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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 1,729 records · Page 96

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NASA NTRS1973

Achieving ultrahigh accuracy with a body pointing CMG/RW control system.

The purpose of the Large Space Telescope (LST) program is to place a three-meter diffraction limited telescope in a 270-nautical mile orbit in order to perform astronomical observations that are not presently possible with earth bound telescopes due to atmospheric obscuration. In order to determine whether the stringent pointing requirements could be met, a complex simulation model was defined which consisted of detailed dynamic representations of control moment gyros (CMGs) and reaction wheels including their noise characteristics, dynamic sensor representations with sensor noise, shock mounts for the CMG actuators, and a detailed flexible body structural model with all significant vehicle and solar panel bending modes. On the basis of both stability and performance studies utilizing this model, it was determined that a body pointing system will meet LST requirements.

Rybak, S. C.↗

NASA NTRS1976

Ultrasonic corona sensor study

The overall objective of this program is to determine the feasibility of using ultrasonic (above 20 kHz) corona detection techniques to detect low order (non-arcing) coronas in varying degrees of vacuum within large high vacuum test chambers, and to design, fabricate, and deliver a prototype ultrasonic corona sensor.

Harrold, R. T.↗

NASA NTRS1977

NASA software specification and evaluation system: Software verification/validation techniques

NASA software requirement specifications were used in the development of a system for validating and verifying computer programs. The software specification and evaluation system (SSES) provides for the effective and efficient specification, implementation, and testing of computer software programs. The system as implemented will produce structured FORTRAN or ANSI FORTRAN programs, but the principles upon which SSES is designed allow it to be easily adapted to other high order languages.

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NASA NTRS1977

Global atmospheric sampling program

Automated instruments were installed on a commercial B-747 aircraft, during the program, to obtain baseline data and to monitor key atmospheric constituents associated with emissions of aircraft engines in order to determine if aircraft are contributing to pollution of the upper atmosphere. Data thus acquired on a global basis over the commercial air routes for 5 to 10 years will be analyzed. Ozone measurements in the 29,000 to 45,000 foot altitude were expanded over what has been available from ozonesondes. Limited aerosol composition measurements from filter samples show low levels of sulfates and nitrates in the upper troposphere. Recently installed instruments for measurement of carbon monoxide and condensation nuclei are beginning to return data.

Lezberg, E. A.↗

NASA NTRS1977

Hierarchy of simulation models for a turbofan gas engine

Steady-state and transient performance of an F-100-like turbofan gas engine are modeled by a computer program, DYNGEN, developed by NASA. The model employs block data maps and includes about 25 states. Low-order nonlinear analytical and linear techniques are described in terms of their application to the model. Experimental comparisons illustrating the accuracy of each model are presented.

Longenbaker, W. E.↗

NASA NTRS1978

The development of methods for the prediction of primary creep behavior in metals

The applicability of a thermodynamic constitutive theory of deformation to the prediction of primary creep and creep strain relaxation behavior in metals is examined. Constitutive equations derived from the theory are subjected to a parametric analysis in order to determine the influence of several parameters on the curve forms generated by the equations. A computer program is developed which enables the solution of a generalized constitutive equation using experimental data as input. Several metals were tested to form a data base of primary creep and relaxation behavior. The extent to which these materials conformed to the constitutive equation showed wide variability, with the alloy Ti-6Al-4V exhibiting the most consistent results. Accordingly, most of the analysis is concentrated upon data from that alloy, although creep and relaxation data from all the materials tested are presented. Experimental methods are outlined as well as some variations in methods of analysis. Various theoretical and practical implications of the work are discussed.

Zerwekh, R. P.↗

NASA NTRS1980

Satellite Power System (SPS) FY 79 program summary

The Satellite Power System (SPS) program a joint effort to develop an initial understanding of the technical feasibility, the economic practicality, and the social and environmental acceptability of the SPS concept is discussed. This is being accomplished through implementation of the Concept Development and Evaluation Program Plan which is scheduled for completion by the end of FY 1980. This Program Summary not only covers FY 1979 but includes work completed in FY 1977 and FY 1978 in order to give a comprehensive picture of the DOE involvement in the SPS concept development and evaluation process.

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NASA NTRS1982

Dynamic responses of graphite/epoxy laminated beam to impact of elastic spheres

Wave propagation in 90/45/90/-45/902s and 0/45/0/-45/02s laminates of a graphite/epoxy composite due to impact of a steel ball was investigated experimentally and also by using a high order beam finite element. Dynamic strain responses at several locations were obtained using strain gages. The finite element program which incorporated statically determined contact laws was employed to calculate the contact force history as well as the target beam dynamic deformation. The comparison of the finite element solutions with the experimental data indicated that the static contact laws for loading and unloading (developed under this grant) are adequate for the dynamic impact analysis. It was found that for the 0/45/0/-45/02s laminate which has a much larger longitudinal bending rigidity, the use of beam finite elements is not suitable and plate finite element should be used instead.

Sun, C. T.↗

NASA NTRS1983

Flow rate/pressure drop data gathered from testing a sample of the Space Shuttle Strain Isolation Pad (SIP): Effects of ambient pressure combined with tension and compression conditions

Tests were conducted on a sample of strain isolation pad (SIP) typical of that used in the shuttle orbiter thermal protection system to determine the characteristics of SIP internal flow. Data obtained were pressure drop as a function of flow rate for a range of ambient pressures representing various points along the Shuttle trajectory and for stretched and compressed conditions of the SIP. Flow was in the direction of the weave parallel to most of the fibers. The data are plotted in several standard engineering formats in order to be of maximum utility to the user. In addition to providing support to the Space Shuttle Program, these data are a source of experimental information on flow through fiberous (rather than the more usual sand bed type) porous media.

Springfield, R. D.↗

NASA NTRS1983

Radiation of sound from unflanged cylindrical ducts

Calculations of sound radiated from unflanged cylindrical ducts are presented. The numerical simulation models the problem of an aero-engine inlet. The time dependent linearized Euler equations are solved from a state of rest until a harmonic solution is attained. A fourth order accurate finite difference scheme is used and solutions are obtained from a fully vectorized Cyber-203 computer program. Cases of both plane waves and spin modes are treated. Spin modes model the sound generated by a turbofan engine. Boundary conditions for both plane waves and spin modes are treated. Solutions obtained are compared with experiments conducted at NASA Langley Research Center.

Hartharan, S. L.↗

NASA NTRS1984

CIM's bridge from CADD to CAM: Data management requirements for manufacturing engineering

Manufacturing engineering represents the crossroads of technical data management in a Computer Integrated Manufacturing (CIM) environment. Process planning, numerical control programming and tool design are the key functions which translate information from as engineered to as assembled. In order to transition data from engineering to manufacturing, it is necessary to introduce a series of product interpretations which contain an interim introduction of technical parameters. The current automation of the product definition and the production process places manufacturing engineering in the center of CAD/CAM with the responsibility of communicating design data to the factory floor via a manufacturing model of the data. A close look at data management requirements for manufacturing engineering is necessary in order to establish the overall specifications for CADD output, CAM input, and CIM integration. The functions and issues associated with the orderly evolution of computer aided engineering and manufacturing are examined.

Ford, S. J.↗

NASA NTRS1983

Validation methods for flight crucial systems

Research to develop techniques that can aid in determining the reliability and performance of digital electronic fault-tolerant systems, that have probability of catastrophic system failure on the order of 10 to the -9th at 10 hours, is reviewed. The computer-aided reliability estimation program (CARE III) provides general-purpose reliability analysis and a design tool for fault-tolerant systems; large reduction of state size; and a fault-handling model based on probabilistic description of detection, isolation, and recovery mechanisms. The application of design proof techniques as part of the design and development of the software implemented fault-tolerance computer is mentioned. Emulation techniques and experimental procedures are verified using specimens of fault-tolerant computers and the capabilities of the validation research laboratory, AIRLAB.

Holt, H. M.↗

NASA NTRS1983

Review of NASA ACLS research

An experimental investigation was conducted to evaluate a method of maintaining stability of an air cushion vehicle and also to evaluate several concepts to brake and steer an ACLS-equipped vehicle. The investigation used a modified airboat equipped with an air cushion landing system. The pressure relief door stability concept was characterized by the ACLS pressure time histories. The pressure relief doors vented excess cavity and lobe pressures and consistently maintained vehicle heave and pitch stability. Braking concepts were characterized by the average deceleration of the vehicle. Reduced lobe flow and cavity venting braking concepts were evaluated in this program. The cavity venting concept demonstrated the best performance, producing decelerations on the test vehicle on the same order as moderate braking with conventional wheel brakes. Steering concepts were evaluated by recording the path taken while attempting to follow a prescribed maneuver. The steering concepts evaluated included using rudders only, using differential lobe flow, and using rudders combined with a lightly loaded, nonsteering center wheel. The latter concept proved to be the most accurate means of steering the vehicle on the ACLS, producing translational deviations which, while two to three times higher than those from conventional nose gear steering, were still felt to provide reasonably precise steering control for this type vehicle.

Daugherty, R. H.↗

NASA NTRS1984

Trajectory determination support and analysis for ISEE-3 from halo orbit to escape from the earth/moon system

The analyses performed in altering the ISEE-3 spacecraft path from a liberation point to a helicocentric orbit for intercepting the Giacobini-Zimmer cometary tail are reviewed. The initial calculations considered the expected accuracy, the best temporal lengths to be used for the calculations and the maneuver points. The early maneuvers were also constrained to a maximum number of crossings of the terrestrial magnetotail for data collection purposes. Three earth-based tracking stations trajectory data collection schedules were projected, and programs were prepared for comparing tracking data with predictions. Delta- V maneuvers were set for perigee locations in order to conserve fuel. A 21-day span was selected for tracking, expect during maneuver periods. Accuracies of 0.1-10 km and 0.3-2.0 cm/sec were obtained.

Joyce, J. B.↗

NASA NTRS1984

Elevated temperature crack growth

Critical gas turbine engine hot section components such as blades, vanes, and combustor liners tend to develop minute cracks during early stages of operations. The ability of currently available path-independent (P-I) integrals to correlate fatigue crack propagation under conditions that simulate the turbojet engine combustor liner environment was determined. To date, an appropriate specimen design and a crack displacement measurement method were determined. Alloy 718 was selected as the analog material based on its ability to simulate high temperature behavior at lower temperatures in order to facilitate experimental measurements. Available P-I integrals were reviewed and the best approaches are being programmed into a finite element post processor for eventual comparison with experimental data. The experimental data will include cyclic crack growth tests under thermomechanical conditions, and, additionally, thermal gradients.

Kim, K. S.↗

NASA NTRS1987

Analytical approach to peel stresses in bonded composite stiffened panels

A closed-form solution was obtained for the stresses and displacements of two bonded beams. A system of two fourth-order and two second-order differential equations with the associated boundary equations was determined using a variational work approach. A FORTRAN computer program was devised to solve for the eigenvalues and eigenvectors of this system and to calculate the coefficients from the boundary conditions. The results were then compared with NASTRAN finite-element solutions and shown to agree closely.

Barkey, Derek A.↗

NASA NTRS1988

Physical processes in comets

When this program began in 1975 only limited photometry had been carried out on comets at any wavelength. Program goals were to observe many comets, including faint periodic comets, at a range of heliocentric distances in order to begin to understand the range of behavior among comets and in a given comet during its approach and departure from the sun. Then a study of the continuum of scattered light from dust was added. More recently the value of joint team observations in visible and infrared light has been recognized and utilized as often as possible. All 1978 to 1982 data was reanalyzed and 1983 to 1986 data analyzed in the framwork of the post-Halley paradigm, covering 25 comets in all. Four observing runs (June, July, Sept., and Jan.) with Hanner produced excellent results on Wilson, Bradfield, P/Klemola, and P/Borrelly and lesser data on other objects, including the last reported IR photometry of P/Halley. The Wilson and Halley data have been reduced.

Newburn, Ray L., Jr.↗

NASA NTRS1990

Computing Scattering Matrices For Circular Waveguides

Scattering Matrix Program for Circular Waveguide Junctions computes scattering matrix for series of circular waveguide sections. Sections must have same axis, but radius and length of each section completely arbitrary. Devices analyzed include simple waveguide step discontinuity like that used in a dual-mode horn, stepped matching section, or corrugated waveguide section with constant or varying slot depth. Certain types of corrugated horns also analyzed with program. Mathematical model used in program accurately predicts reflection and transmission characteristics of such devices, taking into account excitation of modes of higher order as well as multiple reflections and energy stored at each discontinuity. Written in FORTRAN 77.

Hoppe, Daniel J.↗