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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 1,387 records · Page 77

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NASA NTRS1981

A radiation-hardened star scanner for spacecraft guidance and control

A star scanner for the Galileo Project is described. Because it must function in the intense Jupiter radiation field, which consists primarily of high-energy electrons and protons, this star scanner is designed with radiation-hardness as a prime objective. The optics and the multiplier phototube are specially designed to minimize fluorescence and Cerenkov effects, and the electronic components to minimize ionization and displacement damage. The star-scanner layout provides maximum shielding for the optics and phototube. Test results predict successful operation in the expected Jovian radiation environment.

Birnbaum, M. M.↗

NASA NTRS1981

Effects of rectilinear acceleration, optokinetic and caloric stimuli in space

The set of experiments comprising the Spacelab 1ES201 package designed to investigate the human vestibular system and equilibratory function in weightlessness are described. The specific objectives of the experiments include: (1) the determination of the threshold of perception of linear oscillatory motion; (2) measurement of physiological and subjective responses to supra threshold, linear and angular motion stimuli; (3) study of the postural adjustments, eye movements, and illusions of attitude and motion evoked by optokinetic stimuli, (i.e., moving visual patterns) in order to assess visual/vestibular interactions; (4) examination of the effect of thermal stimulations of the vestibular apparatus to determine if the eye movements elicited by the 'caloric test' are used by a density gradient in the semicircular canal; and (5) investigation of the pathogenesis of space motion sickness by recording signs and symptoms during the course of vestibular stimulation and, specifically, when the test subject is exposed to sustained, linear oscillatory motion.

Vonbaumgarten, R.↗

NASA NTRS1982

Space Operations Center system analysis study extension. Volume 1: Executive summary

The analysis fo Space Operations Center (SOC) systems is summarized. Design considerations, configurations of the manned orbital space station, planned operational and research missions, and subsystem tradeoffs are considered. Integration into the space transportation system is discussed. A modular design concept permitting growth of the SOC as its functions are expanded is described. Additional considerations are special requirements for habitat modules, design modifications needed to operate in geosynchronous orbits, and use of the external tank for cryogenic propellant storage or as a pressurized hangar. A cost summary is presented.

Source record↗

NASA NTRS1982

LMSS communication network design

The architecture of the telecommunication network as the first step in the design of the LMSS system is described. A set of functional requirements including the total number of users to be served by the LMSS are hypothesized. The design parameters are then defined at length and are systematically selected such that the resultant system is capable of serving the hypothesized number of users. The design of the backhaul link is presented. The number of multiple backhaul beams required for communication to the base stations is determined. A conceptual procedure for call-routing and locating a mobile subscriber within the LMSS network is presented. The various steps in placing a call are explained, and the relationship between the two sets of UHF and S-band multiple beams is developed. A summary of the design parameters is presented.

Source record↗

NASA NTRS1981

Realizable feed-element patterns for multibeam reflector antenna analysis

The radiation pattern of a feed element is approximately described by a simple function (cos theta) to the q power. For a given element spacing of the feed array, simple formulas for estimating the practical value of q when the element is an open-ended rectangular waveguide, an open-ended circular waveguide, a pyramidal horn, or a cigar antenna are given.

Rahmat-Samii, Y.↗

NASA NTRS1981

Space tracking and data systems; Proceedings of the Symposium, Arlington, VA, June 16-18, 1981

The AIAA/NASA Symposium on Space Tracking and Data Systems, held in Pentagon City, Virginia, on June 16-18, 1981, had the purpose of reviewing international activities in space tracking and data systems for civil use in the 1980-2000 time frame. Participants included 225 representatives from industrial and government organizations in eight nations. The nations represented include the United States, France, Germany, India, Japan, Norway, Spain, and Sweden. The major functions of the systems described at the Symposium are related to the initial downlink of telemetry and spacecraft status data, attendant tracking activities, and uplink of spacecraft commands; communication between the associated acquisition sites and central processing and control stations; formulation and implementation of commands that control the spacecraft and its payload; and processing of spacecraft data needed to make command decisions. Attention is given to an overview of current activities and plans, and supporting developments, taking into account the time from 1980 to 1990. New developments are also considered.

Grey, J.↗

NASA NTRS1982

The inverse problem of constructing a gravimetric geoid

Computation of a single geoidal height from gravity acceleration data formally requires that the latter be known everywhere on the earth. A computational procedure based on linear inverse theory for estimating geoidal heights from incomplete sets of data is presented. The same scheme can be used to estimate gravity accelerations from altimetry-derived geoids. The systematic error owing to lack of data and the choice of a particular inverse operator is described by using resolution functions and their spherical harmonic expansions. An rms value of this error is also estimated by assuming a spectrum for the unknown geoid. The influence of the size of the data region, the spacing between data, the filtering applied to the data, and the model weighting function chosen are all quantified in a spherical geometry. The examples presented show that when low degree spherical harmonic coefficients are available - from satellite orbit analysis - a band-passed version of the geoid can be constructed from local gravity data, even with a relatively restricted data set.

Zlotnicki, V.↗

NASA NTRS1983

Numerical Aerodynamic Simulation (NAS)

The history of the Numerical Aerodynamic Simulation Program, which is designed to provide a leading-edge capability to computational aerodynamicists, is traced back to its origin in 1975. Factors motivating its development and examples of solutions to successively refined forms of the governing equations are presented. The NAS Processing System Network and each of its eight subsystems are described in terms of function and initial performance goals. A proposed usage allocation policy is discussed and some initial problems being readied for solution on the NAS system are identified.

Peterson, V. L.↗

NASA NTRS1983

Statistical correlation of structural mode shapes from test measurements and NASTRAN analytical values

The software and procedures of a system of programs used to generate a report of the statistical correlation between NASTRAN modal analysis results and physical tests results from modal surveys are described. Topics discussed include: a mathematical description of statistical correlation, a user's guide for generating a statistical correlation report, a programmer's guide describing the organization and functions of individual programs leading to a statistical correlation report, and a set of examples including complete listings of programs, and input and output data.

Purves, L.↗

NASA NTRS1984

Army aviation today and tomorrow

Military helicopters and their functions in combat are described. Electronic countermeasures, target acquisition, surveillance, reconnaissance, weapons systems, night flight capability, troop transport, and nap-of-the-earth navigation are discussed.

Philips, G.↗

NASA NTRS1985

Land mobile satellite transmission measurements at 869 MHz: Selected results from the dedicated stratospheric balloon experiment of November 12 and 13, 1984

Satellite transmissions were simulated by placing an 869 MHz and a 1501 MHz transmitter aboard a stratospheric balloon. The balloon was followed on the ground by a van equipped with receivers and data acquisition equipment capable of creating a permanent record of the variations of the received signal amplitude and phase at the two signal frequencies. Results from simulated satellite transmission measurements at 869 MHz are presented. The data show that attenuation by roadside trees can be a limiting factor in systems with a 5 dB fade margin, if 84% availability is not acceptable. In less extreme environments, fading is much less severe. Without fading present, the signal power density function often could be described as Ricean with direct to scattered ratio power ratios of about 100. Phase fluctuations were apparent whenever the signal amplitude fluctuated. The duration of the fades and nonfades tended to cluster close to one wavelength. The power spectrum of both the amplitude and the phase show that most of the fluctuations occur at frequencies below the Doppler shift.

Vogel, W. J.↗

NASA NTRS1984

Variational calculations of muonic-molecule energy levels

The best variational energies obtained to date of the bound states of muonic molecules containing nucleons of unit charge or isotopes of hydrogen are reported. Hylleraas wave functions are used to describe the three-particle systems, and the convergence of the energies is carefully studied; as many as 440 terms have been included in some cases. These results are compared with the best previous values.

Bhatia, A. K.↗

NASA NTRS1983

Advanced 30/20 GHz multiple beam antenna for future communications satellites

The technologies which will be implemented in advanced satellite communications systems being studied by NASA and the intended coverage scenarios are described. The systems will function at 30/20 GHz with 2.5 GHz bandwidth for the uplink and downlink. Subfrequencies will have 500 MHz bandwidth and operations will include TDMA modes. Sample scan patterns are presented for the centerminous U.S. The signals will be broadcast from a multibeam offset Cassegrain reflector antenna to obtain a low sidelobe, wide angle scan. Three contiguous low sidelobe beams will be generated with a diplex feed cluster and a 19 element scanning beam-forming network. The same technology will be used to double the capacity of current 14/12 GHz satellites.

Chen, C. C.↗

NASA NTRS1985

Hydrogen-like atoms on the surface of neutron stars - Intense magnetic field effects

It is known that very strong (greater than 1-TG) magnetic fields exist on the surface of some neutron stars. The properties of atoms in fields of this nature are considerably different from those of atoms in field-free regions. Because of the mixing of spherical and cylindrical symmetries, the analytical solution to the problem of a hydrogen atom in a uniform magnetic field is impossible to obtain. In this work, a variational wave function is used to describe the properties of hydrogen like atoms in intense magnetic fields including first-order relativistic effects. Special attention is given to the transition matrix elements for the 2p(0) - 1s(0) transition in Fe XXVI.

Williams, A. C.↗

NASA NTRS1986

Signal Detection Techniques for Diagnostic Monitoring of Space Shuttle Main Engine Turbomachinery

An investigation to develop, implement, and evaluate signal analysis techniques for the detection and classification of incipient mechanical failures in turbomachinery is reviewed. A brief description of the Space Shuttle Main Engine (SSME) test/measurement program is presented. Signal analysis techniques available to describe dynamic measurement characteristics are reviewed. Time domain and spectral methods are described, and statistical classification in terms of moments is discussed. Several of these waveform analysis techniques have been implemented on a computer and applied to dynamc signals. A laboratory evaluation of the methods with respect to signal detection capability is described. A unique coherence function (the hyper-coherence) was developed through the course of this investigation, which appears promising as a diagnostic tool. This technique and several other non-linear methods of signal analysis are presented and illustrated by application. Software for application of these techniques has been installed on the signal processing system at the NASA/MSFC Systems Dynamics Laboratory.

Coffin, Thomas↗

NASA NTRS1985

A simulation study of kilometric radiation generation along an auroral field line

A model for the high-altitude auroral zone is combined with local particle simulations in order to assess the quantitative implications of relativistic dispersion for the generation of auroral kilometric radiation. The auroral zone model is described, including the distribution functions for the primary and secondary electron populations and the variations of the total number density with altitude. The analysis shows that the most intense cyclotron maser emission should occur in the 1.75-2.0 R(E) altitude range. At lower altitudes, the secondary electrons are dominant, and the instability saturates at a low level. At higher altitudes, the energy of the primary electron is lower, and again the radiation level drops. The simulations indicate that linear growth rates of the order of 0.002 Omega(e) occur in this region and that the conversion of primary electron energy into AKR is about one percent.

Pritchett, P. L.↗

NASA NTRS1986

The equilibrium structure of thin magnetic flux tubes. II

The thermal structure of the medium inside thin, vertical magnetic flux tubes embedded in a given external atmosphere is investigated, assuming cylindrical symmetry and a depth-independent plasma beta. The variation with tube radius of the temperature on the tube axis is computed and the temperature on the tube wall is estimated. The temperature variation across the flux tube is found to be due to the depth variation of the intensity and to the density stratification of the atmosphere. Since the temperature difference between the axis and the wall is small in thin flux tubes (of the order of 10 percent), the horizontal temperature gradient may often be neglected and the temperature in a tube of given radius may be described by a single function of depth. Thus, a more detailed numerical treatment of the radiative transfer within thin flux tubes can be substantially simplified by neglecting horizontal temperature differences within the flux tube proper.

Kalkofen, W.↗

NASA NTRS1985

Modelisation of the optical scattering behaviour of the vegetation canopies

The three dimensional model of Kimes (1984) which can treat three dimensional variability in heterogeneous scenes, was used to test and expand physical scattering mechanisms involved in reflectance distribution dynamics by analyzing modeling and field data. The major physical phenomena causing the directional scattering behavior of vegetation canopies are presented. These include the strong anisotropic properties of the soil, and the anisotropic scattering properties of the vegetation as described by the phase function of the leaves and the geometric effects caused by vertical layers of leaves. This knowledge serves as a basis for defining optimum directional view angles for remote sensing strategies. An example on using knowledge of the scattering behavior of vegetation to develop techniques for extracting vegetation parameters (spectral albedo) from directional reflectance data is presented.

Kimes, D. S.↗