SEARCH · Engineering Papers
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.
Topics covered include: data systems and quality; analysis and assimilation techniques; impacts on forecasts; tropical forecasts; analysis intercomparisons; improvements in predictability; and heat sources and sinks.
An assessment of the status of research using Global Weather Experiment (GWE) data and of the progress in meeting the objectives of the GWE, i.e., better knowledge and understanding of the atmosphere in order to provide more useful weather prediction services. Volume Two consists of a compilation of the papers presented during the workshop. These cover studies that addressed GWE research objectives and utilized GWE information. The titles in Part 2 of this volume include General Circulation Planetary Waves, Interhemispheric, Cross-Equatorial Exchange, Global Aspects of Monsoons, Midlatitude-Tropical Interactions During Monsoons, Stratosphere, Southern Hemisphere, Parameterization, Design of Observations, Oceanography, Future Possibilities, Research Gaps, with an Appendix.
Activities of the National Climate Program since 1978 are reviewed, and outlines new directions which should be emphasized over the next five years or so. These are discussed under the subentities of climate system research; climate impacts; and climatic data, information, and services.
The Shuttle is the first launch system deployed by NASA with full redundancy in the on-board computer systems. Fault-tolerance, i.e., restoring to a backup with less capabilities, was the method selected for Apollo. The Gemini capsule was the first to carry a computer, which also served as backup for Titan launch vehicle guidance. Failure of the Gemini computer resulted in manual control of the spacecraft. The Apollo system served vehicle flight control and navigation functions. The redundant computer on Skylab provided attitude control only in support of solar telescope pointing. The STS digital, fly-by-wire avionics system requires 100 percent reliability. The Orbiter carries five general purpose computers, four being fully-redundant and the fifth being soley an ascent-descent tool. The computers are synchronized at input and output points at a rate of about six times a second. The system is projected to cause a loss of an Orbiter only four times in a billion flights.
A technique is described for arriving at improved measurements of the rain structure near the earth's surface from satellite-borne radars. The method uses deconvolution and Fourier transform procedures and assumes a knowledge of the antenna beam pattern. As an example, the method is directed toward the application of future spaceborne radar altimeters that may contain additional range gates to permit the measurement of rain in the lower troposphere. Using a radar-measured rain reflectivity profile acquired at Wallops Island, VA, in a simulation example, it is specifically demonstrated that improved measurements of the spatial frequency spectrum of the rain structure may be deduced by means of deconvolution methods, as compared to the measured spectrum derived by beam averaging. Rain measurements are considered vital from the standpoint of providing a flag for altimeter data that may be corrupted by rain. Such measurement capabilities should also provide sorely needed data on rain over the oceans where few or no such data are available for the meteorologist or the communicator interested in space diversity communications.
Multibeam systems of the future using monolithic microwave integrated circuits to provide phase control and power gain are contrasted with discrete microwave power amplifiers from 10 to 75 W and their associated waveguide feeds, phase shifters and power splitters. Challenging new enabling technology areas include advanced electrooptical control and signal feeds. Large scale MMIC's will be used incorporating on chip control interfaces, latching, and phase and amplitude control with power levels of a few watts each. Beam forming algorithms for 80 to 90 deg wide angle scanning and precise beam forming under wide ranging environments will be required. Satellite systems using these dynamically reconfigured multibeam antenna systems will demand greater degrees of beam interconnectivity. Multiband and multiservice users will be interconnected through the same space platform. Monolithic switching arrays operating over a wide range of RF and IF frequencies are contrasted with current IF switch technology implemented discretely. Size, weight, and performance improvements by an order of magnitude are projected.
There has been recent interest in multidisciplinary multilevel optimization applied to large engineering systems. The usual approach is to divide the system into a hierarchy of subsystems with ever increasing detail in the analysis focus. Equality constraints are usually placed on various design quantities at every successive level to ensure consistency between levels. In many previous applications these equality constraints were eliminated by reducing the number of design variables. In complex systems this may not be possible and these equality constraints may have to be retained in the optimization process. In this paper the impact of such a retention is examined for a simple portal frame problem. It is shown that the equality constraints introduce numerical difficulties, and that the numerical solution becomes very sensitive to optimization parameters for a wide range of optimization algorithms.
Various issues associated with getting technology development of nuclear power systems moving at a pace which will support the anticipated need for such systems in later years is discussed. The projected power needs of such advanced space elements as growth space stations and lunar and planetary vehicles and bases are addressed briefly, and the relevance of nuclear power systems is discussed. A brief history and status of the U.S. nuclear reactor systems is provided, and some of the problems (real and/or perceived) are dealt with briefly. Key areas on which development attention should be focused in the near future are identified, and a suggested approach is recommended to help accelerate the process.
The Voyager 2 encounter with Uranus, ground-based and spacecraft observations of Comet Halley, and other NASA solar system exploration is reviewed. The Challenger tragedy significantly delayed the next NASA planetary mission, Galileo, as well as the Ulysses and the Space Telescope missions, all of which will provide data vital to understanding of the solar system. However, the results anticipated from these missions, as well as those from the 1989 Voyager encounter with Neptune and from other approved and planned planetary missions promise that NASA's future role in solar system exploration will remain alive and vital.
A study has been made of the effects of adding small amounts of In (0.2-1.2 pct) to GaAs grown by molecular beam epitaxy. The density of four electron traps decreases in concentration by an order of magnitude, and the peak intensities of prominent emissions in the excitonic spectra are reduced with increase in In content. Based on the higher surface migration rate of In, compared to Ga, at the growth temperatures it is apparent that the traps and the excitonic transitions are related to point defects. This agrees with earlier observations by Briones and Collins (1982) and Skromme et al. (1985).
The tandem-arranged parallel plate manipulator (TAPPM) presently used to generate a flow with net drag reduction is conditionally sampled and found to exhibit significant changes of the boundary layer's large-scale motions at 20 delta(0), where delta(0) is the boundary layer thickness at the upstream plate of the TAPPM. Flow fields in the 'valleys' are equally affected. Both turbulent and irrotational flows then reestablish themselves by 50 delta(0). Flow visualization indicates that the TAPPM wake is very coherent at 20 delta(0), and has not yet spread into the wall region, while large scale motions and the ambient response flow continue to exhibit dynamic changes. This indicates that the shielding effect of the TAPPM's wake prolongs suppression of large-scale motions, thereby reducing skin friction over a sufficiently long extent of the boundary layer to overcome device drag and yield net drag reductions.
There is considerable interest in determining the optimal polarizations that maximize contrast between two scattering classes in polarimetric radar images. A systematic approach is presented for obtaining the optimal polarimetric matched filter, i.e., that filter which produces maximum contrast between two scattering classes. The maximization procedure involves solving an eigenvalue problem where the eigenvector corresponding to the maximum contrast ratio is an optimal polarimetric matched filter. To exhibit the physical significance of this filter, it is transformed into its associated transmitting and receiving polarization states, written in terms of horizontal and vertical vector components. For the special case where the transmitting polarization is fixed, the receiving polarization which maximizes the contrast ratio is also obtained. Polarimetric filtering is then applies to synthetic aperture radar images obtained from the Jet Propulsion Laboratory. It is shown, both numerically and through the use of radar imagery, that maximum image contrast can be realized when data is processed with the optimal polarimeter matched filter.
The currently common sequential design process for engineering systems is likely to lead to suboptimal designs. Recently developed decomposition methods offer an alternative for coming closer to optimum by breaking the large task of system optimization into smaller, concurrently executed and, yet, coupled tasks, identified with engineering disciplines or subsystems. The hierarchic and non-hierarchic decompositions are discussed and illustrated by examples. An organization of a design process centered on the non-hierarchic decomposition is proposed.
A systematic approach is presented for obtaining the optimal polarimetric matched filter, which produces maximum contrast between two scattering classes in polarimetric radar images. The maximization procedure involves solving an eigenvalue problem when the eigenvector corresponding to the maximum contrast ratio is optimal polarimetric matched filter. It is shown how to realize the filter in terms of an equivalent transmitting and receiving polarization pair. The case where the radar transmitting polarization state is fixed is addressed. Here, the receiving polarization state is optimized so that the maximum constrast ratio is attained under this constraint.
A group of propagation researchers have joined to prepare for a major campaign of propagation experiments for fixed satellite services using the Olympus satellite. For several years, the receiving hardware and data processing procedures have been planned, now, with the launch of the Olympus satellite imminent, experimenters are eager to start the real work. A short review is given of the accomplishments made since the last NAPEX meeting.
The concept is advanced of carrying out space based remote missions using a cooperative of low cost robot specialists rather than monolithic, multipurpose systems. A simulation is described wherein a control architecture for such a system of specialists is being investigated. Early results show such co-ops to be robust in the face of unforeseen circumstances. Descriptions of the platforms and sensors modeled and the beacon and retriever creatures that make up the co-op are included.
Distributed software engineering techniques and methods for improving the specification and testing phases are considered. With multiversion development, multiple implementations allow the use of an automated approach to testing called back-to-back (B/B) testing in which the outputs are compared to detect any discrepancies. However, a specification defect may lead to similar errors in the multiple versions and the underlying fault may not be detected with a B/B testing approach. The use of diverse formal specifications has been proposed as a solution to this problem, since defects in independently written specifications are likely to be different. To examine these issues, an experiment was performed using the design diversity approach in the specification, design, implementation, and testing of distributed software. In the experiment, three diverse formal specifications were used to produce multiple independent implementations of a distributed communication protocol in Ada. The problems encountered in building complex concurrent processing systems in Ada were also studied. Many pitfalls were discovered in mapping the formal specifications into Ada implementations.
Space elevator concepts for low-cost space launches are reviewed. Previous concepts suffered from requirements for ultra-high-strength materials, dynamically unstable systems, or from danger of collision with space debris. The use of magnetic grain streams solves these problems. Magnetic grain streams can support short space elevators for lifting payloads cheaply into Earth orbit, overcoming the material strength problem in building space elevators. Alternatively, the stream could support an international spaceport circling the Earth daily tens of miles above the equator, accessible to advanced aircraft. Mars could be equipped with a similar grain stream, using material from its moons Phobos and Deimos. Grain-stream arcs about the sun could be used for fast launches to the outer planets and for accelerating starships to near lightspeed for interstellar reconnaisance. Grain streams are essentially impervious to collisions, and could reduce the cost of space transportation by an order of magnitude.