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At least 253 records · Page 14

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NASA NTRS1989

Querying databases of trajectories of differential equations: Data structures for trajectories

One approach to qualitative reasoning about dynamical systems is to extract qualitative information by searching or making queries on databases containing very large numbers of trajectories. The efficiency of such queries depends crucially upon finding an appropriate data structure for trajectories of dynamical systems. Suppose that a large number of parameterized trajectories gamma of a dynamical system evolving in R sup N are stored in a database. Let Eta is contained in set R sup N denote a parameterized path in Euclidean Space, and let the Euclidean Norm denote a norm on the space of paths. A data structure is defined to represent trajectories of dynamical systems, and an algorithm is sketched which answers queries.

Grossman, Robert↗

NASA NTRS1989

Lakshmi Planum: A distinctive highland volcanic province

Lakshmi Planum, a broad smooth plain located in western Ishtar Terra and containing two large oval depressions (Colette and Sacajawea), has been interpreted as a highland plain of volcanic origin. Lakshmi is situated 3 to 5 km above the mean planetary radius and is surrounded on all sides by bands of mountains interpreted to be of compressional tectonic origin. Four primary characteristics distinguish Lakshmi from other volcanic regions known on the planet, such as Beta Regio: (1) high altitude, (2) plateau-like nature, (3) the presence of very large, low volcanic constructs with distinctive central calderas, and (4) its compressional tectonic surroundings. Building on the previous work of Pronin, the objective is to establish the detailed nature of the volcanic deposits on Lakshmi, interpret eruption styles and conditions, sketch out an eruption history, and determine the relationship between volcanism and the tectonic environment of the region.

Roberts, Kari M.↗

NASA NTRS1989

A distributed program composition system

A graphical technique for creating distributed computer programs is investigated and a prototype implementation is described which serves as a testbed for the concepts. The type of programs under examination is restricted to those comprising relatively heavyweight parts that intercommunicate by passing messages of typed objects. Such programs are often presented visually as a directed graph with computer program parts as the nodes and communication channels as the edges. This class of programs, called parts-based programs, is not well supported by existing computer systems; much manual work is required to describe the program to the system, establish the communication paths, accommodate the heterogeneity of data types, and to locate the parts of the program on the various systems involved. The work described solves most of these problems by providing an interface for describing parts-based programs in this class in a way that closely models the way programmers think about them: using sketches of diagraphs. Program parts, the computational modes of the larger program system are categorized in libraries and are accessed with browsers. The process of programming has the programmer draw the program graph interactively. Heterogeneity is automatically accommodated by the insertion of type translators where necessary between the parts. Many decisions are necessary in the creation of a comprehensive tool for interactive creation of programs in this class. Possibilities are explored and the issues behind such decisions are presented. An approach to program composition is described, not a carefully implemented programming environment. However, a prototype implementation is described that can demonstrate the ideas presented.

Brown, Robert L.↗

NASA NTRS1990

Geoscience and a Lunar Base: A Comprehensive Plan for Lunar Exploration

This document represents the proceedings of the Workshop on Geoscience from a Lunar Base. It describes a comprehensive plan for the geologic exploration of the Moon. The document begins by explaining the scientific importance of studying the Moon and outlines the many unsolved problems in lunar science. Subsequent chapters detail different, complementary approaches to geologic studies: global surveys, including orbiting spacecraft such as Lunar Observer and installation of a global geophysical network; reconnaissance sample return mission, by either automated rovers or landers, or by piloted forays; detailed field studies, which involve astronauts and teleoperated robotic field geologists. The document then develops a flexible scenario for exploration and sketches the technological developments needed to carry out the exploration scenario.

Taylor, G. Jeffrey↗

NASA NTRS1990

Space Station Freedom pressurized element interior design process

The process used to develop the on-orbit working and living environment of the Space Station Freedom has some very unique constraints and conditions to satisfy. The goal is to provide maximum efficiency and utilization of the available space, in on-orbit, zero G conditions that establishes a comfortable, productive, and safe working environment for the crew. The Space Station Freedom on-orbit living and working space can be divided into support for three major functions: (1) operations, maintenance, and management of the station; (2) conduct of experiments, both directly in the laboratories and remotely for experiments outside the pressurized environment; and (3) crew related functions for food preparation, housekeeping, storage, personal hygiene, health maintenance, zero G environment conditioning, and individual privacy, and rest. The process used to implement these functions, the major requirements driving the design, unique considerations and constraints that influence the design, and summaries of the analysis performed to establish the current configurations are described. Sketches and pictures showing the layout and internal arrangement of the Nodes, U.S. Laboratory and Habitation modules identify the current design relationships of the common and unique station housekeeping subsystems. The crew facilities, work stations, food preparation and eating areas (galley and wardroom), and exercise/health maintenance configurations, waste management and personal hygiene area configuration are shown. U.S. Laboratory experiment facilities and maintenance work areas planned to support the wide variety and mixtures of life science and materials processing payloads are described.

Hopson, George D.↗

NASA NTRS1990

Geostationary platform study: Advanced ESGP/evolutionary SSF accommodation study

The implications on the evolutionary space station of accommodating geosynchronous Earth Orbit (GEO) facilities are assessed. These facilities include unmanned satellites and platforms, manned elements, and transportation and servicing vehicles/elements. The latest existing definitions of typical unmanned GEO facilities and transportation and servicing vehicles/elements are utilized. The physical design, functional design, and operations implications at the space station are determined. Various concepts of the space station from past studies are utilized ranging from the IOC Multifunction Space Station to a branched transportation node space station and the implications of accommodating the GEO infrastructure at each type are assessed. Where possible, parametric data is provided to show the implications of variations in sizes and quantities of elements, launch rates, crew sizes, etc. The use of advanced automation, robotics equipment, and an efficient mix of manned/automated support for accomplishing necessary activities at the space station are identified and assessed. The products of this study are configuration sketches, resource requirements, trade studies, and parametric data.

Source record↗

NASA NTRS1990

Geostationary platform study: Advanced ESGP/evolutionary SSF accommodation study

The implications on the evolutionary space station of accommodating geosynchronous Earth Orbit (GEO) facilities including unmanned satellites and platforms, manned elements, and transportation and servicing vehicles/elements. The latest existing definitions of typical unmanned GEO facilities and transportation and servicing vehicles/elements are utilized. The physical design, functional design, and operations implications at the space station are determined. Various concepts of the space station from past studies are utilized ranging from the IOC Multifunction Space Station to a branched transportation node space station, and the implications of the accommodation the GEO infrastructure of each type are assessed. Where possible, parametric data are provided to show the implications of variations in sizes and quantities of elements, launch rates, crew sizes, etc. The use of advanced automation, robotics equipment, and an efficient mix of manned/automated support for accomplishing necessary activities at the space station are identified and assessed. The products of this study are configuration sketches, resource requirements, trade studies, and parametric data.

Source record↗

NASA NTRS1990

Hidden interaction in SBO galaxies

Galaxies, like plants, show a large variety of grafts: an individual of some type connects physically with a neighborhood of same or different type. The effects of these interactions between galaxies have a broad range of morphologies depending, among other quantities, on the distance of the closest approach between systems and the relative size of the two galaxies. A sketch of the possible situations is shown in tabular form. This botanical classification is just indicative, because the effects of interactions can be notable also at relatively large separations, when additional conditions are met, as for example low density of the interacting systems or the presence of intra-cluster gas. In spite of the large variety of encounters and effects, in the literature the same terms are often used to refer to different types of interactions. Analysis indicates that only few of the situations show evident signs of interaction. They appear to be most relevant when the size of the two galaxies is comparable. Bridges and tails, like the well known case of NGC 4038/39, the Antennae, are only observed for a very low percentage of all galaxies (approx. 0.38 percent, Arp and Madore 1977). In most cases of gravitational bond between two galaxies, the effects of interactions are not relevant or evident. For instance, the detection of stellar shells (Malin and Carter 1983), which have been attributed to the accretion of gas stripped from another galaxy or to the capture and disruption of a small stellar system (Quinn 1984), requires particular observing and reduction techniques. Besides these difficulties of detection, time plays an important role in erasing, within a massive galaxy, the effects of interactions with smaller objects. This can happen on a timescale shorter than the Hubble time, so the number of systems now showing signs of interaction suggests lower limits to the true frequency of interactions in the life-time of a stellar system.

Galletta, G.↗

NASA NTRS1990

C formal verification with unix communication and concurrency

The results of a NASA SBIR project are presented in which CSP-Ariel, a verification system for C programs which use Unix system calls for concurrent programming, interprocess communication, and file input and output, was developed. This project builds on ORA's Ariel C verification system by using the system of Hoare's book, Communicating Sequential Processes, to model concurrency and communication. The system runs in ORA's Clio theorem proving environment. The use of CSP to model Unix concurrency and sketch the CSP semantics of a simple concurrent program is outlined. Plans for further development of CSP-Ariel are discussed. This paper is presented in viewgraph form.

Hoover, Doug N.↗

NASA NTRS1991

Active and passive vibration suppression for space structures

The relative benefits of passive and active vibration suppression for large space structures (LSS) are discussed. The intent is to sketch the true ranges of applicability of these approaches using previously published technical results. It was found that the distinction between active and passive vibration suppression approaches is not as sharp as might be thought at first. The relative simplicity, reliability, and cost effectiveness touted for passive measures are vitiated by 'hidden costs' bound up with detailed engineering implementation issues and inherent performance limitations. At the same time, reliability and robustness issues are often cited against active control. It is argued that a continuum of vibration suppression measures offering mutually supporting capabilities is needed. The challenge is to properly orchestrate a spectrum of methods to reap the synergistic benefits of combined advanced materials, passive damping, and active control.

Hyland, David C.↗

NASA NTRS1989

On polynomial preconditioning for indefinite Hermitian matrices

The minimal residual method is studied combined with polynomial preconditioning for solving large linear systems (Ax = b) with indefinite Hermitian coefficient matrices (A). The standard approach for choosing the polynomial preconditioners leads to preconditioned systems which are positive definite. Here, a different strategy is studied which leaves the preconditioned coefficient matrix indefinite. More precisely, the polynomial preconditioner is designed to cluster the positive, resp. negative eigenvalues of A around 1, resp. around some negative constant. In particular, it is shown that such indefinite polynomial preconditioners can be obtained as the optimal solutions of a certain two parameter family of Chebyshev approximation problems. Some basic results are established for these approximation problems and a Remez type algorithm is sketched for their numerical solution. The problem of selecting the parameters such that the resulting indefinite polynomial preconditioners speeds up the convergence of minimal residual method optimally is also addressed. An approach is proposed based on the concept of asymptotic convergence factors. Finally, some numerical examples of indefinite polynomial preconditioners are given.

Freund, Roland W.↗

NASA NTRS1990

Space Station Freedom pressurized element interior design process

Hopson, George D.↗

NASA NTRS1991

The Danish SAR system - Design and initial tests

In January 1986, the design of a high-resolution airborne C-band SAR started at the Electromagnetics Institute of the Technical University of Denmark. The initial system test flights took place in November and December 1989. The authors describe the design of the system, its implementation, and its performance. They show how digital technology has been utilized to realize a very flexible radar with variable resolution, swath-width, and imaging geometry. The motion-compensation algorithms implemented to obtain the high resolution and the special features built into the system to ensure proper internal calibration are outlined. The data processing system, developed for image generation and quality assurance, is sketched, with special emphasis on the flexibility of the system. Sample images and a preliminary performance evaluation are presented, demonstrating that the design goals have been met. The ongoing system upgrades and the planned scientific utilization of the C-band SAR are described.

Madsen, Soren N.↗

NASA NTRS1992

Moving And Working On Space Structures

Clawlike device attaches boots to rails. Memorandum presents, in sketches and brief text, concept for boot-toe clip helping astronaut move about outside on structures being built at Space Station. Clip also helps astronaut maintain stable position at worksite. Concept adaptable to underwater work on such structures as offshore oil rigs.

Mclaughlin, Pat B.↗

NASA NTRS1991

Tethys geology and tectonics revisited

Tethys, a medium sized icy satellite of Saturn, was imaged by both Voyager 1 and 2 spacecraft at sufficiently high resolution to allow some geologic analysis. One fairly complete and several brief descriptions of Tethys' geology have been given. Partial results are given herein of a new analysis of Tethys' geology done as part of a comparative tectonic and cryovolcanic study of the saturnian satellites. A new geologic sketch map of Tethys' north polar area is given. This map is based on a sequence of images transformed to a polar stereographic projection at the same scale. The images present the same area under different illuminations, each of which brings out different features. A new global map is in progress.

Croft, Steven K.↗

NASA NTRS1991

Iapetus: Tectonic structure and geologic history

Many papers have been written about the surface of Iapetus, but most of these have discussed either the nature of the strongly contrasting light and dark materials or the cratering record. Little has been said about other geologic features on Iapetus, such as tectonic structures, which would provide constraints on Iapetus' thermal history. Most references have suggested that there is no conclusive evidence for any tectonic activity, even when thermal history studies indicate that there should be. However, a new study of Iapetus' surface involving the use of stereo pairs, an extensive tectonic network has been recognized. A few new observations concerning the craters and dark material were also made. Thus the geology and geologic history of Iapetus can be more fully outlined than before. The tectonic network is shown along with prominent craters and part of the dark material in the geologic/tectonic sketch map. The topology of crater rims and scarps are quite apparent and recognizable in the different image pairs. The heights and slopes of various features given are based on comparison with the depths of craters 50 to 100 km in diameter, which are assumed to have the same depths as craters of similar diameter on Rhea and Titania.

Croft, Steven K.↗

NASA NTRS1991

Mars geologic mapping: Dao, Harmakhis, and Reull Valles region

The east rim of Hellas basin is a complex geologic region affected by volcanic, tectonic, channeling, and resurfacing processes. A regional geologic map of the area between 27.5-42.4 degrees S and 260-275 degrees W was compiled in order to establish general stratigraphic relationships between and among the geologic units exposed in the region. The southern one-third of the regional map, the area convered by three MGM 1:500,000 quadrangles -40272, -40267, and -40262, is to be mapped in more detail in this project. Outflow channel deposits were subdivided into three facies and interpreted. A geologic sketch map of the Hadriaca Patera region on the east rim of the Hellas basin is presented.

Price, Katherine H.↗

NASA NTRS1991

A Common Lunar Lander (CLL) for the Space Exploration Initiative

Information is given in viewgraph form on the Artemis project, a plan to establish a permanent base on the Moon. Information includes a summary of past and future events, the program rationale, a summary of potential payloads, the physical characteristics of experiments, sketches of equipment, design study objectives, and details of such payloads as the Geophysical Station Network, teleoperated rovers, astronomical telescopes, a Moon-Earth radio interferometer, very low frequency radio antennas, the Lunar Polar Crater Telescope, Lunar Resource Utilization Experiments, and biological experiments.

Bailey, Stephen↗