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At least 595 records · Page 33

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NASA NTRS1988

Transform fault earthquakes in the North Atlantic - Source mechanisms and depth of faulting

The centroid depths and source mechanisms of 12 large earthquakes on transform faults of the northern Mid-Atlantic Ridge were determined from an inversion of long-period body waveforms. The earthquakes occurred on the Gibbs, Oceanographer, Hayes, Kane, 15 deg 20 min, and Vema transforms. The depth extent of faulting during each earthquake was estimated from the centroid depth and the fault width. The source mechanisms for all events in this study display the strike slip motion expected for transform fault earthquakes; slip vector azimuths agree to 2 to 3 deg of the local strike of the zone of active faulting. The only anomalies in mechanism were for two earthquakes near the western end of the Vema transform which occurred on significantly nonvertical fault planes. Secondary faulting, occurring either precursory to or near the end of the main episode of strike-slip rupture, was observed for 5 of the 12 earthquakes. For three events the secondary faulting was characterized by reverse motion on fault planes striking oblique to the trend of the transform. In all three cases, the site of secondary reverse faulting is near a compression jog in the current trace of the active transform fault zone. No evidence was found to support the conclusions of Engeln, Wiens, and Stein that oceanic transform faults in general are either hotter than expected from current thermal models or weaker than normal oceanic lithosphere.

Bergman, Eric A.↗

NASA NTRS1988

A review of dynamic mechanical characterization of high temperature PMR polyimides and composites

This paper reviews the applications of dynamic mechanical characterization for high-temperature PMR polyimides and their graphite-fiber-reinforced composites. This characterization technique provides insights into the processability, performance, and structure property relationships of the polyimides and composites. The dynamic mechanical properties of various molding powders, commercially obtained prepregs, neat resins, and as-fabricated as well as aged composites are presented. Some applied aspects of the dynamic mechanical data are discussed.

Pater, Ruth H.↗

NASA NTRS1989

Measuring Mechanical Properties Of Optical Glasses

Report discusses mechanical tests measuring parameters of strength and fracture mechanics of optical glasses. To obtain required tables of mechanical properties of each glass of interest, both initial-strength and delayed-fracture techniques used. Modulus of rupture measured by well-known four-point bending method. Initial bending strength measured by lesser-known double-ring method, in which disk of glass supported on one face near edge by larger ring and pressed on its other face by smaller concentric ring. Method maximizes stress near center, making it more likely specimen fractures there, and thereby suppresses edge effects. Data from tests used to predict reliabilities and lifetimes of glass optical components of several proposed spaceborne instruments.

Tucker, Dennis S.↗

NASA NTRS1989

Cryogenic Shutter Mechanism

Electromagnetic shutter mechanism operates at ambient and cryogenic temperatures to shield optical element, such as mirror, filter, polarizer, beam splitter, or detector, from external light and radiation in cryogenic Dewar equipped with window for optical evaluation. Shutter mechanism in Dewar container alternately shields and exposes optical element as paddle rotates between mechanical stops. Mounted on cold plate of liquid-helium reservoir. Paddle, shaft, and magnet constitutes assembly rotated by electromagnetic field on coil.

Barney, Richard D.↗

NASA NTRS1988

Magnetic attachment mechanism

A magnetic attachment mechanism adapted for interfacing with the manipulator arm of a remote manipulator system and comprising a pair of permanent magnets of rare earth material are arranged in a stator-rotor relationship. The rotor magnet is journalled for rotation about its longitudinal axis between pole plates of the stator magnet, each of which includes an adhering surface. In a first rotary position corresponding to the ON condition, each of the poles of the rotor magnet is closely adjacent to a stator magnet pole plate of like polarity whereby the respective magnet fields are additive for producing a strong magnetic field emanating from the adhering surfaces for attracting a ferrous magnetic plate, or the like, affixed to the payload. When the rotor magnet is rotated to a second position corresponding to the OFF condition, each of the poles of the rotor magnet is disposed closely adjacent to a pole plate of unlike polarity whereby the magnetic fields of the magnets are in cancelling relationship at the adhering surfaces, which permits the release of a payload. An actuator for selectively rotating the rotor magnet between the ON and OFF positions is provided for interfacing and connecting the magnetic attachment mechanism with a manipulator arm. For affecting an optimal rigidized attachment the payload is provided with guide means cooperable with guide means on the housing of the mechanism for directing adhering surfaces of the polar plates to the ferrous plate.

Wu, Mitchell B.↗

NASA NTRS1988

Strategies for adding adaptive learning mechanisms to rule-based diagnostic expert systems

Rule-based diagnostic expert systems can be used to perform many of the diagnostic chores necessary in today's complex space systems. These expert systems typically take a set of symptoms as input and produce diagnostic advice as output. The primary objective of such expert systems is to provide accurate and comprehensive advice which can be used to help return the space system in question to nominal operation. The development and maintenance of diagnostic expert systems is time and labor intensive since the services of both knowledge engineer(s) and domain expert(s) are required. The use of adaptive learning mechanisms to increment evaluate and refine rules promises to reduce both time and labor costs associated with such systems. This paper describes the basic adaptive learning mechanisms of strengthening, weakening, generalization, discrimination, and discovery. Next basic strategies are discussed for adding these learning mechanisms to rule-based diagnostic expert systems. These strategies support the incremental evaluation and refinement of rules in the knowledge base by comparing the set of advice given by the expert system (A) with the correct diagnosis (C). Techniques are described for selecting those rules in the in the knowledge base which should participate in adaptive learning. The strategies presented may be used with a wide variety of learning algorithms. Further, these strategies are applicable to a large number of rule-based diagnostic expert systems. They may be used to provide either immediate or deferred updating of the knowledge base.

Stclair, D. C.↗

NASA NTRS1988

Berthing mechanism final test report and program assessment

The purpose is to document the testing performed on both hardware and software developed under the Space Station Berthing Mechanisms Program. Testing of the mechanism occurred at three locations. Several system components, e.g., actuators and computer systems, were functionally tested before assembly. A series of post assembly tests were performed. The post assembly tests, as well as the dynamic testing of the mechanism, are presented.

Source record↗

NASA NTRS1989

A heat-pipe mechanism for volcanism and tectonics on Venus

A heat-pipe mechanism is proposed for the transport of heat through the lithosphere of Venus. This mechanism allows the crust and lithosphere on Venus to be greater than 150 km. thick. A thick basaltic crust on Venus is expected to transform eclogite at a depth of 60 to 80 km; the dense eclogite would contribute to lithospheric delamination that returns the crust to the interior of the planet completing the heat-pipe cycle. Topography and the associated gravity anomalies can be explained by Airy compensation of the thick crust. The principal observation that is contrary to this hypothesis is the mean age of the surface that is inferred from crater statistics; the minimum mean age is about 130 Myr and this implies an upper limit of 2 cubic kilometers per year for the surface volcanic flux. If the heat-pipe mechanism was applicable on the Earth in the Archean it would provide the thick lithosphere implied by isotopic data from diamonds.

Turcotte, D. L.↗

NASA NTRS1989

A heat-pipe mechanism for volcanism and tectonics on Venus

A heat-pipe mechanism is proposed for the transport of heat through the lithosphere of Venus. This mechanism allows the crust and lithosphere on Venus to be greater than 150 km thick. A thick basaltic crust on Venus is expected to transform eclogite at a depth of 60 to 80 km; the dense eclogite would contribute to lithospheric delamination that returns the crust to the interior of the planet completing the heat-pipe cycle. Topography and the associated gravity anomalies can be explained by Airy compensation of the thick crust. The principal observation that is contrary to this hypothesis is the mean age of the surface that is inferred from crater statistics; the minimum mean age is about 130 Myr and this implies an upper limit of 2 cubic kilometers per year for the surface volcanic flux. If the heat-pipe mechanism was applicable on the earth in the Archean it would provide the thick lithosphere implied by isotopic data from diamonds.

Turcotte, D. L.↗

NASA NTRS1989

Mechanics of composite materials - Past, present and future

Composite mechanics disciplines are presented and described at their various levels of sophistication and attendant scales of application. Correlation with experimental data is used as the prime discriminator between alternative methods and level of sophistication. Major emphasis is placed on: (1) where composite mechanics has been; (2) what it has accomplished; (3) where it is headed, based on present research activities; and (4) at the risk of being presumptuous, where it should be headed. The discussion is developed using selected, but typical examples of each composite mechanics discipline identifying degree of success, with respect to correlation with experimental data, and problems remaining. The discussion is centered about fiber/resin composites drawn mainly from the author's research activities/experience spanning two decades at Lewis.

Chamis, Christos C.↗

NASA NTRS1987

Biaxial thermo-mechanical fatigue

Stress-strain and durability information is often desirable for situations in which strain and temperature are changing simultaneously. To obtain such information, strain controlled uniaxial push-pull tests have typically been done. In order to control the mechanical strain, it is necessary in such tests to compute the mechanical strain from the total measured strain using measured temperature and the thermal expansion properties of the specimen. A system for conducting torsional thermomechanical tests is described which has the great advantage that the torsional strain is unaffected by the changing temperature and thus real time computations of quantities is not required for control of the test and the mechanical strain need not be determined from the subtraction of two measured qnantities as is the case in the uniaxial test. In addition to describing torsional thermomechanical tests, guidelines for software to be used in running biaxial thermomechanical tests will also be presented.

Jordan, Eric H.↗

NASA NTRS1987

Independent Orbiter Assessment (IOA): Analysis of the mechanical actuation subsystem

The results of the Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis (FMEA) and Critical Items List (CIL) are presented. The IOA approach features a top-down analysis of the hardware to determine failure modes, criticality, and potential critical items. To preserve independence, this analysis was accomplished without reliance upon the results contained within the NASA FMEA/CIL documentation. This report documents the independent analysis results corresponding to the Orbiter Mechanical Actuation System (MAS) hardware. Specifically, the MAS hardware consists of the following components: Air Data Probe (ADP); Elevon Seal Panel (ESP); External Tank Umbilical (ETU); Ku-Band Deploy (KBD); Payload Bay Doors (PBD); Payload Bay Radiators (PBR); Personnel Hatches (PH); Vent Door Mechanism (VDM); and Startracker Door Mechanism (SDM). The IOA analysis process utilized available MAS hardware drawings and schematics for defining hardware assemblies, components, and hardware items. Each level of hardware was evaluated and analyzed for possible failure modes and effects. Criticality was assigned based upon the severity of the effect for each failure mode.

Bacher, J. L.↗

NASA NTRS1988

Independent Orbiter Assessment (IOA): Assessment of the mechanical actuation subsystem, volume 1

The results of the Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis (FMEA) and Critical Items List (CIL) are presented. The IOA approach features a top-down analysis of the hardware to determine draft failure modes, criticality, and potential critical items. To preserve independence, this analysis was accomplished without reliance upon the results contained within the NASA FMEA/CIL documentation. The IOA results were then compared to the proposed Post 51-L NASA FMEA/CIL baseline that was available. A resolution of each discrepancy from the comparison was provided through additional analysis as required. These discrepancies were flagged as issues, and recommendations were made based on the FMEA data available at the time. This report documents the results of that comparison for the Orbiter Mechanical Actuation System (MAS) hardware. Specifically, the MAS hardware consists of the following components: Air Data Probe (ADP); Elevon Seal Panel (ESP); External Tank Umbilical (ETU); Ku-Band Deploy (KBD); Payload Bay Doors (PBD); Payload Bay Radiators (PBR); Personnel Hatches (PH); Vent Door Mechanism (VDM); and Startracker Door Mechanism (SDM). Criticality was assigned based upon the severity of the effect for each failure mode.

Bradway, M. W.↗

NASA NTRS1988

Independent Orbiter Assessment (IOA): Assessment of the mechanical actuation subsystem, volume 2

The results of the Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis (FMEA) and Critical Items List (CIL) are presented. The IOA approach features a top-down analysis of the hardware to determine draft failure modes, criticality, and potential critical items. To preserve independence, this analysis was accomplished without reliance upon the results contained within the NASA FMEA/CIL documentation. The IOA results were then compared to the proposed Post 51-L NASA FMEA/CIL baseline that was available. A resolution of each discrepancy from the comparison was provided through additional analysis as required. These discrepancies were flagged as issues, and recommendations were made based on the FMEA data available at the time. This report documents the results of that comparison for the Orbiter Mechanical Actuation System (MAS) hardware. Specifically, the MAS hardware consists of the following components: Air Data Probe (ADP); Elevon Seal Panel (ESP); External Tank Umbilical (ETU); Ku-Band Deploy (KBD); Payload Bay Doors (PBD); Payload Bay Radiators (PBR); Personnel Hatches (PH); Vent Door Mechanism (VDM); and Startracker Door Mechanism (SDM). Criticality was assigned based upon the severity of the effect for each failure mode. Volume 2 continues the presentation of IOA analysis worksheets and contains the potential critical items list, detailed analysis, and NASA FMEA/CIL to IOA worksheet cross reference and recommendations.

Bradway, M. W.↗

NASA NTRS1990

Compact scheme for systems of equations applied to fundamental problems of mechanics of continua

Compact scheme formulation was used in the treatment of boundary conditions for a system of coupled diffusion and Poisson equations. Models and practical solutions of specific engineering problems arising in solid mechanics, chemical engineering, heat transfer and fuid mechanics are described and analyzed for efficiency and accuracy. Only 2-D cases are discussed and a new method of numerical treatment of boundary conditions common in the fundamental problems of mechanics of continua is presented.

Klimkowski, Jerzy Z.↗

NASA NTRS1990

SPOT 4 space magnetic recorder mechanisms

The design of the SPOT 4 satellite will be quite different from the previous ones. The design of the new magnetic tape recorder, which was derived from industrial knowledge and mission requirements; the main technical characteristics of the recorder; and the mechanical subsystems of the recorder and their locations and contributions to the final performance are all discussed. The philosophy of the development program, required to achieve the desired performance and reliability for each flight model, is described, and information on the schedule and current development is presented. The components of the tape plate system, (the transmission belts, tape rollers of the recorders, and reel hub ball bearings) which are subjected to heavy mechanical operation, fatigue, and wear in the thermal environment of the mission, are discussed. For each of the components, a description of its function in the recorder is given, as well as the mechanical stress imposed during the various operational phases. The quality testing program, which was used to verify the design safety margins, is described. Finally, the first test results of a functioning model of the flight system are presented.

Borrien, A.↗

NASA NTRS1990

Relatchable launch restraint mechanism for deployable booms

A new Relatchable Launch Mechanism was developed which enables a deployable system to be restrained and released repeatedly rather than the normal one shot release systems of the past. The deployable systems are of the self extending type which rely on a lanyard attached to a drive motor to control the deployment and retraction. The Relatch Mechanism uses the existing drive motor to also actuate the latch. The design and kinematics of the Relatch Mechanism as used on two flight programs are described.

Warden, Robert M.↗

NASA NTRS1988

SKITTER/implement mechanical interface

SKITTER (Spacial Kinematic Inertial Translatory Tripod Extremity Robot) is a three-legged transport vehicle designed to perform under the unique environment of the moon. The objective of this project was to design a mechanical interface for SKITTER. This mechanical latching interface will allow SKITTER to use a series of implements such as drills, cranes, etc., and perform different tasks on the moon. The design emphasized versatility and detachability; that is, the interface design is the same for all implements, and connection and detachment is simple. After consideration of many alternatives, a system of three identical latches at each of the three interface points was chosen. The latching mechanism satisfies the design constraints because it facilitates connection and detachment. Also, the moving parts are protected from the dusty environment by housing plates.

Cash, John Wilson, III↗