Search NASA⌕ Search

SEARCH · Search NASA

Results for “Describing function”

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.

At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Conversion of positions and proper motions from B1950.0 to the IAU system at J2000.0

The complete transformation of positions and proper motions from B1950.0 to J2000.0 on the basis of IAU recommendations including the transition from FK4 to FK5 equinox may be rigorously accomplished with a simple vector equation. The equation is first presented in this paper and then subsequently derived. The transformation of the FK4 to FK5 system described by functions f(alpha, delta, m) is in preparation in Heidelberg.

Standish, E. M., Jr.↗
NASA NTRS1983

NASA multipurpose airborne DIAL system and measurements of ozone and aerosol profiles

The hardware, operational characteristics, data processing system, and applications of the NASA airborne differential absorption lidar (DIAL) system are described. DIAL functions by assessing the average gas concentration over a specified range interval by analyzing the difference in lidar backscatter signals for laser wavelengths tuned on and off of the molecular absorption line of a gas under investigation. The system comprises two frequency-doubled Nd:YAG lasers pumping two high conversion efficiency tunable dye lasers emitting pulses separated by 100 microsec or less. The return signals are digitized and stored on magnetic tape. The signal collector consists of photomultiplier tubes implanted in a cassegrain telescope. Flight tests of the system involved on-measurements at 285.95 nm and off-measurements at 299.40 nm, which yielded a differential cross section of 1.74 x 10 to the -16th sq cm. In situ measurements with another plane at a nominal altitude of 3.2 km for comparison purposes showed accuracy to within 10% in and above the boundary layer. The system is considered as a test apparatus for more developed versions to be flown on the Shuttle

Browell, E. V.↗
NASA NTRS1983

Spline Classification Methods

The use of spline functions in the development of classification algorithms is discussed. A method is formulated for producing spline approximations to univariate density functions when each density function is described by a histogram of measurements. The resulting approximations are then incorporated into a Bayesian classification procedure for which the probability of misclassification can be readily computed. Some preliminary numerical results are presented to illustrate the method.

Guseman, L. F., Jr.↗
NASA NTRS1984

Upper and lower bounds for semi-Markov reliability models of reconfigurable systems

This paper determines the information required about system recovery to compute the reliability of a class of reconfigurable systems. Upper and lower bounds are derived for these systems. The class consists of those systems that satisfy five assumptions: the components fail independently at a low constant rate, fault occurrence and system reconfiguration are independent processes, the reliability model is semi-Markov, the recovery functions which describe system configuration have small means and variances, and the system is well designed. The bounds are easy to compute, and examples are included.

White, A. L.↗
NASA NTRS1984

Characterization of the LANDSAT sensors' spatial responses

The characteristics of the thematic mapper (TM) and multispectral scanner (MSS) sensors on LANDSATs 4 and 5 affecting their spatial responses are described, and functions defining the response of the system to an arbitrary input spatial pattern are derived, i.e., transfer functions (TF) and line spread functions (LSF). These design LSF's and TF's were modified based on prelaunch component and system measurements to provide improved estimates. Prelaunch estimates of LSF/FT's are compared to in-orbit estimates. For the MSS instruments, only limited prelaunch scan direction square-wave response (SWR) data were available. Design estimates were modified by convolving in Gaussian blur till the derived LSF/TF's produced SWR's comparable to the measurements. The two MSS instruments were comparable at their temperatures of best focus; separate calculations were performed for bands 1 and 3, band 2 and band 4. The pre-sample nadir effective instantaneous field's of view (EIFOV's) based on the .5 modulation transfer function (MTF) criteria vary from 70 to 75 meters in the track direction and 79 to 82 meters in the scan direction. For the TM instruments more extensive prelaunch measurements were available. Bands 1 to 4, 5 and 7, and 6 were handled separately as were the two instruments. Derived MTF's indicate nadir pre-sample EIFOV's of 32 to 33 meter track (bands 1 to 5, 7) and 36 meter scan (bands 1 to 5, 7) and 1245 meter track (band 6) and 141 meter scan (band 6) for both TM's.

Markham, B. L.↗
NASA NTRS1984

Characterizing the scientific potential of satellite sensors

Eleven thematic mapper (TM) radiometric calibration programs were tested and evaluated in support of the task to characterize the potential of LANDSAT TM digital imagery for scientific investigations in the Earth sciences and terrestrial physics. Three software errors related to integer overflow, divide by zero, and nonexist file group were found and solved. Raw, calibrated, and corrected image groups that were created and stored on the Barker2 disk are enumerated. Black and white pixel print files were created for various subscenes of a San Francisco scene (ID 40392-18152). The development of linear regression software is discussed. The output of the software and its function are described. Future work in TM radiometric calibration, image processing, and software development is outlined.

Source record↗
NASA NTRS1985

Man-machine interface and control of the shuttle digital flight system

The space shuttle main engine (SSME) presented new requirements in the design of controls for large pump fed liquid rocket engine systems. These requirements were the need for built in full mission support capability, and complexity and flexibility of function not previously needed in this type of application. An engine mounted programmable digital control system was developed to meet these requirements. The engine system and controller and their function are described. Design challenges encountered during the course of development included accommodation for a very severe engine environment, the implementation of redundancy and redundancy management to provide fail operational/fail safe capability, removal of heat from the package, and significant constraints on computer memory size and processing time. The flexibility offered by programmable control reshaped the approach to engine design and development and set the pattern for future controls development in these types of applications.

Burghduff, R. D.↗
NASA NTRS1985

Operating system for a real-time multiprocessor propulsion system simulator. User's manual

The NASA Lewis Research Center is developing and evaluating experimental hardware and software systems to help meet future needs for real-time, high-fidelity simulations of air-breathing propulsion systems. Specifically, the real-time multiprocessor simulator project focuses on the use of multiple microprocessors to achieve the required computing speed and accuracy at relatively low cost. Operating systems for such hardware configurations are generally not available. A real time multiprocessor operating system (RTMPOS) that supports a variety of multiprocessor configurations was developed at Lewis. With some modification, RTMPOS can also support various microprocessors. RTMPOS, by means of menus and prompts, provides the user with a versatile, user-friendly environment for interactively loading, running, and obtaining results from a multiprocessor-based simulator. The menu functions are described and an example simulation session is included to demonstrate the steps required to go from the simulation loading phase to the execution phase.

Cole, G. L.↗
NASA NTRS1985

Space station configuration and flight dynamics identification

The Space Station will be assembled in low earth orbit by a combination of deployable and space erectable modules that are progressively integrated during successive flights of the Shuttle. The crew assisted space construction will result in a configuration which is a large scale composite of structural elements having connectivity with a wide range of possible end conditions and imprecisely known dynamic characteristics. The generic applications of Flight Dynamics Identification to the candidate Space Station configurations currently under consideration are described. Identification functions are categorized, and the various methods for extracting parameter estimates are correlated with the sensing of parameter estimates are correlated with the sensing of specific characteristics of interest to both engineering subsystems and users of the Station's commercial and scientific facilities. Onboard implementation architecture and constraints are discussed from the viewpoint of maximizing integration of the Identification process with the flight subsystem's data and signal flow.

Metter, E.↗
NASA NTRS1985

Chromophores with auxochrome-like function

Chromophores exist which can exert an auxochromic effect in addition to their chromophoric one. Styryl and cyan radicals are considered. Numerous chromophores were checked and those with auxochromic functions are described and tabulated.

Kauffmann, H.↗
NASA NTRS1984

Development of a para-orthohydrogen catalytic converter for a solid hydrogen cooler

Design features of a tested catalytic converter for altering vented cryogenic parahydrogen used as a coolant on spacecraft into a para-ortho equilibrium for channeling to other cooling functions are described. The hydrogen is expected to be stored in either liquid or solid form. A high surface area Ni-on-Si catalyst was selected for tests at an operating pressure of 2 torr at a ratio of 1000 gr catalyst for a gr/sec hydrogen flow. Cylindrical and radial flow geometries were tried and measurements centered on the converter efficiencies at different operating temperatures when the converter was placed in the vent line of the H2 cooler. Efficiencies ranging from 10-100 percent were obtained for varying flow rates. Further testing is necessary to characterize the converter performance under a wider range of operating temperatures and environments.

Nast, T. C.↗
NASA NTRS1983

Programming the gradient projection algorithm

The gradient projection method of numerical optimization which is applied to problems having linear constraints but nonlinear objective functions is described and analyzed. The algorithm is found to be efficient and thorough for small systems, but requires the addition of auxiliary methods and programming for large scale systems with severe nonlinearities. In order to verify the theoretical results a digital computer is used to simulate the algorithm.

Hargrove, A.↗
NASA NTRS1986

Research Program for Vibration Control in Structures

Purpose of program to apply control theory to large space structures (LSS's) and design practical compensator for suppressing vibration. Program models LSS as distributed system. Control theory applied to produce compensator described by functional gains and transfer functions. Used for comparison of robustness of low- and high-order compensators that control surface vibrations of realistic wrap-rib antenna. Program written in FORTRAN for batch execution.

Mingori, D. L.↗
NASA NTRS1986

Analytical comparison of transient and steady state visual evoked cortical potentials

To better describe the linear-dynamic properties of the human visual-cortical response system, transient and steady state Visual Evoked Response Potentials (VERP) were observed. The stimulus presentation device provided both the evoking stimulus (flickering or pulsing lights) and a video task display. The steady state stimulus was modulated by a complex, ten frequency, sum-of-sines, wave. The transient VERP was the time-locked average of the EEG to a series of narrow light pulses (pulse width of 10 msec). The Fourier transform of the averaged pulses had properties that approximate band limited white noise, i.e., a flat spectrum over the frequency region spanned by the 10 summed sines. The Fourier transform of both the steady state and the transient evoked potentials resulted in transfer that are equivalent and therefore comparable. To investigate the effects of task loading on evoked potentials, a grammatical reasoning task was provided. Results support the relevancy of continued application of a systems engineering approach for describing neurosensory functioning.

Junker, A. M.↗
NASA NTRS1985

Tetrahedron array of reaction wheels for attitude control and energy storage

A spacecraft subsystem, working in conjunction with a solar array, which provides 3-axis attitude control as well as some power system functions is described. Four flywheels, driven by variable-field d.c. motors and arranged in a tetrahedron configuration, are employed. In sunlight, the system provides voltage regulation while the wheels are accelerated to some maximum speed. In the dark, the motors become flywheel-driven generators which provide regulated power to other spacecraft electrical loads. A microprocessor is used to compute field current levels for each of the 4 motor/generators, based on measurements of the system voltage level, the flywheel speeds, and the attitude control torques desired.

Flatley, T. W.↗
NASA NTRS1985

Shuttle environment database

The proceedings of a workshop on the development of a data base for the Space Shuttle environment are summarized. The data base is intended for use by experimenters in designing scientific payloads for Shuttle missions. The status of currently available data on the Shuttle environment is reviewed, with emphasis given to ten specific topics which are believed to be of concern to Shuttle experiment designers. These topics include: flight dynamics, vibration and acoustics, orbiter motion effects, EMI, and thermal and humidity effects. Attention is also given to: the Shuttle particulate environment; surface interactions inside and on the exterior of the spacecraft, and the natural Shuttle environment. Recent experimental results concerning Vehicle Glow on the spacecraft surface material are discussed in detail. A schematic diagram describing the functional organization of computer hardware for the Shuttle environment data base is provided.

Lauriente, M.↗
NASA NTRS1986

A performance evaluation of the software-implemented fault-tolerance computer

The results of a performance evaluation of the Software-Implemented Fault-Tolerance (SIFT) computer system conducted in the NASA Avionics Integration Research Laboratory are presented. The essential system functions are described and compared to both earlier design proposals and subsequent design improvements. Using SIFT's specimen task load, the executive tasks, such as reconfiguration, clock synchronization, and interactive consistency, are found to consume significant computing resources. Together with other system overhead (e.g., voting and scheduling), the operating system overhead is in excess of 60 percent. The authors propose specific design changes that reduce this overhead burden significantly.

Palumbo, D. L.↗
NASA NTRS1986

Space Station overall management approach for operations

An Operations Management Concept developed by NASA for its Space Station Program is discussed. The operational goals, themes, and design principles established during program development are summarized. The major operations functions are described, including: space systems operations, user support operations, prelaunch/postlanding operations, logistics support operations, market research, and cost/financial management. Strategic, tactical, and execution levels of operational decision-making are defined.

Paules, G.↗