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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Average correlation functions in on-line testing of linear systems

This paper is a report on new methods for on-line testing of single-input/single-output linear and time-invariant systems. No interruption of system operation is necessary, since the signals used in this test procedure are the normal operating signals. Test results indicate that detectable system errors using finite amounts of data are well within tolerance for normal operation in all but the most stringent applications.

Mix, D. F.↗
NASA NTRS1977

FORTRAN code-evaluation system

Automated code evaluation system can be used to detect coding errors and unsound coding practices in any ANSI FORTRAN IV source code before they can cause execution-time malfunctions. System concentrates on acceptable FORTRAN code features which are likely to produce undesirable results.

Capps, J. D.↗
NASA NTRS1984

Acoustic propagation in a thermally stratified atmosphere

This report describes the activities during the fourth six month period of the investigation of acoustic propagation in the atmosphere with a realistic lapse temperature profile. A significant error was detected since the previous semi-annual report and has been corrected in both the plane wave and point source solutions. This report then describes both of these problems in some detail along with presenting some numerical results from the model. Work will begin this summer on the model of propagation in an inversion.

Vanmoorhem, W. K.↗
NASA NTRS1986

Language and Program for Documenting Software Design

Software Design and Documentation Language (SDDL) provides effective communication medium to support design and documentation of complex software applications. SDDL supports communication among all members of software design team and provides for production of informative documentation on design effort. Use of SDDL-generated document to analyze design makes it possible to eliminate many errors not detected until coding and testing attempted. SDDL processor program translates designer's creative thinking into effective document for communication. Processor performs as many automatic functions as possible, freeing designer's energy for creative effort. SDDL processor program written in PASCAL.

Kleine, H.↗
NASA NTRS1986

Cloud detection by lidar extinction calculations

A new lidar method of measuring cloud ceiling height using the Klett solution to the lidar equation was developed. This simple technique will find cloud ceiling height for clouds that rangefinder-like lidars cannot theoretically detect. In addition, the noise signals that do not correspond to clouds removed by using the convergence of the Klett solution to discriminate between signal changes and broader signal changes due to clouds. Clouds above rain or light fog can be detected without error, and it is possible to discriminate against haze layers by the magnitude of their maximum extinction.

Lentz, W. J.↗
NASA NTRS1988

Human factors in aviation operations: The hearback problem

This report covers a study of ASRS reports wherein ATC controllers failed to monitor adequately (hearback) incorrect readbacks of ATC clearances. A total of 417 reports received over a period of 29 months from April 1981 through July 1983 comprised the study data set. Factors examined were: the reasons for a flight crew's getting clearances incorrectly, the operating factors that caused controllers to mishear or not hear the correct readbacks, and consequences of the various types of hearback misses. The principle conclusion of the study takes the form of a precaution to flight crews that a controller's not challenging a readback does not necessariliy mean the readback is correct and that flight crews must explicitly question any doubtful or unusual aspects of clearances rather than depending on controllers to detect readback errors.

Monan, William P.↗
NASA NTRS1989

A simplified procedure for decoding the (23,12) and (24,12) Golay codes

A simplified procedure is developed to decode the three possible erors in a (23,12) Golay codeword. A computer simulation shows that this algorithm is modular, regular and naturally suitable for both Very Large Scale Integration (VLSI) and software implementation. An extension of this new decoding procedure is used also to decode the 1/2-rate (24,12) Golay code, thereby correcting three and detecting four errors.

Truong, T. K.↗
NASA NTRS1989

Extended observability of linear time-invariant systems under recurrent loss of output data

Recurrent loss of sensor data in integrated control systems of an advanced aircraft may occur under different operating conditions that include detected frame errors and queue saturation in computer networks, and bad data suppression in signal processing. This paper presents an extension of the concept of observability based on a set of randomly selected nonconsecutive outputs in finite-dimensional, linear, time-invariant systems. Conditions for testing extended observability have been established.

Luck, Rogelio↗
NASA NTRS1992

A 100Mbps coherent optical link demonstration using frequency stabilized solid state lasers

The design, implementation, and performance evaluation of a 100Mbps binary phase shift keying (BPSK) coherent optical link using frequency stabilized solid state lasers is described. In this demonstration, the transmitted data is binary phase modulated at 100Mbps using an external resonant cavity phase modulator. At the receiving end, the signal is detected using a balanced heterodyne detector. An auxiliary frequency tracking loop (FTL) is used to help the initial frequency acquisition before handing over to the carrier phase tracking loop. The FTL is implemented using a delay line discriminator, and the detected frequency error is fed back to the local oscillator laser to close the tracking loop. Phase coherent reception is achieved by synchronizing the carrier phase using a Costas tracking loop. The demonstration showed that a high data rate phase coherent optical link can be implemented using frequency stabilized solid state lasers.

Chen, CHIEN-C.↗
NASA NTRS1994

Fracture mechanics life analytical methods verification testing

The objective was to evaluate NASCRAC (trademark) version 2.0, a second generation fracture analysis code, for verification and validity. NASCRAC was evaluated using a combination of comparisons to the literature, closed-form solutions, numerical analyses, and tests. Several limitations and minor errors were detected. Additionally, a number of major flaws were discovered. These major flaws were generally due to application of a specific method or theory, not due to programming logic. Results are presented for the following program capabilities: K versus a, J versus a, crack opening area, life calculation due to fatigue crack growth, tolerable crack size, proof test logic, tearing instability, creep crack growth, crack transitioning, crack retardation due to overloads, and elastic-plastic stress redistribution. It is concluded that the code is an acceptable fracture tool for K solutions of simplified geometries, for a limited number of J and crack opening area solutions, and for fatigue crack propagation with the Paris equation and constant amplitude loads when the Paris equation is applicable.

Favenesi, J. A.↗
NASA NTRS1996

Relativity effects for space-based coherent lidar experiments

An effort was initiated last year in the Astrionics Laboratory at Marshall Space Flight Center to examine and incorporate, if necessary, the effects of relativity in the design of space-based lidar systems. A space-based lidar system, named AEOLUS, is under development at Marshall Space Flight Center and it will be used to accurately measure atmospheric wind profiles. Effects of relativity were also observed in the performance of space-based systems, for example in case of global positioning systems, and corrections were incorporated into the design of instruments. During the last summer, the effects of special relativity on the design of space-based lidar systems were studied in detail, by analyzing the problem of laser scattering off a fixed target when the source and a co-located receiver are moving on a spacecraft. Since the proposed lidar system uses a coherent detection system, errors even in the order of a few microradians must be corrected to achieve a good signal-to-noise ratio. Previous analysis assumed that the ground is flat and the spacecraft is moving parallel to the ground, and developed analytical expressions for the location, direction and Doppler shift of the returning radiation. Because of the assumptions used in that analysis, only special relativity effects were involved. In this report, that analysis is extended to include general relativity and calculate its effects on the design.

Gudimetla, V. S. Rao↗