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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Laser power stations in orbit.

Potential laser applications for space-borne power generation are discussed in the light of the current state of the art. The feasible ranges of various laser classes with standing waves are estimated. Power and efficiency, mirror factors, phased-array performance and beam patterns are analyzed as selection characteristics. Other topics include the maximum receiving-element size, energy conversion, pointing and tracking, causes of deformation, and mirror distortions. It is theorized that a nuclear-fueled laser satellite could beam power to distances twice the earth-sun distance with predictable pointing accuracies.

Hansen, C. F.↗
NASA NTRS1974

Nonproportional loading limit for structures

The design of most structures involves ensuring integrity for several independent loading conditions. Often, it is rational to design these, exploiting the ductility of the materials to reduce structural costs. Then, ensuring integrity evokes the need for nonmonotonic limit analyses. A groundwork is laid for implementing these analyses. An alternate limit load characterization to that of Greenberg is provided, a mathematical statement of the problem leading to both monotonic (proportional) and nonmonotonic limit loads values is formulated, a direct limit load analysis procedure for analysis within a finite-element framework is described, and limit loads for sets of simple structures are evaluated. A direct limit analysis process is described, and monotonic limit loads are characterized. The process furnishes 'exact' values of limit loads with increasing efficiency as the number of structural elements and force redundancy decreases. Tests show that the accuracy of predicting nonmonotonic limit loads is very sensitive to the number of degrees of freedom in the analysis compared with the total number in the model.

Melosh, R. J.↗
NASA NTRS1974

Research study on high energy radiation effect and environment solar cell degradation methods

The most detailed and comprehensively verified analytical model was used to evaluate the effects of simplifying assumptions on the accuracy of predictions made by the external damage coefficient method. It was found that the most serious discrepancies were present in heavily damaged cells, particularly proton damaged cells, in which a gradient in damage across the cell existed. In general, it was found that the current damage coefficient method tends to underestimate damage at high fluences. An exception to this rule was thick cover-slipped cells experiencing heavy degradation due to omnidirectional electrons. In such cases, the damage coefficient method overestimates the damage. Comparisons of degradation predictions made by the two methods and measured flight data confirmed the above findings.

Horne, W. E.↗
NASA NTRS1977

Effects of mismatch on group delay of microwave transmission

Calculation method can be applied to transmission lines operating in TEM mode or to single-mode propagation in waveguides. Derived data are useful for estimating limits on variation of group delay with frequency or in determining how much discontinuity reduction is necessary to achieve given accuracy in predicting group delay.

Beatty, R. W.↗
NASA NTRS1977

Studies of perception of information on the spatial position of an aircraft

Problems of pilot visual perception were identified, specifically problems of identifiying the surface of the earth at moment of transition from flight-instrument observation. The percepted difficulties studied were: (1) the accuracy of defining the slope of the flight path during lack of visibility of the actual line of the horizon, (2) the accuracy of predicting the time remaining before landing under conditions of limited external visibility, and (3) the structure of the shape of the earth's surface necessary for the maximum accurate determination of flight-path slope and prediction of time remaining to landing.

Zebrowski, M.↗
NASA NTRS1978

Selection of a seventh spectral band for the LANDSAT-D thematic mapper

The author has identified the following significant results. Each of the candidate bands were examined in terms of the feasibility of gathering high quality imagery from space while taking into account solar illumination, atmospheric attenuation, and the signal/noise ratio achievable within the TM sensor constraints. For the 2.2 micron region and the thermal IR region, inband signal values were calculated from representative spectral reflectance/emittance curves and a linear discriminant analysis was employed to predict classification accuracies. Based upon the substantial improvement (from 78 t0 92%) in discriminating zones of hydrothermally altered rocks from unaltered zones, over a broad range of observation conditions, a 2.08-2.35 micron spectral band having a ground resolution of 30 meters was recommended.

Holmes, Q. A.↗
NASA NTRS1978

The Annular Suspension and Pointing System

The Annular Suspension and Pointing System (ASPS) is a general purpose mount designed to provide orientation, mechanical isolation, and fine pointing for space experiments. The ASPS consists of two assemblies, the first being a set of two gimbals attached to a carrier spacecraft (e.g., Space Shuttle) and providing coarse pointing, and the second a magnetic vernier pointing and isolation assembly attached to the inner gimbal of the first assembly and providing fine pointing. Discussion of the evolution of this concept, required related technology, and data from analyses and simulations predicting pointing accuracies that allowed the specification of hardware design requirements is presented.

Anderson, W. W.↗
NASA NTRS1979

A study of the blown flap/jet flap analogy

A study of the blown flap/jet flap analogy has been undertaken. Analytical predictions were made using both improved lifting line and optimized vortex lattice models for the jet flap. Results were compared with experimental data for three propulsive lift systems; the jet augmented flap, the externally blown flap, and the upper surface blown flap. Force increments due to changes in geometry and jet parameters were well approximated in most cases, although the absolute values of the aerodynamic forces were usually underestimated. The relatively simple jet-flap models gave performance predictions of accuracy comparable to more complex analyses.

Hough, G. R.↗
NASA NTRS1979

Short-term solar activity forecasting

A method of forecasting the level of activity of every active region on the surface of the Sun within one to three days is proposed in order to estimate the possibility of the occurrence of ionospheric disturbances and proton events. The forecasting method is a probability process based on statistics. In many of the cases, the accuracy in predicting the short term solar activity was in the range of 70%, although there were many false alarms.

Xie-Zhen, C.↗
NASA NTRS1980

Phase 1 Navstar/GPS ephemeris and space vehicle clock performance summary

The Navstar/Global Positioning System (GPS) is considered. The issue of control segment accuracy in predicting space vehicle (SV) clock and ephemeris states for broadcast to the user community is addressed. Both the highly precise ephemeris and clock prediction data blocks and the less precise (but longer period of utility) almanac data block are evaluated.

Bierman, A. B.↗
NASA NTRS1979

Gravity anomaly and geoid undulation results in local areas from GEOS-3 altimeter data

The adjusted GEOS-3 altimeter data, taken as averages within a data frame, have been used to construct free air anomaly and geoid undulation profiles and maps in areas of geophysical interest. Profiles were constructed across the Philippine Trench (at a latitude of 6 deg) and across the Bonin Trench (at a latitude of 28 deg). In the latter case an anomaly variation of 443 mgals in 143 km was derived from the altimeter data. These variations agreed reasonably with terrestrial estimates, considering the predicted point accuracy was about + or - 27 mgals. An area over the Patton Sea mounts was also investigated with the altimeter anomaly field agreeing well with the terrestrial data except for the point directly over the top of the sea mount. It is concluded that the GEOS-3 altimeter data is valuable not only for determining 5 deg and 1 deg x 1 deg mean anomalies, but also can be used to describe more local anomaly variations.

Rapp, R. H.↗
NASA NTRS1981

An airport wind shear detection and warning system using Doppler radar: A feasibility study

A feasibility study was conducted to determine whether ground based Doppler radar could measure the wind along the path of an approaching aircraft with sufficient accuracy to predict aircraft performance. Forty-three PAR approaches were conducted, with 16 examined in detail. In each, Doppler derived longitudinal winds were compared to aircraft measured winds; in approximately 75 percent of the cases, the Doppler and aircraft winds were in acceptable agreement. In the remaining cases, errors may have been due to a lack of Doppler resolution, a lack of co-location of the two sampling volumes, the presence of eddy or vortex like disturbances within the pulse volume, or the presence of point targets in antenna side lobes. It was further concluded that shrouding techniques would have reduced the side lobe problem. A ground based Doppler radar operating in the optically clear air, provides the appropriate longitudinal winds along an aircraft's intended flight path.

Mccarthy, J.↗
NASA NTRS1981

Estimation of the propagation delay through the troposphere from microwave radiometer data

Microwave propagation delay through the troposphere is studied as a means of estimating the adverse effect of atmospheric water vapor on the accuracy of measurements made with very long baseline interferometry. Vertical profiles of temperature and water vapor density were obtained from a total of 240 radiosonde launches taken simultaneously at three New England locations in 1974; all studies were made at the 19 and 22.2 GHz frequency operating range of the radiometers. The wet path length in the zenith direction could be estimated from the surface water vapor density to an accuracy of 5 cm for the summer data and 2 cm for winter data, and with the brightness temperatures, it could be estimated to an accuracy of 0.3 cm. Two dual-frequency radiometers were also used to determine the accuracy of prediction of the path length from real radiometry data. The rms error for the estimation of wet path length from surface meteorological parameters was 3.2 cm, and for the radiometer brightness temperatures the rms error was 1.5 cm.

Moran, J. M.↗
NASA NTRS1981

Estimation of solar gravitational harmonics with Starprobe radiometric tracking data

The potential gravitational science return of a proposed spacecraft mission, called Starprobe, is investigated. The current mission plan is to place a spacecraft in a highly eccentric, highly inclined solar orbit with a perihelion distance of four solar radii. A covariance analysis based on Kalman filtering theory is performed to predict the accuracies with which gravitational parameters associated with the nonsphericity of the sun and relativistic effects can be estimated with radiometric tracking data. The accuracies are computed as functions of the quality and quantity of the radiometric data, the orbital parameters, the magnitude and character of the nongravitational accelerations acting on the spacecraft, and the errors in the tracking station locations and the ephemeris of the earth relative to the sun.

Mease, K. D.↗
NASA NTRS1982

Influence of the number of vehicles in the emergence of sound events on the annoyance expressed - experimental study

The acoustical index leg was studied to determine its accuracy in predicting annoyance from traffic noise. Annoyance was tested in experimental situations where the frequency of the number of heavy vehicles varied from 3 to 30 HV/30 min for different classes of the Leg level at 50, 55, 60 dB(A) of traffic noise. The results showed that: (1) for a constant Leg level the annoyance increases as a function of the number of HV up to a certain threshold at which the annoyance is stabilized; (2) for a constant frequency of passage of HV, the annoyance increases with the Leg level; (3) composite indexes of the type Leg + Log NHV, L1 + EMER or L1 + L10 give a predictive value greater than that of the Leg pr Log nHV taken alone.

Vallet, M.↗
NASA NTRS1982

Tests of general relativity using Starprobe radio metric tracking data

The potential of a proposed spacecraft mission, called Starprobe, for testing general relativity and providing information on the interior structure and dynamics of the sun is investigated. Parametric, gravitational perturbation terms are derived which represent relativistic effects and effects due to spatial and temporal variations in the solar potential at a given radial distance. A covariance analysis based on Kalman filtering theory predicts the accuracies with which the free parameters in the perturbation terms can be estimated with radio metric tracking data through the process of trajectory reconstruction. It is concluded that Starprobe can contribute significant information on both the nature of gravitation and the structure and dynamics of the solar interior.

Mease, K. D.↗
NASA NTRS1982

Labeling research in support of through-the-season area estimation

The development of LANDSAT-based through-the-season labeling procedures for corn and soybeans is discussed. A model for predicting labeling accuracy within key time periods throughout the growing season is outlined. Two methods for establishing the starting point of one key time period, viz., early season, are described. In addition, spectral-temporal characteristics for separating crops in the early season time period are discussed.

Colwell, R. N.↗