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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

The effects of thermal cycling on the thermal deformation of graphite-polyimide

The effects of repetitive thermal cycling on the thermal deformation of graphite-fiber-reinforced polyimide laminates are investigated. Unsymmetric and unidirectional laminate specimens were cycled in an oven between room temperature and 180 or 315 C five times, and temperature and deformation were recorded as a function of time in order to measure thermal deformation. The results of the lower temperature cycling reveal a hysteresis-like effect in the temperature-thermal deformation relation for a single cycle, while no differences are detected from one cycle to the next. The response of an eight-layer curved specimen is found to agree well with predictions based on a piecewise-linear lamination theory, however, four-layer laminate response could not be explained. The results of the high-temperature tests also indicate a dependence of the strain on whether the specimen was being heated or cooled, however quantitative results are considered unreliable, due to strain gage difficulties.

Hyer, M. W.↗
NASA NTRS1978

ATS6-satellite radio beacon measurements at Ootacamund, India

In August 1975 the ATS6 was repositioned at 35 deg E. Radio beacon measurements of time delay, Faraday rotation and signal amplitude, made at Ootacamund, India in October 1975, are discussed with emphasis on the problem of determining the Faraday content under essentially transverse propagation conditions. It is shown that at the low geomagnetic latitude of Ootacamund the use of a fixed conversion coefficient gives an unreliable Faraday content. It is shown also that corrections to the measured Faraday rotation are important because of pitch and yaw of the satellite, particularly at night when the rotation on 140 MHz can be of the order of 10 to 20 deg. The shape factor shows a low predawn minimum indicating the nearly complete erosion of the F2 layer peak. Amplitude scintillation usually decreases with increase of radio frequency but exceptions are discussed.

Davies, K.↗
NASA NTRS1981

Ceramic and coating applications in the hostile environment of a high temperature hypersonic wind tunnel

A Mach 7, blowdown wind tunnel was used to investigate aerothermal structural phenomena on large to full scale high speed vehicle components. The high energy test medium, which provided a true temperature simulation of hypersonic flow at 24 to 40 km altitude, was generated by the combustion of methane with air at high pressures. Since the wind tunnel, as well as the models, must be protected from thermally induced damage, ceramics and coatings were used extensively. Coatings were used both to protect various wind tunnel components and to improve the quality of the test stream. Planned modifications for the wind tunnel included more extensive use of ceramics in order to minimize the number of active cooling systems and thus minimize the inherent operational unreliability and cost that accompanies such systems. Use of nonintrusive data acquisition techniques, such as infrared radiometry, allowed more widespread use of ceramics for models to be tested in high energy wind tunnels.

Puster, R. L.↗
NASA NTRS1981

Helicopter propulsion system reliability and engine monitoring assessments

The major short life, unreliable, and high maintenance engine and power components and subsystems in current civil helicopters were identified. Categories included both reciprocating and turbine engines, single and multiple engine configurations, single and tandem trotor vehicles, and light, medium, and heavy helicopters. The major focus was on the following parameters: accident rate data; maintenance rate data; and direct operator input.

Murphy, J. A.↗
NASA NTRS1980

UDU/T/ covariance factorization for Kalman filtering

There has been strong motivation to produce numerically stable formulations of the Kalman filter algorithms because it has long been known that the original discrete-time Kalman formulas are numerically unreliable. Numerical instability can be avoided by propagating certain factors of the estimate error covariance matrix rather than the covariance matrix itself. This paper documents filter algorithms that correspond to the covariance factorization P = UDU(T), where U is a unit upper triangular matrix and D is diagonal. Emphasis is on computational efficiency and numerical stability, since these properties are of key importance in real-time filter applications. The history of square-root and U-D covariance filters is reviewed. Simple examples are given to illustrate the numerical inadequacy of the Kalman covariance filter algorithms; these examples show how factorization techniques can give improved computational reliability.

Thornton, C. L.↗
NASA NTRS1981

Reliability study of refractory gate gallium arsenide MESFETS

Refractory gate MESFET's were fabricated as an alternative to aluminum gate devices, which have been found to be unreliable as RF power amplifiers. In order to determine the reliability of the new structures, statistics of failure and information about mechanisms of failure in refractory gate MESFET's are given. Test transistors were stressed under conditions of high temperature and forward gate current to enhance failure. Results of work at 150 C and 275 C are reported.

Yin, J. C. W.↗
NASA NTRS1982

Process Research ON Semix Silicon Materials (PROSSM)

A cost effective process sequence was identified, equipment was designed to implement a 6.6 MW per year automated production line, and a cost analysis projected a $0.56 per watt cell add-on cost for this line. Four process steps were developed for this program: glass beads back clean-up, hot spray antireflective coating, wave soldering of fronts, and ion milling for edging. While spray dopants were advertised as an off the shelf developed product, they were unreliable with shorter than advertised shelf life.

Wohlgemuth, J. H.↗
NASA NTRS1982

The implementation and use of Ada on distributed systems with high reliability requirements

The use and implementation of Ada in distributed environments in which the hardware components are assumed to be unreliable is investigated. The possibility that a distributed system can be programmed entirely in Ada so that the individual tasks of the system are unconcerned with which processor they are executing on, and that failures can occur in the underlying hardware is considered. The reduced cost of computer hardware and the advantages of distributed processing (for example, increased reliability through redundancy and greater flexibility) indicate that many aerospace computer systems can be distributed. The use of Ada and distributed systems is a good combination for aerospace embedded systems.

Knight, J. C.↗
NASA NTRS1982

The rotation of Uranus

The determination of the rotation rate of Uranus based on available observational evidence is discussed. Previous determinations of the rotation rate since the work of Lowell and Slipher (1912), which tended to converge on a period of 10.8 days until the mid 1970s, most likely due to mutual reinforcement between unreliable results, are reviewed. Recent independent determinations based on (1) the use of theoretical interior models together with observations of oblateness and the gravitational moment J2; (2) periodic brightness fluctuations; and (3) spectrographic measurements of Doppler shifts are then presented which yield a weighted mean value of 16.31 + or - 0.27 h for the rotational period of Uranus. It is noted that the detection of the motion of surface features across the disk by future high-resolution imaging and Voyager 2 observations may allow a direct determination of the rotational period of Uranus.

Goody, R. M.↗
NASA NTRS1981

The effect of abnormal cell proportion on specimen classifier performance

An analysis is presented of the results obtained from a cell classifier which is confronted with an abnormal/normal cell ratio which is different from the ratio assumed in the calibration of the classifier. False negative and false positive error rates are determined in advance for classifier operation, along with the necessary sample size in order to validate the predicted distributions. Changes are demonstrated to happen only regarding the false negative rate, where reductions in the abnormal cell rate below the expected rates would cause totally unreliable data. Substantial overproduction of abnormal cells would be quickly noticeable, while production rates beyond, but close to, the expected rates would only require more extensive sampling. Classifier systems for 10% proportions of abnormal cells are concluded to be possible, but difficulties are present with much lower rates

Castleman, K. R.↗
NASA NTRS1982

An intercomparison of ground-based total ozone instruments

Five ground-based total ozone spectrophotometers were intercompared at Wallops Island, VA between October 1979 and January 1981. The tests were conducted to evaluate the stability and accuracy of each instrument over an extended time period. Acceptable performance regarding these two characteristics is essential if an instrument is to be useful in field measurements and network monitoring of the atmospheric total ozone content. The Dobson spectrophotometer was used as the standard of comparison for the Brewer grating spectrophotometer, the USSR M-83 ozonometer, the Canterbury filter photometer, and the SenTran filter photometer. The grating instrument was found to be potentially the equal of the Dobson but was subject to unreliable performance by its rather sophisticated electronic components. The filter photometers performed acceptably for short periods but filter aging and eventual degradation rendered both units unusable before the end of the intercomparison. Finally, the M-83 results were found to be in acceptable agreement with the Dobson throughout the period when certain qualifications are invoked. The accuracy of a single M-83 ozone measurement may be low. Averages tend to improve its agreement with the Dobson.

Parsons, C. L.↗
NASA NTRS1982

The cost of software fault tolerance

The proposed use of software fault tolerance techniques as a means of reducing software costs in avionics and as a means of addressing the issue of system unreliability due to faults in software is examined. A model is developed to provide a view of the relationships among cost, redundancy, and reliability which suggests strategies for software development and maintenance which are not conventional.

Migneault, G. E.↗
NASA NTRS1983

Comparative analysis of data base management systems

A study to determine if the Remote File Inquiry (RFI) system would handle the future requirements of the user community is discussed. RFI is a locally written and locally maintained on-line query/update package. The current and future on-line requirements of the user community were studied. Additional consideration was given to the types of data structuring the users required. The survey indicated the features of greatest benefit were: sort, subtotals, totals, record selection, storage of queries, global updating and the ability to page break. The major deficiencies were: one level of hierarchy, excessive response time, software unreliability, difficult to add, delete and modify records, complicated error messages and the lack of ability to perform interfield comparisons. Missing features users required were: formatted screens, interfield comparions, interfield arithmetic, multiple file access, security and data integrity. The survey team recommended Kennedy Space Center move forward to state-of-the-art software, a Data Base Management System which is thoroughly tested and easy to implement and use.

Smith, R.↗
NASA NTRS1983

Use of Landsat data to predict the trophic state of Minnesota lakes

Near-concurrent Landsat Multispectral Scanner (MSS) and ground data were obtained for 60 lakes distributed in two Landsat scene areas. The ground data included measurement of secchi disk depth, chlorophyll-a, total phosphorous, turbidity, color, and total nitrogen, as well as Carlson Trophic State Index (TSI) values derived from the first three parameters. The Landsat data best correlated with the TSI values. Prediction models were developed to classify some 100 'test' lakes appearing in the two analysis scenes on the basis of TSI estimates. Clouds, wind, poor image data, small lake size, and shallow lake depth caused some problems in lake TSI prediction. Overall, however, the Landsat-predicted TSI estimates were judged to be very reliable for the secchi-derived TSI estimation, moderately reliable for prediction of the chlorophyll-a TSI, and unreliable for the phosphorous value. Numerous Landsat data extraction procedures were compared, and the success of the Landsat TSI prediction models was a strong function of the procedure employed.

Lillesand, T. M.↗
NASA NTRS1983

Reliability issues in active control of large flexible space structures

The unreliability of control system components was investigated in our attempt to deal with that problem. This matter is of concern in large space structure control because of the large number of components required to achieve specified performance in some situations, and the long operating period required between maintenance visits. The detection and isolation of component failures during system operation, and algorithms for reconfiguring control systems following detection and isolation of a failure were emphasized.

Vandervelde, W. E.↗
NASA NTRS1984

The implementation and use of Ada on distributed systems with high reliability requirements

The use and implementation of Ada (a trade mark of the US Dept. of Defense) in distributed environments in which the hardware are assumed to be unreliable were investigated. The possibility that a distributed system is programmed entirely in Ada so that the individual tasks of the system are unconcerned with which processors they are executing on and failures occurring in the underlying hardware were examined.

Knight, J. C.↗
NASA NTRS1984

Thermal contacts between metal and glass for use at cryogenic temperatures

Thermal contacts designed to cool a 50-cm diam fused-silica mirror to 5 K without serious distortion of the optical surfaces were tested. Rubber cement and copper-filled rubber cement were found to be well suited for maintaining thermal contact between the fused-silica and copper straps. A variety of other adhesives proved to be unreliable because they spalled the glass. The thermal resistances of the rubber cement and copper-filled rubber cement were determined. For the copper-filled rubber cement, the thermal resistances varied from 570 K/W at 60 K to 15,000 K/W at 10 K.

Obrien, K.↗
NASA NTRS1983

Cardiovascular responses to hypogravic environments

The cardiovascular deconditioning observed during and after space flight is characterized in a review of human space and simulation studies and animal simulations. The various simulation techniques (horizontal bed rest, head-down tilt, and water immersion in man, and immobilization of animals) are examined, and sample results are presented in graphs. Countermeasures such as exercise regimens, fluid replacement, drugs, venous pooling, G-suits, oscillating beds, electrostimulation of muscles, lower-body negative pressure, body-surface cooling, and hypoxia are reviewed and found to be generally ineffective or unreliable. The need for future space experimentation in both humans and animals is indicated.

Sandler, H.↗