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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 361 records · Page 20

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NASA NTRS1994

The 7.5K lbf thrust engine preliminary design for Orbit Transfer Vehicle

This document summarizes the preliminary design of the Aerojet version of the Orbit Transfer Vehicle main engine. The concept of a 7500 lbf thrust LO2/GH2 engine using the dual expander cycle for optimum efficiency is validated through power balance and thermal calculations. The engine is capable of 10:1 throttling from a nominal 2000 psia to a 200 psia chamber pressure. Reservations are detailed on the feasibility of a tank head start, but the design incorporates low speed turbopumps to mitigate the problem. The mechanically separate high speed turbopumps use hydrostatic bearings to meet engine life requirements, and operate at sub-critical speed for better throttling ability. All components were successfully packaged in the restricted envelope set by the clearances for the extendible/retractable nozzle. Gimbal design uses an innovative primary and engine out gimbal system to meet the +/- 20 deg gimbal requirement. The hydrogen regenerator and LOX/GH2 heat exchanger uses the Aerojet platelet structures approach for a highly compact component design. The extendible/retractable nozzle assembly uses an electric motor driven jack-screw design and a one segment carbon-carbon or silicide coated columbium nozzle with an area ratio, when extended, of 1430:1. A reliability analysis and risk assessment concludes the report.

Hayden, Warren R.↗

NASA NTRS1993

Design and control of a hand exoskeleton for use in extravehicular activities

To counter problems inherent in extravehicular activities (EVA) and complex space operations, an exoskeleton, a unique adaptive structure, has been designed. The exoskeleton fits on the hand and powers the proximal and middle phalanges of the index finger, the middle finger, and the combined ring and little finger. A kinematic analysis of the exoskeleton joints was performed using the loop-closure method. This analysis determined the angular displacement and velocity relationships of the exoskeleton joints. This information was used to determine the output power of the exoskeleton. Three small DC motors (one for each finger) are used to power the exoskeleton. The motors are mounted on the forearm. Power is transferred to the exoskeleton using lead screws. The control system for the exoskeleton measures the contact force between the operator and the exoskeleton. This information is used as the input to drive the actuation system. The control system allows the motor to rotate in both directions so that the operator may close or open the exoskeleton.

Shields, B.↗

NASA NTRS1991

A physical control interface with proprioceptive feedback and multiple degrees of freedom

The use of the drug thalidomide by pregnant mothers in Britain resulted in a variety of deformities including the birth of children having no arms. Such children were provided with powered artificial arms with up to five degrees of freedom simultaneously controlled in real time by shoulder movement. The physiological sense of proprioception was extended from the user into the device, reducing the need for visual feedback and conscious control. With the banning of thalidomide, this technique fell into disuse but it is now being re-examined as a control mechanism for other artificial limbs and it may have other medical applications to allow patients to control formerly paralyzed limbs moved by electrical stimulation. It may also have commercial applications in robotic manipulation or physical interaction with virtual environments. To allow it to be investigated further, the original pneumatic control system has recently been converted to an electrical analogue to allow interfacing to electronic and computer-assisted systems. A harness incorporates force-sensitive resistors and linear potentiomenters for sensing position and force at the interface with the skin, and miniature electric motors and lead screws for feeding back to the user the position of the robotic arm and the forces applied to it. In the present system, control is applied to four degrees of freedom using elevation/depression and protraction/reaction of each shoulder so that each collar bone emulates a joystick. However, both electrical and mechanical components have been built in modular form to allow rapid replication and testing of a variety of force and position control strategies.

Creasey, G. H.↗

NASA NTRS1993

The use of designed experiments in the process development of continuous propellant mixing

A continuous mix pilot plant was constructed at Aerojet Propulsion Division in Sacramento, California to develop a robust propellant mixing process for the full scale plant that was to be built at the NASA Advanced Solid Rocket Motor facility Yellow Creek, Mississippi. The plant was used to conduct dozens of subsystem and full system mixing tests for evaluation of equipment, processing methods, and control schemes for later use at the production plant. As a culmination to this work, a series of designed experiments were conducted using an eight run Taguchi analysis with four factors at two levels each to determine the primary effect of processing parameters on propellant ballistic and mechanical properties. The factors examined in these runs included the propellant production rate (454 (1000) and 622 kg/hr (1371 Ib/hr)), the product temperature out of the mixer (49 (120) and 63 deg C (145 deg F)), mixer screw speed (75 and 90 rpm), and the deaerator excess capacity (20 and 80 percent). Measured response variables included the uncured and cured density, Crawford Bomb liquid strand burning rates, and selected mechanical properties. The experiment revealed that several of the response variables displayed significant changes from run-to-run with the product temperature being the single most important factor. After concluding this experiment, a twenty-six hour confirmation run was conducted to verify the conclusions reached in the designed experiment. The extended run produced over 12,250 kgs (27,000 lbs) of propellant meeting all of the pre-run targeted properties including density (1.803 g/cc (0.065 lb/in(exp 3)) with a 0.12 percent coefficient of variation (CV) at 25 deg C (77 deg F)), liquid strand burn rate (0.889 cm/s (0.350 in/s) with a 0.69 percent CV at 4210 KPa (610 psig), 15.6 deg C (60 deg F)), nominal maximum stress (828 KPa (120 psig) with a 2.84 percent CV, S&E at 25 deg C (77 deg F), 5.08 cm/min (2 in/min)), strain at nominal maximum (47.4 percent with a 3.96 percent CV), and initial tangent modulus (5349 KPa (775 psig) with a 7.26 percent CV).

Campbell, J. A.↗

NASA NTRS1994

Bevel gear driver and method having torque limit selection

This invention comprises a torque drive mechanism utilizing axially translatable, mutually engageable transmission members having mating crown gears, driven and driving members with a three-element drive train being biased together by resilient means or by a fluid actuator system, the apparatus being operable to transmit a precisely controlled degree of torque to a driven member. The apparatus is applicable for use in hand tools and as a replacement for impact torque drivers, torque wrenches, motorized screw drivers, or the like, wherein the applied torque must be precisely controlled or limited. The bevel torque drive includes a drive gear which is axially displaceable and rotatable within cylindrical driver housing, a rotatable intermediate gear, and an output gear. Key rotationally secures displaceable gear with respect to input shaft but permits axial movement therebetween. A thrust bearing is preferably connected to the lower end of shaft for support to reduce play and friction between shaft and a transmission joint disc during rotation of the gear train. Coaxially mounted coiled spring is footed against displaceable gear for biasing the displaceable gear toward and into engagement with the intermediate gear for driving intermediate gear and output gear. Torque control is achieved by the use of straight or spiral beveled gears which are of configurations adapted to withdraw from mutual engagement upon the torque exceeding a predetermined limit. The novel, advantageous features of the invention include the configuration of the mating, crown gear sets and the axially translatable, slidable drive gear. The mechanism is capable of transmitting a high degree of torque within a narrow, compact transmission housing. The compact size and narrow, elongated configuration of the housing is particularly applicable for use in hand tools and in multiple torque driver mechanisms in which it is necessary to drive multiple fasteners which are located in close proximity. Prior torque drivers such as 'click-type' torque wrenches do not actually limit torque application but only provide an audible warning that the limit has been reached.

Cook, Joseph S., Jr.↗

NASA NTRS1994

Displaceable spur gear torque controlled driver and method

Methods and apparatus are provided for a torque driver including a laterally displaceable gear support member to carry an output spur gear. A biasing assembly biases the output spur gear into engagement with a pinion to which is applied an input torque greater than a desired output torque limit for a threaded fastener such as a nut or screw. A coiled output linkage connects the output spur gear with a fastener adaptor which may be a socket for a nut. A gear tooth profile provides a separation force that overcomes the bias to limit torque at the desired torque limit. Multiple fasteners may be rotated simultaneously to a desired torque limit if additional output spur gears are provided. A gauged selector mechanism is provided to laterally displace multiple driver members for fasteners arranged in differing configurations. The torque limit is selectably adjustable and may be different for fasteners within the same fastener configuration.

Cook, Joseph S., Jr.↗

NASA NTRS1995

CAE for thermal management of aerospace electronic boards using the BETAsoft program

Aerospace electronic boards require special attention to thermal management due to constraints such as their need to be light, small, and maintain high power densities. Also, cooling is mainly through conductive and radiative modes with minor or negligible convective cooling. Due to these particular requirements, thermal design has become an integrated part of the electronic design process in order to avoid expensive repeat prototyping and to ensure high reliability. To achieve high speed simulations, the BETAsoft code uses semi-empirical formulations and an advanced finite difference scheme that incorporates local adaptive grids. Detailed conduction, convection and radiation heat transfer is considered. Various benchmark verifications of the software simulation compared to infrared images typically prove to be within 10% of each other. The thermal analysis of a sample avionic card in a natural convection environment is shown. Then, the individual effects of attaching metal screws to the casing, increasing radiative emissivities of the casing, increasing the conductance of the wedge lock, adding an aluminum core to the board, adding metal strips in board layers, inserting conduction pads under components, and adding heat sinks to components are demonstrated.

Bobish, Kimberly↗

NASA NTRS1993

An electrorheologically controlled semi-active landing gear

This study is to explore the application of electrorheology (ER) to the real-time control of damping forces that are transmitted through the nose landing gear for an F-106B aircraft. The main part of the landing gear is a strut that consists of a pneumatic spring and an ER controlled damper that is situatted on the strut centerline and applies a force directly opposing the vertical displacement of the nose wheel. The damping element rotates in response to strut displacement, employing a co-axial arrangement of stator and rotor plates connected to the opposing electrodes in the control circuit. The vertical displacement is conveted into rotation of the damper through a screw-nut mechanism. The ER fluid between the electrodes is thus engaged in shear along circumferential lines of action. This design results in a fast time response and a high ratio of strut forces achieved under Er-vs. zero-field control. Compact size and simplicity in fabrication are also attained. The analysis shows that when using an ER fluid of a yield stress of 7kPa, the energy absorption efficiency of the landing gear can reach almost 100% at various sink rates.

Lou, Zheng↗

NASA NTRS1995

Vapor Degreasing Of A Large Tank

Vapor degreasing procedure provides for removal of relatively non-volatile oils and greases from insides of large vessels. Solvent refluxed to concentrate less volatile contaminants at bottom. Procedure ensures required degrees of cleaniness in high-purity chemical processing and high-vacuum processing vessels. Devised for cleaning complexly-shaped stainless-steel vacuum chamber containing numerous difficult-to-clean features like screw holes and abutting surfaces. Solvent can be chlorofluorocarbon, if means provided to recover most and minimize portion escaping into air. Alternatively, hydrocarbon or other flammable solvent used, provided flammability tolerable in particular application.

Frazer, Robert E.↗

NASA NTRS1995

Compact Microadjusters For Optical Components

Compact microadjusters for fine positioning of optical components designed to fit into small, confined spaces. Used in place of micrometer-style adjusters, most of which are at least one inch (2.54 cm) long and often too big for compact optical setups. Also used in place of other screw adjusters, resolutions of which often not fine enough.

Pfeifer, Nathan R.↗

NASA NTRS1995

Tool For Driving Many Fasteners Simultaneously

Proposed tool tightens or loosens several bolts, screws, nuts, or other threaded fasteners arranged in circle on compressor head, automotive wheel, pipe-end flange, or similar object. Enables assembly or disassembly in fraction of time needed to tighten fasteners one at a time. Simultaneously applies same torque to all fasteners, preventing distortion and enhancing reliability. Concept not limited to circular fastener patterns. Adapted to rectangular configurations like on engine intake manifolds, by adding gears to drive train to provide proper spacing. Designed to deliver fixed or adjustable maximum torque. To ensure even seal loading, piston pressure simultaneously ramped from initial to final values to maintain relatively constant torque loading on all fasteners until final specifications limit achieved.

Cook, Joseph S., Jr.↗

NASA NTRS1995

Adjustable Tool For Driving Multiple Fasteners

Proposed tool tightens or loosens several bolts, screws, nuts, or other threaded fasteners arranged in circle on compressor head, automotive wheel, pipe-end flange, or similar object. Combines some features of related mechanism described in, "Tool for Driving Many Fasteners Simultaneously" (MSC-22386). Unique feature of proposed mechanism; lateral positions of output shafts adjusted, by use of mechanism called "selector," to fit fastener patterns with larger or smaller bolt circles. Concept extended from circular pattern to rectangular pattern for application to automobile headers and intake manifolds.

Cook, Joseph S., Jr.↗

NASA NTRS1995

Tool Indicates Contact Angles In Bearing Raceways

Tool devised for use in measuring contact angles between balls and races in previously operated ball bearings. Used on both inner and outer raceways of bearings having cross-sectional widths between approximately 0.5 and 2.0 in. Consists of integral protractor mounted in vertical plane on bracket equipped with leveling screws and circular level indicator. Protractor includes rotatable indicator needle and set of disks of various sizes to fit various raceway curvatures.

Akian, Richard A.↗

NASA NTRS1996

Apparatus Measures Thicknesses Of Ice On Bars

Semiautomated apparatus measures diameters, at selected lengthwise positions, of nine vertical ice-coated bars in icing-research wind tunnel. Includes measuring head that travels on rails parallel to bar, driven by ball screw actuated by stepping motor. Position of measuring head along bar measured by string potentiometer, providing position feedback for closed-loop control circuit. Circuit provides for smooth motion of measuring head, and used to select various programmed sequences of motions and measurements. Measurements needed to determine degree of uniformity of icing conditions for experiments on aircraft models.

Gibson, Theresa L.↗

NASA NTRS1996

Hole-Aligning Tool

Tool designed for use in aligning holes in plates or other structural members to be joined by bolt through holes. Holes aligned without exerting forces perpendicular to planes of holes. Tool features screw-driven-wedge design similar to (but simpler than) that of some automotive exhaust-pipe-expanding tools.

Collins, Frank A.↗

NASA NTRS1996

Development Of A Magnetic Directional-Solidification Furnace

Report describes development of directional-solidification furnace in which axial magnetic field is imposed by surrounding ring permanent magnets and/or electromagnets and pole pieces. Furnace provides controlled axial temperature gradients in multiple zones, through which ampoule containing sample of material to be solidified is translated at controlled speed by low-vibration, lead-screw, stepping-motor-driven mechanism. Intended for use in low-gravity (spaceflight) experiments on melt growth of high-purity semiconductor crystals.

Aldrich, Bill R.↗

NASA NTRS1996

Propellers And Fans Based On The Moebius Strip

Moebius strip proposed as basis for optimally shaped airplane and boat propellers, fans, helicopter rotors, mixing screws, coffee grinders, and concrete mixers. Basic idea of optimal shaping of such device to increase working efficiency by increasing area for capture of still medium without increasing power needed for rotation.

Seiner, John Milton↗

NASA NTRS1996

Trends and Issues in Fuzzy Control and Neuro-Fuzzy Modeling

Everyday experience in building and repairing things around the home have taught us the importance of using the right tool for the right job. Although we tend to think of a 'job' in broad terms, such as 'build a bookcase,' we understand well that the 'right job' associated with each 'right tool' is typically a narrowly bounded subtask, such as 'tighten the screws.' Unfortunately, we often lose sight of this principle when solving engineering problems; we treat a broadly defined problem, such as controlling or modeling a system, as a narrow one that has a single 'right tool' (e.g., linear analysis, fuzzy logic, neural network). We need to recognize that a typical real-world problem contains a number of different sub-problems, and that a truly optimal solution (the best combination of cost, performance and feature) is obtained by applying the right tool to the right sub-problem. Here I share some of my perspectives on what constitutes the 'right job' for fuzzy control and describe recent advances in neuro-fuzzy modeling to illustrate and to motivate the synergistic use of different tools.

Chiu, Stephen↗