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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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NASA NTRS1988

Estimating water flow through a hillslope using the massively parallel processor

A new two-dimensional model of water flow in a hillslope has been implemented on the Massively Parallel Processor at the Goddard Space Flight Center. Flow in the soil both in the saturated and unsaturated zones, evaporation and overland flow are all modelled, and the rainfall rates are allowed to vary spatially. Previous models of this type had always been very limited computationally. This model takes less than a minute to model all the components of the hillslope water flow for a day. The model can now be used in sensitivity studies to specify which measurements should be taken and how accurate they should be to describe such flows for environmental studies.

Devaney, Judy E.↗

NASA NTRS2002

Defining Top-of-Atmosphere Flux Reference Level for Earth Radiation Budget Studies

To estimate the earth's radiation budget at the top of the atmosphere (TOA) from satellite-measured radiances, it is necessary to account for the finite geometry of the earth and recognize that the earth is a solid body surrounded by a translucent atmosphere of finite thickness that attenuates solar radiation differently at different heights. As a result, in order to account for all of the reflected solar and emitted thermal radiation from the planet by direct integration of satellite-measured radiances, the measurement viewing geometry must be defined at a reference level well above the earth s surface (e.g., 100 km). This ensures that all radiation contributions, including radiation escaping the planet along slant paths above the earth s tangent point, are accounted for. By using a field-of- view (FOV) reference level that is too low (such as the surface reference level), TOA fluxes for most scene types are systematically underestimated by 1-2 W/sq m. In addition, since TOA flux represents a flow of radiant energy per unit area, and varies with distance from the earth according to the inverse-square law, a reference level is also needed to define satellite-based TOA fluxes. From theoretical radiative transfer calculations using a model that accounts for spherical geometry, the optimal reference level for defining TOA fluxes in radiation budget studies for the earth is estimated to be approximately 20 km. At this reference level, there is no need to explicitly account for horizontal transmission of solar radiation through the atmosphere in the earth radiation budget calculation. In this context, therefore, the 20-km reference level corresponds to the effective radiative top of atmosphere for the planet. Although the optimal flux reference level depends slightly on scene type due to differences in effective transmission of solar radiation with cloud height, the difference in flux caused by neglecting the scene-type dependence is less than 0.1%. If an inappropriate TOA flux reference level is used to define satellite TOA fluxes, and horizontal transmission of solar radiation through the planet is not accounted for in the radiation budget equation, systematic errors in net flux of up to 8 W/sq m can result. Since climate models generally use a plane-parallel model approximation to estimate TOA fluxes and the earth radiation budget, they implicitly assume zero horizontal transmission of solar radiation in the radiation budget equation, and do not need to specify a flux reference level. By defining satellite-based TOA flux estimates at a 20-km flux reference level, comparisons with plane-parallel climate model calculations are simplified since there is no need to explicitly correct plane-parallel climate model fluxes for horizontal transmission of solar radiation through a finite earth.

Loeb, N. G.↗

NASA NTRS2019

Towards Resilient Autonomous Navigation of Drones

Robots and particularly drones are especially useful in exploring extreme environments that pose hazards to humans. To ensure safe operations in these situations, usually perceptually degraded and without good GNSS, it is critical to have a reliable and robust state estimation solution. The main body of literature in robot state estimation focuses on developing complex algorithms favoring accuracy. Typically, these approaches rely on a strong underlying assumption: the main estimation engine will not fail during operation. In contrast, we propose an architecture that pursues robustness in state estimation by considering redundancy and heterogeneity in both sensing and estimation algorithms. The architecture is designed to expect and detect failures and adapt the behavior of the system to ensure safety. To this end, we present HeRO (Heterogeneous Redundant Odometry): a stack of estimation algorithms running in parallel supervised by a resiliency logic. This logic carries out three main functions: a) perform confidence tests both in data quality and algorithm health; b) re-initialize those algorithms that might be malfunctioning; c) generate a smooth state estimate by multiplexing the inputs based on their quality. The state and quality estimates are used by the guidance and control modules to adapt the mobility behaviors of the system. The validation and utility of the approach are shown with real experiments on a ying robot for the use case of autonomous exploration of subterranean environments, with particular results from the STIX event of the DARPA Subterranean Challenge.

Agha-mohammadi, Ali-akbar↗

NASA NTRS1988

Multiprocessor speed-up, Amdahl's Law, and the Activity Set Model of parallel program behavior

An important issue in the effective use of parallel processing is the estimation of the speed-up one may expect as a function of the number of processors used. Amdahl's Law has traditionally provided a guideline to this issue, although it appears excessively pessimistic in the light of recent experimental results. In this note, Amdahl's Law is amended by giving a greater importance to the capacity of a program to make effective use of parallel processing, but also recognizing the fact that imbalance of the workload of each processor is bound to occur. An activity set model of parallel program behavior is then introduced along with the corresponding parallelism index of a program, leading to upper and lower bounds to the speed-up.

Gelenbe, Erol↗

NASA NTRS1989

Novel techniques for data decomposition and load balancing for parallel processing of vision systems: Implementation and evaluation using a motion estimation system

Computer vision systems employ a sequence of vision algorithms in which the output of an algorithm is the input of the next algorithm in the sequence. Algorithms that constitute such systems exhibit vastly different computational characteristics, and therefore, require different data decomposition techniques and efficient load balancing techniques for parallel implementation. However, since the input data for a task is produced as the output data of the previous task, this information can be exploited to perform knowledge based data decomposition and load balancing. Presented here are algorithms for a motion estimation system. The motion estimation is based on the point correspondence between the involved images which are a sequence of stereo image pairs. Researchers propose algorithms to obtain point correspondences by matching feature points among stereo image pairs at any two consecutive time instants. Furthermore, the proposed algorithms employ non-iterative procedures, which results in saving considerable amounts of computation time. The system consists of the following steps: (1) extraction of features; (2) stereo match of images in one time instant; (3) time match of images from consecutive time instants; (4) stereo match to compute final unambiguous points; and (5) computation of motion parameters.

Choudhary, Alok Nidhi↗

NASA NTRS2014

Exploratory Study for Continuous-time Parameter Estimation of Ankle Dynamics

Recently, a parallel pathway model to describe ankle dynamics was proposed. This model provides a relationship between ankle angle and net ankle torque as the sum of a linear and nonlinear contribution. A technique to identify parameters of this model in discrete-time has been developed. However, these parameters are a nonlinear combination of the continuous-time physiology, making insight into the underlying physiology impossible. The stable and accurate estimation of continuous-time parameters is critical for accurate disease modeling, clinical diagnosis, robotic control strategies, development of optimal exercise protocols for longterm space exploration, sports medicine, etc. This paper explores the development of a system identification technique to estimate the continuous-time parameters of ankle dynamics. The effectiveness of this approach is assessed via simulation of a continuous-time model of ankle dynamics with typical parameters found in clinical studies. The results show that although this technique improves estimates, it does not provide robust estimates of continuous-time parameters of ankle dynamics. Due to this we conclude that alternative modeling strategies and more advanced estimation techniques be considered for future work.

neuromuscular systems↗

NASA NTRS1972

Advanced missions safety. Volume 3: Appendices. Part 1: Space shuttle rescue capability

The space shuttle rescue capability is analyzed as a part of the advanced mission safety study. The subjects discussed are: (1) mission evaluation, (2) shuttle configurations and performance, (3) performance of shuttle-launched tug system, (4) multiple pass grazing reentry from lunar orbit, (5) ground launched ascent and rendezvous time, (6) cost estimates, and (7) parallel-burn space shuttle configuration.

Source record↗

NASA NTRS1988

The relationship between the Eddington limit, the observed upper luminosity limit for massive stars, and the luminous blue variables

The observed upper luminosity limits in the Galaxy and the LMC are compared with the Eddington limit as estimated for plane-parallel LTE model atmospheres which include the full effects of metal line opacities in the ultraviolet. It is shown that the Humphreys-Davidson (HD) limit corresponds to the locus of extremely low effective gravities. This result suggests that stars approaching the HD limit will suffer high mass-loss rates because of the reduction of the effective gravity due to radiation pressure. These high mass-loss rates ultimtely lead to the core mass fraction reaching its critical value and the reversal of the stellar evolution tracks. It is shown that radiation pressure, as an agent for producing enhanced mass loss near the HD limit, can in a natural way explain the kink in the HD limit near T(eff) roughly 10,000 K and the upper luminosity limit for yellow and red supergiants. The high mass-loss rates of the luminous blue variables, their location in the HR diagram, and their evolutionary stage are also discussed.

Lamers, Henny J. G. L. M.↗

NASA NTRS1991

The Io sulfur torus in 1981

Io torus spectrometry obtained in the S II and S III forbidden lines during February-March 1981 indicate that these emissions are correlated in the warm torus, and possess similar scale heights along the magnetic field lines. The observed emission scale heights can be used to estimate the ion temperature parallel to the magnetic field, given the effective ion mass. Attention is also given to simultaneous measurements of the S II forbidden 6731 line profile obtained on one night with a Fabry-Perot scanning spectrophotometer.

Oliversen, Ronald J.↗

NASA NTRS2015

Predicting the Redshift 2 H-Alpha Luminosity Function Using [OIII] Emission Line Galaxies

Upcoming space-based surveys such as Euclid and WFIRST-AFTA plan to measure Baryonic Acoustic Oscillations (BAOs) in order to study dark energy. These surveys will use IR slitless grism spectroscopy to measure redshifts of a large number of galaxies over a significant redshift range. In this paper, we use the WFC3 Infrared Spectroscopic Parallel Survey (WISP) to estimate the expected number of H-alpha emitters observable by these future surveys. WISP is an ongoing Hubble Space Telescope slitless spectroscopic survey, covering the 0.8 - 1.65 micrometers wavelength range and allowing the detection of H-alpha emitters up to z approximately equal to 1.5 and [OIII] emitters to z approximately equal to 2.3. We derive the H-alpha-[OIII] bivariate line luminosity function for WISP galaxies at z approximately equal to 1 using a maximum likelihood estimator that properly accounts for uncertainties in line luminosity measurement, and demonstrate how it can be used to derive the H-alpha luminosity function from exclusively fitting [OIII] data. Using the z approximately equal to 2 [OIII] line luminosity function, and assuming that the relation between H-alpha and [OIII] luminosity does not change significantly over the redshift range, we predict the H-alpha number counts at z approximately equal to 2 - the upper end of the redshift range of interest for the future surveys. For the redshift range 0.7 less than z less than 2, we expect approximately 3000 galaxies per sq deg for a flux limit of 3 x 10(exp −16) ergs per sec per sq cm (the proposed depth of Euclid galaxy redshift survey) and approximately 20,000 galaxies per sq deg for a flux limit of approximately 10(exp −16) ergs per sec per sq cm (the baseline depth of WFIRST galaxy redshift survey).

Redshift↗

NASA NTRS1992

An analysis of I/O efficient order-statistic-based techniques for noise power estimation in the HRMS sky survey's operational system

Noise power estimation in the High-Resolution Microwave Survey (HRMS) sky survey element is considered as an example of a constant false alarm rate (CFAR) signal detection problem. Order-statistic-based noise power estimators for CFAR detection are considered in terms of required estimator accuracy and estimator dynamic range. By limiting the dynamic range of the value to be estimated, the performance of an order-statistic estimator can be achieved by simpler techniques requiring only a single pass of the data. Simple threshold-and-count techniques are examined, and it is shown how several parallel threshold-and-count estimation devices can be used to expand the dynamic range to meet HRMS system requirements with minimal hardware complexity. An input/output (I/O) efficient limited-precision order-statistic estimator with wide but limited dynamic range is also examined.

Zimmerman, G. A.↗

NASA NTRS1994

High performance compression of science data

Two papers make up the body of this report. One presents a single-pass adaptive vector quantization algorithm that learns a codebook of variable size and shape entries; the authors present experiments on a set of test images showing that with no training or prior knowledge of the data, for a given fidelity, the compression achieved typically equals or exceeds that of the JPEG standard. The second paper addresses motion compensation, one of the most effective techniques used in the interframe data compression. A parallel block-matching algorithm for estimating interframe displacement of blocks with minimum error is presented. The algorithm is designed for a simple parallel architecture to process video in real time.

Storer, James A.↗

NASA NTRS1994

High Performance Compression of Science Data

Two papers make up the body of this report. One presents a single-pass adaptive vector quantization algorithm that learns a codebook of variable size and shape entries; the authors present experiments on a set of test images showing that with no training or prior knowledge of the data, for a given fidelity, the compression achieved typically equals or exceeds that of the JPEG standard. The second paper addresses motion compensation, one of the most effective techniques used in interframe data compression. A parallel block-matching algorithm for estimating interframe displacement of blocks with minimum error is presented. The algorithm is designed for a simple parallel architecture to process video in real time.

Storer, James A.↗

NASA NTRS1992

The new challenge of computational aeroscience

This paper discusses NASA's Computational Aerosciences (CAS) Project of the High Performance Computing and Communications Program (HPCCP). The project is aimed at developing advanced, multidisciplinary simulation capabilities for aerospace vehicle and propulsion system design. It is also aimed at overcoming computational performance barriers by accelerating the development of parallel computer technology. The goals and approach of the CAS Project are described and the challenges to its implementation are addressed. Specific vehicle class simulations to be demonstrated and the principal mutidisciplinary modeling approaches to be emphasized are described. The computational speed and memory requirements for representative multidisciplinary applications are estimated. Finally, the state of parallel computer technology including programming issues and the results of performance measurements are explored.

Bailey, F. R.↗

NASA NTRS2021

The role of analysis error in the convergence of reanalysis production streams in MERRA-2

Due to production time constraints, most reanalyses are produced in multiple parallel streams instead of a single continuous one. These streams cover separate segments of the reanalysis time period with short overlaps to allow reconstruction of the official record. A fundamental assumption justifying this approach is that the streams will be assimilating the same observations during the periods where they overlap, and so will eventually converge to a similar atmospheric state, making discontinuities at stream junctions negligible. This assumption is revisited in this work by examining the impact of analysis error on the differences between MERRA-2 overlapping streams in three historical periods. Comparison results are shown in terms of standard deviations of stream differences as well as the spectral decomposition of the variance of their differences. Residual differences were found at the end of each year of overlap, with larger values observed in the earlier segments of the presatellite era. By drawing parallels with analysis error statistics estimated from the GMAO OSSE system, these differences are shown to reflect the varying constraint of data with the varying observing network, and to further carry the imprint of errors that the data assimilation process is not able to mitigate. As such, they are unlikely to be reduced by longer spinup periods. The ability of data assimilation to ensure continuity in the parallel streams is put into question when the observing system coverage is inadequate or simply when the data assimilation system as a whole is suboptimal.

Amal El Akkraoui↗

NASA NTRS1982

On the geodetic applications of simultaneous range-differencing to LAGEOS

The possibility of improving the accuracy of geodetic results by use of simultaneously observed ranges to Lageos, in a differencing mode, from pairs of stations was studied. Simulation tests show that model errors can be effectively minimized by simultaneous range differencing (SRD) for a rather broad class of network satellite pass configurations. The methods of least squares approximation are compared with monomials and Chebyshev polynomials and the cubic spline interpolation. Analysis of three types of orbital biases (radial, along- and across track) shows that radial biases are the ones most efficiently minimized in the SRC mode. The degree to which the other two can be minimized depends on the type of parameters under estimation and the geometry of the problem. Sensitivity analyses of the SRD observation show that for baseline length estimations the most useful data are those collected in a direction parallel to the baseline and at a low elevation. Estimating individual baseline lengths with respect to an assumed but fixed orbit not only decreases the cost, but it further reduces the effects of model biases on the results as opposed to a network solution. Analogous results and conclusions are obtained for the estimates of the coordinates of the pole.

Pablis, E. C.↗

NASA NTRS1972

System efficiency of a microwave power tube with a multistage depressed collector

The efficiencies of a microwave power tube with a multistage depressed collector and of the power supply driving the tube are computed. An analytical expression for the collector efficiency, which includes the effect of secondary emission and the radial component of velocity, is derived for a hypothetical current probability distribution function. In addition, collector efficiency is calculated with the aid of a digital computer for a specific current distribution. The efficiency of the power supply required to operate the tube in a space environment is estimated by using a simple parallel inverter system.

Dayton, J. A., Jr.↗

NASA NTRS1984

Orbit selection for a Mars geoscience/climatology orbiter

This paper is a presentation of recent work to provide orbit design and selection criteria for a close, nearly polar, nearly circular orbit of Mars. The main aspects of the work are the evaluation of atmospheric drag for altitude selection, the orbit evolution for variations in periapsis altitude, and the interactions of those factors with the science objectives of the MGCO mission. A dynamic model of the Mars atmosphere is available from parallel efforts and the latest estimates of the upper atmospheric density and its time history are incorporated into the analysis to provide a final orbit that satisfies planetary quarantine requirements.

Uphoff, C.↗