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NASA NTRS1978

The driving force for magnetospheric convection

Viscously driven magnetospheric models, as well as a model involving interconnection between the geomagnetic field and the magnetic field in the solar wind, have been proposed to describe the driving force for magnetospheric convection. Lack of a satisfactory theory for the interconnection in the latter model and, in the case of the viscous interaction models, inadequacies in predicting the quantity of the driving force, make these two classes of models less than successful. Accordingly, a mechanically driven magnetospheric model is proposed: solar wind plasma enters the magnetosphere around the neutral points, covers the inner surface of the magnetopause and subsequently expands, driving convection as it escapes from the open tail.

Johnson, F. S.↗

NASA NTRS1972

Numerical isolation of flaws in the lunar theory.

The general concept of a numerical study of the lunar motion is examined and a particular case is discussed in greater detail than was possible in an earlier paper. Particular emphasis is placed upon the distinction to be made between model inadequacies and numerical artifacts, since either type of problem may be present in a given study, but the sensitivity to one or the other depends on the methodology used.

Mulholland, J. D.↗

NASA NTRS1973

Potentialities of lunar laser ranging for measuring tectonic motions.

The lunar laser-ranging system at McDonald Observatory, Texas, is currently attaining accuracies of plus or minus 15 cm, and plus or minus 3 cm appears feasible. Numerical error analyses containing 97 parameters (35 of them for error sources) indicate that the plus or minus 3 cm system would measure station motions to plus or minus 1 cm/year accuracy within a year for east-west motions and within about 3 years for north-south. Furthermore, the correlations of station motions with other parameters are low, so that it is unlikely that the estimate is too optimistic because of modeling inadequacies of the error analysis.

Kaula, W. M.↗

NASA NTRS1982

The computation of Laplacian smoothing splines with examples

Laplacian smoothing splines (LSS) are presented as generalizations of graduation, cubic and thin plate splines. The method of generalized cross validation (GCV) to choose the smoothing parameter is described. The GCV is used in the algorithm for the computation of LSS's. An outline of a computer program which implements this algorithm is presented along with a description of the use of the program. Examples in one, two and three dimensions demonstrate how to obtain estimates of function values with confidence intervals and estimates of first and second derivatives. Probability plots are used as a diagnostic tool to check for model inadequacy.

Wendelberger, J. G.↗

NASA NTRS1991

A probabilistic design analysis approach for launch systems

This paper discusses a probabilistic design analysis (PDA) approach to support the conventional deterministic structural design methods that are currently used. The probabilistic approach takes into consideration the modeling inadequacies and uncertainties in many design variables such as loads, environments, and material properties. In addition to providing a systematic way for evaluating reliability, this approach provides a tool for comparing reliabilities of competing designs and identifies weak spots through sensitivity analysis. An overview of the probabilistic design approach is included to emphasize the importance of the approach in engineering design. An actual example is included to demonstrate that these approaches have been used with success. Different methodologies for implementing PDA are also discussed. Finally, recommendations for using PDA are provided.

Safie, Fayssal↗

NASA NTRS1991

Ultrasonic sensing of porous granular media

The existence of phenomena for sensing porosity and grain growth in powder metallurgical processes using ultrasonic techniques is demonstrated. Ultrasonic velocity is a strong function of pore concentration and provides a potential means for in situ measurement of this quantity. Ultrasonic attenuation, measured in the low megahertz range, depends on grain size and pore content. When velocity data and a scattering theory are used to account for the attenuation due to pores, attenuation data may be used to infer the grain size. Predictions of existing scattering theories are compared with experimental observations, and substantial disagreements are attributed to modeling inadequacies.

Parthasarathi, Sanjai↗

NASA NTRS1992

Statistical characterization of life drivers for a probabilistic design analysis

This paper discusses the issue of statistical characterization of life drivers for a probabilistic design analysis (PDA) approach to support the conventional deterministic structural design methods that are currently used. The probabilistic approach takes into consideration the modeling inadequacies and uncertainties in many design variables such as loads, environments, and material properties. The importance of the distributional assumption is motivated by illustrating an example where the results differ substantially due to the distribution selected. Different types of distributions are discussed and techniques for estimating the parameters are given. Given this information, procedures are outlined for selecting the appropriate distribution based on the particular type of variable (i.e., dimensional, performance) as well as the information that is available (i.e., test data, engineering analysis). Finally, techniques are given for generating random numbers from these selected distributions within the PDA process.

Fox, Eric P.↗

NASA NTRS1999

Hot Gas Testing Results of Stagnant Volume Filling Through a Back-Filled RSRM Nozzle Joint

Silicone rubber is back-filled into RSW nozzle joints after assembly. A possible artifact of this process is the formation of small pathways through this filter leading to sensitive sealing materials within the joint. At motor ignition, hot gases fill the stagnant volumes within the joint through this path. A series of 14 test has been completed studying this scenario and providing anchoring data for thermal/flow models. Parameters such as gas path cross section, gas path length, gas path materials, fill volume size, and post path gas spreading prior to unpingement on seal material, have been investigated. Tests were accomplished using geometry similar to RSRM nozzle joint 4 with attached volumes replicating the free volume and flow friction in the actual hardware. The test hardware simulated 8 inches of the full-scale circumference. Testing has pointed to changes required in model boundary condition assumptions and gas dynamics corrections for gas paths of this size and geometry. Areas ,where this date has provided improvement in analysis models will be covered as well as model inadequacies that require separate specialized efforts. Questions remaining after this testing and a possible direction for future testing will be suggested.

Prince, Andrew S.↗

NASA NTRSDate not supplied

Challenges in Understanding Radiation Belt Dynamics: Insights from Two Storm Periods

The periods of May 27 - June 5, 2017 and Oct 24 — 29, 2016 are 'unusual' in terms of radiation belt dynamics and their solar wind driving conditions. The first period was under the influence of a slow CME-led major geomagnetic storm with Dstmin = -125 nT and the second period was under high speed solar wind streams. Observations from Van Allen Probes show great variabilities in different electron energy channels for both periods. During the second period of Oct 24 - 29, 2016, electron fluxes are found to be near the highest upper limit among various storms during 2013–2018 (Hua, Bortnik and Ma, 2022). In this paper, we provide solar wind sources and geomagnetic conditions for these two storm periods and point out challenges in understanding, modeling, and forecasting radiation belt dynamics. In-depth analysis of modeling results utilizing radiation belt models available at the Community Coordinated Modeling Center such as VERB and CIMI will be performed. Initial modeling results indicate rather large discrepancies with the observations. Model validation using different metrics introduced in Zheng et al. (2019) will be carried out to gain a deeper understanding of the physical processes involved and to identity potential causes of modeling inadequacies.

Yihua Zheng↗

NASA NTRS2006

Radiation Environment Modeling for Spacecraft Design: New Model Developments

A viewgraph presentation on various new space radiation environment models for spacecraft design is described. The topics include: 1) The Space Radiatio Environment; 2) Effects of Space Environments on Systems; 3) Space Radiatio Environment Model Use During Space Mission Development and Operations; 4) Space Radiation Hazards for Humans; 5) "Standard" Space Radiation Environment Models; 6) Concerns about Standard Models; 7) Inadequacies of Current Models; 8) Development of New Models; 9) New Model Developments: Proton Belt Models; 10) Coverage of New Proton Models; 11) Comparison of TPM-1, PSB97, AP-8; 12) New Model Developments: Electron Belt Models; 13) Coverage of New Electron Models; 14) Comparison of "Worst Case" POLE, CRESELE, and FLUMIC Models with the AE-8 Model; 15) New Model Developments: Galactic Cosmic Ray Model; 16) Comparison of NASA, MSU, CIT Models with ACE Instrument Data; 17) New Model Developmemts: Solar Proton Model; 18) Comparison of ESP, JPL91, KIng/Stassinopoulos, and PSYCHIC Models; 19) New Model Developments: Solar Heavy Ion Model; 20) Comparison of CREME96 to CREDO Measurements During 2000 and 2002; 21) PSYCHIC Heavy ion Model; 22) Model Standardization; 23) Working Group Meeting on New Standard Radiation Belt and Space Plasma Models; and 24) Summary.

Barth, Janet↗

NASA NTRS1976

A comparison of one-dimensional theoretical models of stratospheric minor constituents

The density profiles of stratospheric minor constituents are compiled from several one-dimensional theoretical models that have appeared in the literature. The models are compared with each other and also with observations if data are available. The similarity and disparity of the models are clarified and discussed. If a large difference exists among the models, attempts are made to interpret it as much as possible in terms of the physical and chemical data employed in each model. The inadequacy of one-dimensional models in calculating the realistic ozone density distributions and the problems related to it are briefly discussed.

Shimazaki, T.↗

NASA NTRS1974

Critical problems in establishing the morphology of substorms in space

A phenomenological model of the magnetospheric substorm has been developed which divides the substorm into three phases: a growth phase, an expansion phase, and a recovery phase. Current research is reviewed in the light of criticism of this model. The most important inadequacies of the model concern the fact that the tail lobe and the plasma sheet do not always react as single entities as previously supposed. Further research is needed on the problems of substorm variability, errors in onset time, the number of distinct spatial regions, and the dependence of magnetic activity on past history.

Mcpherron, R. L.↗

NASA NTRS1993

Vertical Ocean Loading Amplitudes From VLBI Measurements

Vertical ocean loading amplitudes are determined by analysis of IRIS geodetic VLBI data. Vertical ocean loading amplitudes can thus be inferred from VLBI data at a level which improves the overall model, but detailed assessment of individual tidal components is presently obscured by inadequacies in modeling other tidal effects.

ocean↗

NASA NTRS1973

Probabilistic models of planetary contamination

Likely fundamental inadequacies in the model of planetary contamination advanced by Sagan and Coleman are discussed. It is shown that a relatively minor modification of the basic Sagan-Coleman formula yields approximations that are generally adequate with data in the range of interest. This approximation formula differs from the original Sagan-Coleman version only through an initial conditioning on landing outcome. It always yields an upper (conservative) bound for the total probability of contamination, this appealing feature is lost if the conditioning on landing outcome is deleted.

Harrison, J. M.↗

NASA NTRS2012

Assimilation of GRACE Terrestrial Water Storage into a Land Surface Model: Evaluation 1 and Potential Value for Drought Monitoring in Western and Central Europe

A land surface model s ability to simulate states (e.g., soil moisture) and fluxes (e.g., runoff) is limited by uncertainties in meteorological forcing and parameter inputs as well as inadequacies in model physics. In this study, anomalies of terrestrial water storage (TWS) observed by the Gravity Recovery and Climate Experiment (GRACE) satellite mission were assimilated into the NASA Catchment land surface model in western and central Europe for a 7-year period, using a previously developed ensemble Kalman smoother. GRACE data assimilation led to improved runoff correlations with gauge data in 17 out of 18 hydrological basins, even in basins smaller than the effective resolution of GRACE. Improvements in root zone soil moisture were less conclusive, partly due to the shortness of the in situ data record. In addition to improving temporal correlations, GRACE data assimilation also reduced increasing trends in simulated monthly TWS and runoff associated with increasing rates of precipitation. GRACE assimilated root zone soil moisture and TWS fields exhibited significant changes in their dryness rankings relative to those without data assimilation, suggesting that GRACE data assimilation could have a substantial impact on drought monitoring. Signals of drought in GRACE TWS correlated well with MODIS Normalized Difference Vegetation Index (NDVI) data in most areas. Although they detected the same droughts during warm seasons, drought signatures in GRACE derived TWS exhibited greater persistence than those in NDVI throughout all seasons, in part due to limitations associated with the seasonality of vegetation.

Li, Bailing↗

NASA NTRS1992

On the estimation of risk associated with an attenuation prediction

Viewgraphs from a presentation on the estimation of risk associated with an attenuation prediction is presented. Topics covered include: link failure - attenuation exceeding a specified threshold for a specified time interval or intervals; risk - the probability of one or more failures during the lifetime of the link or during a specified accounting interval; the problem - modeling the probability of attenuation by rainfall to provide a prediction of the attenuation threshold for a specified risk; and an accounting for the inadequacy of a model or models.

Crane, R. K.↗

NASA NTRS1993

Spectral analysis of the gravity and topography of Mars

New spherical harmonic models of the gravity and topography of Mars place important constraints on the structure and dynamics of the interior. The gravity and topography models are significantly phase coherent for harmonic degrees n less than 30 (wavelengths greater than 700 km). Loss of coherence below that wavelength is presumably due to inadequacies of the models, rather than a change in behavior of the planet. The gravity/topography admittance reveals two very different spectral domains: for n greater than 4, a simple Airy compensation model, with mean depth of 100 km, faithfully represents the observed pattern; for degrees 2 and 3, the effective compensation depths are 1400 and 550 km, respectively, strongly arguing for dynamic compensation at those wavelengths. The gravity model has been derived from a reanalysis of the tracking data for Mariner 9 and the Viking Orbiters, The topography model was derived by harmonic analysis of the USGS digital elevation model of Mars. Before comparing gravity and topography for internal structure inferences, we must ensure that both are consistently referenced to a hydrostatic datum. For the gravity, this involves removal of hydrostatic components of the even degree zonal coefficients. For the topography, it involves adding the degree 4 equipotential reference surface, to get spherically referenced values, and then subtracting the full degree 50 equipotential. Variance spectra and phase coherence of orthometric heights and gravity anomalies are addressed.

Bills, Bruce G.↗

NASA NTRS1972

The lunar conductivity profile and the nonuniqueness of electromagnetic data inversion.

A review of the theory for the electromagnetic functional used to date to determine the lunar conductivity profile from spectral analyses of lunar magnetometer data. The 'hard' boundary condition used by Sonett et al. (1971) and others appears to be a good approximation for the sunlit lunar hemisphere. The use of the spectral data in conjunction with the functional to find a least squares conductivity profile is examined from the point of view of the nonuniqueness of nonlinear estimation. An unsuccessful search was carried out to find models that were both geophysically reasonable and consistent with the data. It is asserted that the failure to find these models is due to the inadequacy of the functional. Of the models generated, those that best fit the data all have a conductivity peak at a depth of 240 km similar to that of the model discussed by Sonett et al. However, all of these models are quite distinct elsewhere in the profile. It is shown how such models are dependent on both the nature of the functional as well as the initial guess in the least squares procedure. A correlation analysis shows that the only resolvable features from this type of model are a low conductivity crust, a high conductivity peak of limited radial extent, and a low conductivity zone beneath the peak.

Phillips, R. J.↗