is still the largest rocket ever launched. The new moon rocket is called Ares V. It will insert 40% more payload into low earth orbit than Saturn V; and after docking with the crew spacecraft, it will insert 50% more payload onto the translunar trajectory than Saturn V. The current design of Ares V calls for two liquid-fueled stages and 2 "strap-on" solid rockets. The solid rockets are extended-length versions of the solid rockets used on the Shuttle. The diameter of the liquid stages is at least as large as the first stage of the Saturn V; the height of the lower liquid stage (called the core stage) is longer than the external tank of the Shuttle. Huge rockets require huge infrastructure and, during the Saturn/Apollo era, America invested significantly in manufacturing, assembly and launch facilities which are still in use today. Since the Saturn/Apollo era, America has invested in additional infrastructure for the Shuttle program. Ares V must utilize this existing infrastructure, with reasonable modifications. Building a rocket with 50% more capability in the same buildings, testing it in the same test stands, shipping on the same canals under the same bridges, assembling it in the same building, rolling it to the pad on the same crawler, and launching it from the same launch pad is an engineering and logistics challenge which goes hand-in-hand with designing the structure, tanks, turbines, engines, software, etc. necessary to carry such a large payload to earth orbit and to the moon. This paper quantitatively discusses the significant "tight fits" that are constraining Ares V. The engineers designing and building the infrastructure for the Saturn/Apollo program usually added margins and growth capability; sometimes the size of existing facilities (such as the width of a draw bridge) was not a constraint. Ares V may utilize the "extra" space in the existing facilities and expand other tight fits. Some of the tight fits cannot be overcome without great expense; raising the roof on the Vertical Assembly Building for example. Other tight fits are easily overcome; the transporter at the manufacturing facility for the core stage can pass under low ceilings and later over a dike (without dragging the middle) by retracting or extending the struts which support the stage. Tight fits discussed in this paper include manufacturing (jigs, widths, heights, and local transportation), testing (test stand sizes and crane capability), transportation to the test stands and the launch site (barge, waterway, and rail), assembly (VAB internal dimensions and door size), roll-out limits, and launch pad size.