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NASA NTRS2014

Vision Algorithm for the Solar Aspect System of the High Energy Replicated Optics to Explore the Sun Mission

This work covers the design and test of a machine vision algorithm for generating high- accuracy pitch and yaw pointing solutions relative to the sun on a high altitude balloon. It describes how images were constructed by focusing an image of the sun onto a plate printed with a pattern of small cross-shaped fiducial markers. Images of this plate taken with an off-the-shelf camera were processed to determine relative position of the balloon payload to the sun. The algorithm is broken into four problems: circle detection, fiducial detection, fiducial identification, and image registration. Circle detection is handled by an "Average Intersection" method, fiducial detection by a matched filter approach, and identification with an ad-hoc method based on the spacing between fiducials. Performance is verified on real test data where possible, but otherwise uses artificially generated data. Pointing knowledge is ultimately verified to meet the 20 arcsecond requirement.

0000000↗

NASA NTRS1987

Nonuniform sampling techniques for antenna applications

A two-dimensional sampling technique, which can employ irregularly spaced samples (amplitude and phase) in order to generate the complete far-field patterns is presented. The technique implements a matrix inversion algorithm, which depends only on the nonuniform sampled data point locations and with no dependence on the actual field values at these points. A powerful simulation algorithm is presented to allow a real-life simulation of many reflector/feed configurations and to determine the usefulness of the nonuniform sampling technique for the copolar and cross-polar patterns. Additionally, an overlapped window concept and a generalized error simulation model are discussed to identify the stability of the technique for recovering the field data among the nonuniform sampled data. Numerical results are tailored for the pattern reconstruction of a 20-m offset reflector antenna operating at L-band. This reflector is planned to be used in a proposed measurement concept of large antenna aboard the Space Shuttle, whereby it would be almost impractical to accurately control the movement of the Shuttle with respect to the RF source in prescribed directions in order to generate uniform sampled points. Also, application of the nonuniform sampling technique to patterns obtained using near-field measured data is demonstrated. Finally, results of an actual far-field measurement are presented for the construction of patterns of a reflector antenna from a set of nonuniformly distributed measured amplitude and phase data.

Rahmat-Samii, Yahya↗

NASA NTRS1967

The analysis of Gemini 7 EEG data by three different computer oriented methods

The problem in assessment of electroencephalograms has been the subject element in visual evaluations of such records as well as the need for extensive training (2 or 3 years) before suitable candidate is capable to perform this task. There have been variety of computer type analyses of EEG during the past ten years or more, and we are still searching for a reliable, inexpensive, online data processing procedure for this task. We are aware our Soviet colleagues are routinely using computer assessment of EEGs, using relatively inexpensive hardware. In our report we endeavor to show how four different assessment procedures (visual assessment, zero crossing technique, smoothing and peak counting technique, and Weibull Statistic) may be utilized, and indicate the advantages and disadvantages peculiar to each. We wish to point out that in the Gemini 7 EEG analog records supplied to the Henry Ford Hospital, Channel II (mid-line central to mid-line occipital electrodes) could not be assessed reliably after approximately 26 hours of flight. Channel I (left central to left occipital electrodes) provided the more assessable EEG up to approximately 54 hours of flight. These channels were compared during the first 26 hours of flight, and no significant difference was found by our various assessment procedures. We, therefore, have limited this report to the findings on the analyses of Channel I during its approximate 54 hours of flight.

Proctor, L. D.↗

NASA NTRS1972

Lunar reflectivity at 0.86-centimeter wavelength.

Measurement of backscattering of 0.86-cm circularly polarized radiation by 29 regions on the moon. Both circular polarizations were received. At a given angle of incidence, power received in the 'expected' polarization was greater for the highland regions than for the seas by roughly 1 dB. For moderately large angles of incidence phi, this return diminishes more rapidly than cosine phi, although perhaps not as rapidly as it does at longer wavelengths. The cross section of the whole moon is 5 plus or minus 2% of the geometric cross section; about 80% of the cross section is ascribable to diffuse scattering. The polarization ratio for the echoes varies smoothly with the angle of incidence, from 0.7 at the subradar point to 0.4 at 70 deg. The depolarization is the same for marial and highland regions, and at large angles of incidence it is the same as has been found at 23 and 68 cm by other workers.

Mccue, J. J. G.↗

NASA NTRS1972

Analysis of the Injection of a Heated, Turbulent Jet into a Moving Mainstream, with Emphasis on a Thermal Discharge in a Waterway

An experimental and theoretical investigation was undertaken to study the trajectory and growth of thermal effluents having a range of discharge velocities and temperatures. The discharge of a turbulent effluent into a waterway was mathematically modeled as a submerged jet injection process by using an integral method which accounts for natural fluid mechanisms such as turbulence, entrainment, buoyancy, and heat transfer. The analytical results are supported by experimental data and demonstrate the usefulness of the theory for estimating the location and size of the effluent with respect to the discharge point. The capability of predicting jet flow properties, as well as two- and three-dimensional jet paths, was enhanced by obtaining the jet cross-sectional area during the solution of the conservation equations. Realistic estimates of temperature in the effluent were acquired by accounting for heat losses in the jet flow due to forced convection and to entrainment of free-stream fluid into the jet.

Campbell, J. F.↗

NASA NTRS1979

Bonded orthotropic strips with cracks

The elastostatic problem for a nonhomogeneous plane which consists of two sets of periodically arranged dissimilar orthotropic strips is considered. It is assumed that the plane contains a series of collinear cracks perpendicular to the interfaces and is loaded in tension away from and perpendicular to the cracks. The problem of cracks fully imbedded into the homogeneous strips is considered. The singular behavior of the stresses for two special crack geometries is studied. The first is the case of a broken laminate in which the crack tips touch the interfaces. The second is the case of cracks crossing the interfaces. An interesting result found from the analysis of the latter is that for certain orthotropic material combinations the stress state at the point of intersection of a crack and an interface may be bounded whereas in isotropic materials at this point stresses are always singular. A number of numerical examples are worked out to separate the primary material parameters influencing the stress intensity factors and the powers of stress singularity, and to determine the trends regarding the influence of the secondary parameters. Some numerical results are given for the stress intensity factors in certain basic crack geometries and for typical material combinations.

Delale, F.↗

NASA NTRS1980

Large Antenna Multifrequency Microwave Radiometer (LAMMR) system design

The large Antenna Multifrequency Microwave Radiometer (LAMMR) is a high resolution 4 meter aperture scanning radiometer system designed to determine sea surface temperature and wind speed, atmospheric water vapor and liquid water, precipitation, and various sea ice parameters by interpreting brightness temperature images from low Earth orbiting satellites. The LAMMR with dual linear horizontal and vertical polarization radiometer channels from 1.4 to 91 GHZ can provide multidiscipline data with resolutions from 105 to 7 km. The LAMMR baseline radiometer system uses total power radiometers to achieve delta T's in the 0.5 to 1.7 K range and system calibration accuracies in the 1 to 2 deg range. A cold sky horn/ambient load two point calibration technique is used in this baseline concept and the second detector output uses an integrated and dump circuit to sample the scanning cross-tract resolution cells.

King, J. L.↗

NASA NTRS1989

Off-nadir radar altimetry

The characteristics of nadir versus off-nadir altimetry are reviewed and contrasted and a potentially serious problem has been pointed out that has been overlooked by earlier investigators, who focused on the nongeophysical error sources in off-nadir altimetry. Spatial gradients of radar cross section on the sea surface, caused by wind or current gradients or the variation of radar cross section with incidence angle, could introduce significant range errors in off-nadir altimeter. This potentially crippling effect can be overcome by leaving the traditional 13-GHz frequency and implementing the multibeam altimeter at 36 GHz. A multibeam altimeter proposed for the EOS (Earth Observing System) is described as well as a multimode airborne radar altimeter being developed to study problems inherent in off-nadir altimetry.

Parsons, Chester L.↗

NASA NTRS1990

Changes in geometrical and biomechanical properties of immature male and female rat tibia

The differences in the geometry and mechanical properties of immature male and female rat tibiae were detailed in order to provide comparative data for spaceflight, exercise, or disease experiments that use immature rats as an animal model. The experiment focuses on the particularly rapid period of growth that occurs in the Sprague-Dawley rat between 40 and 60 d of age. Tibial length and middiaphysical cross-sectional data were analyzed for eight different groups of rats according to age and sex, and tibial mechanical properties were obtained via three-point bending tests to failure. Results indicate that, during the 15 d period of rapid growth, changes in rat tibial geometry are more important than changes in bone material properties for influencing the mechanical properties of the tibia. Male tibiae changed primarily in structural properties, while in the female rats major changes in mechanical properties of the tibia were only attributable to changes in the structural properties of the bone.

Zernicke, Ronald F.↗

NASA NTRS1990

Scattering by an impedance sphere coated with a chiral layer

The scattering of a plane, linearly polarized electromagnetic wave by a sphere on whose surface an impedance boundary condition holds, and that is covered with a concentric layer of chiral material, is considered. Exact, explicit expressions are derived for the scattered field coefficients. The co-polarized and cross-polarized components of the far backscattered field are determined and discussed. The value of this canonical problem as a benchmark for computer codes is pointed out.

Uslenghi, Piergiorgio L. E.↗

NASA NTRS1996

Research In Nonlinear Flight Control for Tiltrotor Aircraft Operating in the Terminal Area

The research during the first year of the effort focused on the implementation of the recently developed combination of neural net work adaptive control and feedback linearization. At the core of this research is the comprehensive simulation code Generic Tiltrotor Simulator (GTRS) of the XV-15 tilt rotor aircraft. For this research the GTRS code has been ported to a Fortran environment for use on PC. The emphasis of the research is on terminal area approach procedures, including conversion from aircraft to helicopter configuration. This report focuses on the longitudinal control which is the more challenging case for augmentation. Therefore, an attitude command attitude hold (ACAH) control augmentation is considered which is typically used for the pitch channel during approach procedures. To evaluate the performance of the neural network adaptive control architecture it was necessary to develop a set of low order pilot models capable of performing such tasks as, follow desired altitude profiles, follow desired speed profiles, operate on both sides of powercurve, convert, including flaps as well as mastangle changes, operate with different stability and control augmentation system (SCAS) modes. The pilot models are divided in two sets, one for the backside of the powercurve and one for the frontside. These two sets are linearly blended with speed. The mastangle is also scheduled with speed. Different aspects of the proposed architecture for the neural network (NNW) augmented model inversion were also demonstrated. The demonstration involved implementation of a NNW architecture using linearized models from GTRS, including rotor states, to represent the XV-15 at various operating points. The dynamics used for the model inversion were based on the XV-15 operating at 30 Kts, with residualized rotor dynamics, and not including cross coupling between translational and rotational states. The neural network demonstrated ACAH control under various circumstances. Future efforts will include the implementation into the Fortran environment of GTRS, including pilot modeling and NNW augmentation for the lateral channels. These efforts should lead to the development of architectures that will provide for fully automated approach, using similar strategies.

Calise, A. J.↗

NASA NTRS2007

Risk Reduction and Measures of Injury for EVA Associated Upper Extremity Medical Issues: Extended Vent Tube Study

During Neutral Buoyancy Lab (NBL) training sessions, a large amount of moisture accumulates in the EVA gloves. The glove design restricts the extension of the EVA suit s ventilation/cooling system to the hand. Subungual redness and fingernail pain develops for many astronauts following their NBL training sessions with subsequent oncholysis occurring over succeeding weeks. Various attempts have been made to reduce or avoid this problem. The causal role of moisture has yet to be defined. Methods: To determine the contribution that moisture plays in the injury to the fingers and fingernails during EVA training operations in NBL, the current Extravehicular Mobility Unit (EMU), with a Portable Life Support System (PLSS) was configured with a ventilation tube that extended down a single arm of the crewmember during the test and compared with the unventilated contralateral arm; with the ventilated hand serving as the experimental condition (E) and the opposite arm as the control (C). A cross-over design was used with opposite handedness for the vent tube on a subsequent NBL training run. Moisture content measures were conducted at six points on each hand with three types of moisture meters. A questionnaire was administered to determine subjective thermal hand discomfort, skin moisture perception, and hand and nail discomfort. Photographs and video were recorded. Measures were applied to six astronauts pre- and post-run in the NBL. Results: The consistent trends in relative hydration ratios at the dorsum, from 3.34 for C to 2.11 for E, and first ring finger joint locations, from 2.46 for C to 1.96 for E, indicated the extended vent tube promoted skin drying. The experimental treatment appeared to be more effective on the left hand versus the right hand, implying an interaction with hand anthropometry and glove fit. Video analyses differentiated fine and gross motor training tasks during runs and will be discussed. Conclusions: This potential countermeasure was effective in reducing the risks of hand and nail discomfort symptoms from moderate to low in two of six subjects. Improved design in the ventilation pattern of such a countermeasure is expected to improve the countermeasure s efficiency.

Jones, Jeffrey A.↗

NASA NTRS2012

Multi-Beam Approach for Accelerating Alignment and Calibration of HyspIRI-Like Imaging Spectrometers

A paper describes an optical stimulus that produces more consistent results, and can be automated for unattended, routine generation of data analysis products needed by the integration and testing team assembling a high-fidelity imaging spectrometer system. One key attribute of the system is an arrangement of pick-off mirrors that provides multiple input beams (five in this implementation) to simultaneously provide stimulus light to several field angles along the field of view of the sensor under test, allowing one data set to contain all the information that previously required five data sets to be separately collected. This stimulus can also be fed by quickly reconfigured sources that ultimately provide three data set types that would previously be collected separately using three different setups: Spectral Response Function (SRF), Cross-track Response Function (CRF), and Along-track Response Function (ARF), respectively. This method also lends itself to expansion of the number of field points if less interpolation across the field of view is desirable. An absolute minimum of three is required at the beginning stages of imaging spectrometer alignment.

Eastwood, Michael L.↗

NASA NTRS1988

Tip aerodynamics and acoustics test: A report and data survey

In a continuing effort to understand helicopter rotor tip aerodynamics and acoustics, a flight test was conducted by NASA Ames Research Center. The test was performed using the NASA White Cobra and a set of highly instrumented blades. All aspects of the flight test instrumentation and test procedures are explained. Additionally, complete data sets for selected test points are presented and analyzed. Because of the high volume of data acquired, only selected data points are presented. However, access to the entire data set is available to the researcher on request.

Cross, Jeffrey L.↗

NASA NTRS1994

Correlation of finite element free vibration predictions using random vibration test data

Finite element analysis is regularly used during the engineering cycle of mechanical systems to predict the response to static, thermal, and dynamic loads. The finite element model (FEM) used to represent the system is often correlated with physical test results to determine the validity of analytical results provided. Results from dynamic testing provide one means for performing this correlation. One of the most common methods of measuring accuracy is by classical modal testing, whereby vibratory mode shapes are compared to mode shapes provided by finite element analysis. The degree of correlation between the test and analytical mode shapes can be shown mathematically using the cross orthogonality check. A great deal of time and effort can be exhausted in generating the set of test acquired mode shapes needed for the cross orthogonality check. In most situations response data from vibration tests are digitally processed to generate the mode shapes from a combination of modal parameters, forcing functions, and recorded response data. An alternate method is proposed in which the same correlation of analytical and test acquired mode shapes can be achieved without conducting the modal survey. Instead a procedure is detailed in which a minimum of test information, specifically the acceleration response data from a random vibration test, is used to generate a set of equivalent local accelerations to be applied to the reduced analytical model at discrete points corresponding to the test measurement locations. The static solution of the analytical model then produces a set of deformations that once normalized can be used to represent the test acquired mode shapes in the cross orthogonality relation. The method proposed has been shown to provide accurate results for both a simple analytical model as well as a complex space flight structure.

Chambers, Jeffrey A.↗

NASA NTRS2010

The Atacama Cosmology Telescope: A Measurement of the 600 less than l less than 8000 Cosmic Microwave Background Power Spectrum at 148 GHz

We present a measurement of the angular power spectrum of the cosmic microwave background (CMB) radiation observed at 148 GHz. The measurement uses maps with 1.4' angular resolution made with data from the Atacama Cosmology Telescope (ACT). The observations cover 228 deg(sup 2) of the southern sky, in a 4 deg. 2-wide strip centered on declination 53 deg. South. The CMB at arc minute angular scales is particularly sensitive to the Silk damping scale, to the Sunyaev-Zel'dovich (SZ) effect from galaxy dusters, and to emission by radio sources and dusty galaxies. After masking the 108 brightest point sources in our maps, we estimate the power spectrum between 600 less than l less than 8000 using the adaptive multi-taper method to minimize spectral leakage and maximize use of the full data set. Our absolute calibration is based on observations of Uranus. To verify the calibration and test the fidelity of our map at large angular scales, we cross-correlate the ACT map to the WMAP map and recover the WMAP power spectrum from 250 less than l less than 1150. The power beyond the Silk damping tail of the CMB (l approximately 5000) is consistent with models of the emission from point sources. We quantify the contribution of SZ clusters to the power spectrum by fitting to a model normalized to sigma 8 = 0.8. We constrain the model's amplitude A(sub sz) less than 1.63 (95% CL). If interpreted as a measurement of as, this implies sigma (sup SZ) (sub 8) less than 0.86 (95% CL) given our SZ model. A fit of ACT and WMAP five-year data jointly to a 6-parameter ACDM model plus point sources and the SZ effect is consistent with these results.

Fowler, J. W.↗

NASA NTRS1972

Theoretical study of corrugated plates: Shearing of a corrugated plate with curvilinear corrugations

A theoretical elastic analysis is presented for the in-plane shear of a corrugated plate with curvilinear corrugations and with discrete attachments between the ends of the corrugations and the surrounding members. The purpose of the analysis is to obtain information about the effective shear stiffness of the plate and the flexural strains that develop in it during the shearing process as a result of the attendant cross-sectional deformations. The crests and troughs of the corrugation cross section are assumed to be identical circular arcs. The following four kinds of discrete attachment at the corrugation ends are considered in the analysis: (1) point attachments in the troughs, (2) point attachments at the crests and in the troughs, (3) point attachments at mid-height, and (4) point attachments at mid-height, at the crests, and in the troughs.

Wu, L.↗

NASA NTRS1973

Numerical simulation of noise propagation in jet engine ducts

A finite difference formulation is presented which is useful in the study of acoustically treated inlet and exhaust ducts used in turbofan engines. The difference formulation can readily handle acoustic flow field complications, such as axial variations in wall impedance and cross-sectional area, that would occur in a sonic inlet. In formulating the difference solutions, the continuous acoustic field is lumped into a series of grid points spread uniformly throughout the field. At each point, the pressure is separated into its real and imaginary terms. Example solutions are presented for sound propagation in a one-dimensional straight hard-wall duct and in a two-dimensional straight soft-wall duct without steady flow.

Baumeister, K. J.↗