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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Civil Application of Differential GPS Using a Single Channel Sequential Receiver

The Global Positioning System (GPS) and its potential for area navigation, landing, and takeoff under minimum ceilings and advanced air traffic control operation is discussed. The following topics are reported: status of the GPS system; GPS signal availability for the civil community; alternative differential GPS concepts; predicted performance enhancement achievable with differential GPS and the operational improvements which will result; and a development program to test and evaluate differential GPS concepts, performance and operational procedures applicable to helicopters. Potential benefits which will be derived from helicopter use of GPS in the differential mode are identified.

Source record↗
NASA NTRS1980

The multicategory case of the sequential Bayesian pixel selection and estimation procedure

A Bayesian technique for stratified proportion estimation and a sampling based on minimizing the mean squared error of this estimator were developed and tested on LANDSAT multispectral scanner data using the beta density function to model the prior distribution in the two-class case. An extention of this procedure to the k-class case is considered. A generalization of the beta function is shown to be a density function for the general case which allows the procedure to be extended.

Pore, M. D.↗
NASA NTRS1982

Sequential deployment of truss structures

The geometry investigated most intensively was the triangular tetrahedral truss. A square type truss having the same topology was also investigated. The tetrahedral truss is composed of surface struts and core members. In the deployable form, the entire truss is viewed as being made up of a number of parallel truss ribs connected to each other by interrib struts and members. The packaging efficiency of the truss was evaluated.

Hedgebeth, J. M.↗
NASA NTRS1982

Apparatus for sequentially transporting containers

Apparatus for transferring and manipulating a plurality of containers in a sequence is disclosed including a mechanical manipulator arm having a gripping device which automatically picks up a container at a fixed pickup position P and transfers it to a processing station. At a processing station X, the container is loaded with silicon wafers and thereafter returned by the arm to the fixed position P at the pickup and return station Y. A plurality of the containers may be processed in sequence from the fixed pickup position by providing a movable carriage upon which container pedestal platforms are supported, at least one of which is an elevator platform. The platforms include abutments for properly positioning the containers for accurate pickup by the manipulator arm.

Hudgins, J. L.↗
NASA NTRS1983

Instrument for determining coincidence and elapse time between independent sources of random sequential events

An instrument that receives pulses from a primary external source and one or more secondary external sources and determines when there is coincidence between the primary and one of the secondary sources is described. The instrument generates a finite time window (coincidence aperture) during which coincidence is defined to have occurred. The time intervals between coincidence apertures in which coincidences occur are measured.

Clemmons, J. I., Jr.↗
NASA NTRS1982

Stacbeam - An efficient, low-mass, sequentially deployable structure

Design features of the stacking triangular articulated compact beam (Stacbeam) as a candidate truss structure for GEOS spacecraft solar power arrays are explored. Solar arrays of increasing size require folding, noninterfering structures, minimal thermal effects, slow and controlled deployment, and a high aspect ratio. The Stacbeam consists of a triangular batten frame perpendicular to the beam axis, three longerons attached at the corners of the batten frame and mounted parallel to the beam axis, and three diagonals to provide shear and torsional stiffness. Locking hinges are installed at the midpoint and ends of each longeron and at the midpoint and ends of each diagonal. The material is graphite/epoxy composite with a 120 GPa modulus and a 1500 kg/sq m density. Successful vertical deployment on the ground has been effected with a prototype deployer, together with horizontal cantilever in a fully deployed configuration.

Adams, L. R.↗
NASA NTRS1982

Examples of sequential radar images from Washington, Arizona and Alaska

Radar image time sequences of three areas were obtained to illustrate the capability for change detection over time intervals that range from two to fourteen years. The image sequences show geomorphic changes caused by volcanic eruption at Mount St. Helens, Washington, changes that have resulted from mining activities in the Sierrita Mining District, Arizona, and differences in the Ikpikpuk River drainage area, Alaska, that are mostly dependent on imaging system characteristics. Enhancement, suppression or distortion of features on the images are related in each case to interaction between the illumination geometry of the imaging system and the characteristics of the terrane surface. The radar images are contrasted with Landsat multispectral scanner images to illustrate the importance of resolution and shadowing for feature perception.

Ford, J. P.↗
NASA NTRS1984

Estimating net rainfall, evaporation and water storage of a bare soil from sequential L-band emissivities

A general method to use a time series of L-band emissivities as an input to a hydrological model for continuously monitoring the net rainfall and evaporation as well as the water content over the entire soil profile is proposed. The model requires a sufficiently accurate and general relation between soil emissivity and surface moisture content. A model which requires the soil hydraulic properties as an additional input, but does not need any weather data was developed. The method is shown to be numerically consistent.

Stroosnijder, L.↗
NASA NTRS1985

Sequentially-Deployable Tetrahedral Beam

Beam geometry varied three-dimensionally after beam is deployed. When tetrahedral beam completely retracted, each longeron shortened indefinitely so frames at each end of longeron folded together to lie one against other. Each tetrahedral of beam so retracted to achieve compact packaging of entire beam. Each longeron shortened by folding at midlength and ends, by telescoping, or by other means. Beam becomes crane, manipulator arm, antenna feed support, or other type of lineal structural member. Beam completely packageable, automatically deployable, and capable of having geometry varied during use.

Mikulas, Martin M., Jr.↗
NASA NTRS1987

Effects of sequential treatment with fluorine and bromine on graphite fibers

Three pitch based graphite fibers with different degrees of graphitization and one polyacryonitrile (PAN) based carbon fiber from Amoco Corporation were treated with 1 atm, room temperature fluorine gas for 90 hrs. Fluorination resulted in higher electrical conductivity for all pitch fibers. Further bromination after ambient condition defluorination resulted in further increases in electrical defluorination conductivity for less graphitized, less structurally ordered pitch fibers (P-55) which contain about 3% fluorine by weight before bromination. This product can be stable in 200 C air, or 100% humidity at 60 C. Due to its low cost, this less graphitized fiber may be useful for industrial application, such as airfoil deicer materials. The same bromination process, however, resulted in conductivity decreases for fluorine rich, more graphitized, structurally oriented pitch fibers (P-100 and P-75). Such decreases in electrical conductivity were partially reversed by heating the fibers at 185 C in air. Differential scanning calorimetric (DSC) data indicated that the more graphitized fibers (P-100) contained BrF3, whereas the less graphitized fibers (P-55) did not.

Hung, Ching-Cheh↗
NASA NTRS1990

Evaluation of the maximum cross-correlation method of estimating sea surface velocities from sequential satellite images

The maximum cross correlation (MCC) method of Leese et al. (1971) for estimating sea surface velocities from sequences of satellite images is evaluated by comparing the MCC fields obtained from sequences of AVHRR and CZCS with in situ data and velocity fields calculated with a high-resolution quasi-geostrophic model. The rms differences and vector correlations between the velocity field produced by the MCC method and the model's field are presented. It is shown that much of the difference between the MCC fields and either the in situ data or the model velocity fields can be accounted for by considering physical and biological processes not included in the MCC method. The conditions under which the method is likely to be most successful are discussed.

Tokmakian, Robin↗
NASA NTRS1992

Sequential design of a linear quadratic controller for the Deep Space Network antennas

A new linear quadratic controller design procedure is proposed for the NASA/JPL Deep Space Network antennas. The antenna model is divided into a tracking subsystem and a flexible subsystem. Controllers for the flexible and tracking parts are designed separately by adjusting the performance index weights. Ad hoc weights are chosen for the tracking part of the controller and the weights of the flexible part are adjusted. Next, the gains of the tracking part are determined, followed by the flexible controller final tune-up. In addition, the controller for the flexible part is designed separately for each mode; thus the design procedure consists of weight adjustment for small-size subsystems. Since the controller gains are obtained by adjusting the performance index weights, determination of the weight effect on system performance is a crucial task. A method of determining this effect that allows an on-line improvement of the tracking performance is presented in this article. The procedure is illustrated with the control system design for the Deep Space Station (DSS)-13 antenna.

Gawronski, W.↗
NASA NTRS1992

The stellar content of LH 9 and 10 (N11) in the LMC - A case for sequential star formation

The young OB associations Lucke-Hodge 9 and 10 are studied with UBV photometry that is independent of reddening to determine the IMF directly from star counts. The temperature and reddening of the stars are determined which, in conjunction with the spectroscopic classification of the earliest stars, is employed to place the stellar groups on the theoretical H-R diagram. Observations are also presented of the highly compact H II region/knot N11A and the multiple system HD 32228, and LH 9 and 10 are compared. The Lyman ionizing flux calculated at 4.9-7.2 x 10 exp 50/s agrees well with flux required to generate the H-alpha luminosity of the H II region. LH 10 has a much flatter slope, a higher ratio of higher-mass to lower-mass stars, and greater reddening than LH 9, and LH 10 contains all of the O stars earlier than O6. It is concluded that LH 9 is older than LH 10 and probably contributed to the initiation of star formation in LH 10.

Parker, Joel WM.↗