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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

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NASA NTRS1987

A measurement-based model of software reliability in a production environment

In this paper, a semi-Markov model is built to describe the software error and recovery process in a large mainframe system. The model is based on low-level error data from the MVS operating system running on an IBM 3081 machine. The semi-Markov model developed provides a quantification of system error characteristics and the interaction between different types of errors. As an example, a detailed model is provided, and an analysis is made of multiple errors, which constitute approximately an 17 percent of all software errors and result in considerable recovery overhead.

Hsueh, M. C.↗

NASA NTRS2000

A simulator for evaluating methods for the detection of lesion-deficit associations

Although much has been learned about the functional organization of the human brain through lesion-deficit analysis, the variety of statistical and image-processing methods developed for this purpose precludes a closed-form analysis of the statistical power of these systems. Therefore, we developed a lesion-deficit simulator (LDS), which generates artificial subjects, each of which consists of a set of functional deficits, and a brain image with lesions; the deficits and lesions conform to predefined distributions. We used probability distributions to model the number, sizes, and spatial distribution of lesions, to model the structure-function associations, and to model registration error. We used the LDS to evaluate, as examples, the effects of the complexities and strengths of lesion-deficit associations, and of registration error, on the power of lesion-deficit analysis. We measured the numbers of recovered associations from these simulated data, as a function of the number of subjects analyzed, the strengths and number of associations in the statistical model, the number of structures associated with a particular function, and the prior probabilities of structures being abnormal. The number of subjects required to recover the simulated lesion-deficit associations was found to have an inverse relationship to the strength of associations, and to the smallest probability in the structure-function model. The number of structures associated with a particular function (i.e., the complexity of associations) had a much greater effect on the performance of the analysis method than did the total number of associations. We also found that registration error of 5 mm or less reduces the number of associations discovered by approximately 13% compared to perfect registration. The LDS provides a flexible framework for evaluating many aspects of lesion-deficit analysis.

NASA Program Biomedical Research and Countermeasur↗

NASA NTRS1974

Model wall and recovery temperature effects on experimental heat transfer data analysis

Basic analytical procedures are used to illustrate, both qualitatively and quantitatively, the relative impact upon heat transfer data analysis of certain factors which may affect the accuracy of experimental heat transfer data. Inaccurate knowledge of adiabatic wall conditions results in a corresponding inaccuracy in the measured heat transfer coefficient. The magnitude of the resulting error is extreme for data obtained at wall temperatures approaching the adiabatic condition. High model wall temperatures and wall temperature gradients affect the level and distribution of heat transfer to an experimental model. The significance of each of these factors is examined and its impact upon heat transfer data analysis is assessed.

Throckmorton, D. A.↗

NASA NTRS2008

Measuring Positions of Objects using Two or More Cameras

An improved method of computing positions of objects from digitized images acquired by two or more cameras (see figure) has been developed for use in tracking debris shed by a spacecraft during and shortly after launch. The method is also readily adaptable to such applications as (1) tracking moving and possibly interacting objects in other settings in order to determine causes of accidents and (2) measuring positions of stationary objects, as in surveying. Images acquired by cameras fixed to the ground and/or cameras mounted on tracking telescopes can be used in this method. In this method, processing of image data starts with creation of detailed computer- aided design (CAD) models of the objects to be tracked. By rotating, translating, resizing, and overlaying the models with digitized camera images, parameters that characterize the position and orientation of the camera can be determined. The final position error depends on how well the centroids of the objects in the images are measured; how accurately the centroids are interpolated for synchronization of cameras; and how effectively matches are made to determine rotation, scaling, and translation parameters. The method involves use of the perspective camera model (also denoted the point camera model), which is one of several mathematical models developed over the years to represent the relationships between external coordinates of objects and the coordinates of the objects as they appear on the image plane in a camera. The method also involves extensive use of the affine camera model, in which the distance from the camera to an object (or to a small feature on an object) is assumed to be much greater than the size of the object (or feature), resulting in a truly two-dimensional image. The affine camera model does not require advance knowledge of the positions and orientations of the cameras. This is because ultimately, positions and orientations of the cameras and of all objects are computed in a coordinate system attached to one object as defined in its CAD model.

Klinko, Steve↗

NASA NTRS2012

The Mars Science Laboratory (MSL) MMRTG In-Flight: A Power Update

The MSL Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) was fueled on October 28, 2008 by the Department Of Energy (DOE) in preparation for a late 2009 launch. Shortly after, the MSL launch was delayed approximately 2 years until 2011. The fueled MMRTG was placed in storage to await the new date for liftoff. Occasional measurements of the MMRTG's power output were taken and compared with power predictions that pre-dated fueling. An error in the predictive models was quickly recognized and remedied. The predictions, while improved, carried significant uncertainty. This uncertainty did not deter the launch of MSL, but did alter the planned mission on the surface of Mars. Once launched, the MSL spacecraft provided a hi-fidelity telemetry stream measuring the generator's electrical and thermal performance. These data were used to update the predictive models and a new prediction of the performance of the MMRTG on the surface of Mars was run just before Entry, Descent, and Landing (EDL) at Mars. The MSL MMRTG is working extremely well, providing power above predictions and operating within its flight allowable temperature limits. The generator was producing approximately 114 W at the beginning of the surface mission. This paper will elaborate on power modeling for the MSL MMRTG along with a review of some of the data recorded from the MSL cruise to Mars, EDL, and the early days of the surface mission.

thermoelectric generator↗

NASA NTRS1977

Ionospheric range-rate effects in satellite-to-satellite tracking

Investigation of ionospheric range and range-rate corrections in satellite-to-satellite tracking were investigated. Major problems were cited and the magnitude of errors that have to be considered for communications between satellites and related experiments was defined. The results point to the need of using a sophisticated modeling approach incorporating daily solar data, and where possible actual ionospheric measurements as update information, as a simple median model cannot possibly account for the complex interaction of the many variables. The findings provide a basis from which the residual errors can be estimated after ionospheric modeling is incorporated in the reduction. Simulations were performed for satellites at various heights: Apollo, Geos, and Nimbus tracked by ATS-6; and in two different geometric configurations: coplanar and perpendicular orbits.

Lipofsky, J. R.↗

NASA NTRS1974

Measurement error analysis in determination of small-body gravity fields

We consider analytically the use of existing instrumentation in determining asteroid gravity fields from orbiting spacecraft. Asteroids (Eros as an example) are modeled as homogeneous triaxial ellipsoids, with gravitational potential given by a sperical-harmonic expansion. Mass concentrations are modeled as point masses. The character of spacecraft orbits about asteroids is discussed, along with detectibility of gravitational coefficients and of mass concentrations. A Kalman-filtering treatment of the observation process, for Eros as example, shows that using DSN tracking and onboard gravity gradiometry, radar altimetry, and celestial angle measurements, a single orbit yields asteroid mass to 0.03% and coefficients C20 to C44 to 1% accuracies.

Friedlander, A. L.↗

NASA NTRS2013

The Mars Science Laboratory (MSL) MMRTG In-Flight: A Power Update

The MSL Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) was fueled on October 28, 2008 by the Department Of Energy (DOE) in preparation for a late 2009 launch. Shortly after, the MSL launch was delayed approximately 2 years until 2011. The fueled MMRTG was placed in storage to await the new date for liftoff. Occasional measurements of the MMRTG's power output were taken and compared with power predictions that pre-dated fueling. An error in the predictive models was quickly recognized and remedied. The resultant predictions, while improved, carried significant uncertainty. This uncertainty did not deter the launch of MSL, but did alter the planned mission on the surface of Mars. Once launched, the MSL spacecraft provided a hi-fidelity telemetry stream measuring the generator's electrical and thermal performance. These data were used to update the predictive models and a new prediction of the performance of the MMRTG on the surface of Mars was run just before Entry, Descent, and Landing (EDL) at Mars. The MSL MMRTG is working extremely well, providing power above predictions and operating within its flight allowable temperature limits. The generator was producing approximately 114 W at the beginning of the surface mission. This paper will elaborate on power modeling for the MSL MMRTG along with a review of some of the data recorded from the MSL cruise to Mars, EDL, and the early days of the surface mission.

thermoelectric↗

NASA NTRS2000

A comparison of depth dependence of dose and linear energy transfer spectra in aluminum and polyethylene

A set of four tissue-equivalent proportional counters (TEPCs), with their detector heads at the centers of 0 (bare), 3, 7 and 9-inch-diameter aluminum spheres, were flown on Shuttle flight STS-89. Five such detectors at the centers of polyethylene spheres were flown 1 year earlier on STS-81. The results of dose-depth dependence for the two materials convincingly show the merits of using material rich in hydrogen to decrease the radiation exposure to the crew. A comparison of the calculated galactic cosmic radiation (GCR) absorbed dose and dose-equivalent rates using the radiation transport code HZETRN with nuclear fragmentation model NUCFRG2 and the measured GCR absorbed dose rates and dose-equivalent rates shows that they agree within root mean square (rms) error of 12.5 and 8.2%, respectively. However, there are significant depth-dependent differences in the linear energy transfer (LET) spectra. A comparison for trapped protons using the proton transport code BRYNTRN and the AP-8 MIN trapped-proton model shows a systematic bias, with the model underpredicting dose and dose-equivalent rates. These results show the need for improvements in the radiation transport and/or fragmentation models.

manned↗

NASA NTRS2003

Comparison of Flow-Dependent and Static Error Correlation Models in the DAO Ozone Data Assimilation System

In a data assimilation system the forecast error covariance matrix governs the way in which the data information is spread throughout the model grid. Implementation of a correct method of assigning covariances is expected to have an impact on the analysis results. The simplest models assume that correlations are constant in time and isotropic or nearly isotropic. In such models the analysis depends on the dynamics only through assumed error standard deviations. In applications to atmospheric tracer data assimilation this may lead to inaccuracies, especially in regions with strong wind shears or high gradient of potential vorticity, as well as in areas where no data are available. In order to overcome this problem we have developed a flow-dependent covariance model that is based on short term evolution of error correlations. The presentation compares performance of a static and a flow-dependent model applied to a global three- dimensional ozone data assimilation system developed at NASA s Data Assimilation Office. We will present some results of validation against WMO balloon-borne sondes and the Polar Ozone and Aerosol Measurement (POAM) III instrument. Experiments show that allowing forecast error correlations to evolve with the flow results in positive impact on assimilated ozone within the regions where data were not assimilated, particularly at high latitudes in both hemispheres and in the troposphere. We will also discuss statistical characteristics of both models; in particular we will argue that including evolution of error correlations leads to stronger internal consistency of a data assimilation ,

Wargan, K.↗

NASA NTRS1971

Metric analysis of minitrack optical and interferometer data

The network analysis program (NAP-2), which has the capability of simultaneously solving for orbits and tracking station error model terms, was, after several modifications, used in the calibration of minitrack stations using minitrack satellite measurements (self-calibration). Several support programs were written to aid in this task. A simultaneous four-arc solution was obtained. A comparison with optically determined arcs for the same time spans showed rms position differences of 67m, 86m, 124m and 168m for the 4 arcs considered. An apparatus incorporating a diffraction grating was designed and successfully used to measure the drift rate of the Fort Myers MOTS camera drive.

Brown, D. C.↗

NASA NTRS1975

Prediction of payload vibration environments by mechanical admittance test techniques

A series of experiments was conducted with simple beam and mass launch vehicle and payload models in order to determine the validity of mechanical admittance/impedance techniques applied to development of improved payload vibration tests. Admittances and impedances were measured from tests of the individual components to form matrices which were combined analytically to allow prediction of responses for the complete system. Results were computed for a transmission matrix approach and an admittance matrix approach. Both a rigid body and a flexible payload model were considered. The results clearly demonstrate that the transmission matrix method is too sensitive to measurement error to be practical for this application, while the pure admittance matrix method produces quite satisfactory results. The effects of various errors on the final results are demonstrated.

Kana, D. D.↗

NASA NTRS1977

Shuttle program: Ground tracking data program document shuttle OFT launch/landing

The equations for processing ground tracking data during a space shuttle ascent or entry, or any nonfree flight phase of a shuttle mission are given. The resulting computer program processes data from up to three stations simultaneously: C-band station number 1; C-band station number 2; and an S-band station. The C-band data consists of range, azimuth, and elevation angle measurements. The S-band data consists of range, two angles, and integrated Doppler data in the form of cycle counts. A nineteen element state vector is used in Kalman filter to process the measurements. The acceleration components of the shuttle are taken to be independent exponentially-correlated random variables. Nine elements of the state vector are the measurement bias errors associated with range and two angles for each tracking station. The biases are all modeled as exponentially-correlated random variables with a typical time constant of 108 seconds. All time constants are taken to be the same for all nine state variables. This simplifies the logic in propagating the state error covariance matrix ahead in time.

Lear, W. M.↗

NASA NTRS1979

Low-cost inertial navigation for moderate-g missions

A low cost inertial navigation system (INS) concept is described for flight missions characterized by moderate accelerations and limited attitude variations. These missions involve general aviation aircraft, helicopters, or remotely piloted vehicles. The significance of the moderate acceleration and limited attitude is reviewed with respect to platform mechanization and instrumentation. A hybrid mechanization, partially gimballed and partially strapdown, is presented. The INS is implemented by an unbalanced two axis gimbal system and controlled by a two degree of freedom gyro. The INS provides locally level two axis acceleration information along with pitch and roll measurements. Heading information is provided by a second gyro mounted in the inner gimbal. The system error model is equivalent to that of a conventional platform with a tilt error determined by the integral of the gyro drift rate and an equivalent accelerometer type errors are also cancelled. Rapid gyro-compassing, implemented with opened gimbal control loops, and a strapdown procedure provides calibration of gyro drift rate biases.

Merhav, S.↗

NASA NTRS1984

Thematic Mapper Image Processing System (TIPS) Processing Status

Radiometric and geometric correction performance is considered. A one quantum level requirement was met in all spectral bands with an occasional band 7 exception. Initial post launch calibration was accomplished. An absolute radiometric calibration is in progress including an investigation of low impact solution to scan striping. Initial and three downstream updates as well as coordination with LANDSAT D' instrument calibration are planned. Methods and problems in measuring geometric correction performance are examined with an emphasis on temporal registration, geodetic registrtion, and the modeling error budget. Planned efforts include eliminating band 2, band 5 chips; continued performance monitoring; calibration of profile, misalignment angles, and filer parameters; studying the need for seasonal geodetic control points; and improvement of the subpixel correlation technique.

Brooks, J.↗

NASA NTRS1985

Improving the absolute positioning accuracy of robot manipulators

The absolute positioning accuracy of robot manipulator can be increased substantially by updating the nominal link parameters in the control software. This paper presents a general method to estimate the link parameter errors for any serial link manipulator (i.e., n links, and any combination of revolute and prismatic joints). The parameters are estimated through a linear kinematic model which relates the link bias errors to the end-effector positioning error. Only end-effector measurements are required instead of individual link measurements to implement this method.

Hayati, S.↗

NASA NTRS1986

A four-dimensional analysis exactly satisfying equations of motion

A four-dimensional analysis is applied to spectral nonlinear models of the atmosphere. The experiment reveals that the four-dimensional analysis errors are smaller than measurement errors, the method is stable in an assimilation cycle, and an accurate estimate of the velocity field is maintained using only temperature observations. It is concluded that the four-dimensional analyses display rapid initial error growth and therefore are better than ordinary forecasts from observations for only the first 24 hours.

Hoffman, R. N.↗

NASA NTRS1998

Effects of Shear, Defocus, and Wavefront Error on the Theoretical Performance of the Composite Infrared Spectrometer for Cassini

The combined effects on performance of shear between the two arms, defocus of die detector, and difference in wavefront between the two arms of a Fourier transform spectrometer using cube corner retroreflectors were investigated. Performance was characterized by the amplitude of the fringe signals coming from a detector as the path-length difference was scanned. A closed-form expression was found for the combined effects of shear and defocus, and it was found that defocus had no effect in the absence of shear. The effect of wavefront error was modeled numerically and assumed to be independent of shear and defocus. Results were compared with measurements made on the breadboard and engineering model of the Composite Infrared Spectrometer for the Cassini mission to Saturn, and good agreement was found.

Martino, Antonio J.↗