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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 901 records · Page 50
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NASA NTRS1987

Optimization of aircraft trajectories through severe microbursts

A method of defining performance envelopes for aircraft microburst penetration is being developed. A trajectory is computed for a given aircraft/control law configuration and given microburst parameters (either a downdraft or a head/tailwind type microburst). The maximum deviation from the nominal altitude is recorded for that trajectory. Then the microburst parameters are varied, and the process is repeated. Thus a three dimensional plot of maximum altitude deviation versus microburst range scale and intensity is generated. Finally, a certain maximum altitude deviation, say 50 feet, is defined as the safe penetration limit. Then the 50 foot level contour becomes the performance limit for safe operation as a function of microburst intensity and range. Control inputs from deterministic trajectory optimization are used in the above described calculations to define the maximal performance limit. These limits provide targets for the designer of practical control laws.

Psiaki, Mark L.↗
NASA NTRS1986

Joint thunderstorm operations using the NASA F-106B and FAATC/AFWAL Convair 580 airplanes

During the 1985 thunderstorm season, three joint thunderstorm research flights were conducted within 100 n.mi. of NASA Langley by the NASA Storm Hazards F-106B and the FAA/USAF CV-580 research airplanes with ground-based weather radar measurements by NASA Wallops. This paper discusses the thunderstorm penetration capabilities of each airplane and the techniques used to safely place the two airplanes into the same thunderstorm cell for collection of correlated EM data. It is concluded that joint thunderstorm research operations of two aircraft with significantly dissimilar thunderstorm penetration capabilities are counterproductive to both airplanes.

Fisher, B. D.↗
NASA NTRS1987

Control of aircraft landing approach in wind shear

Wind and wind shear components are estimated and used for controlling an externally-blown flap STOL aircraft and a B-727 during landing approach under the JAWS microburst profile. A combination of feedforward and feedback concepts is used. The objective is tracking of airspeed and glide slope. Both an asymptotic disturbance rejection scheme, which is equivalent to MIMO zero assignment, and a linear quadratic scheme prove to be successful. Higher angle-of-attack is used only after thrust saturation. Downdraft is found to be more difficult to counter for STOL aircraft than is horizontal wind shear. A third design formulation based on successive loop closure is also presented. A 'Wind Shear Penetration Index' is described, which offers a simple and quantitative evaluation of an aircraft's ability to safely penetrate a wind shear. This index is particularly useful if used with Doppler radars.

Chu, Peter Yaohwa↗
NASA NTRS1987

A nondestructive technique for predicting the strength remaining in filament wound composites subjected to low-level impact

A model for predicting the fracture strength of homogeneous materials is proposed. Impacted FWC samples were evaluated using ultrasonic testing and an X-ray dye penetration method. The ability of the model to measure fracture strength was also examined. The relation between attenuation and velocity measurements is studied. It is observed that the X-ray method is not useful for predicting fracture strength because the dye could not penetrate the matrix. It is noted that fracture strength predictions derived from the fracture mechanical model and the ultrasonic measurements correlate well with actual measured fracture strengths.

Madaras, E. I.↗
NASA NTRS1987

On the 3-dimensional structure of plasmoids

The hypothesis that the IMF penetrates plasmoids causing them to be three- rather than two-dimensional is tested by comparing observations of By within plasmoids and related tail structures to upstream IMF By data. The magnetic topologies that result from the mergings of closed plasma sheet flux tubes and open tail lobe flux tubes at a near-earth neutral line, and merging near the tail flanks are described and studied. The particle signals and isotropic electron distributions are examined. It is observed that the IMF By penetrates plasmoids and that their structure is three-dimensional. In the three-dimensional model of plasmoids the reconnected plasma sheet field lines form a magnetic flux-ropelike structure. The three-dimensional model is utilized to analyze stagnant, slowly moving and earthward moving structures.

Hughes, W. J.↗
NASA NTRS1987

Automated detection of severe thunderstorms using geosynchronous infrared data

A procedure to identify thunderstorms from short-interval (5 min) GOES infrared (IR) data and to estimate their intensity (updraft strength) in an automated fashion is described. Thunderstorms are identified in the IR field by a simple pattern-recognition approach. For mature thunderstorms, two key parameters are used to estimate intensity: the amount of penetration above the neutral point and the occurrence (or not) of a cold-warm couplet in the IR TB field. Based on cloud model results, the amount of penetration is related to the maximum updraft speed, which is converted to an index. Application of the algorithm to a case study is presented.

Adler, Robert F.↗
NASA NTRS1988

Assessment of the effects of space debris and meteoroids environment on the space station solar array assembly

The methodology used to assess the probability of no impact of space debris and meteoroids on a spacecraft structure is applied to the Space Station solar array assembly. Starting with the space debris and meteoroids flux models, the projected surface area of the solar cell string circuit of the solar array panel and the mast longeron, and the design lifetime, the possibility of no impact on the solar array mast and solar cell string circuits was determined as a function of particle size. The probability of no impact on the cell string circuits was used to derive the probability of no open circuit panel. The probability of meeting a certain power requirement at the end of the design lifetime was then calculated as a function of impacting particle size. Coupled with a penetration and damage models/correlations which relate the particle size to the penetration depth and damage, the results of this analysis can be used to determine the probability of meeting the lower power requirement given a degree of redundancy, and the probability of no impact on the solar array mast.

Nahra, Henry K.↗
NASA NTRS1987

A probabilistic model of brittle crack formation

Probability of a brittle crack formation in an elastic solid with fluctuating strength is considered. A set Omega of all possible crack trajectories reflecting the fluctuation of the strength field is introduced. The probability P(X) that crack penetration depth exceeds X is expressed as a functional integral over Omega of a conditional probability of the same event taking place along a particular path. Various techniques are considered to evaluate the integral. Under rather nonrestrictive assumptions, the integral is reduced to solving a diffusion-type equation. A new characteristic of fracture process, 'crack diffusion coefficient', is introduced. An illustrative example is then considered where the integration is reduced to solving an ordinary differential equation. The effect of the crack diffusion coefficient and of the magnitude of strength fluctuations on probability density of crack penetration depth is presented. Practical implications of the proposed model are discussed.

Chudnovsky, A.↗
NASA NTRS1987

Electron precipitation near L = 4 - Longitudinal variation

Observations of penetrating electron precipitation at two L of about 4 stations in the southern hemisphere, Kerguelen and Siple Station, Antarctica, are summarized. The nearly complete absence of precipitation at Kerguelen and its frequent occurrence at Siple Station is explained in terms of their location with respect to the center of the South Atlantic geomagnetic anomaly at L of about 4. Conclusions which result from this explanation are discussed along with questions which remain concerning penetrating electron precipitation.

Sheldon, W. R.↗
NASA NTRS1988

Hypervelocity impact damage assessment for Space Station

To inhibit damage and limit the probability of penetration of the Space Station pressure wall by micrometeoroids and orbital debris, a shield placed away from the wall is used to form a double wall. To determine shield effectiveness and assess impact damage, existing test data were reviewed and additional testing was performed for Space Station double wall designs. Empirical spallation and penetration functions derived from the data show that shield thickness and impact angle affect the damage to the wall. Thick shields reduce wall damage for low angle impacts but increase damage for oblique impacts. Multilayer insulation between the shield and wall reduces impact damage to the wall. A relationship between impact velocity and spall damage to the wall is demonstrated. Preliminary test results on Li-Al shield material indicate possible improved effectiveness over Al shields.

Coronado, Alex R.↗
NASA NTRS1988

Studies of molecular-beam epitaxy growth of GaAs on porous Si substrates

GaAs has been grown on porous Si directly and on Si buffer layer-porous Si substrates by molecular-beam epitaxy. In the case of GaAs growth on porous Si, transmission electron microscopy (TEM) reveals that the dominant defects in GaAs layers grown on porous Si are microtwins and stacking faults, which originate from the GaAs/porous Si interface. GaAs is found to penetrate into the porous Si layers. By using a thin Si buffer layer (50 nm), GaAs penetration diminishes and the density of microtwins and stacking faults is largely reduced and localized at the GaAs/Si buffer interface. However, there is a high density of threading dislocations remaining. Both Si (100) aligned and four degree tilted substrates have been examined in this study. TEM results show no observable effect of the tilted substrates on the quality of the GaAs epitaxial layer.

Mii, Y. J.↗
NASA NTRS1988

Shielding against debris

The damage to spacecraft caused by debris and design of the Space Station to minimize damage from debris are discussed. Although current estimates of the debris environment show that fragments bigger than 2 cm are not likely to hit the Space Station, orbital debris from about 0.5 mm to 2 cm will pose a hazard, especially on brittle surfaces, such as glass. Spacesuits are being designed to reduce debris caused dangers to astronauts during EVA. About 5 cm of high-strength aluminum are needed to prevent penetration by a 1 cm piece of aluminum with a mass near 1.5 g colliding at 10 km/sec. Because aluminum bumpers have the drawback of metallic debris ejected outward after a hypervelocity collision, the use of nonmetallic materials for bumpers is being studied. Methods of reducing the weight and volume of the shield for the Space Station are also being researched. A space station habitation module using bumpers has a 99.6 percent chance of avoiding penetration during its lifetime.

Cour-Palais, Burton G.↗
NASA NTRS1988

Fatigue behavior of 5Ni-Cr-Mo-V steel weldments containing fabrication discontinuities

The applicability of linear elastic fracture mechanics to characterize the fatigue behavior of high-strength steel weldments containing lack-of-penetration (LOP) and slag/lack-of-fusion (S/LOF) discontinuities is explored. Full penetration, double-V butt welds with reinforcements removed were tested under zero-to-tension axial loading. Various filler metals and welding techniques were used. Both sound welds and welds containing discontinuities were cycled to failure. Where possible, cycles to crack initiation were estimated by strain gage measurements. The fracture mechanics approach was successful in correlating the fatigue lifetimes of specimens containing single LOP discontinuities of varying size. However, the fatigue behavior of specimens containing multiple S/LOF discontinuities proved to be much more complex and difficult to analyze.

Gill, Steven J.↗
NASA NTRS1988

Satellite remote sensing and cloud modeling of St. Anthony, Minnesota storm clouds and dew point depression

Rawinsonde data and geosynchronous satellite imagery were used to investigate the life cycles of St. Anthony, Minnesota's severe convective storms. It is found that the fully developed storm clouds, with overshooting cloud tops penetrating above the tropopause, collapsed about three minutes before the touchdown of the tornadoes. Results indicate that the probability of producing an outbreak of tornadoes causing greater damage increases when there are higher values of potential energy storage per unit area for overshooting cloud tops penetrating the tropopause. It is also found that there is less chance for clouds with a lower moisture content to be outgrown as a storm cloud than clouds with a higher moisture content.

Hung, R. J.↗
NASA NTRS1986

Grain boundary oxidation and its effects on high temperature fatigue life

Fatigue lives at elevated temperatures are often shortened by creep and/or oxidation. Creep causes grain boundary void nucleation and grain boundary cavitation. Grain boundary voids and cavities will accelerate fatigue crack nucleation and propagation, and thereby shorten fatigue life. The functional relationships between the damage rate of fatigue crack nucleation and propagation and the kinetic process of oxygen diffusion depend on the detailed physical processes. The kinetics of grain boundary oxidation penetration was investigated. The statistical distribution of grain boundary penetration depth was analyzed. Its effect on high temperature fatigue life are discussed. A model of intermittent micro-ruptures of grain boundary oxide was proposed for high temperature fatigue crack growth. The details of these studies are reported.

Liu, H. W.↗
NASA NTRS1988

PLANECHG: Earth orbit to lunar orbit delta V estimation program. User and technical documentation

The PLANECNG computer program calculates velocities for Earth-to-Mooon and Moon-to-Earth trajectories. The flight to be analyzed originates in a circular orbit of any inclination and altitude about one of the bodies, and culminates in a circular orbit of any inclination and altitude about the other body. An intermedate delta V and plane change occurs at the Lunar Sphere of Influence (SOI), the region where the vehicle is near its lowest velocity in the trajectory, and therefore where it is able to make the plane change with the lowest delta V. A given flight may penetrate the SOI at a number of points. Each point has associated with it a unique set of delta V's and total velocity. The program displays the velocities, in matrix form, for a representative set of SOI penetration points. An SOI point is identified by projecting Lunar latitude and longitude onto the SOI. The points recorded for a given flight are defined by the user, who provides a starting longitude and latitude, and an increment for each. A matrix is built with 10 longitudes forming the columns and 19 latitudes forming the rows. This matrix is presented in six reports, each containing different velocity or node information in the body of the matrix.

Source record↗
NASA NTRS1989

Contamination of liquid oxygen by pressurized gaseous nitrogen

The penetration of pressurized gaseous nitrogen (GN2) into liquid oxygen (LOX) was investigated experimentally in the 7-inch High Temperature Tunnel, the pilot tunnel for the 8-foot High Temperature Tunnel (8'HTT) at Langley Research Center. A preliminary test using a nuclear monitor revealed the extent of the liquid nitrogen (LN2) build-up at the LOX interface as a function of GN2 pressure. Then an adaptation of the differential flash vaporization technique was used to determine the binary diffusivity of the LOX-LN2 system at a temperature of 90.2 K. The measured value D equals 0.000086 sq cm/s + or - 25 percent together with two prior measurements at lower temperatures revealed an excellent fit to the Arrhenius equation, yielding a pre-exponential factor D sub 0 equals 0.0452 sq cm/s and an activation enthalpy H equals 1.08 kcal/mol. At a pressure of 1700 psi and holding time of 15 min, the penetration of LN2 into LOX (to a 1 percent contamination level) was found to be 0.9 cm, indicating but minimal impact upon 8'HTT operations.

Zuckerwar, Allan J.↗
NASA NTRS1988

Optimization and guidance of landing trajectories in a windshear

The problem of the optimization and guidance of landing trajectories in the presence of a windshear is considered with emphasis on abort landing and penetration landing. For abort landing, optimal trajectories are determined by minimizing the peak value of the altitude drop. For penetration landing, optimal trajectories are determined by minimizing a performance index measuring the deviation of the altitude of the flight trajectory from that of the nominal trajectory, with touchdown path inclination, touchdown velocity tolerance, and touchdown distance tolerance specified.

Miele, A.↗