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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 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Transmission overhaul and replacement predictions using Weibull and renewel theory

A method to estimate the frequency of transmission overhauls is presented. This method is based on the two-parameter Weibull statistical distribution for component life. A second method is presented to estimate the number of replacement components needed to support the transmission overhaul pattern. The second method is based on renewal theory. Confidence statistics are applied with both methods to improve the statistical estimate of sample behavior. A transmission example is also presented to illustrate the use of the methods. Transmission overhaul frequency and component replacement calculations are included in the example.

Savage, M.↗
NASA NTRS1988

Development of a satellite SAR image spectra and altimeter wave height data assimilation system for ERS-1

The applicability of ERS-1 wind and wave data for wave models was studied using the WAM third generation wave model and SEASAT altimeter, scatterometer and SAR data. A series of global wave hindcasts is made for the surface stress and surface wind fields by assimilation of scatterometer data for the full 96-day SEASAT and also for two wind field analyses for shorter periods by assimilation with the higher resolution ECMWF T63 model and by subjective analysis methods. It is found that wave models respond very sensitively to inconsistencies in wind field analyses and therefore provide a valuable data validation tool. Comparisons between SEASAT SAR image spectra and theoretical SAR spectra derived from the hindcast wave spectra by Monte Carlo simulations yield good overall agreement for 32 cases representing a wide variety of wave conditions. It is concluded that SAR wave imaging is sufficiently well understood to apply SAR image spectra with confidence for wave studies if supported by realistic wave models and theoretical computations of the strongly nonlinear mapping of the wave spectrum into the SAR image spectrum. A closed nonlinear integral expression for this spectral mapping relation is derived which avoids the inherent statistical errors of Monte Carlo computations and may prove to be more efficient numerically.

Hasselmann, Klaus↗
NASA NTRS1989

Sodium sulfur battery flight experiment definition study

Sodium-sulfur batteries were identified as the most likely successor to nickel-hydrogen batteries for space applications. One advantage of the Na/S battery system is that the usable specific energy is two to three times that of nickel-hydrogen batteries. This represents a significant launch cost savings or increased payload mass capabilities. Sodium-sulfur batteries support NASA OAST's proposed Civil Space Technology Initiative goal of a factor of two improvement in spacecraft power system performance, as well as the proposed Spacecraft 2000 initiative. The sodium-sulfur battery operates at between 300 and 400 C, using liquid sodium and sulfur/polysulfide electrodes and solid ceramic electrolyte. The transport of the electrode materials to the surface of the electrolyte is through wicking/capillary forces. These critical transport functions must be demonstrated under actual microgravity conditions before sodium-sulfur batteries can be confidently utilized in space. Ford Aerospace Corporation, under contract to NASA Lewis Research Center, is currently working on the sodium-sulfur battery space flight experiment definition study. The objective is to design the experiment that will demonstrate operation of the sodium-sulfur battery/cell in the space environment with particular emphasis on evaluation of microgravity effects. Experimental payload definitions were completed and preliminary designs of the experiment were defined.

Chang, Rebecca R.↗
NASA NTRS1989

Atomic oxygen effects on materials

Understanding of the basic processes of atomic oxygen interaction is currently at a very elementary level. However, measurement of erosion yields, surface morphology, and optical properties for low fluences have brought about much progress in the past decade. Understanding the mechanisms and those factors that are important for proper simulation of low Earth orbit is at a much lower level of understanding. The ability to use laboratory simulations with confidence to quantifiably address the functional performance and durability of materials in low Earth orbit will be necessary to assure long-term survivability to the natural space environment.

Banks, Bruce A.↗
NASA NTRS1989

Launch commit criteria performance trending analysis, phase 1, revision A. SRM and QA mission services

An assessment of quantitative methods and measures for measuring launch commit criteria (LCC) performance measurement trends is made. A statistical performance trending analysis pilot study was processed and compared to STS-26 mission data. This study used four selected shuttle measurement types (solid rocket booster, external tank, space shuttle main engine, and range safety switch safe and arm device) from the five missions prior to mission 51-L. After obtaining raw data coordinates, each set of measurements was processed to obtain statistical confidence bounds and mean data profiles for each of the selected measurement types. STS-26 measurements were compared to the statistical data base profiles to verify the statistical capability of assessing occurrences of data trend anomalies and abnormal time-varying operational conditions associated with data amplitude and phase shifts.

Source record↗
NASA NTRS1989

Predeployment validation of fault-tolerant systems through software-implemented fault insertion

Fault injection-based automated testing (FIAT) environment, which can be used to experimentally characterize and evaluate distributed realtime systems under fault-free and faulted conditions is described. A survey is presented of validation methodologies. The need for fault insertion based on validation methodologies is demonstrated. The origins and models of faults, and motivation for the FIAT concept are reviewed. FIAT employs a validation methodology which builds confidence in the system through first providing a baseline of fault-free performance data and then characterizing the behavior of the system with faults present. Fault insertion is accomplished through software and allows faults or the manifestation of faults to be inserted by either seeding faults into memory or triggering error detection mechanisms. FIAT is capable of emulating a variety of fault-tolerant strategies and architectures, can monitor system activity, and can automatically orchestrate experiments involving insertion of faults. There is a common system interface which allows ease of use to decrease experiment development and run time. Fault models chosen for experiments on FIAT have generated system responses which parallel those observed in real systems under faulty conditions. These capabilities are shown by two example experiments each using a different fault-tolerance strategy.

Czeck, Edward W.↗
NASA NTRS1989

Solar dynamic power module design

Studies have shown that use of solar dynamic (SD) power for the growth eras of the Space Station Freedom program will result in life cycle cost savings when compared to power supplied by photovoltaic sources. In the SD power module, a concentrator collects and focuses solar energy into a heat receiver which has integral thermal energy storage. A power conversion unit (PCU) based on the closed Brayton thermodynamic cycle removes thermal energy from the receiver and converts that energy to electrical energy. Since the closed Brayton cycle is a single phase gas cycle, the conversion hardware (heat exchangers, turbine, compressor, etc.) can be designed for operation in low earth orbit, and tested with confidence in test facilities on earth before launch into space. The concentrator subassemblies will be aligned and the receiver/PCU/radiator combination completely assembled and charged with gas and cooling liquid on earth before launch to, and assembly on orbit.

Space power↗
NASA NTRS1989

Workshop on Two-Phase Fluid Behavior in a Space Environment

The Workshop was successful in achieving its main objective of identifying a large number of technical issues relating to the design of two-phase systems for space applications. The principal concern expressed was the need for verified analytical tools that will allow an engineer to confidently design a system to a known degree of accuracy. New and improved materials, for such applications as thermal storage and as heat transfer fluids, were also identified as major needs. In addition to these research efforts, a number of specific hardware needs were identified which will require development. These include heat pumps, low weight radiators, advanced heat pipes, stability enhancement devices, high heat flux evaporators, and liquid/vapor separators. Also identified was the need for a centralized source of reliable, up-to-date information on two-phase flow in a space environment.

Swanson, Theodore D.↗
NASA NTRS1987

Tracking 3-D body motion for docking and robot control

An advanced method of tracking three-dimensional motion of bodies has been developed. This system has the potential to dynamically characterize machine and other structural motion, even in the presence of structural flexibility, thus facilitating closed loop structural motion control. The system's operation is based on the concept that the intersection of three planes defines a point. Three rotating planes of laser light, fixed and moving photovoltaic diode targets, and a pipe-lined architecture of analog and digital electronics are used to locate multiple targets whose number is only limited by available computer memory. Data collection rates are a function of the laser scan rotation speed and are currently selectable up to 480 Hz. The tested performance on a preliminary prototype designed for 0.1 in accuracy (for tracking human motion) at a 480 Hz data rate includes a worst case resolution of 0.8 mm (0.03 inches), a repeatability of plus or minus 0.635 mm (plus or minus 0.025 inches), and an absolute accuracy of plus or minus 2.0 mm (plus or minus 0.08 inches) within an eight cubic meter volume with all results applicable at the 95 percent level of confidence along each coordinate region. The full six degrees of freedom of a body can be computed by attaching three or more target detectors to the body of interest.

Donath, M.↗
NASA NTRS1989

Coronagraph observations and analyses of the ultraviolet solar corona

The major activities on the Spartan Ultraviolet Coronal Spectrometer project include both scientific and experimental/technical efforts. In the scientific area, a detailed analysis of the previously reported Doppler dimming of HI Ly-alpha from the July 1982 rocket flight has determined an outflow velocity at 2 solar radii from sun center to be between 153 and 251 km/s at 67 percent confidence. The technical activities include, several improvements made to the instrument that will result in enhanced scientific performance or in regaining a capability that had deteriorated during the delay time in the launch date. These include testing and characterizing the detector for OVI radiation, characterizing a serrated occulter at UV and visible wavelengths, fabricating and testing telescope mirrors with improved edges, testing and evaluating a new array detector system, modifying the slit mask mechanism and installing a mask in the instrument to block the Ly-alpha resonance line when the electron scattered component is being observed.

Kohl, John L.↗
NASA NTRS1988

The origins of the stellar corona

A critical review is presented of present observational facts and theoretical developments related to the causes of the active X-ray corona and to coronal holes in the sun and other late-type stars. Observations indicate that the active X-ray corona represents a superposition of large numbers of nanoflares. Presumably individual nanoflares occur at the many small tangential discontinuities in the field. Nothing about the active corona can be asserted with scientific confidence until the Fourier spectrum of the motions of the magnetic fibrils at the photosphere has been determined observationally.

Parker, E. N.↗
NASA NTRS1989

Time variability of the X-ray sources in M33

The results of a variability study of the X-ray sources detected by the Einstein Observatory in the galaxy M33 are reported. Two of the 15 known sources are variable above the 99.73 percent confidence level. The light curve of one of these sources, M33 X-7, exhibits a variability pattern of high and low states, suggesting an eclipsing binary X-ray source. Such a finding would be the first identification of a close accreting binary system with an X-ray source in an external galaxy other than the Magellanic Clouds. The data suggest a binary period of 1.7857 day and an eclipse duration of about 0.4 day. The nuclear source M33 X-8 varies only in the softest part of the spectrum. The observations suggest a rapid variability and show a rapid flare with a rise time shorter than three days together with longer timescale variability.

Peres, G.↗
NASA NTRS1989

Chondrules in the Sharps H3 chondrite - Evidence for intergroup compositional differences among ordinary chondrite chondrules

Bulk compositions of 19 chondrules and one matrix-rich sample from H3.4 Sharps were determined by instrumental neutron activation analysis. Samples were characterized petrographically, and mineral compositions were determined by electron microprobe analysis. There is constancy among ordinary chondrite (OC) groups in the compositional interrelationships of different chondrule types; e.g., in H3 as well as L3 and LL3 chondrites, porphyritic chondrules are more refractory than nonporphyritic chondrules. Precursor components of H3 chondrules are closely related to those of LL3 chondrules. The mean Ir/Ni, Ir/Co, and Ir/Au ratios of H3 chondrules differ from the corresponding ratios of LL3 chondrules at the 99, 90, and 79 percent confidence levels, respectively. The ratios in H3 chondrules exceed those in LL3 chondrules by amounts similar to those by which H whole-rocks exceed LL whole-rocks. These data suggest that there are primary systematic differences in bulk composition between H and LL chondrules. These differences support the inference that chondrule formation occurred after major nebular fractionation events had established the observed bulk compositional differences among OC groups.

Rubin, Alan E.↗
NASA NTRS1988

Shuttle rendezvous radar performance evaluation and simulation

The US Space Shuttle's Ku-band system was specifically designed for communications and tracking functions which are required during on-orbit operations with other spacecraft. Operating modes permit search and acquisition to be accomplished by computer designation or under manual control by the astronaut. Ku-band system data channels drive on-board dedicated displays and are incorporated into state vector updates by Shuttle guidance and navigation computers. Radar-cross-section estimates were used in computer simulations to predict the range at which radar detection and acquisition can be expected. Validity of the simulationi model and the radar design and performance were verified by flight tests on the White Sands test range. It is concluded that results of the testing established confidence in the capability of the system to provide the relative position and rate information which is needed for Shuttle work involving other spacecraft.

Griffin, John W.↗
NASA NTRS1989

Anisotropy of the diffuse background at millimeter wavelengths

The anisotropy of the diffuse background radiation has been measured with a 10-deg FWHM beam in a broad spectral band from 0.6 to 4.0 mm. A dipole anisotropy is detected with magnitude consistent with previous measurements; the present data may, however, be contaminated by atmospheric emission. Upper limits are set to fluctuations at higher-order multipoles. The most stringent limit is at l = 4, where a 95-percent confidence-level limit of less than 0.00025 is set. The observed level of isotropy sharply constrains the possibility of local astronomical origin for the submillimeter excess.

Bernstein, G. M.↗
NASA NTRS1988

Boundary conditions for the origin of the solar system

From the meteoritic results presented in the preceding chapters, a set of boundary conditions is identified that can be applied, with variable degrees of confidence, as constraints to models that attempt to describe the origin and early evolution of the solar system. Those constraints bear upon the time scale, physical and chemical environment, and processes that characterized the early solar system.

Kerridge, John F.↗
NASA NTRS1989

Airborne infrared spectroscopy of Comet Wilson (1986l) and comparisons with Comet Halley

H2O and possibly CH4 have been detected in near-infrared spectra of Comet Wilson (1986l). The observed number and relative intensities of cometary H2O lines in the nu3 band at 2.65 microns were consistent with fluorescent excitation pumped by solar infrared photons. The H2O production rate in Comet Wilson was approximately 3 x 10 to the 29th/s at R = 1.2 AU; no pronounced temporal variability was observed. Lines in the nu3 band of CH4 at 3.3 microns were possibly detected at the 3 sigma confidence level. The CH4 abundance is in the range CH4/H2O = 0.014-0.045; the uncertainty is due primarily to the assumed effective excitation temperature of CH4. The CH4 abundance in this dynamically 'new' comet is similar to that observed in P/Halley. These values are low for equilibrium compositional models and very high for disequilibrium condensation in the solar nebula.

Larson, Harold P.↗
NASA NTRS1988

Statistical analysis of censored motion sickness latency data using the two-parameter Weibull distribution

The suitability of the two-parameter Weibull distribution for describing highly censored cat motion sickness latency data was evaluated by estimating the parameters with the maximum likelihood method and testing for goodness of fit with the Kolmogorov-Smirnov statistic. A procedure for determining confidence levels and testing for significance of the difference between Weibull parameters is described. Computer programs for these procedures may be obtained from an archival source.

Park, Won J.↗