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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Geometric error analysis for shuttle imaging spectrometer experiment

The demand of more powerful tools for remote sensing and management of earth resources steadily increased over the last decade. With the recent advancement of area array detectors, high resolution multichannel imaging spectrometers can be realistically constructed. The error analysis study for the Shuttle Imaging Spectrometer Experiment system is documented for the purpose of providing information for design, tradeoff, and performance prediction. Error sources including the Shuttle attitude determination and control system, instrument pointing and misalignment, disturbances, ephemeris, Earth rotation, etc., were investigated. Geometric error mapping functions were developed, characterized, and illustrated extensively with tables and charts. Selected ground patterns and the corresponding image distortions were generated for direct visual inspection of how the various error sources affect the appearance of the ground object images.

Wang, S. J.↗
NASA NTRS1984

A geometric analysis of surface deformation - Implications for the tectonic evolution of Ganymede

The identification of various types of surface deformation of Ganymede by a geometric study of the furrow system and an analysis of circularity of impact craters is addressed. The hypothesis that the furrow system was initially concentric and that the present configuration of the furrows provides a measure of lateral motion of dark terrain is tested by determining the present centers of the furrow system in several dark terrain blocks and observing the amount of deformation in bright terrain regions which separate these blocks. An upper scale limit is placed on the amount of extension associated with bright terrain formation by using the deviation from circularity of impact craters to calculate the strain field around wedge-shaped regions of bright terrain. Penetrative deformation in Ganymede's lithosphere is identified by examining the circularity of impact craters in dark terrain.

Zuber, M. T.↗
NASA NTRS1983

Geometric correction process for the Landsat-4 Thematic Mapper

The processing approaches which form the basis of the Landsat-4 Thematic Mapper (TM) geometric correction system are summarized. The correction is accomplished in two phases. In the first phase, correction data are generated. The spacecraft position, TM frame attitude, TM scanning mirror position, and detector sampling are found as a function of time through a combination of flight segment measurements, ground segment modeling, and control point information. The data, along with the earth position and geoid model, are used to determine the earth location for each TM image sample. Then, using map projections, correction data can be generated which define the location of each TM image sample on the output coordinate system. In the second phase, the correction data are used to resample TM detector samples onto the output coordinate system.

Beyer, E. P.↗
NASA NTRS1984

A geometric model for excavation and modification at terrestrial simple impact craters

A geometric model for the excavation and modification stages of simple crater development is presented. Cavity modification is modelled from an analytical derivation of the dimensions of the so-called transient cavity (Dence, 1973; Dence et al., 1977). The final cavity as it appears in terrestrial craters and the primary elements of excavation are approximated by a variation of the so-called Z model. The applicability of the model is tested with data from the Meteor and Brent craters. In the case of Meteor, the modelled final crater diameter at the original ground plane is within 26 m of the observed value and the modelled breccia lens and the rim crest volumes of the final true crater are within 9.5 percent and 2.5 percent, respectively, of the observed values. The correspondence for the more degraded Brent crater is less precise.

Grieve, R. A. F.↗
NASA NTRS1985

The geometric extent of C II (UV 0.01) emitting regions around luminous, late-type stars

A method is presented by which the geometric extent of the chromospheres around late-type stars can be estimated from measurements of the total emission-line flux and line ratios within the C II (UV 0.01) multiplet. Application of this technique to a sample of 15 late-type stars indicates a clear difference in the radial extent of the chromospheres around coronal and noncoronal stars. The former stars appear to have very thin chromospheres (of no more than 0.1 percent of the photospheric radius), while the latter stars have chromospheres extending, on average, out to 2.5 photospheric radii. This, in principle, provides information for understanding structural differences between late-type giant and supergiant stars with and without coronae, and could lead to an understanding of the mass-loss mechanisms involved.

Carpenter, K. G.↗
NASA NTRS1983

Robot arm geometric link parameter estimation

A general method for estimating serial link manipulator geometric parameter errors is proposed in this paper. The positioning accuracy of the end-effector may be increased significantly by updating the nominal link parameters in the control software to represent the physical system more accurately. The proposed method is applicable for serial link manipulators with any combination of revolute or prismatic joints, and is not limited to a specific measurement technique.

Hayati, S. A.↗
NASA NTRS1986

Deformable Subreflector Computed by Geometric Optics

Distorted antenna surfaces forced to produce a uniform wave front. SUBFORMING employs geometric optics in determining subreflector coordinates to match main reflector surface with known distortions. Antenna with distorted paraboloidal reflecting surface forced to produce uniform wave front by using a Cassegrainian geometry with path-length-compensating subreflector. Program written in FORTRAN V for batch execution.

Williams, W. F.↗
NASA NTRS1983

Geometric and structural properties of a rectangular supercritical wing oscillated in pitch for measurement of unsteady transonic pressure distributions

Wind-tunnel tests to measure unsteady aerodynamic data in the transonic region have been completed on an aspect ratio 2.0 rectangular wing with a supercritical airfoil. The geometric and structural properties of the wing are presented. (Other references contain the measured aerodynamic data.) Both measured and design airfoil coordinates are presented and compared. In addition, measured wing bending and torsional stiffness distributions and some trailing-edge flexibility influence coefficients are presented.

Ricketts, R. H.↗
NASA NTRS1986

Effect of crystallographical and geometrical changes of a ferrite head on magnetic signals during the sliding process with magnetic tape

This paper reviews changes in the crystalline structure and geometry of lapped Mn-Zn ferrite heads in sliding contact with magnetic tape and the effects of these changes on magnetic signals. A highly textured, polycrystalline structure was produced on the surface of a single-crystal Mn-Zn ferrite head when it was finished with an aluminum oxide lapping tape. Sliding this lapped surface against a magnetic tape produced a nearly amorphous structure. The sliding process led to a degradation in readback signal of 1 to 2 dB (short-wavelength recording). Furthermore, wear of the magnetic head caused geometrical changes in the head surface. The signal read back with the worn magnetic head was sensitive to operating parameters such as head displacement and tape tension. A change in operating parameters created head-to-tape spacings and, consequently, excessive gains or losses in the readback signal.

Miyoshi, K.↗
NASA NTRS1985

Geometric accuracy of Landsat-4 and Landsat-5 Thematic Mapper images

The geometric accuracy (GA) and errors in imagery by Landsat-4 and -5 were examined using data from regions with a minimal topography. A least-squares comparison was made between ground truth digitized photographs and TM data for prominent features displayed on a 1:24,000 map. The algorithms used for the transformation of the Landsat data to a Cartesian system are provided. Landsat-5 images had a calculated error of 11.2 m (0.4 pixel) and could not be improved with skew and affine-distortion corrections. However, the digitized images, including road tracks, were considered detailed enough for standard 1:50,000 maps. Landsat-5 imagery, when fully corrected, was consistently superior to Landsat-4 data.

Batson, R. M.↗
NASA NTRS1985

Geometric correction of Landsat 4 and 5 Thematic Mapper data

Landsat-4 was launched on July 16, 1982, while the launch of Landsat-5 took place on March 1, 1984. The earth-observing instruments employed were the Multispectral Scanner (MSS), which has flown since 1972 on Landsat satellites, and the Thematic Mapper (TM). The TM provides improved spatial radiance and spectral resolution. The improved capabilities of the TM, the use of different scanning mechanisms relative to the MSS, and the use of a new spacecraft with different mechanical operating characteristics led to a significant challenge in processing the TM and MSS data. The current paper has mainly the objective to present recent results which can provide information regarding the quality of processing as measured against specifications. The results obtained so far for the Thematic Mapper Image Processing System (TIPS), though limited, are found to be quite encouraging as far as the geometric processing of the TM is concerned.

Beyer, E. P.↗
NASA NTRS1986

The structure of the Uranian atmosphere - Constraints from the geometric albedo spectrum and H2 and CH4 line profiles

Recent high quality spectral observations have allowed the derivation of constraints on the atmospheric structure of Uranus. The present analysis, which is based on the detailed modeling of a broadband geometric albedo spectrum and high resolution observations of the H2 4-0 quadrupole and 6818.9-A CH4 features, yields (1) a family of models which parameterize an upper tropospheric haze layer, (2) a lower, optically infinite cloud at a given pressure level, (3) the cloud-level methane molar fraction, and (4) the mean ortho/para ratio in the visible atmosphere. The single scattering albedo of atmospheric aerosols exhibits a steep darkening between 5890 and 6040 A.

Baines, K. H.↗
NASA NTRS1986

Geometrization of spin and the Weyssenhoff fluid conjecture

It is shown that the logical treatment of spinning perfect fluids occurs in a metric-torsion space-time with or without mass conservation. The Lagrangian formulation of a spin density fluid is reviewed, concentrating on the relationship between spin and torsion for metric-torsion space-times. The significance of the mass constraint is discussed, and its consequences for the variation of the Lagrangian is given. That consequence is the geometrization of spin; that is, the Weyssenhoff form relating spin and the trace-free torsion is obtained without any ad hoc assumption.

Smalley, L. L.↗
NASA NTRS1986

Landsat D Thematic Mapper image dimensionality reduction and geometric correction accuracy

To characterize and quantify the performance of the Landsat thematic mapper (TM), techniques for dimensionality reduction by linear transformation have been studied and evaluated and the accuracy of the correction of geometric errors in TM images analyzed. Theoretical evaluations and comparisons for existing methods for the design of linear transformation for dimensionality reduction are presented. These methods include the discrete Karhunen Loeve (KL) expansion, Multiple Discriminant Analysis (MDA), Thematic Mapper (TM)-Tasseled Cap Linear Transformation and Singular Value Decomposition (SVD). A unified approach to these design problems is presented in which each method involves optimizing an objective function with respect to the linear transformation matrix. From these studies, four modified methods are proposed. They are referred to as the Space Variant Linear Transformation, the KL Transform-MDA hybrid method, and the First and Second Version of the Weighted MDA method. The modifications involve the assignment of weights to classes to achieve improvements in the class conditional probability of error for classes with high weights. Experimental evaluations of the existing and proposed methods have been performed using the six reflective bands of the TM data. It is shown that in terms of probability of classification error and the percentage of the cumulative eigenvalues, the six reflective bands of the TM data require only a three dimensional feature space. It is shown experimentally as well that for the proposed methods, the classes with high weights have improvements in class conditional probability of error estimates as expected.

Ford, G. E.↗
NASA NTRS1987

A higher-order theory for geometrically nonlinear analysis of composite laminates

A third-order shear deformation theory of laminated composite plates and shells is developed, the Navier solutions are derived, and its finite element models are developed. The theory allows parabolic description of the transverse shear stresses, and therefore the shear correction factors of the usual shear deformation theory are not required in the present theory. The theory also accounts for the von Karman nonlinear strains. Closed-form solutions of the theory for rectangular cross-ply and angle-ply plates and cross-ply shells are developed. The finite element model is based on independent approximations of the displacements and bending moments (i.e., mixed finite element model), and therefore, only C sup o -approximation is required. The finite element model is used to analyze cross-ply and angle-ply laminated plates and shells for bending and natural vibration. Many of the numerical results presented here should serve as references for future investigations. Three major conclusions resulted from the research: First, for thick laminates, shear deformation theories predict deflections, stresses and vibration frequencies significantly different from those predicted by classical theories. Second, even for thin laminates, shear deformation effects are significant in dynamic and geometrically nonlinear analyses. Third, the present third-order theory is more accurate compared to the classical and firt-order theories in predicting static and dynamic response of laminated plates and shells made of high-modulus composite materials.

Reddy, J. N.↗
NASA NTRS1986

Geometric radiating surfaces for spacecraft thermal control

Various geometric radiating surface (GRS) configurations are evaluated analytically and experimentally for potential use in spacecraft thermal control systems. Egg-crate, honeycomb, flat-parallel, curved-parallel, chevron-shape, and composite fin radiator panel designs were evaluated in terms of mass, apparent emissivity, meteoroid protection, and ease of fabrication; the parallel-finned GRS in composite form was chosen as the most efficient design. The performance of the composite-finned GRS was compared with that of a silver-backed Teflon radiator. The emissivity and dissipative power capabilities of the GRS and radiator are measured. It is observed that the composite-finned GRS has 34 percent less surface area, 34 percent higher heat flux capability, greater meteoroid protection, and 2.8 times higher mass than the Teflon radiator. Future developments and applications for GRCs are discussed.

Keddy, M. D.↗
NASA NTRS1985

Thematic Mapper Image Processing System - Geometric correction performance for Landsat-5

Geometric correction performance data are presented for the Landsat-5 Thematic Mapper and the Thematic Mapper Image Processing System. Temporal registration and geodetic rectification results are displayed in the form of 90 percent errors. Both error estimation and direct measurements demonstrate that the instrument and system meet performance requirements.

Brooks, J.↗
NASA NTRS1986

A geometric approach to the synthesis of failure detection filters

A geometric formulation of Beard's failure detection filter problem is stated using the concepts of (C, A)-invariant and unobservability subspaces. The notions of output separable and mutually detectable families of subspaces introduced by Beard are also clarified. It is shown that mutual detectability is a necessary and sufficient condition for the existence of a detection filter with arbitrarily assignable spectrum. Moreover, it is shown that the failure detection filter problem has a computationally simple solution when the failure events satisfy some mild restrictions. Finally, the complete duality between a generalization of Beard's detection filter problem and the restricted control decoupling problem is illustrated.

Massoumnia, M.-A.↗