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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Semilinear (topological) spaces and applications

Semivector spaces are defined and some of their algebraic aspects are developed including some structure theory. These spaces are then topologized to obtain semilinear topological spaces for which a hierarchy of local convexity axioms is identified. A number of fixed point and minmax theorems for spaces with various local convexity properties are established. The spaces of concern arise naturally as various hyperspaces of linear and semilinear (topological) spaces. It is indicated briefly how all this can be applied in socio-economic analysis and optimization.

Prakash, P.↗
NASA NTRS1973

New hardware realizations of nonrecursive digital filters.

Analysis of the bit-level operations involved in the convolution realizing a nonrecursive digital filter leads to hardware designs of digital filters based on the operation of counting. Two distinct designs are outlined: the first one is capable of very high speed but is rather expensive; the second is quite slow but has the advantages of low cost and high flexibility. The basic designs considered utilize fixed-point representation for the data and filter coefficients. Variants allowing floating-point representation of the coefficients are also described.

Zohar, S.↗
NASA NTRS1973

Lp-stability (1 less than or equal to p less than or equal to infinity) of multivariable nonlinear time-varying feedback systems that are open-loop unstable

A class of multivariable, nonlinear time-varying feedback systems with an unstable convolution subsystem as feedforward and a time-varying nonlinear gain as feedback was considered. The impulse response of the convolution subsystem is the sum of a finite number of increasing exponentials multiplied by nonnegative powers of the time t, a term that is absolutely integrable and an infinite series of delayed impulses. The main result is a theorem. It essentially states that if the unstable convolution subsystem can be stabilized by a constant feedback gain F and if incremental gain of the difference between the nonlinear gain function and F is sufficiently small, then the nonlinear system is L(p)-stable for any p between one and infinity. Furthermore, the solutions of the nonlinear system depend continuously on the inputs in any L(p)-norm. The fixed point theorem is crucial in deriving the above theorem.

Callier, F. M.↗
NASA NTRS1974

Implementation of digital filters for minimum quantization errors

In this paper a technique is developed for choosing programing forms and bit configurations for digital filters that minimize the quantization errors. The technique applies to digital filters operating in fixed-point arithmetic in either open-loop or closed-loop systems, and is implemented by a digital computer program that is based on a digital simulation of the system. As an output the program gives the programing form required for minimum quantization errors, the total bit configuration required in the filter, and the location of the binary decimal point at each quantizer within the filter.

Phillips, C. L.↗
NASA NTRS1972

Second generation timing system for ranging experiment Apollo lunar laser

The status of the timing electronics for the lunar laser ranging station in Hawaii is discussed. The aim of the experiment is to measure, with high accuracy, the distance from a fixed point on earth to a retroreflector array which was placed on the lunar surface. The operating procedure for conducting the experiment is described. The components of the system are analyzed to show the effectiveness and accuracy of the facility.

Currie, D. G.↗
NASA NTRS1975

Numerical study of sound propagation in a jet flow

An improved computer oriented solution method for problems involving the propagation of sound through a nonuniform jet flow is developed. The method seeks to optimize the use of computer resources such as core storage space and central memory time. Complete formulation details are presented for a jet flow model consisting of a fixed point source on the jet center line in the potential core.

Padula, S. L.↗
NASA NTRS1974

An improved version of the table look-up algorithm for pattern recognition

The table look-up approach to pattern recognition has been used for 3 years at several research centers in a variety of applications. A new version has been developed which is faster, requires significantly less core memory, and retains full precision of the input data. The new version can be used on low-cost minicomputers having 32K words (16 bits each) of core memory and fixed-point arithmetic; no special-purpose hardware is required. An initial FORTRAN version of this system can classify an ERTS computer-compatible tape into 24 classes in less than 15 minutes.

Eppler, W. G.↗
NASA NTRS1977

Measuring mandibular motions

Mandibular motion along three axes is measured by three motion transducers on floating yoke that rests against mandible. System includes electronics to provide variety of outputs for data display and processing. Head frame is strapped to test subject's skull to provide fixed point of reference for transducers.

Dimeff, J.↗
NASA NTRS1975

Multidimensional stochastic approximation using locally contractive functions

A Robbins-Monro type multidimensional stochastic approximation algorithm which converges in mean square and with probability one to the fixed point of a locally contractive regression function is developed. The algorithm is applied to obtain maximum likelihood estimates of the parameters for a mixture of multivariate normal distributions.

Lawton, W. M.↗
NASA NTRS1975

Introduction to the restricted Jupiter orbiter problem

We consider a restricted six-body problem. The Galilean satellites' orbits are circular and coplanar; Io, Europa, and Ganymede are in exact resonance; their mean longitudes obey the Laplace relation. We seek periodic orbits which avoid close approaches to any satellite; such orbits are of interest for mission planning. They are approximated as fixed points of sets of variational equations associated with time-averaged disturbing functions. Stability of the solutions is also determined. The orbits of greatest interest are: planar - twice Callisto's period, eccentricity less than or equal to 0.6; planar - four times Callisto's period, eccentricity less than or equal to 0.75; slightly inclined - twice Callisto's period, eccentricity arbitrary; and planar - 4/5 or 5/4 Europa's period.

Heppenheimer, T. A.↗
NASA NTRS1976

Periodic motion in a class of nth-order autonomous differential equations

Sufficient conditions are obtained for the existence of periodic motion in a class of autonomous nonlinear differential equations of order greater than two. The approach is based on the decomposition of an equation into a linear and a nonlinear part. The analysis relies on some basic ideas from linear analysis and geometry. Sufficient conditions for a periodic solution are derived by means of a general topological principle referred to as the torus principle. The existence of a periodic solution is concluded by an appropriate use of the Brouwer fixed-point theorem.

Williamson, D.↗
NASA NTRS1977

Compatibility check of measured aircraft responses using kinematic equations and extended Kalman filter

An extended Kalman filter smoother and a fixed point smoother were used for estimation of the state variables in the six degree of freedom kinematic equations relating measured aircraft responses and for estimation of unknown constant bias and scale factor errors in measured data. The computing algorithm includes an analysis of residuals which can improve the filter performance and provide estimates of measurement noise characteristics for some aircraft output variables. The technique developed was demonstrated using simulated and real flight test data. Improved accuracy of measured data was obtained when the data were corrected for estimated bias errors.

Klein, V.↗
NASA NTRS1977

Proving the correctness of a flight-director program for an airborne minicomputer

Program verification procedures are described and used to determine the correctness of a program written for an airborne computer. The basic method relies on the inductive assertion method of Floyd (1967), modified and extended for application to a machine-language situation. Correctness considerations in the flight director program include self-modification, system correctness, executable instructions, overflow, approximate calculations with fractional quantities, and fixed point scaling. An example proof of correctness, which proceeds by proving the correctness of a certain subroutine, is provided.

Maurer, W. D.↗
NASA NTRS1977

The optimization of self-phased arrays for diurnal motion tracking of synchronous satellites

The diurnal motion of a synchronous satellite necessitates mechanical tracking when a large aperture, high gain antenna is employed at the earth terminal. An alternative solution to this tracking problem is to use a self phased array consisting of a number of fixed pointed elements, each with moderate directivity. Non-mechanical tracking and adequate directive gain are achieved electronically by phase coherent summing of the element outputs. The element beamwidths provide overlapping area coverage of the satellite motion but introduce a diurnal variation into the array gain. The optimum element beamwidth and pointing direction of these elements can be obtained under the condition that the array gain is maximized simultaneously with the minimization of the diurnal variation.

Theobold, D. M.↗
NASA NTRS1977

Evaluation Program for Secondary Spacecraft Cells: Synchronous Orbit Testing of Sealed Nickel Cadmium Cells

Performance data concerning sealed nickel-cadmium cells operating under a synchronous orbit regime are presented. A space satellite maintaining a position over a fixed point on earth as the earth rotates on its axis and revolves about the sun was simulated. Results include: (1) exposure to synchronous orbit testing at a temperature of 40 C yields less than 6 years of life; (2) performance at -20 C presents a low capacity problem; (3) the capacity check, performed at the middle of each show period, provides a temporary red reconditioning effect on the cells in that the end-of-discharge voltages are higher, for approximately 7 to 10 days, following the capacity check than they were 7 to 10 days prior to the capacity check; (4) all the test packs at -20 C and 40 C have either failed or were discontinued because of low capacity; and (5) test packs at temperatures of 0 C and 10 C have delivered the best capacity during life and packs tested at 20 C showed better life capability than packs tested at -20 C and 40 C.

Harkness, J. D.↗
NASA NTRS1978

Vision-based guidance for an automated roving vehicle

A controller designed to guide an automated vehicle to a specified target without external intervention is described. The intended application is to the requirements of planetary exploration, where substantial autonomy is required because of the prohibitive time lags associated with closed-loop ground control. The guidance algorithm consists of a set of piecewise-linear control laws for velocity and steering commands, and is executable in real time with fixed-point arithmetic. The use of a previously-reported object tracking algorithm for the vision system to provide position feedback data is described. Test results of the control system on a breadboard rover at the Jet Propulsion Laboratory are included.

Griffin, M. D.↗
NASA NTRS1979

The digital implementation of control compensators: The coefficient wordlength issue

There exists a number of mathematical procedures for designing discrete-time compensators. However, the digital implementation of these designs, with a microprocessor for example, has not received nearly as thorough an investigation. The finite-precision nature of the digital hardware makes it necessary to choose an algorithm (computational structure) that will perform 'well-enough' with regard to the initial objectives of the design. This paper describes a procedure for estimating the required fixed-point coefficient wordlength for any given computational structure for the implementation of a single-input single-output LOG design. The results are compared to the actual number of bits necessary to achieve a specified performance index.

Moroney, P.↗