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At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

UV testing of INTELSAT-7, 7A, and 8 solar cells

A 4000 hour experiment, conducted in late 1992 through mid 1993, confirmed earlier results on the ultraviolet damage effects in covered solar cells of various types being used, or proposed for use, in INTELSAT programs. Two different UV test systems were used to identify systematic errors and to study the effects of UV source-bulb age on degradation rate. After correction for contamination and UV source-bulb aging, the extrapolated degradation rates for irradiated and unirradiated INTELSAT-5, -6 single AR(SAR) coated cells and INTELSAT-7, -7A, -8 double layer AR(DAR) coated cells in both the 1993 tests confirm the following hypotheses resulting from the 1992 experiment. (a) Irradiated cells display significantly more UV degradation than do the unirradiated cells for tests exceeding 2000 hours. The new data indicates that degradation effects from electron irradiation are proportional to t(exp 2) (the square of the UV hours), at least for times less than or equal to 3000 hours. (b) This difference does not depend upon entire reflective coating, cell resistivity, or manufacturer within the sensitivity and reproducibility of the experiment. (c) There is a clear difference in degradation rate between single AR coated cells (TiO(x)) and double layer AR coated cells (SiO(x) and Al2O3?). At 100,000 hours (11.4 years) the DAR coated cells display more degradation than do the SAR coated cells, even though at 1,000 hours the DAR cells display less degradation. (d) UV degradation rates, to modern covered silicon solar cells, at the beginning of bulb life drop from approximately 2 times the average rate to near zero after 2000 hours (average end-of-life for the xenon short-arc lamps used in the tests). The effects of 1 MeV electron irradiation (10(exp 15) e(-)/sq cm) prior to UV exposure are clearly indicated in the plot of percent change in cell open circuit voltage (Voc) versus percent change in short circuit current (Isc) during the UV test and post-test cleanup of the cells. Clearly, extended UV testing produces a permanent photo-induced redegradation of previously irradiated cells. However, this photo-induced redegradation may be caused by the long-wavelength light, not the UV light.

Meulenberg, A.↗
NASA NTRS2024

Low-Cost Sensor Performance Intercomparison, Correction Factor Development, and 2+ Years of Ambient PM2.5 Monitoring in Accra, Ghana

Particulate matter air pollution is a leading cause of global mortality, particularly in Asia and Africa. Addressing the high and wide-ranging air pollution levels requires ambient monitoring, but many low- and middle-income countries (LMICs) remain scarcely monitored. To address these data gaps, recent studies have utilized low-cost sensors. These sensors have varied performance, and little literature exists about sensor intercomparison in Africa. By colocating 2 QuantAQ Modulair-PM, 2 PurpleAir PA-II SD, and 16 Clarity Node-S Generation II monitors with a reference-grade Teledyne monitor in Accra, Ghana, we present the first intercomparisons of different brands of low-cost sensors in Africa, demonstrating that each type of low-cost sensor PM2.5 is strongly correlated with reference PM2.5, but biased high for ambient mixture of sources found in Accra. When compared to a reference monitor, the QuantAQ Modulair-PM has the lowest mean absolute error at 3.04 μg/m3, followed by PurpleAir PA-II (4.54 μg/m3) and Clarity Node-S (13.68 μg/m3). We also compare the usage of 4 statistical or machine learning models (Multiple Linear Regression, Random Forest, Gaussian Mixture Regression, and XGBoost) to correct low-cost sensors data, and find that XGBoost performs the best in testing (R2: 0.97, 0.94, 0.96; mean absolute error: 0.56, 0.80, and 0.68 μg/m3 for PurpleAir PA-II, Clarity Node-S, and Modulair-PM, respectively), but tree-based models do not perform well when correcting data outside the range of the colocation training. Therefore, we used Gaussian Mixture Regression to correct data from the network of 17 Clarity Node-S monitors deployed around Accra, Ghana, from 2018 to 2021. We find that the network daily average PM2.5 concentration in Accra is 23.4 μg/m3, which is 1.6 times the World Health Organization Daily PM2.5 guideline of 15 μg/m3. While this level is lower than those seen in some larger African cities (such as Kinshasa, Democratic Republic of the Congo), mitigation strategies should be developed soon to prevent further impairment to air quality as Accra, and Ghana as a whole, rapidly grow.

Humidity↗
NASA NTRS1983

On error detection in the dynamics part of primitive equation models

Rossby-Haurwitz waves have been commonly employed as initial conditions for testing the dynamics part of global atmospheric models. Difficulties arise in connection with the primitive equation (PE) model. Chao and Geller (1982) have suggested that it would be better if normal mode solutions of the linearized primitive equations would be used as initial conditions. However, tests involving normal mode conditions are not adequate for the detection of errors in the nonlinear terms. The present investigation has the objective to review the study conducted by Chao and Geller and to provide tests for the nonlinear terms.

Chao, W. C.↗
NASA NTRS2016

The Impact of Truth Surrogate Variance on Quality Assessment/Assurance in Wind Tunnel Testing

Minimum data volume requirements for wind tunnel testing are reviewed and shown to depend on error tolerance, response model complexity, random error variance in the measurement environment, and maximum acceptable levels of inference error risk. Distinctions are made between such related concepts as quality assurance and quality assessment in response surface modeling, as well as between precision and accuracy. Earlier research on the scaling of wind tunnel tests is extended to account for variance in the truth surrogates used at confirmation sites in the design space to validate proposed response models. A model adequacy metric is presented that represents the fraction of the design space within which model predictions can be expected to satisfy prescribed quality specifications. The impact of inference error on the assessment of response model residuals is reviewed. The number of sites where reasonably well-fitted response models actually predict inadequately is shown to be considerably less than the number of sites where residuals are out of tolerance. The significance of such inference error effects on common response model assessment strategies is examined.

DeLoach, Richard↗
NASA NTRS1979

Methodology for error analysis and simulation of lidar aerosol measurements

A methodology is presented for objective and automated determination of the uncertainty in lidar aerosol measurements. This methodology is based on standard error-propagation procedures, a large data base on atmospheric behavior, and long experience in lidar data processing. Algebraic expressions for probable error are derived as a function of the relevant parameters. The validity of these expressions is then tested by making simulated measurements and analyses in which random errors of appropriate size are injected at proper steps of the measurement and analysis process. An illustrative example is given where the methodology is applied to a new lidar system now being used for airborne measurements of the stratospheric aerosol.

Russell, P. B.↗
NASA NTRS1991

Designing Accelerated Tests Of Electromigration

Method for design of accelerated tests of electromigration (as in microscopic conductors in integrated circuits) based partly on simplified mathematical model of electromigration and partly on error analysis. Objective to determine quickly operating life of tested components under normal operating conditions by extrapolation from lifetime measurements at operating stresses greater than normal. Involves compromise between reducing testing time by increasing stresses and reducing uncertainty in extrapolated lifetime by decreasing stresses.

Buehler, Martin G.↗
NASA NTRS1993

Advanced communications technology satellite high burst rate link evaluation terminal communication protocol software user's guide, version 1.0

The Communication Protocol Software was developed at the NASA Lewis Research Center to support the Advanced Communications Technology Satellite High Burst Rate Link Evaluation Terminal (ACTS HBR-LET). The HBR-LET is an experimenters terminal to communicate with the ACTS for various experiments by government, university, and industry agencies. The Communication Protocol Software is one segment of the Control and Performance Monitor (C&PM) Software system of the HBR-LET. The Communication Protocol Software allows users to control and configure the Intermediate Frequency Switch Matrix (IFSM) on board the ACTS to yield a desired path through the spacecraft payload. Besides IFSM control, the C&PM Software System is also responsible for instrument control during HBR-LET experiments, uplink power control of the HBR-LET to demonstrate power augmentation during signal fade events, and data display. The Communication Protocol Software User's Guide, Version 1.0 (NASA CR-189162) outlines the commands and procedures to install and operate the Communication Protocol Software. Configuration files used to control the IFSM, operator commands, and error recovery procedures are discussed. The Communication Protocol Software Maintenance Manual, Version 1.0 (NASA CR-189163, to be published) is a programmer's guide to the Communication Protocol Software. This manual details the current implementation of the software from a technical perspective. Included is an overview of the Communication Protocol Software, computer algorithms, format representations, and computer hardware configuration. The Communication Protocol Software Test Plan (NASA CR-189164, to be published) provides a step-by-step procedure to verify the operation of the software. Included in the Test Plan is command transmission, telemetry reception, error detection, and error recovery procedures.

Reinhart, Richard C.↗
NASA NTRS2015

Thermal Testing and Model Correlation of the Magnetospheric Multiscale (MMS) Observatories

The Magnetospheric Multiscale (MMS) mission is a Solar Terrestrial Probes mission comprising four identically instrumented spacecraft that will use Earth's magnetosphere as a laboratory to study the microphysics of three fundamental plasma processes: magnetic reconnection, energetic particle acceleration, and turbulence. This paper presents the complete thermal balance (TB) test performed on the first of four observatories to go through thermal vacuum (TV) and the minibalance testing that was performed on the subsequent observatories to provide a comparison of all four. The TV and TB tests were conducted in a thermal vacuum chamber at the Naval Research Laboratory (NRL) in Washington, D.C. with the vacuum level higher than 1.3 x 10 (sup -4) pascals (10 (sup -6) torr) and the surrounding temperature achieving -180 degrees Centigrade. Three TB test cases were performed that included hot operational science, cold operational science and a cold survival case. In addition to the three balance cases a two hour eclipse and a four hour eclipse simulation was performed during the TV test to provide additional transient data points that represent the orbit in eclipse (or Earth's shadow) The goal was to perform testing such that the flight orbital environments could be simulated as closely as possible. A thermal model correlation between the thermal analysis and the test results was completed. Over 400 1-Wire temperature sensors, 200 thermocouples and 125 flight thermistor temperature sensors recorded data during TV and TB testing. These temperature versus time profiles and their agreements with the analytical results obtained using Thermal Desktop and SINDA/FLUINT are discussed. The model correlation for the thermal mathematical model (TMM) is conducted based on the numerical analysis results and the test data. The philosophy of model correlation was to correlate the model to within 3 degrees Centigrade of the test data using the standard deviation and mean deviation error calculation. Individual temperature error goal is to be within 5 degrees Centigrade and the heater power goal is to be within 5 percent of test data. The results of the model correlation are discussed and the effect of some material and interface parameters on the temperature profiles are presented.

Correlation↗
NASA NTRS1988

Initial test results on state estimation on the SCOLE mast

Modal state estimation tests are performed on the SCOLE mast for the fixed Shuttle platform case. Kalman filter state estimation results from a five mode computer model of the SCOLE mast, developed from a finite element analysis, are compared with those state estimates obtained from laboratory tests. Two comparison runs are presented, one an excitation of the first two bending modes, another, an excitation of the first torsional mode of the mast. Results from both runs show poor agreement in modal estimation between the computer model simulations and the laboratory test data. At present, the reason(s) for this poor performance is unknown. Both the laboratory hardware and software and the computer model are being checked for possible sources of errors. Further computer simulations as well as laboratory testing will be performed.

Sparks, D., Jr.↗
NASA NTRS1993

Long Duration Exposure Facility (LDEF) low temperature Heat Pipe Experiment Package (HEPP) flight results

The Low Temperature Heat Pipe Flight Experiment (HEPP) is a fairly complicated thermal control experiment that was designed to evaluate the performance of two different low temperature ethane heat pipes and a low-temperature (182 K) phase change material. A total of 390 days of continuous operation with an axially grooved aluminum fixed conductance heat pipe and an axially grooved stainless steel heat pipe diode was demonstrated before the data acquisition system's batteries lost power. Each heat pipe had approximately 1 watt applied throughout this period. The HEPP was not able to cool below 188.6 K during the mission. As a result, the preprogrammed transport test sequence which initiates when the PCM temperature drops below 180 K was never exercised, and transport tests with both pipes and the diode reverse mode test could not be run in flight. Also, because the melt temperature of the n-heptane PCM is 182 K, its freeze/thaw behavior could not be tested. Post-flight thermal vacuum tests and thermal analyses have indicated that there was an apparent error in the original thermal analyses that led to this unfortunate result. Post-flight tests have demonstrated that the performance of both heat pipes and the PCM has not changed since being fabricated more than 14 years ago. A summary of HEPP's flight data and post-flight test results are presented.

Mcintosh, Roy↗
NASA NTRS2003

Radiant Temperature Nulling Radiometer

A self-calibrating nulling radiometer for non-contact temperature measurement of an object, such as a body of water, employs a black body source as a temperature reference, an optomechanical mechanism, e.g., a chopper, to switch back and forth between measuring the temperature of the black body source and that of a test source, and an infrared detection technique. The radiometer functions by measuring radiance of both the test and the reference black body sources; adjusting the temperature of the reference black body so that its radiance is equivalent to the test source; and, measuring the temperature of the reference black body at this point using a precision contact-type temperature sensor, to determine the radiative temperature of the test source. The radiation from both sources is detected by an infrared detector that converts the detected radiation to an electrical signal that is fed with a chopper reference signal to an error signal generator, such as a synchronous detector, that creates a precision rectified signal that is approximately proportional to the difference between the temperature of the reference black body and that of the test infrared source. This error signal is then used in a feedback loop to adjust the reference black body temperature until it equals that of the test source, at which point the error signal is nulled to zero. The chopper mechanism operates at one or more Hertz allowing minimization of l/f noise. It also provides pure chopping between the black body and the test source and allows continuous measurements.

Robert Ryan↗
NASA NTRS1984

A System for Controlling the Oxygen Content of a Gas Produced by Combustion

A mixture of air, CH4 and OH(2) is burned in a combustion chamber to produce a product gas in the test section. The OH(2) content of the product gas is compared with the OH(2) content of reference air in an OH(2) sensor. If there is a difference an error signal is produced at the output of a control circuit which by the means of a solenoid valve, regulates the flow of OH(2) into the combustion chamber to make the error signal zero. The product gas in the test section has the same oxygen content as air.

Singh, J. J.↗
NASA NTRS2014

VARED: Verification and Analysis of Requirements and Early Designs

Requirements are a part of every project life cycle; everything going forward in a project depends on them. Good requirements are hard to write, there are few useful tools to test, verify, or check them, and it is difficult to properly marry them to the subsequent design, especially if the requirements are written in natural language. In fact, the inconsistencies and errors in the requirements along with the difficulty in finding these errors contribute greatly to the cost of the testing and verification stage of flight software projects [1]. Large projects tend to have several thousand requirements written at various levels by different groups of people. The design process is distributed and a lack of widely accepted standards for requirements often results in a product that varies widely in style and quality. A simple way to improve this would be to standardize the design process using a set of tools and widely accepted requirements design constraints. The difficulty with this approach is finding the appropriate constraints and tools. Common complaints against the tools available include ease of use, functionality, and available features. Also, although preferable, it is rare that these tools are capable of testing the quality of the requirements.

Badger, Julia↗
NASA NTRS1991

Update on parts SEE suspectibility from heavy ions

JPL and the Aerospace Corporation have collected a fourth set of heavy ion single event effects (SEE) test data. Trends in SEE susceptibility (including soft errors and latchup) for state-of-the-art parts are displayed. All data are conveniently divided into two tables: one for MOS devices, and one for a shorter list of recently tested bipolar devices. In addition, a new table of data for latchup tests only (invariably CMOS processes) is given.

Nichols, D. K.↗
NASA NTRS1984

Data and results of a laboratory investigation of microprocessor upset caused by simulated lightning-induced analog transients

A methodology was developed a assess the upset susceptibility/reliability of a computer system onboard an aircraft flying through a lightning environment. Upset error modes in a general purpose microprocessor were studied. The upset tests involved the random input of analog transients which model lightning induced signals onto interface lines of an 8080 based microcomputer from which upset error data was recorded. The program code on the microprocessor during tests is designed to exercise all of the machine cycles and memory addressing techniques implemented in the 8080 central processing unit. A statistical analysis is presented in which possible correlations are established between the probability of upset occurrence and transient signal inputs during specific processing states and operations. A stochastic upset susceptibility model for the 8080 microprocessor is presented. The susceptibility of this microprocessor to upset, once analog transients have entered the system, is determined analytically by calculating the state probabilities of the stochastic model.

Belcastro, C. M.↗
NASA NTRS1985

An experimental evaluation of error seeding as a program validation technique

A previously reported experiment in error seeding as a program validation technique is summarized. The experiment was designed to test the validity of three assumptions on which the alleged effectiveness of error seeding is based. Errors were seeded into 17 functionally identical but independently programmed Pascal programs in such a way as to produce 408 programs, each with one seeded error. Using mean time to failure as a metric, results indicated that it is possible to generate seeded errors that are arbitrarily but not equally difficult to locate. Examination of indigenous errors demonstrated that these are also arbitrarily difficult to locate. These two results support the assumption that seeded and indigenous errors are approximately equally difficult to locate. However, the assumption that, for each type of error, all errors are equally difficult to locate was not borne out. Finally, since a seeded error occasionally corrected an indigenous error, the assumption that errors do not interfere with each other was proven wrong. Error seeding can be made useful by taking these results into account in modifying the underlying model.

Knight, J. C.↗
NASA NTRS1981

Methodology evaluation: Effects of independent verification and intergration on one class of application

The effects of an independent verification and integration (V and I) methodology on one class of application are described. Resource profiles are discussed. The development environment is reviewed. Seven measures are presented to test the hypothesis that V and I improve the development and product. The V and I methodology provided: (1) a decrease in requirements ambiguities and misinterpretation; (2) no decrease in design errors; (3) no decrease in the cost of correcting errors; (4) a decrease in the cost of system and acceptance testing; (5) an increase in early discovery of errors; (6) no improvement in the quality of software put into operation; and (7) a decrease in productivity and an increase in cost.

Page, J.↗
NASA NTRS1984

Writing executable assertions to test flight software

An executable assertion is a logical statement about the variables or a block of code. If there is no error during execution, the assertion statement results in a true value. Executable assertions can be used for dynamic testing of software. They can be employed for validation during the design phase, and exception and error detection during the operation phase. The present investigation is concerned with the problem of writing executable assertions, taking into account the use of assertions for testing flight software. They can be employed for validation during the design phase, and for exception handling and error detection during the operation phase The digital flight control system and the flight control software are discussed. The considered system provides autopilot and flight director modes of operation for automatic and manual control of the aircraft during all phases of flight. Attention is given to techniques for writing and using assertions to test flight software, an experimental setup to test flight software, and language features to support efficient use of assertions.

Mahmood, A.↗