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Results for “Transfer functions”

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 667 records · Page 37

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NASA NTRS1972

Utilization of a CRT display light pen in the design of feedback control systems

A hierarchical structure of the interlinked programs was developed to provide a flexible computer-aided design tool. A graphical input technique and a data structure are considered which provide the capability of entering the control system model description into the computer in block diagram form. An information storage and retrieval system was developed to keep track of the system description, and analysis and simulation results, and to provide them to the correct routines for further manipulation or display. Error analysis and diagnostic capabilities are discussed, and a technique was developed to reduce a transfer function to a set of nested integrals suitable for digital simulation. A general, automated block diagram reduction procedure was set up to prepare the system description for the analysis routines.

Thompson, J. G.↗

NASA NTRS1972

New considerations for pogo prevention on space shuttle

Recommendations for improving the methodology of pogo suppression for the space shuttle include: Consideration of inter-pump location for accumulator or active device, inclusion of tank outflow effects in dynamic structural analysis, the use of simplified transfer functions in systems studies, three phase dynamic testing program for turbopump with development of dynamic flowmeters, and the use of a linearized mathematical model for engine physics studies.

Rubin, S.↗

NASA NTRS1972

Experimental dynamic response of a two-dimensional, Mach 2.7, mixed compression inlet

A test program was conducted on a two-dimensional supersonic inlet. Internal disturbances in diffuser exit mass flow were produced by oscillating overboard bypass doors. Open-loop dynamic responses of shock position, throat exit and diffuser exit static pressures are presented. The steady-state and dynamic coupling between ducts were also obtained. The experimental results from the two-dimensional inlet are compared to results from a similar size axisymmetric inlet and also to a transfer function synthesis program.

Baumbick, R. J.↗

NASA NTRS1970

Multipath errors in range rate measurement by a TDRS/VHF - GRARR

Range rate errors due to multipath reflection are calculated for a tracking and data relay satellite system using the VHF Goddard range and range rate (GRARR) system. At VHF the reflection is primarily specular, and the strength of the multipath relative to the direct path can be modeled in terms of the geometry and the surface characteristics, specifically the root-mean-square (rms) ocean wave height. The uplink and downlink multipath introduces phase jitter on the GRARR carrier and subcarrier. The derivation of these effects is reviewed leading to an expression for the rms range rate error. The derivation assumed the worst-case orbital configurations in which there was very little relative specular Doppler. This means that the specular multipath interference was not attenuated by the carrier and subcarrier PLL transfer functions. Curves of range rate error are presented as a function of grazing angle with wave height 0.3 to 0.7 meters and spacecraft altitude 100 to 700 miles as parameters.

Sohn, S. J.↗

NASA NTRS1971

Development of optimized techniques and requirements for computer enhancement of structural weld radiographs. Volume 1: Technical report

A hardware and software specification covering requirements for the computer enhancement of structural weld radiographs was considered. Three scanning systems were used to digitize more than 15 weld radiographs. The performance of these systems was evaluated by determining modulation transfer functions and noise characteristics. Enhancement techniques were developed and applied to the digitized radiographs. The scanning parameters of spot size and spacing and film density were studied to optimize the information content of the digital representation of the image.

Adams, J. R.↗

NASA NTRS1971

Digital correction of geometric and radiometric errors in ERTS data.

The sensor systems of the ERTS-A satellite are discussed and sources of geometric and radiometric errors in the received images are identified. Digital algorithms are presented for detection of reseau and ground control points, for rapid implementation of geometric corrections, and for radiometric correction of errors caused by shading, image motion, modulation transfer function, and quantum and systematic noise.

Bakis, R.↗

NASA NTRS1971

Frequency domain stability criteria for distributed nonlinear sampled-data systems.

Popov-type sufficient conditions are presented for the absolute stability of a class of closed loop sampled-data systems. The closed loop system consists of a linear distributed element, a feedback controller (linear or nonlinear), a sampler, and possibly a zero-order hold circuit. The distributed element is assumed to be finite Hankel transformable, and such that its dynamics can be represented by a transfer function which is the ratio of the multiple (Laplace and finite Hankel) transforms of output and input. The input is assumed to be distributed. The stability criterion presented here parallels the criterion for distributed systems that are finite Fourier transformable. An example is given to illustrate the applications of the stability criterion.

Nagarajan, N.↗

NASA NTRS1971

Capabilities of a single scan TV-radiographic system for digital data acquisition.

A single scan TV-radiography system capable of providing analogue signals ready for A-D conversion for input to a computer has been investigated. Modulation transfer functions of both horizontal and vertical resolution have been obtained. The capability for gray scale reproduction was also investigated. The output data rate of the system is 16 KHz thereby providing compatibility to A-D converters generally available for most computers. In general, the capability of the system was found to exceed the input capabilities of available image-amplifiers and is therefore acceptable for quantitative fluoroscopic applications.

Baily, N. A.↗

NASA NTRS1972

Dynamic response of a plane-symmetrical exothermic reaction center.

?sger,An analysis of the dynamic behavior of an idealized, plane-symmetrical exothermic reaction center is presented. The conservation equations for the reaction center are combined and yield a single integral equation expressing a nonlinear transfer function of the system for which the input is provided by a given time profile of the heat released per unit mass while the output gives the pressure pulse it generates under the restriction of plane-symmetrical motion. The solution is governed by a Daumk]hler number. For a given form of the exothermic power pulse profile, the dynamic behavior of the system is completely specified in terms of only this Daumk]hler number and the heat of reaction per unit mass of the combustible medium. Specific solutions are worked out for a set of typical elementary power pulse profiles, and the practical significance of the results is illustrated by their application to the problem of transition to detonation in an explosive gas.

Meyer, J. W.↗

NASA NTRS1972

A quadratic pulse height analyzer for space applications.

A flight-worthy pulse height analyzer that has a quadratic transfer function is described. This quadratic function permits optimum usage of the entire PHA dynamic range due to the quadratic nature of the gamma ray spectrometer's resolution vs energy. After the theoretical design discussion, the implementation of the design is examined and test results described. The analyzer is part of the University of New Hampshire gamma ray monitor for OSO-H.

Burtis, D. W.↗

NASA NTRS1972

Digital controller for high pressure rocket engine.

Description of a general approach for the design of an adaptive digital control system for liquid bipropellant rocket engines. The technique employs linearized transfer functions derived from perturbations of an engine simulation. The linear models serve as a basis on which to develop candidate closed-loop control laws quickly and economically.

Thompson, Z.↗

NASA NTRS1972

Recent results in convolution feedback systems.

Survey of recent results obtained by the authors concerning certain types of multiinput, multioutput feedback systems. The discrete-time case as well as the continuous-time case are considered. In each case three theorems are shown. These give insight into the nature of the relationship between the open-loop operator and the closed-loop operator of the system, as well as necessary and sufficient conditions for stability of the closed-loop system when 'unstable' poles are present in their open-loop transfer function.

Desoer, C. A.↗

NASA NTRS1972

High resolution imagery with the large space telescope.

A number of general characteristics of a diffraction limited telescope are examined, giving attention to the optical system of the Stratoscope II instrument. The optical resolution of a telescope can be described in at least three different ways, involving the wavefront error, the optical transfer function, and the point spread function. The Stratoscope II tolerance budget and the performance of the instrument are discussed together with a goal for the resolution of the large space telescope (LST) which is to be designed. The very high resolving power of the LST will be utilized in many ways. The imagery of extended objects with low surface contrast is considered along with the photometry of very faint stars.

Danielson, R. E.↗

NASA NTRS1972

Determination of the inflight OTF of orbital earth resources sensors

There are no author-identified significant results in this report. A technique has been investigated that is particularly applicable to evaluation of earth-orbiting multispectral sensors. In all programs employing such sensors, simultaneous underflight photography from aircraft is made during passes of the spacecraft. To evaluate the spacecraft imagery, the two sets of photographs are scanned and digitized with a microdensitometer. The data are then Fourier analyzed, and the spatial frequency spectra is calculated. The spatial frequencies in the underflight trace are scaled to those in the spacecraft trace, and the ratio of the spectra gives the in-flight optical transfer function (OTF) for the orbiting sensor. The method has been applied to an Apollo 9 frame and the sensor OTF has been calculated. The results are good enough to encourage use of the technique and to indicate the accuracies required of the various measurements involved in determining in-flight sensor OTF by this method. A technique for determining correct scan registration and scaling between the two sets of imagery and a promising approach to noise reduction, in the form of weighted averaging of OTF's, are discussed.

Slater, P. N.↗

NASA NTRS1972

Aircraft handling qualities data

Available information on weight and inertia, aerodynamic derivatives, control characteristics, and stability augmentation systems is documented for 10 representative contemporary airplanes. Data sources are given for each airplane. Flight envelopes are presented and dimensional derivatives, transfer functions for control inputs, and several selected handling qualities parameters have been computed and are tabulated for 10 different flight conditions including the power approach configuration. The airplanes documented are the NT-33A, F-104A, F-4C, X-15, HL-10, Jetstar, CV-880M, B-747, C-5A, and XB-70A.

Heffley, R. K.↗

NASA NTRS1972

Study of the detail content of Apollo orbital photography

The results achieved during a study of the Detail Content of Apollo Orbital Photography are reported. The effect of residual motion smear or image reproduction processes upon the detail content of lunar surface imagery obtained from the orbiting command module are assessed. Data and conclusions obtained from the Apollo 8, 12, 14 and 15 missions are included. For the Apollo 8, 12 and 14 missions, the bracket-mounted Hasselblad camera had no mechanism internal to the camera for motion compensation. If the motion of the command module were left totally uncompensated, these photographs would exhibit a ground smear varying from 12 to 27 meters depending upon the focal length of the lens and the exposure time. During the photographic sequences motion compensation was attempted by firing the attitude control system of the spacecraft at a rate to compensate for the motion relative to the lunar surface. The residual smear occurring in selected frames of imagery was assessed using edge analyses methods to obtain and achieved modulation transfer function (MTF) which was compared to a baseline MTF.

Kinzly, R. E.↗

NASA NTRS1972

Nightside electromagnetic response of the moon

The electromagnetic response of the Moon to excitation by the time dependent fluctuations of the interplanetary magnetic field is given for the dark or antisolar hemisphere of the Moon. Six hours of time series data from the Explorer 35 magnetometer and the lunar surface magnetometer on Apollo 12 are used to obtain the Fourier spectral amplitudes of the surface and interplanetary fields from which transfer functions are calculated for the east-west, north-south, and vertical directions at the Apollo site. A critical discussion of lunar conductivity profiles derived from night side radial magnetic field data and vacuum scattering theory is presented. Limitations are shown that there is no evidence for a lunar core as conducting as 0.01 mhos/m.

Schubert, G.↗

NASA NTRS1973

The induced magnetosphere of the moon. 1: Theory

An analytic solution for the magnetic field in the space defined by a spherical moon and its downstream cylindrical cavity formed by the solar wind is derived for interplanetary magnetic fields both parallel and perpendicular to the cavity axis. By superposition, the solution is obtained for arbitrary orientations of the interplanetary field. The theory is quasi-static and is formulated in terms of a scalar magnetic potential. Thus the moon model consists of a core of arbitrary size and infinite electrical conductivity surrounded by a nonconducting shell; the cavity volume is assumed to be nonconducting. The variation of the magnetic field on the lunar surface, both on the sunlit and on the dark side hemispheres, and on the cavity boundary is presented for various values of core radius. The solution yields the distribution of currents on the lunar sunlit surface and the surface of the cavity. Theoretical transfer functions are presented and their variations with position on the lunar surface and with core size are discussed.

Schubert, G.↗