Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “LaN”

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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Unsteady aerodynamic models for maneuvering aircraft

Forced oscillation tests over a large angle-of-attack range for an F-18 model are conducted in the NASA Langley 12-foot low-speed tunnel. The resulting dynamic longitudinal data are analyzed with an unsteady aerodynamic modeling method based on Fourier functional analysis and the indicial formulation. The method is extensively examined and improved to automate the calculation of model coefficients, and to evaluate more accurately the indicial integral. The results indicate that the general model equation obtained from harmonic test data in a range of reduced frequency is capable of accurately modeling the nonlinear responses with large hysteresis effect, except in the region where a delayed flow reattachment occurs at low angles of attack in down strokes. The indicial formulation is used to calculate the response to harmonic motion, harmonic ramp motion, constant-rate pitching motion and smaller-amplitude harmonic motion. The results show that more accurate results can be obtained when the motion starts from a low angle of attack where hysteresis effect is not important.

Hu, Chien-Chung↗
NASA NTRS1990

Optimal design of control systems for prevention of aircraft flight departure

Control system design for general nonlinear flight dynamic models is considered through numerical simulation. The design is accomplished through a numerical optimizer coupled with analysis of flight dynamic equations. In the analysis, the general nonlinear flight dynamic equations with nonlinear aerodynamics are numerically integrated; and the dynamic characteristics needed in the optimization process are then identified from the dynamic response. To assure a reasonable solution, the initial input values of the design variables are estimated through a sensitivity analysis. To demonstrate the method, the pitch departure prevention for an F-16 configuration is demonstrated.

Lan, C. Edward↗
NASA NTRS1993

Flexible polycrystalline thin-film photovoltaics for space applications

Polycrystalline thin-film photovoltaics (PV), such as CIS and CdTe, have received considerable attention recently with respect to space power applications. Their combination of stability, efficiency, and economy from large-scale monolithic-integration of modules can have significant impact on cost and weight of PV arrays for spacecraft and planetary experiments. An added advantage, due to their minimal thickness (approximately 6 microns sans substrate), is the ability to manufacture lightweight, flexible devices (approximately 2000 W/kg) using large-volume manufacturing techniques. The photovoltaic effort at Martin Marietta and ISET is discussed, including large-area, large-volume thin-film deposition techniques such as electrodeposition and rotating cylindrical magnetron sputtering. Progress in the development of flexible polycrystalline thin-film PV is presented, including evaluation of flexible CIS cells. In addition, progress on flexible CdTe cells is presented. Finally, examples of lightweight, flexible arrays and their potential cost and weight impact is discussed.

Armstrong, J. H.↗
NASA NTRS1993

Atomic oxygen interaction with spacecraft materials: Relationship between orbital and ground-based testing for materials certification

The effects of atomic oxygen on boron nitride (BN), silicon nitride (Si3N4), Intelsat 6 solar cell interconnects, organic polymers, and MoS2 and WS2 dry lubricant, were studied in Low Earth Orbit (LEO) flight experiments and in a ground based simulation facility. Both the inflight and ground based experiments employed in situ electrical resistance measurements to detect penetration of atomic oxygen through materials and Electron Spectroscopy for Chemical Analysis (ESCA) analysis to measure chemical composition changes. Results are given. The ground based results on the materials studied to date show good qualitative correlation with the LEO flight results, thus validating the simulation fidelity of the ground based facility in terms of reproducing LEO flight results. In addition it was demonstrated that ground based simulation is capable of performing more detailed experiments than orbital exposures can presently perform. This allows the development of a fundamental understanding of the mechanisms involved in the LEO environment degradation of materials.

Cross, Jon B.↗
NASA NTRS1994

Nimbus-7 Earth radiation budget calibration history. Part 2: The Earth flux channels

Nine years (November 1978 to October 1987) of Nimbus-7 Earth radiation budget (ERB) products have shown that the global annual mean emitted longwave, absorbed shortwave, and net radiation were constant to within about + 0.5 W/sq m. Further, most of the small annual variations in the emitted longwave have been shown to be real. To obtain this measurement accuracy, the wide-field-of-view (WFOV) Earth-viewing channels 12 (0.2 to over 50 micrometers), 13 (0.2 to 3.8 micrometers), and 14 (0.7 to 2.8 micrometers) have been characterized in their satellite environment to account for signal variations not considered in the prelaunch calibration equations. Calibration adjustments have been derived for (1) extraterrestrial radiation incident on the detectors, (2) long-term degradation of the sensors, and (3) thermal perturbations within the ERB instrument. The first item is important in all the channels; the second, mainly in channels 13 and 14, and the third, only in channels 13 and 14. The Sun is used as a stable calibration source to monitor the long-term degradation of the various channels. Channel 12, which is reasonably stable to both thermal perturbations and sensor degradation, is used as a reference and calibration transfer agent for the drifting sensitivities of the filtered channels 13 and 14. Redundant calibration procedures were utilized. Laboratory studies complemented analyses of the satellite data. Two nearly independent models were derived to account for the thermal perturbations in channels 13 and 14. The global annual mean terrestrial shortwave and longwave signals proved stable enough to act as secondary calibration sources. Instantaneous measurements may still, at times, be in error by as much as a few Wm(exp -2), but the long-term averages are stable to within a fraction of a Wm(exp -2).

Kyle, H. Lee↗
NASA NTRS1991

WTEC panel report on European nuclear instrumentation and controls

Control and instrumentation systems might be called the 'brain' and 'senses' of a nuclear power plant. As such they become the key elements in the integrated operation of these plants. Recent developments in digital equipment have allowed a dramatic change in the design of these instrument and control (I&C) systems. New designs are evolving with cathode ray tube (CRT)-based control rooms, more automation, and better logical information for the human operators. As these new advanced systems are developed, various decisions must be made about the degree of automation and the human-to-machine interface. Different stages of the development of control automation and of advanced digital systems can be found in various countries. The purpose of this technology assessment is to make a comparative evaluation of the control and instrumentation systems that are being used for commercial nuclear power plants in Europe and the United States. This study is limited to pressurized water reactors (PWR's). Part of the evaluation includes comparisons with a previous similar study assessing Japanese technology.

White, James D.↗
NASA NTRS1994

Nimbus-7 Earth Radiation Budjet compact solar data set user's guide

Nimbus-7 Earth Radiation Budget (ERB) solar measurements extend from November 16, 1978, to December 13, 1993, but with data gaps in 1992 and 1993. The measurements include the total solar irradiance plus six broadband spectral components. The Channel 10c total irradiance data appears very stable, and the calibration, well done. A number of characterization problems remain in the spectral measurements. In the original program, the solar and Earth flux measurements were intermixed and spread over about 170 computer tapes. For easier access, the solar data have been collected into two compact data sets. All of the data are collected into 14 Summary Solar Tapes (SST's). In addition, two Channel 10c Solar Tapes (CST's) give a separate listing of the stable total solar irradiance measurements. Channel 10c calibration and orbital irradiance values are given on separate PC disks. This document gives data descriptions and formats, together with quality control and calibration procedures.

Kyle, H. Lee↗
NASA NTRS1994

Advances in polycrystalline thin-film photovoltaics for space applications

Polycrystalline, thin-film photovoltaics represent one of the few (if not the only) renewable power sources which has the potential to satisfy the demanding technical requirements for future space applications. The demand in space is for deployable, flexible arrays with high power-to-weight ratios and long-term stability (15-20 years). In addition, there is also the demand that these arrays be produced by scalable, low-cost, high yield, processes. An approach to significantly reduce costs and increase reliability is to interconnect individual cells series via monolithic integration. Both CIS and CdTe semiconductor films are optimum absorber materials for thin-film n-p heterojunction solar cells, having band gaps between 0.9-1.5 ev and demonstrated small area efficiencies, with cadmium sulfide window layers, above 16.5 percent. Both CIS and CdTe polycrystalline thin-film cells have been produced on a laboratory scale by a variety of physical and chemical deposition methods, including evaporation, sputtering, and electrodeposition. Translating laboratory processes which yield these high efficiency, small area cells into the design of a manufacturing process capable of producing 1-sq ft modules, however, requires a quantitative understanding of each individual step in the process and its (each step) effect on overall module performance. With a proper quantification and understanding of material transport and reactivity for each individual step, manufacturing process can be designed that is not 'reactor-specific' and can be controlled intelligently with the design parameters of the process. The objective of this paper is to present an overview of the current efforts at MMC to develop large-scale manufacturing processes for both CIS and CdTe thin-film polycrystalline modules. CIS cells/modules are fabricated in a 'substrate configuration' by physical vapor deposition techniques and CdTe cells/modules are fabricated in a 'superstrate configuration' by wet chemical methods. Both laser and mechanical scribing operations are used to monolithically integrate (series interconnect) the individual cells into modules. Results will be presented at the cell and module development levels with a brief description of the test methods used to qualify these devices for space applications. The approach and development efforts are directed towards large-scale manufacturability of established thin-film, polycrystalline processing methods for large area modules with less emphasis on maximizing small area efficiencies.

Lanning, Bruce R.↗
NASA NTRS1995

Atomic oxygen dosimetry measurements made on STS-46 by CONCAP 2

With increasing flight duration and the possibility of a permanent facility in space, long-term monitoring of material degradation due to atomic oxygen is increasing in importance. Reliance on models to determine the fluence of atomic oxygen is not only necessarily complex but also imprecise due to the strong dependence of oxygen concentration on day/night, latitude and solar activity. Mass-spectroscopy, the traditional method for determining the gas phase species densities at low pressure, is not only expensive but is limited in the area that it can monitor. Our group has developed a simple and inexpensive dosimeter to measure the atomic oxygen fluence via the change in resistance as the sensor element is gradually oxidized. The sensors consisted of thin-film circuit elements deposited on a suitable substrate. Four-point resistance measurements were used to monitor the change in resistance. Results obtained using silver and carbon dosimeters flown on STS-46 (CONCAP 2-01) will be discussed.

Gregory, J. C.↗
NASA NTRS1994

A finding list of faint UV-bright stars in the galactic plane, 2

Fifty-three UV-bright stars have been found on three two-color 48-in. Schmidt plates centered on the galactic plane. The sources detected range in U-B color from near U- B = 0 to U - B = -1.5, and in magnitude from m(sub B) approximately = 10 to approximately 21. Some of the more interesting sources are discussed, and finding charts are included for all sources listed. Additionally, follow-up spectroscopic and postitional information is provided for several objects first listed in Paper I of this series. One new cataclysmic variable discovered during the course of this portion of the survey has been published previously and is discussed herein.

Lanning, Howard H.↗
NASA NTRS1993

Low Bandwidth Robust Controllers for Flight

Through throttle manipulations, engine thrust can be used for emergency flight control for multi-engine aircraft. Previous study by NASA Dryden has shown the use of throttles for emergency flight control to be very difficult. In general, manual fly-by-throttle is extremely difficult - with landing almost impossible, but control augmentation makes runway landings feasible. Flight path control using throttles-only to achieve safe emergency landing for a large jet transport airplane, Boeing 720, was investigated using Quantitative Feedback Theory (QFT). Results were compared to an augmented control developed in a previous simulation study. The control augmentation corrected the unsatisfactory open-loop characteristics by increasing system bandwidth and damping, but increasing the control bandwidth substantially proved very difficult. The augmented pitch control is robust under no or moderate turbulence. The augmented roll control is sensitive to configuration changes.

Biezad, Daniel J.↗
NASA NTRS1996

Pilot-in-the-Loop Analysis of Propulsive-Only Flight Control Systems

Longitudinal control system architectures are presented which directly couple flight stick motions to throttle commands for a multi-engine aircraft. This coupling enables positive attitude control with complete failure of the flight control system. The architectures chosen vary from simple feedback gains to classical lead-lag compensators with and without prefilters. Each architecture is reviewed for its appropriateness for piloted flight. The control systems are then analyzed with pilot-in-the-loop metrics related to bandwidth required for landing. Results indicate that current and proposed bandwidth requirements should be modified for throttles only flight control. Pilot ratings consistently showed better ratings than predicted by analysis. Recommendations are made for more robust design and implementation. The use of Quantitative Feedback Theory for compensator design is discussed. Although simple and effective augmented control can be achieved in a wide variety of failed configurations, a few configuration characteristics are dominant for pilot-in-the-loop control. These characteristics will be tested in a simulator study involving failed flight controls for a multi-engine aircraft.

Chou, Hwei-Lan↗
NASA NTRS1996

Application of QFT to the Problem of Failed In-Flight Controllers During Approach and Landing of a B720 Aircraft

Previous studies by NASA Dryden have shown the use of throttles for emergency flight control to be extremely difficult, especially for landing. Flight control using only the throttles to achieve safe landing for a large jet transport airplane, the Boeing 720, is investigated using Quantitative Feedback Theory (QFT). Results are compared to an augmented control developed in a previous study. The controller corrected unsatisfactory open-loop characteristics by increasing system bandwidth and damping, but improving the control bandwidth substantially proved very difficult. The pitch controller is robust in conditions of no or moderate turbulence. The roll controller performed well in conditions of no turbulence, but is sensitive to moderate turbulence. Handling qualities of the augmented control for approach and landing were evaluated by piloted simulation flights.

Chou, Hwei-Lan↗
NASA NTRS1997

Rain Fade Compensation for Ka-Band Communications Satellites

This report provides a review and evaluation of rain fade measurement and compensation techniques for Ka-band satellite systems. This report includes a description of and cost estimates for performing three rain fade measurement and compensation experiments. The first experiment deals with rain fade measurement techniques while the second one covers the rain fade compensation techniques. The third experiment addresses a feedback flow control technique for the ABR service (for ATM-based traffic). The following conclusions were observed in this report; a sufficient system signal margin should be allocated for all carriers in a network, that is a fixed clear-sky margin should be typically in the range of 4-5 dB and should be more like 15 dB in the up link for moderate and heavy rain zones; to obtain a higher system margin it is desirable to combine the uplink power control technique with the technique that implements the source information rate and FEC code rate changes resulting in a 4-5 dB increase in the dynamic part of the system margin. The experiments would assess the feasibility of the fade measurements and compensation techniques, and ABR feedback control technique.

Mitchell, W. Carl↗
NASA NTRS1995

Object-Oriented Software Metrics for Predicting Reusability and Estimating Size

As object-oriented software development methods come into more widespread use, basic questions of software quality assurance must be reconsidered. We will highlight efforts now underway at NASA's Jet Propulsion Laboratory to both assess the quality of software systems developed using object oriented technology and develop guidelines for future development of such systems. The current focus is on design and code reusability., and system size estimation. A number of metrics are proposed and two software systems measured and analyzed. The preliminary results reported here should be useful to software development and quality assurance personnel working in C++ implementation environment.

Sanderson, D. Peter↗
NASA NTRS1997

A Comprehensive Reliability Methodology for Assessing Risk of Reusing Failed Hardware Without Corrective Actions with and Without Redundancy

This paper deals with the development of a reliability methodology to assess the consequences of using hardware, without failure analysis or corrective action, that has previously demonstrated that it did not perform per specification. The subject of this paper arose from the need to provide a detailed probabilistic analysis to calculate the change in probability of failures with respect to the base or non-failed hardware. The methodology used for the analysis is primarily based on principles of Monte Carlo simulation. The random variables in the analysis are: Maximum Time of Operation (MTO) and operation Time of each Unit (OTU) The failure of a unit is considered to happen if (OTU) is less than MTO for the Normal Operational Period (NOP) in which this unit is used. NOP as a whole uses a total of 4 units. Two cases are considered. in the first specialized scenario, the failure of any operation or system failure is considered to happen if any of the units used during the NOP fail. in the second specialized scenario, the failure of any operation or system failure is considered to happen only if any two of the units used during the MOP fail together. The probability of failure of the units and the system as a whole is determined for 3 kinds of systems - Perfect System, Imperfect System 1 and Imperfect System 2. in a Perfect System, the operation time of the failed unit is the same as that of the MTO. In an Imperfect System 1, the operation time of the failed unit is assumed as 1 percent of the MTO. In an Imperfect System 2, the operation time of the failed unit is assumed as zero. in addition, simulated operation time of failed units is assumed as 10 percent of the corresponding units before zero value. Monte Carlo simulation analysis is used for this study. Necessary software has been developed as part of this study to perform the reliability calculations. The results of the analysis showed that the predicted change in failure probability (P(sub F)) for the previously failed units is as high as 49 percent above the baseline (perfect system) for the worst case. The predicted change in system P(sub F) for the previously failed units is as high as 36% for single unit failure without any redundancy. For redundant systems, with dual unit failure, the predicted change in P(sub F) for the previously failed units is as high as 16%. These results will help management to make decisions regarding the consequences of using previously failed units without adequate failure analysis or corrective action.

Putcha, Chandra S.↗
NASA NTRS2000

Unsteady Aerodynamic Effects on the Flight Characteristics of an F-16XL Configuration

Unsteady aerodynamic models based on windtunnel forced oscillation test data and analyzed with a fuzzy logic algorithm arc incorporated into an F-16XL flight simulation code. The reduced frequency needed in the unsteady models is numerically calculated by using a limited prior time history of state variables in a least-square sense. Numerical examples arc presented to show the accuracy of the calculated reduced frequency. Oscillatory control inputs are employed to demonstrate the differences in the flight characteristics based on unsteady and quasi-steady aerodynamic models. Application of the unsteady aerodynamic models is also presented and the results are compared with one set of F16XIL longitudinal maneuver flight data. It is shown that the main differences in dynamic response are in the lateral-directional characteristics, with the quasi-steady model being more stable than the flight vehicle, while the unsteady model being more unstable. Similar conclusions can also be made in a simulated rapid sideslipping roll. To improve unsteady aerodynamic modeling, it is recommended to acquire test data with coupled motions in pitch, roll and yaw.

Wang, Zhongjun↗