SEARCH · Search NASA
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.
The Vega balloons transmitted in situ measurements of pressure, temperature, vertical wind velocity relative to the balloon craft, cloud-particle backscatter coefficient, and ambient light level in the Venus middle cloud layer. Doppler tracking has yielded estimates for the velocities of atmospheric motion.
The effects of 1-MeV electron irradiation on silicon solar cells with AM0 efficiencies ranging from 17 to 17.7 percent are described. These cells were processed on low-resistivity FZ substrates using techniques recently developed for high-efficiency terrestrial silicon solar cells. Results indicate that these cells are more susceptible to radiation damage. However, they do maintain a greater overall power output than conventional cells to which they were compared. These cells do not demonstrate post-electron-irradiation photon decay as has been described for cells processed on 1-10 ohm-cm FZ silicon.
The transfer of momentum and kinetic energy between planetary bodies forms the basis for wide-ranging problems in planetary science ranging from the collective long-term effects of minor perturbations to the catastrophic singular effect of a major collision. In the former case, the evolution of asteroid spin rates and orientations and planetary rotation rates are cited. In the latter case, the catastrophic angular momenta and the near-global disruption of partially molten planets are included. Although the collisional transfer of momentum and energy were discussed over the last two decades, major issues remain that largely reflect current limitations in earth-based experimental conditions and 3-D numerical codes. Two examples with potential applications in a Space Station laboratory are presented.
Forced convection due to rotational effects has been numerically studied in a stable two-fluid layered system in which the lighter fluid occupies the upper portion of the computational and physical domain. Results are presented for three different fluid height combinations for conditions prevailing in a microgravity environment. It is found that the heavier fluid tends to dominate the flow field, and that equal corotation and counterrotation cases produce nearly identical behavior in the flow and thermal fields.
Wherein a fast (50 ns) rise-time high-frequency square-wave generator capable of switching between arbitrary voltages of high potential difference (1000 V or more) is described utilizing solid-state circuitry of low power consumption. Power field effect transistors are used as the active switching element, which afford compact size and simplified circuit construction. With the addition of monostable multivibrators, high-voltage square-wave pulse trains of controllable phase are produced. The generator should find application in a wide variety of situations where fast switching between high voltages is required, such as in time-of-flight, coincidence, and beams-modulation experiments.
Explore the source record for details and available documents.
Energy stability theory has been applied to a basic state of thermocapillary convection occurring in a cylindrical half-zone of finite length to determine conditions under which the flow will be stable. Because of the finite length of the zone, the basic state must be determined numerically. Instead of obtaining stability criteria by solving the related Euler-Lagrange equations, the variational problem is attacked directly by discretization of the integrals in the energy identity using finite differences. Results of the analysis are values of the Marangoni number below which axisymmetric disturbances to the basic state will decay, for various values of the other parameters governing the problem.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Models describing the steady-state thermal diffusion in a pure system, the thermal-solutal diffusion in a binary system, and heat and momentum transverse in a pure system are presented. The geometry of the model is described by a 2D Cartesian coordinate system that is applicable for crystal sheets. The melting, solidifying, and melt/gas interfacial shapes as well as the thermal, flow, and solutal profiles are analytically evaluated as functions of the heat and ambient temperature profiles and material properties. The solution procedure involves a coupled asymptotic/numerical approach which reduces the coupled set of partial differential equations to ordinary type. The results should be applicable in situations where melt flows are not intense enough to change the thermal field in pure systems, or where the physical properties of the melt are such that the convective field is decoupled from the thermal field, the latter being established primarily by diffusion.
Linear-stability theory has been applied to a basic state of thermocapillary convection in a model half-zone to determine values of the Marangoni number above which instability is guaranteed. The basic state must be determined numerically since the half-zone is of finite, O(1) aspect ratio with two-dimensional flow and temperature fields. This, in turn, means that the governing equations for disturbance quantities will remain partial differential equations. The disturbance equations are treated by a staggered-grid discretization scheme. Results are presented for a variety of parameters of interest in the problem, including both terrestrial and microgravity cases.
Accurate and rapid evaluation of radar signature for alternative aircraft/store configurations would be of substantial benefit in the evolution of integrated designs that meet radar cross-section (RCS) requirements across the threat spectrum. Finite-volume time domain methods offer the possibility of modeling the whole aircraft, including penetrable regions and stores, at longer wavelengths on today's gigaflop supercomputers and at typical airborne radar wavelengths on the teraflop computers of tomorrow. A structured-grid finite-volume time domain computational fluid dynamics (CFD)-based RCS code has been developed at the Rockwell Science Center, and this code incorporates modeling techniques for general radar absorbing materials and structures. Using this work as a base, the goal of the CFD-based CEM effort is to define, implement and evaluate various code development issues suitable for rapid prototype signature prediction.
Explore the source record for details and available documents.
Values of lateral and longitudinal metacentric heights for various seaplanes were calculated by means of approximate formulae derived here. The data are given in tabular form. Upon plotting these metacentric heights against the corresponding gross weights, it appears that the metacentric height is approximately a straight line function of the gross weight. For the lateral metacentric height GM = 13 + .002 W and for longitudinal metacentric height GM = 15 + .002 W, GM is in feet and the gross weight (W) is in pounds. Although only approximate, it is thought that the values indicated here are a reliable guide to current practice. It is recommended that the longitudinal and lateral metacentric heights be made equal and of the value given by GM = 15 = .002 W. The proper length or spacing required to satisfy the indicated value may then be obtained from substitution in the approximate formulae for metacentric height.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.