SEARCH · Search NASA
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
A report on technology assessment (TA) is presented. Topics discussed include: the nature of TA, TA used as an analytical method for natural and social sciences, and the uncertain consequences of TA.
When graphite is used as ablation material in heat shields, very often a prominent carbon species vaporized into the stream is C3. The thermodynamic properties of the C3 molecule are, therefore, important in calculating transport phenomena in the ablation flow field. The nature of the C3 thermodynamic functions has been in doubt because of the uncertain contribution of the bending mode vibrations to the total internal energy of the molecule. An approach for overcoming these difficulties is considered. The results of the computations are presented in the form of graphs and approximating functions.
The orbital evolution of (1685) Toro has been investigated over 5000 yr. The asteroid exhibits a locked resonance through an 8:5 commensurability with the earth for the first 3400 yr of integration and a locked resonance with Venus through a 13:5 commensurability for the last 1000 yr. Control of these resonances passes from the earth to Venus as the distance from the earth's orbit gets greater and the distance to Venus' orbit gets closer as a consequence of the precession of the argument of perihelion. The double resonance may give Toro the ability to avoid collisions with the earth and Venus at the present time but this is still uncertain. Mars perturbations could remove Toro from the deepest part of the resonance in about 3,000,000 yrs.
This paper considers the suboptimal stochastic control of linear discrete-time dynamical systems with uncertain or stochastically varying parameters. The suboptimal scheme is based upon the use of the open-loop-feedback-optimal (OLFO) method. The state and parameter estimates are generated by an extended Kalman filter algorithm. Numerical results for first-order systems are presented.
A square root formulation is presented for the discrete combined state parameter estimation problem with linear plant dynamics, Gaussian random disturbances, and constant but uncertain parameters. The estimator is a combination of the classical Kalman filter and a maximum likelihood algorithm which maximizes the parameter log-likelihood function using a first order search routine.
A flight control system design is presented, that can be implemented by analog hardware, to be used to control an aircraft with uncertain parameters. The design is based upon the use of modern control theory. The ideas are illustrated by considering control of STOL longitudinal dynamics.
The NASTRAN Thermal Analyzer has been intended to do variance analysis and plot the thermal boundary elements. The objective of the variance analysis addition is to assess the sensitivity of temperature variances resulting from uncertainties inherent in input parameters for heat conduction analysis. The plotting capability provides the ability to check the geometry (location, size and orientation) of the boundary elements of a model in relation to the conduction elements. Variance analysis is the study of uncertainties of the computed results as a function of uncertainties of the input data. To study this problem using NASTRAN, a solution is made for both the expected values of all inputs, plus another solution for each uncertain variable. A variance analysis module subtracts the results to form derivatives, and then can determine the expected deviations of output quantities.
When a wide field is sinusoidally modulated both in space and in time, the spatial frequency of the pattern will appear doubled at high rates of modulation. Kelly (1966) proposed that this illusion is due to temporal integration of the nonlinear brightness response of the visual system. The anatomical locus of this temporal integrator is uncertain, and could be subcortical. Results indicate that spatial frequency doubling follows binocular disparity detection and is thus a cortical phenomenon.
Regional relations and characteristics of the dark material as observed on photographs of the Taurus-Littrow region of the moon are reviewed to provide a background for interpretations of its nature and origin. The dark material seems to be a surficial deposit that covers mare and highland areas near the southeastern edge of the Serenitatis Basin. The age of the dark material, as deduced from photogeologic analysis, is ambiguous: contact relations near its western edge suggest that it is older than the central light basalts of Mare Serenitatis; evidence elsewhere indicates that it may be younger. The origin of the dark material is also uncertain, and the following alternate hypotheses are briefly considered: (1) thick regolith, (2) dark impact ejecta, (3) pyroclastic blanket, or (4) a material of different origin in different places.
A range of interstellar electron spectra at energies between 100 MeV and 5 GeV has been derived from an analysis of the observed galactic nonthermal radio spectrum and from consideration of the existing uncertainties in the other relevant physical parameters of the galaxy. We find that for energies larger than about 300 MeV the electron spectrum is uncertain to a factor of 4 due to uncertainties in the galactic magnetic field strength and the total line-of-sight emission length. The uncertainty in the electron spectrum increases towards lower energies, exceeding a factor of 50 near 100 MeV, primarily due to uncertainties in the galactic parameters affecting interstellar radio absorption.
The meteoroid penetration detectors on the Pioneer 10 spacecraft recorded 67 meteoroid penetrations through the 25-micron stainless steel test material while the spacecraft was between 1.0 and 5.1 AU. Ten of these penetrations occurred during the encounter with Jupiter. The cumulative spatial density of meteoroids with masses greater than 2 nanograms has been calculated from these data for interplanetary space and for the near-Jupiter space. The spatial density is found to be essentially constant in interplanetary space between 1 and 5 AU, approximately 1 meteoroid per cubic km, and 1-2 orders of magnitude greater near Jupiter. There was no increase in the spatial density of meteoroids in the asteroid belt and hence no evidence that there is a significant asteroidal component of 2-nanogram meteoroids. It is uncertain whether the meteoroids detected near Jupiter were in orbit about Jupiter or were gravitationally focused toward the planet from solar orbits.
Following a large magnetic storm (17 June 1972), Explorer 45 measured the equatorial particle populations and magnetic field. Using data obtained during the symmetic recovery phase, it is shown that through a series of self-consistent calculations, the measured protons with energies from 1 to 872 keV, can account for the observed ring current magnetic effects within experimental uncertainities. This enables an upper limit to be set for the heavy ion contribution to the storm time ring current.
A statistical evaluation of some of the recent satellite determined gravity models, including some with distinct data base, indicates that the geopotential coefficients of these models are individually meaningful for frequencies with wave numbers n = 2 through 7 certainly and wave numbers n = 8 through 10 probably. Geopotential coefficients in higher frequency ranges while apparently important for computing accurate satellite orbits seem to have little geophysical significance in an individual sense. Differences between various gravity models and those satellite purely between determined geopotential models and their associated combination models show no consistent relationship to surface gravimetric coverage. Additional classical tracking data are important in improving the existing description of the earth's gravity field but their contribution in extending its frequency range beyond what is now available is uncertain.
An overview of the problems of entry aerodynamics and heating is given with emphasis on survival of the probe, predictability of performance, and reliability of performance. Technological challenges to performance prediction are considered and include: turbulent heat transfer, radiation blockage, chemical state of the shock layer, afterbody heat transfer, asymmetric ablation, and real-gas aerodynamics. It is indicated that various obstacles must be overcome in order to achieve technology readiness. These obstacles are considered to be: extrapolations from ground tests to flight; lack of flight experience; lack of parametric data; and uncertain knowledge of atmospherics.
Application of a general method for calculation of inviscid hypersonic flow fields is discussed. General considerations are analyzed along with the sonic corner and the stagnation region. It is concluded that the complications caused by the requirement for sonic flow at the rear corner and particularly by the uncertain position of the stagnation streamline lead to sufficient difficulties with convergence of iterations that a practical procedure is not likely to be found.
A two-parameter scintillation spectrometer system developed and used to obtain proton, deuteron, and triton double differential cross sections from materials under 558-MeV-proton irradiation is described. The system measures both the time of flight of secondary particles over a 488-cm flight path and the energy deposited in a scintillator, 12.7 cm in diameter and 30.48 cm long. The time resolution of the system is 0.39 nsec. The calculated energy resolution based on this time resolution varies with energy from 1.6 precent to 7.75 percent for 50- and 558-MeV protons. Various systematic and statistical errors are evaluated, and the double differential cross sections for secondary proton and deutron production at 20 deg from a 2.35 g/sq cm thick beryllium target are shown as an example of the results obtainable with this system. The uncertainly in the cross sections for secondary protons varies with particle energy from approximately + or - 9 percent at 50 MeV to approximately + or - 11 percent at 558 MeV.
High purity tungsten, which is used for targets in X-ray tubes was considered for space processing. The demand for X-ray tubes was calculated using the growth rates for dental and medical X-ray machines. It is concluded that the cost benefits are uncertain.
This paper reports a reasonably complete theory of necessary and sufficient conditions for a control to be superior with respect to a nonscalar-valued performance criterion. The latter maps into a finite-dimensional integrally closed directed partially ordered linear space. The applicability of the theory to the analysis of dynamic vector estimation problems and to a class of uncertain optimal control problems is demonstrated.