Search NASA⌕ Search

SEARCH · Search NASA

Results for “REVIEWS”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1967

Review of the Lightning Strike Incident at Launch Complex 37 on July 27, 1967, and Comparison to a Gemini Lightning Strike

The Launch Complex 37 lightning strike of July 27, 1967, was reviewed and compared to a similar incident on the Gemini Program. Available data indicate little likelihood of damaging currents having been present in SA-204 Launch Vehicle or the ground equipment during the July 27th incident. Based on the results of subsystem and system testing after the strike, anticipated results of future testing, the six months elapsed time between the strike-and launch, and the fact that much of the critical airborne electrical/electronic equipment has been removed since the strike for other reasons, no new actions are considered necessary at this time in the Gemini case, significant failures occurred in both airborne and ground circuits. Due to the resultant semi, condlictor uncertainty, and the relatively' short time prior to planned launch, all critical airborne components containing semiconduetors were replaced, and a sophisticated data comparison task was implemented.

Llewellyn, J. A.↗
NASA NTRS1979

In depth review of the 1979 AIAA Lighter-Than-Air Systems Technology Conference

The lighter than air (LTA) systems technology conference is reviewed. Highlights of the conference were: (1) the interest shown in patrol and surveillance airships, particularly for coastal patrol missions; (2) the session devoted to overviews of foreign activity; and (3) heavy lift and long range transport aircraft design considerations.

Ardema, M. D.↗
NASA NTRS1979

A review of short-term flare forecasting activities at Toyokawa

Short-term forecasting of solar activity conducted at Toyokawa is briefly reviewed. The forecasts are based on microwave observations of the slowly varying component of solar radiation associated with active regions. It was found that for proton flares which take place in intense active regions, it is possible to predict their occurrence with certain accuracy, but for a certain class of proton flares which occur in a small active region or which are associated with an active region, which evolves very rapidly, or for whose which occur behind the limb, it is almost impossible to forecast their occurrence.

Enome, S.↗
NASA NTRS1979

Review of selected geomagnetic activity indices

Magnetic activity indexes are reviewed. Classifications of magnetograms from single observatories and the global range of potential associated with the equivalent currents which could have produced the variations monitored at a large array of recording sides are addressed. Principal magnetic activity indexes discussed include: the auroral electrojet index and its associated indexes (AU, AL and AO) useful for auroral zone studies; the Kp, ap, aa and am indexes which are measures of midlatitude geomagnetic activity; and the Dst index of magnetic activity recorded at low latitudes. It is concluded that geomagnetic activity indexes are useful in studies of the interaction between solar activity, the interplanetary magnetic field and solar wind, the magnetosphere, ring current, field aligned currents, and ionospheric currents.

Allen, J. H.↗
NASA NTRS1980

Review of Spectroscopic Data for Measurements of Stratospheric Species

Results and recommendations from a two day workshop are discussed. A review of the current status of experimental and theoretical spectroscopic data on molecules of stratospheric interest is given along with recommendations for additional research. Methods for disseminating new and existing data are also discussed.

Goldman, A.↗
NASA NTRS1980

Design considerations for optical heterodyne receivers: A review

The current state of knowledge concerning optical heterodyne receivers is reviewed. Following a discussion of noise processes in the heterodyne receiver and the manner in which sensitivity is increased through time integration of the detected signal, an expression for the mean square signal current is derived by mixing a coherent local oscillator with a partially coherent, quasimonochromatic source. Then the manner in which the IF signal calculation can be transferred to any convenient plane in the optical front end of the receiver is demonstrated. Using these techniques, a relatively simple equation is obtained for the coherently detected signal from an extended incoherent source and applied to the heterodyne detection of an extended thermal source and to the backscatter lidar problem where the antenna patterns of both the transmitter beam and heterodyne receiver must be taken into account. Finally, the detection of a coherent source is considered and, in particular, a distant point source such as a star or laser transmitter in a long range heterodyne communications system is discussed.

Degnan, J. J.↗
NASA NTRS1980

Automation literature: A brief review and analysis

Current thought and research positions which may allow for an improved capability to understand the impact of introducing automation to an existing system are established. The orientation was toward the type of studies which may provide some general insight into automation; specifically, the impact of automation in human performance and the resulting system performance. While an extensive number of articles were reviewed, only those that addressed the issue of automation and human performance were selected to be discussed. The literature is organized along two dimensions: time, Pre-1970, Post-1970; and type of approach, Engineering or Behavioral Science. The conclusions reached are not definitive, but do provide the initial stepping stones in an attempt to begin to bridge the concept of automation in a systematic progression.

Smith, D.↗
NASA NTRS1979

A review of satellite time transfer technology - Accomplishments and future applications

A brief review of the research accomplishments by NASA in meeting the needs of the space program for precise time in satellite tracking is presented. As a major user of precise time signals for clock synchronization of NASA's worldwide satellite tracking networks, the agency provided much of the necessary impetus for the development of stable frequency sources and time synchronization technology. The precision in time required for both satellite tracking and space science experiments has increased at a rate of about 1 order of magnitude per decade from 1 ms in the 1950's to 100 microsec during the Apollo era in the 1960's to 10 microsec in the 1970's. In the 1980's, when the Tracking and Data Relay Satellite System (TDRSS) comes into operation, satellite timing requirements will be extended to 1 microsec and below. These requirements are needed for spacecraft autonomy and data packeting which are now in active planning stages.

Cooper, R. S.↗
NASA NTRS1979

Review and revocation of access privileges distributed through capabilities

The problems of review and revocation of access privileges are presented in the context of the systems that use capabilities for the long-term distribution of access privileges. The approach to solve these two problems requires that a capability propagation graph be maintained in memory spaces associated with subjects (e.g., domains, processes, etc.) that make copies of the respective capability; the graph remains inaccessible to those subjects, however. Parallel processes of the operating system update the graph as the system runs. It is noted that the most important application of the above mechanisms may prove to be the possibility of implementing a capability-based system in which the capability representation is short.

Gligor, V. D.↗
NASA NTRS1979

On the determination of the Hermaean magnetic moment - A critical review

The determination of Mercury's magnetic moment from the spatially and temporally limited observations obtained by the Mariner 10 mission is dependent upon the assumed nature of both the intrinsic planetary magnetic field and that of the magnetospheric current systems. In this paper the methods that have been used for this purpose are reviewed. The results that have been obtained are then considered in comparison with the constraints placed on the planetary field by the solar wind dynamic pressures and stand-off distances inferred from the Mariner 10 magnetic field data by Slavin and Holtzer (1979) which are consistent with an effective dipole moment of 6 + or - 2 x 10 to the 22nd G cu cm. It is found that the models which fit the observations with substantial quadrupole and octupole moments are not consistent with the magnetospheric boundary conditions, presumably owing to incorrect assumptions regarding the magnetopause position, incorrect assumptions regarding solar wind dynamic pressure, and/or averaging over temporal variations in the Mariner 10 data.

Slavin, J. A.↗
NASA NTRS1979

A review of the application of nonattenuating frequency radars for estimating rain attenuation and space-diversity performance

Cumulative rain fade statistics are used by space communications engineers to establish transmitter power and receiver sensitivities for systems operating under various geometries, climates, and radio frequencies. Space-diversity performance criteria are also of interest. This work represents a review, in which are examined the many elements involved in the employment of single nonattenuating frequency radars for arriving at the desired information. The elements examined include radar techniques and requirements, phenomenological assumptions, path attenuation formulations and procedures, as well as error budgeting and calibration analysis. Included are the pertinent results of previous investigators who have used radar for rain-attenuation modeling. Suggestions are made for improving present methods.

Goldhirsh, J.↗
NASA NTRS1979

Review of the metallographic cooling rates of meteorites and a new model for the planetesimals in which they formed

The cooling rates of meteorites through approximately 900 -650 K, as read from their metal alloy compositions, are reviewed. Metallographic cooling rates are compared with the cooling rates that appear to be required by the K/Ar and Ar-40/Ar-39 ages of five meteorite classes, and discrepancies are found in all cases. Either (1) the metallographic cooling rates (and also Pu-244 fission cooling rates) are systematically in error, being too slow by a factor of approximately 6; or (2) the traditional thermal model for parent meteorite planets (having constant dimension and uniform physical properties) is oversimplified and the Ar closure temperatures for chondrites derived by Turner et al. (1978) are too low. An alternative parent planet model is proposed and numerically modeled, in which accretion of thermally insulating particulate matter, heat generation by Al-26 decay, melting or sintering of the particulate matter into conductive rock, and establishment of the properties of the meteorites occurred concurrently. Meteorite chronologies are somewhat easier to understand in this context, since the initially small, hot (thus sintered and conductive) bodies would have cooled rapidly to isotopic closure, but later cooling might have been much slower as a result of the continued accretion of insulating particulate matter.

Wood, J. A.↗
NASA NTRS1980

Passive microwave remote sensing of the ocean - A review

This paper reviews the current status of passive microwave remote sensing of the ocean. The physics of emission and instrumentation are highlighted in order to establish a relationship between the thermal emission and retrieved geophysical parameters. A discussion then follows on measurements of temperature, salinity, windspeed, etc. using passive microwave systems. These measurements are related to the accuracy and spatial resolution required by the users. The status of passive microwave remote sensing is summarized and recommendations for future research are presented.

Swift, C. T.↗
NASA NTRS1979

Solution of electromagnetic scattering and radiation problems using a spectral domain approach - A review

This paper presents a brief review of some recent developments on the use of the spectral-domain approach for deriving high-frequency solutions to electromagnetics scattering and radiation problems. The spectral approach is not only useful for interpreting the well-known Keller formulas based on the geometrical theory of diffraction (GTD), it can also be employed for verifying the accuracy of GTD and other asymptotic solutions and systematically improving the results when such improvements are needed. The problem of plane wave diffraction by a finite screen or a strip is presented as an example of the application of the spectral-domain approach.

Mittra, R.↗
NASA NTRS1980

Review - Axial compressor stall phenomena

Stall in compressors can be associated with the initiation of several types of fluid dynamic instabilities. These instabilities and the different phenomena, surge and rotating stall, which result from them, are discussed in this paper. Assessment is made of the various methods of predicting the onset of compressor and/or compression system instability, such as empirical correlations, linearized stability analyses, and numerical unsteady flow calculation procedures. Factors which affect the compressor stall point, in particular inlet flow distortion, are reviewed, and the techniques which are used to predict the loss in stall margin due to these factors are described. The influence of rotor casing treatment (grooves) on increasing compressor flow range is examined. Compressor and compression system behavior subsequent to the onset of stall is surveyed, with particular reference to the problem of engine recovery from a stalled condition. The distinction between surge and rotating stall is emphasized because of the very different consequences on recoverability. The structure of the compressor flow field during rotating stall is examined, and the prediction of compressor performance in rotating stall, including stall/unstall hysteresis, is described.

Greitzer, E. M.↗
NASA NTRS1980

A review of propeller discrete frequency noise prediction technology with emphasis on two current methods for time domain calculations

A review of propeller noise prediction technology is presented which highlights the developments in the field from the successful attempt of Gutin to the current sophisticated techniques. Two methods for the predictions of the discrete frequency noise from conventional and advanced propellers in forward flight are described. These methods developed at MIT and NASA Langley Research Center are based on different time domain formulations. Brief description of the computer algorithms based on these formulations are given. The output of these two programs, which is the acoustic pressure signature, is Fourier analyzed to get the acoustic pressure spectrum. The main difference between the programs as they are coded now is that the Langley program can handle propellers with supersonic tip speed while the MIT program is for subsonic tip speed propellers. Comparisons of the calculated and measured acoustic data for a conventional and an advanced propeller show good agreement in general.

Farassat, F.↗