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At least 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
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 NTRS1981

Construction and performance characteristics of a prototype NBS/GPS receiver

The construction and performance characteristics of a low-cost, high-accuracy GPS C/A receiver are reviewed. The receiver takes advantage of a simultaneous common view of the same satellites, which could allow time transfer with accuracies on the order of 10 ns or less for baselines as large as 3000 km. Frequency can be measured to better than one part in 10 to the 14th. The software and the receiver are configured to be fully automatic with a Z80A microprocessor setting the amplitude for the lock loops of the receiver and setting the synthesizer with corrects for Doppler shift. The microprocessor can calibrate a 0.1 ns built-in time interval counter.

Davis, D. D.↗
NASA NTRS1983

KSC Construction Cost Index

Kennedy Space Center cost Index aids in conceptual design cost estimates. Report discusses development of KSC Cost Index since January 1974. Index since January 1974. Index provides management, design engineers, and estimators an up-to-data reference for local labor and material process. Also provides mount and rate of change in these costs used to predict future construction costs.

Brown, J. A.↗
NASA NTRS1984

Algorithm for Constructing Contour Plots

General computer algorithm developed for construction of contour plots. algorithm accepts as input data values at set of points irregularly distributed over plane. Algorithm based on interpolation scheme: points in plane connected by straight-line segments to form set of triangles. Program written in FORTRAN IV.

Johnson, W.↗
NASA NTRS1982

Construction of a remotely sensed area sampling frame for Southern Brazil

A remotely sensed area sampling frame was constructed for selected areas in Southern Brazil. The sampling unit information was stored in digital form in a latitudinal/longitudinal characterized population. Computerized sampling procedures were developed which allow for flexibility in sample unit specifications and sampling designs.

Fecso, R.↗
NASA NTRS1983

Space Construction Experiment Definition Study (SCEDS), part 3. Volume 1: Executive summary

Study tasks were directed toward definition of an early shuttle controls and dynamics flight experiment, as well as evolutionary or supplemental experiments, that address the needs of the dynamics and controls community and demonstrates the shuttle system capability to perform construction operations. A requirement that the first bending mode of the SCE be above 0.15 Hertz to avoid coupling with the DAP was adopted.

Source record↗
NASA NTRS1983

Space Construction Experiment Definition Study (SCEDS), part 3. Volume 2: Study results

The essential controls and dynamics community needs for a large space structures is addressed by the basic Space Construction Experiments (SCE)/MAST configuration and enhanced configurations for follow-on flights. The SCE/MAST can be integrated on a single structures technology experiments platform (STEP). The experiment objectives can be accomplished without the need for EVA and it is anticipated that further design refinements will eliminate the requirement to use the remote manipulator system.

Source record↗
NASA NTRS1982

Evolution of the Tharsis province of Mars - The importance of heterogeneous lithospheric thickness and volcanic construction

A new model for the origin and evolution of the Tharsis province that emphasizes that the topography of Tharsis may be produced largely by construction, rather than uplift, is proposed. Underlying the model is the premise that the elastic lithosphere of Mars was laterally heterogeneous early in Martian history; such heterogeneity is discernible later in Martian history from the variable tectonic response of the lithosphere to local surface loads. It is contended that the mechanism for the evolution of Tharsis described here led to permanent topographic and gravity highs and a greatly thickened crust in the Tharsis region. An important advantage of the model is that no anomalous dynamical or chemical properties need be sustained in the Martian mantle beneath Tharsis for billions of years. The mantle beneath Tharsis is thus seen as playing a passive rather than an active role in the regional volcanic and tectonic activity, much like the role of the mantle beneath major midocean ridges on earth.

Solomon, S. C.↗
NASA NTRS1982

Computer constructed imagery of distant plasma interaction boundaries

Computer constructed sketches of plasma boundaries arising from the interaction between the solar wind and the magnetosphere can serve as both didactic and research tools. In particular, the structure of the earth's bow shock can be represented as a nonuniform surfce according to the instantaneous orientation of the IMF, and temporal changes in structural distribution can be modeled as a sequence of sketches based on observed sequences of spacecraft-based measurements. Viewed rapidly, such a sequence of sketches can be the basis for representation of plasma processes by computer animation.

Greenstadt, E. W.↗
NASA NTRS1984

A manned-machine space station construction concept

A design concept for the construction of a permanent manned space station is developed and discussed. The main considerations examined in developing the design concept are: (1) the support structure of the station be stiff enough to preclude the need for an elaborate on-orbit system to control structural response, (2) the station support structure and solar power system be compatible with existing technology, and (3) the station be capable of growing in a systematic modular fashion. The concept is developed around the assembly of truss platforms by pressure-suited astronauts operating in extravehicular activity (EVA), assisted by a machine (Assembly and Transport Vehicle, ATV) to position the astronauts at joint locations where they latch truss members in place. The ATV is a mobile platform that is attached to and moves on the station support structure using pegs attached to each truss joint. The operation of the ATV is described and a number of conceptual configurations for potential space stations are developed.

Mikulas, M. M., Jr.↗
NASA NTRS1984

Using a commercial CAD system for simultaneous input to theoretical aerodynamic programs and wind-tunnel model construction

The Computer Aided Design (CAD) system's common geometry database was used to generate input for theoretical programs and numerically controlled (NC) tool paths for wind tunnel part fabrication. This eliminates the duplication of work in generating separate geometry databases for each type of analysis. Another advantage is that it reduces the uncertainty due to geometric differences when comparing theoretical aerodynamic data with wind tunnel data. The system was adapted to aerodynamic research by developing programs written in Design Analysis Language (DAL). These programs reduced the amount of time required to construct complex geometries and to generate input for theoretical programs. Certain shortcomings of the Design, Drafting, and Manufacturing (DDM) software limited the effectiveness of these programs and some of the Calma NC software. The complexity of aircraft configurations suggests that more types of surface and curve geometry should be added to the system. Some of these shortcomings may be eliminated as improved versions of DDM are made available.

Enomoto, F.↗
NASA NTRS1983

Combustor liner construction

A combustor liner is fabricated from a plurality of individual segments each containing counter/parallel Finwall material and are arranged circumferentially and axially to define the combustion zone. Each segment is supported by a hook and ring construction to an opened lattice frame with sufficient tolerance between the hook and ring to permit thermal expansion with a minimum of induced stresses.

Craig, H. M.↗
NASA NTRS1982

Advanced Strain-Isolation-Pad Material with Bonded Fibrous Construction

The feasibility of utilizing air lay and liquid lay felt deposition techniques to fabricate strain isolation pad (SIP) materials for the Space Shuttle Orbiter was demonstrated. These materials were developed as candidate replacements for the present needled felt SIP used between the ceramic tiles and the aluminum skin on the undersurface of the Orbiter. The SIP materials that were developed consisted of high temperature aramid fibers deposited by controlled fluid (air or liquid) carriers to form low density unbonded felts. The deposited felts were then bonded at the fiber intersections with a small amount of high temperature polyimide resin. This type of bonded felt construction can potentially eliminate two of the problems associated with the present SIP, viz., transmittal of localized stresses into the tiles and load history dependent mechanical response. However, further work is needed to achieve adequate through thickness tensile strength in the bonded felts.

Seibold, R. W.↗
NASA NTRS1985

Boundary to Constructive Solid Geometry Mappings: a Focus on 2-D Issues

The problem of converting boundary representation (B-rep) to constructive solid geometry representation (CSG-rep) (and vice versa) is discussed in two phases. The first phase entails finding a CSG-rep that defines the region bounded by a polygonal profile curve. The second phase utilizes the results of the first phase to find a CSG-rep for many non-polygonal profile curves. A mathematically concise representation of a region bounded by a polygonal is presented. Namely, any polygonal region bounded by an n sided polygon may be represented by a binary tree which has at most n planar halfspaces as leaves. A structure for this representation and an algorithm for calculating is discussed.

Peterson, D. P.↗
NASA NTRS1985

Materials and techniques for model construction

The problems confronting the designer of models for cryogenic wind tunnel models are discussed with particular reference to the difficulties in obtaining appropriate data on the mechanical and physical properties of candidate materials and their fabrication technologies. The relationship between strength and toughness of alloys is discussed in the context of maximizing both and avoiding the problem of dimensional and microstructural instability. All major classes of materials used in model construction are considered in some detail and in the Appendix selected numerical data is given for the most relevant materials. The stepped-specimen program to investigate stress-induced dimensional changes in alloys is discussed in detail together with interpretation of the initial results. The methods used to bond model components are considered with particular reference to the selection of filler alloys and temperature cycles to avoid microstructural degradation and loss of mechanical properties.

Wigley, D. A.↗
NASA NTRS1984

Construction of complementary code sequence sets, part 7.1D

A set of code sequences is a complementary code sequence set if the sum of the aperiodic autocorrelation functions for the sequences is zero everywhere except at the origin. A simple construction for sets of complementary code sequences is discussed.

Sarwate, D. V.↗
NASA NTRS1985

Construction of a cosmic ray air shower telescope

The telescope under construction is mainly for the purpose of locating the arrival directions of energetic particles and quanta which generate air showers of sizes 10 to the 5th power to 10 to the 6th power. Both fast timing method and visual track method are incorporated in determining the arrival directions. The telescope is composed of four stations using scintillators and neon flash tubes as detectors. The system directional resolution is better than 1.5 deg.

Ng, L. K.↗