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Efficient method electroforms fine-mesh nickel screens, or plagues, with uniform hole size and accurate spacing between holes. An electroformed nickel mandrel has nonconducting silicone rubber projections that duplicate the desired hole size and shape in the finished nickel screen.
The NASA Large Civil Tiltrotor (2nd generation, or LCTR2) is a useful reference design for technology impact studies. The present paper takes a broad view of technology assessment by examining the extremes of what aerodynamic improvements might hope to accomplish. Performance was analyzed with aerodynamically idealized rotor, wing, and airframe, representing the physical limits of a large tiltrotor. The analysis was repeated with more realistic assumptions, which revealed that increased maximum rotor lift capability is potentially more effective in improving overall vehicle efficiency than higher rotor or wing efficiency. To balance these purely theoretical studies, some practical limitations on airframe layout are also discussed, along with their implications for wing design. Performance of a less efficient but more practical aircraft with non-tilting nacelles is presented.
The NASA Large Civil Tiltrotor (2nd generation, or LCTR2) has been the reference design for avariety of NASA studies of design optimization, engine and gearbox technology, handling qualities, andother areas, with contributions from NASA Ames, Glenn and Langley Centers, plus academic and industrystudies. Ongoing work includes airfoil design, 3D blade optimization, engine technology studies, andwingrotor aerodynamic interference. The proposed paper will bring the design up to date with the latestresults of such studies, then explore the limits of what aerodynamic improvements might hope toaccomplish. The purpose is two-fold: 1) determine where future technology studies might have the greatestpayoff, and 2) establish a stronger basis of comparison for studies of other vehicle configurations andmissions.
Acoustic tests of a subscale fan and a subscale mixer nozzle were conducted in anechoic chambers over a variety of operating conditions. The subscale fan test was an investigation into the effects of vane/blade ratio and spacing on fan generated noise. A turbulence control structure (TCS) was used to simulate the 'turbulence-free' condition in flight. The subscale mixer nozzle test investigated the acoustic properties of several different forced mixer designs. A tertiary flow was utilized on the mixer model to simulate the forward velocity effects on the jet. The results were scaled up to full size conditions and compared with measured engine data. The comparisons showed good agreement between the component scaled model results and the full scale engine data.
Improvements were carried out on a TWT (traveling wave tube) for use in EMC (electronic countermeasure) systems by applying MDC (multi-stage depressed collector) and spent-beam refocusing techniques. The MDC geometric design consists of six collecting elements (electrodes) at ground and cathode potentials operating in 2 or 4 stage configuration. The refocusing system designed allows a controlled beam expansion to the point that space charge becomes negligible at the MDC entrance. Simultaneously, the standard deviation of the radial velocity (angular spread) is reduced. This system provides an analog real time readout of P(recovered). Data on all tests is obtained with an automated data acquisition system.
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Preliminary design studies were performed on four continuously variable transmission (CVT) concepts for use with a flywheel equipped electric vehicle of 1700 kg gross weight. Requirements of the CVT's were a maximum torque of 450 N-m (330 lb-ft), a maximum output power of 75 kW (100 hp), and a flywheel speed range of 28,000 to 14,000 rpm. Efficiency, size, weight, cost, reliability, maintainability, and controls were evaluated for each of the four concepts which included a steel V-belt type, a flat rubber belt type, a toroidal traction type, and a cone roller traction type. All CVT's exhibited relatively high calculated efficiencies (68 percent to 97 percent) over a broad range of vehicle operating conditions. Estimated weight and size of these transmissions were comparable to or less than equivalent automatic transmission. The design of each concept was carried through the design layout stage.
The Laboratory for Oceans is currently working on the development of compact laser diode array (LD) pumped Nd:YAG lasers for use in space-based altimetry and ranging. Laser diode-array pumping technology promises to increase the electrical to optical efficiency of solid state lasers by an order of magnitude with a lifetime increase of nearly three orders of magnitude relative to today's conventional flashlamp-pumped laser systems. The small size, efficiency, and ruggedness make LD-pumped solid state lasers ideal for space based applications. In an in-house RTOP effort, a novel multiple-pass LD-pumped Nd:YAG laser amplifier was designed and tested to increase the 100 microjoule output pulse energy of the Lightwave laser oscillator. Preliminary results have yielded a round trip amplifier gain of about 15 percent using 7 microjoule LD-pump energy. As a parallel activity, funding was recently obtained to investigate the possible use of custom made fiber optic arrays to obtain an efficient optical coupling mechanism between the emitting laser diode-arrays and the target solid state laser material. Fiber optic coupling arrays would allow for the easy manipulation of the spatial emitting pattern of the diode pump sources to match either an end or side pumping laser configuration.
Thulium doped pulsed fiber lasers are capable of meeting the spectral, temporal, efficiency, size and weight demands of defense and civil applications for pulsed lasers in the eye-safe spectral regime due to inherent mechanical stability, compact "all-fiber" master oscillator power amplifier (MOPA) architectures, high beam quality and efficiency. Thulium fiber's longer operating wavelength allows use of larger fiber cores without compromising beam quality, increasing potential single aperture pulse energies. Applications of these lasers include eye-safe laser ranging, frequency conversion to longer or shorter wavelengths for IR countermeasures and sensing applications with otherwise tough to achieve wavelengths and detection of atmospheric species including CO2 and water vapor. Performance of a portable thulium fiber laser system developed for CO2 sensing via a broadband lidar technique with an etalon based sensor will be discussed. The fielded laser operates with approximately 280 J pulse energy in 90-150ns pulses over a tunable 110nm spectral range and has a uniquely tailored broadband spectral output allowing the sensing of multiple CO2 lines simultaneously, simplifying future potentially space based CO2 sensing instruments by reducing the number and complexity of lasers required to carry out high precision sensing missions. Power scaling and future "all fiber" system configurations for a number of ranging, sensing, countermeasures and other yet to be defined applications by use of flexible spectral and temporal performance master oscillators will be discussed. The compact, low mass, robust, efficient and readily power scalable nature of "all-fiber" thulium lasers makes them ideal candidates for use in future space based sensing applications.
Portable life support systems in future space suits will include a ventilation subsystem driven by a dedicated fan. This ventilation fan must meet challenging requirements for pressure rise, flow rate, efficiency, size, safety, and reliability. This paper describes research and development that showed the feasibility of a regenerative blower that is uniquely suited to meet these requirements. We proved feasibility through component tests, blower tests, and design analysis. Based on the requirements for the Constellation Space Suit ventilation fan, we designed the critical elements of the blower. We measured the effects of key design parameters on blower performance using separate effects tests, and used the results of these tests to design a regenerative blower that will meet the ventilation fan requirements. We assembled a proof-of-concept blower and measured its performance at low pressures that simulate a PLSS environment. We obtained head/flow performance curves over a range of operating speeds, identified the maximum efficiency point for the blower, and used these results to specify the design and operating conditions for the ventilation fan. We designed a compact motor that can drive the blower under all anticipated operating requirements and operate with high efficiency during normal operation. We identified materials for the blower that will enhance safety for operation in a lunar environment. We produced a solid model that illustrates the final design. The proof-of-concept blower produced the flow rate and pressure rise needed for the CSSS ventilation subsystem while running at 5400 rpm and consuming only 9 W of electric power and using a non-optimized, commercial motor and controller and inefficient bearings. Scaling the test results to a complete design shows that a lightweight, compact, reliable, and low power blower can meet the performance requirements for future PLSSs.
Portable life support systems in future space suits will include a ventilation subsystem driven by a dedicated fan. This ventilation fan must meet challenging requirements for pressure rise, flow rate, efficiency, size, safety, and reliability. This paper describes research and development that showed the feasibility of a regenerative blower that is uniquely suited to meet these requirements. We proved feasibility through component tests, blower tests, and design analysis. Based on the requirements for the Constellation Space Suit Element (CSSE) Portable Life Support System (PLSS) ventilation fan, we designed the critical elements of the blower. We measured the effects of key design parameters on blower performance using separate effects tests, and used the results of these tests to design a regenerative blower that will meet the ventilation fan requirements. We assembled a proof-of-concept blower and measured its performance at sub-atmospheric pressures that simulate a PLSS ventilation loop environment. Head/flow performance and maximum efficiency point data were used to specify the design and operating conditions for the ventilation fan. We identified materials for the blower that will enhance safety for operation in a lunar environment, and produced a solid model that illustrates the final design. The proof-of-concept blower produced the flow rate and pressure rise needed for the CSSE ventilation subsystem while running at 5400 rpm, consuming only 9 W of electric power using a non-optimized, commercial motor and controller and inefficient bearings. Scaling the test results to a complete design shows that a lightweight, compact, reliable, and low power regenerative blower can meet the performance requirements for future space suit life support systems.
The rheological properties of the fluid under these certain conditions which precludes the use of most of the conventional instruments for steady state measurement were studied. The only suitable type of instrument is a disk machine where most of the conditions are the same of similar to those in traction drives. From the resulting traction tests, certain models are inferred. To the designer of traction drives, the traction behavior of the fluid under the severe conditions is of utmost importance because of the direct influence that it has on the efficiency, size, and life of a given drive.
For several years, active magnetic bearings (AMB) have demonstrated their capabilities in many fields, from industrial compressors to control wheel suspension for spacecraft. Despite this broad area, no significant advance has been observed in rocket propulsion turbomachinery, where size, efficiency, and cost are crucial design criteria. To this respect, Societe Europeenne de Propulsion (SEP) had funded for several years significant efforts to delineate the advantages and drawbacks of AMB applied to rocket propulsion systems. Objectives of this work, relative technological basis, and improvements are described and illustrated by advanced turbopump layouts. Profiting from the advantages of compact design in cryogenic environments, the designs show considerable improvements in engine life, performances, and reliability. However, these conclusions should still be tempered by high recurrent costs, mainly due to the space-rated electronics. Development work focused on this point and evolution of electronics show the possibility to decrease production costs by an order of magnitude.
An investigation of the deformation and buckling characteristics of a composite, oblate bulkhead that has an inverted geometry and is subjected to pressure-only loading is presented for three bulkhead geometries and thicknesses. The effects of a stiffening support ring at the bulkhead to cylinder interface are also evaluated. Buckling analyses conducted using the axisymmetric shell code BOSOR4 are discussed for several bulkhead configurations. These results are analytically verified using results from the Structural Analysis of General Shells (STAGS) code for a selected bulkhead configuration. The buckling characterization of an inverted, oblate bulkhead requires careful attention as small changes in bulkhead parameters can have a significant effect on the critical buckling load. Comparison of BOSOR4 and STAGS results provided a very good correlation between the two analysis methods. In addition, the analysis code BOSOR4 was found to be an efficient sizing tool that is useful during the preliminary design stage of a practical shell structure. Together, these two aspects should give the design engineer confidence in sizing these stability critical structures. Additional characterization is warranted, especially for a composite tank structure, since only one bulkhead configuration was examined closely.
Scientists have long been able to shift the direction of a laser beam, steering it toward a target, but often the strength and focus of the light is altered. For precision applications, where the quality of the beam cannot be compromised, scientists have typically turned to mechanical steering methods, redirecting the source of the beam by swinging the entire laser apparatus toward the target. Just as the mechanical methods used for turning cars has evolved into simpler, lighter, power steering methods, so has the means by which researchers can direct lasers. Some of the typical contraptions used to redirect lasers are large and bulky, relying on steering gimbals pivoted, rotating supports to shift the device toward its intended target. These devices, some as large and awkward as a piece of heavy luggage, are subject to the same issues confronted by mechanical parts: Components rub, wear out, and get stuck. The poor reliability and bulk not to mention the power requirements to run one of the machines have made mechanical beam steering components less than ideal for use in applications where weight, bulk, and maneuverability are prime concerns, such as on an unmanned aerial vehicle (UAV) or a microscope. The solution to developing reliable, lighter weight, nonmechanical steering methods to replace the hefty steering boxes was to think outside the box, and a NASA research partner did just that by developing a new beam steering method that bends and redirects the beam, as opposed to shifting the entire apparatus. The benefits include lower power requirements, a smaller footprint, reduced weight, and better control and flexibility in steering capabilities. Such benefits are realized without sacrificing aperture size, efficiency, or scanning range, and can be applied to myriad uses: propulsion systems, structures, radiation protection systems, and landing systems.
This paper studies the role of power extraction in gas turbine stability and how an engine may be designed to utilize this extraction to replace engine stability bleed requirements with electrical system requirements. The considered engine architecture contains two engine spools and a power turbine spool. In the baseline, low-pressure compressor stall margin is maintained by bleed air from the back of the low-pressure compressor, which is then dumped to the bypass. Power extraction from the high-pressure and low-pressure shafts are then utilized as a replacement for this bleed. This study considers component performance, sizing, efficiency, and operability, but does not consider weight or cost. Analysis within this paper is general and the concepts could be applied to other dual spool engine types, including a turbofan. Results show it is possible to completely remove the stability bleed between the low pressure and high-pressure compressor by utilizing a 35% power extraction from the high-pressure shaft or a 1.5% power extraction from the low-pressure turbine.
This paper studies the role of power extraction in gas turbine stability and how an engine may be designed to utilize this extraction to replace engine stability bleed requirements with electrical system requirements. The considered engine architecture contains two engine spools and a power turbine spool. In the baseline, low-pressure compressor stall margin is maintained by bleed air from the back of the low-pressure compressor, which is then dumped to the bypass. Power extraction from the high-pressure and low-pressure shafts are then utilized as a replacement for this bleed. This study considers component performance, sizing, efficiency, and operability, but does not consider weight or cost. Analysis within this paper is general and the concepts could be applied to other dual spool engine types, including a turbofan. Results show it is possible to completely remove the stability bleed between the low pressure and high-pressure compressor by utilizing a 35% power extraction from the high-pressure shaft or a 1.5% power extraction from the low-pressure turbine.
The impact of gas phase radiation scattering by dust particle presence in Mars entry scenarios is assessed using a suite of numerical tools. A hypersonic gas and dilute particle multiphase flow is simulated using a mixed continuum model and an efficient size distribution quadrature scheme. Radiative transport is simulated with a hybrid ray-tracing and P1 spherical harmonics model. The NASA HARA radiation code and a Lorentz-Mie scattering model are used to predict the gas-particle mixture radiative properties. Application of the numerical suite to a representative case based on the Mars 2020 entry shows that, even at conditions in excess of the strongest recorded dust storm, the augmentation in surface radiative heat flux due to scattering alone is lower than 1%, and therefore negligible. Predictions with even higher dust loading conditions confirm that even highly uncertain dust mass profiles are unlikely to be a concern for the scattering augmentation mechanism.