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At least 631 records · Page 35
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NASA NTRS1988

Rearrangement procedures in regenerative multibeammobile communications satellites with frequency reuse

After a short overview on the European tendencies about a Land Mobile Satellite Service, this paper describes an advanced system architecture, based on multiple spot-beams and on-board processing, capable of providing message and voice services over a wide European coverage, including some North-Africa and Middle-East countries. A remarkable problem associated with spot-beam configurations is the requirement for flexibility in the capacity offer to the various coverage areas. This means incorporating procedures for changing the on-board modulator-to-spot associations, respecting the constraints imposed by frequency reuse. After discussing the requirements of the rearrangement procedure, an on-purpose algorithm is presented. This paper is derived from work performed on contract to the European Space Agency (ESA).

Colombo, Gianni↗
NASA NTRS1988

The role of aviation technology in the Caribbean Basin

Aviation technology can play a significant role in the development of the countries of the Caribbean Basin. A variety of applications of rotorcraft in the region, the benefits, both economic and political which can result from utilization of rotorcraft in both a public service and commercial role are presented. A computer simulation of rotorcraft used as emergency medical vehicles is applied to compare and evaluate the advantages of using rotorcraft technology such as civil derivatives of the new tiltrotor. It is concluded that by using a civil derivative of the tiltrotor, significant improvements can be obtained in the level of health service in the region. The potential for cargo and passenger transport applications are currently being investigated and a second computer simulation is being developed to be used to evaluate the potential benefits to be derived from such applications.

Smith, Robert W.↗
NASA NTRS1988

Present state of knowledge of the upper atmosphere 1988: An assessment report

This document was issued in response to the Clean Air Act Amendments of 1977, Public Law 95-95, mandating that NASA and other key agencies submit biennial reports to Congress and EPA. NASA is to report on the state of our knowledge of the upper atmosphere, particularly the stratosphere. This is the sixth ozone assessment report submitted to Congress and the concerned regulatory agencies. Part 1 contains an outline of the NASA Upper Atmosphere Research Program and summaries of the research efforts supported during the last two years. An assessment is presented of the state of knowledge as of March 15, 1988 when the Ozone Trends Panel, organized by NASA and co-sponsored by the World Meteorological Organization, NOAA, FAA and the United Nations Environment Program released an executive summary of its findings from a critical in-depth study involving over 100 scientists from 12 countries. Chapter summaries of the International Ozone Trends Panel Report form the major part of this report. Two other sections are Model Predictions of Future Ozone Change and Chemical Kinetics and Photochemical Data for Use in Stratospheric Modeling. Each of these sections and the report in its entirety were peer reviewed.

Watson, R. T.↗
NASA NTRS1987

The NASA tracking and data acquisition networks - Their history and their future

The NASA Tracking and Data Acquisition Networks were begun in the late 1950s as a part of the U.S. activities associated with the 1958-59 International Geophysical Year. The first network, the Minitrack Net, evolved into the Space Tracking and Data Acquisition Network (STADAN) for support of scientific satellites in earth orbit. The NASA Mercury and Apollo manned flight programs produced more demanding requirements for near real-time tracking, communications, and orbit determination, thus providing the impetus for new, more sophisticated networks. The Deep Space Network was also created to meet unique requirements of the planetary exploration programs. All of these programs necessitated establishing ground stations in various countries around the world, thus promoting the concept of international cooperation in space activities which NASA has fostered in many programs. This paper traces these networks from their beginnings through the various stages of development and introduction of new technologies to meet the requirements of increasingly more complex space missions. The paper also discusses the planning for new capabilities for tracking, data acquisition and communications support of future programs, including particularly the Space Station in the next decade.

Force, Charles T.↗
NASA NTRS1987

Remote sensing: Earth's surface and atmosphere; Proceedings of Workshop X and the Topical Meeting of the 26th COSPAR Plenary Meeting, Toulouse, France, June 30-July 11, 1986

The present conference on space-based remote sensing of the earth's surface and atmosphere addresses the two broad issues of remote sensing activities of interest to developing countries and the results obtained to date by the International Satellite Cloud Climatology Project, the Earth Radiation Budget Experiment, and the Stratospheric Aerosol and Gas Experiment (SAGE). Attention is given to the remote sensing of environmental factors affecting health, applications of satellite microwave radiometry, earth science missions for the NASA Space Station, and digitally produced Landsat map images. Also discussed are time-accumulated visible and IR histograms used as cloud cover descriptors, the estimation of the radiation budget's sensitivity to cloud variations, monitoring global surface temperature variations using cloud data sets, and an analysis of preliminary SAGE II data on ozone and NO2.

Carter, W. D.↗
NASA NTRS1987

Zhamanshin and Aouelloul - Craters produced by impact of tektite-like glasses?

It is shown that the enhanced abundance of siderophile elements and chromium in tektite-like glasses from the two impact craters of Zhamanshin and Aouelloul cannot be explained as a result of contamination of the country rock by meteorites nor, probably, comets. The pattern is, however, like that found in certain Australasian tektites, and in Ivory Coast tektites. It is concluded, in agreement with earlier suggestions by Campbell-Smith and Hey, that these craters were formed by the impact of large masses of tektite-like glass, of which the glasses which were studied are fragments. It follows that it is necessary, in considering an impact crater, to bear in mind that the projectile may have been a glass.

O'Keefe, John A.↗
NASA NTRS1987

The exploration of Halley's comet - An example of international cooperation

The history of international cooperation in studies of comets started with observations in 1577 and 1680, when Tycho Brahe and Newton, respectively, collected position measurements made in different countries to determine the paths of the comets observed. In the fall of 1979, a worldwide Comet Halley watch was proposed. As a result of international cooperation, Comet Halley was explored during its recent appearance from the ground, earth orbit, Venus orbit, interplanetary space, and from within the comet itself. The various activities in space were coordinated by the ESA, the USSR Intercosmos, the Japanese ISAS, and NASA, through the Inter-Agency Consultative Group. The activities of the ground-based observers were coordinated by the International Halley Watch.

Rahe, Jurgen H.↗
NASA NTRS1987

Inflight evaluation of pilot workload measures for rotorcraft research

The effectiveness of heart-rate monitoring and the NASA TLX workload rating scale (Hart et al., 1985) in measuring helicopter-pilot workloads is investigated experimentally. Four NASA test pilots flew two 2-h missions each in an SH-3G helicopter, following scenarios with takeoff, hover, cross-country, and landing tasks; pilot performance on the tasks undertaken near the landing area was measured by laser tracking. The results are presented in graphs and discussed in detail, and it is found that the TLX ratings clearly distinguish the flight segments and are well correlated with the performance data. The mean heart rate (measured as interbeat interval) is correlated (r = -0.69) with the TLX workload, but only the standard deviation of the interbeat interval is able to distinguish between flight segments; the correlation between standard deviation and TLX ratings is negative but not significant.

Shively, Robert J.↗
NASA NTRS1989

Survey Of Wind Tunnels At Langley Research Center

Report presented at AIAA 14th Aerodynamic Testing Conference on current capabilities and planned improvements at NASA Langley Research Center's major wind tunnels. Focuses on 14 major tunnels, 8 unique in world, 3 unique in country. Covers Langley Spin Tunnel. Includes new National Transonic Facility (NTF). Also surveys Langley Unitary Plan Wind Tunnel (UPWT). Addresses resurgence of inexpensive simple-to-operate research tunnels. Predicts no shortage of tools for aerospace researcher and engineer in next decade or two.

Bower, Robert E.↗
NASA NTRS1986

History at NASA

The efforts of the National Aeronautics and Space Administration to capture and record the events of the past are described, particularly the research accomplishments of NASA's agency-wide history program. A concise guide to the historical research resources available at NASA Headquarters in Washington, D.C., at NASA facilities around the country, and through the federal records systems is given.

Source record↗
NASA NTRS1988

Comparative study of career development and training programs

Improvement of human capital has been identified as the key to any further increase of productivity for any country engaged in the global economic competition. The same can be said of any organization seeking to enhance its overall performance. This study is aimed at: (1) surveying the current practices of career development and training programs at major corporations and government research organizations; (2) presenting the distributions of various program features among survey respondents; (3) identifying the profile of the training program of a typical research organization, against which each organization can check and identify its relative strengths as well as areas needing further strengthening; (4) conducting an economic analysis of the effectiveness of the training programs at Langley Research Center; and (5) making recommendations as to how to enhance existing training programs.

Tsao, Alan↗
NASA NTRS1988

Short-crack growth behaviour in an aluminum alloy: An AGARD cooperative test program

An AGARD Cooperative Test Program on the growth of short fatigue cracks was conducted to define the significance of the short-crack effect, to compare test results from various laboratories, and to evaluate an existing analytical crack-growth prediction model. The initiation and growth of short fatigue cracks (5 micrometer to 2 mm) from the surface of a semi-circular notch in 2024-T3 aluminum alloy sheet material were monitored under various load histories. The cracks initiated from inclusion particle clusters or voids on the notch surface and generally grew as surface cracks. Tests were conducted under several constant-amplitude (stress ratios of -2, -1, 0, and 0.5) and spectrum (FALSTAFF and Gaussian) loading conditions at 3 stress levels each. Short crack growth was recorded using a plastic-replica technique. Over 250 edge-notched specimens were fatigue tested and nearly 950 cracks monitored by 12 participants from 9 countries. Long crack-growth rate data for cracks greater than 2 mm in length were obtained over a wide range in rates (10 to the -8 to 10 to the -1 mm/cycle) for all constant-amplitude loading conditions. Long crack-growth rate data for the FALSTAFF and Gaussian load sequences were also obtained.

Newman, J. C., Jr.↗
NASA NTRS1988

The national aero-space plane

The National Aerospace Plane is an extremely versatile and adaptable aircraft. It can be developed into an Orient Express that would dramatically improve trade with countries in Asia and elsewhere: a commuter transport to ferry men and materials to space, an advanced tactical fighter or bomber, and an unparalleled high altitude spy-plane to observe troubled spots all over the globe. Utilizing the technology developed by this pilot program, it will be possible to quickly and easily get to low Earth orbit, go halfway around the world in a fraction of the time it previously took, and lead the world in the development of advanced technology to improve our lives and the lives of many others.

Mendez, Bruce↗
NASA NTRS1989

AGARD standard aeroelastic configurations for dynamic response

Since emphasis is on the transonic speed range, special importance is placed on configurations for which available data are sufficient to define accurately a transonic flutter boundary. Only configurations with clean, smooth surfaces are considered suitable. Segmented models or models with surface-slope discontinuities are inappropriate. Excluded also, in general, are configurations and data sets that involve behavior that is uncertain or not well understood, uncertain model properties, or know sensitivities to small variations in model properties. In order to assess the suitability of configurations already tested and the associated data for designation as standard, a survey of AGARD member countries was conducted to seek candidates for the prospective set. The results of that survey are given and summarized along with the initial selection of a standard configuration.

Yates, E. Carson, Jr.↗
NASA NTRS1989

Intermetallic and ceramic matrix composites for 815 to 1370 C (1500 to 2500 F) gas turbine engine applications

Light weight and potential high temperature capability of intermetallic compounds, such as the aluminides, and structural ceramics, such as the carbides and nitrides, make these materials attractive for gas turbine engine applications. In terms of specific fuel consumption and specific thrust, revolutionary improvements over current technology are being sought by realizing the potential of these materials through their use as matrices combined with high strength, high temperature fibers. The U.S. along with other countries throughout the world have major research and development programs underway to characterize these composites materials; improve their reliability; identify and develop new processing techniques, new matrix compositions, and new fiber compositions; and to predict their life and failure mechanisms under engine operating conditions. The status is summarized of NASA's Advanced High Temperature Engine Materials Technology Program (HITEMP) and the potential benefits are described to be gained in 21st century transport aircraft by utilizing intermetallic and ceramic matrix composite materials.

Stephens, Joseph R.↗
NASA NTRS1987

Low cost, microcomputer-based interactive analysis system for direct-reception and archived remote sensing data

A hardware/software system has been developed for use in meteorological field experiments and by developing countries which need low-cost remote sensing data analysis capabilities. The system can directly receive satellite transmissions of the AVHRR, TOVS, Argos, GOES, GMS, and Meteosat systems. Also, the system can process computer tapes from Landsat. Received data are ingested directly into the computer's disk storage, eliminating the need for a wide-band analog tape drive. Data may be interpreted in terms of cloud imagery, cloudtop temperature, sea surface temperature, vegetation index, and temperature/humidity profiles with overlays of geographic boundaries and latitude/longitude grids. The image processing, enhancement functions, and modeling capabilities of the system are discussed.

Vermillion, Charles H.↗
NASA NTRS1989

The impact of summer rainfall on the temperature gradient along the United States-Mexico border

The international border running through the Sonoran Desert in southern Arizona and northern Sonora is marked by a sharp discontinuity in albedo and grass cover. The observed differences in surface properties are a result of long-term, severe overgrazing of the Mexican lands. Recently, investigators have shown the Mexican side of the border to have higher surface and air temperatures when compared to adjacent areas in the United State. The differences in temperatures appear to be more associated with differential evapotranspiration rates than with albedo changes along the border. In this study, the impact of summer rainfall on the observed seasonal and daily gradient in maximum temperature is examined. On a seasonal time scale, the temperature gradient increases with higher moisture levels, probably due to a vegetative response on the United States' side of the border; at the daily level, the gradient in maximum temperature decreases after a rain event as evaporation rates equalize between the countries. The results suggest that temperature differences between vegetated and overgrazed landscapes in arid areas are highly dependent upon the amount of moisture available for evapotranspiration.

Balling, Robert C., Jr.↗
NASA NTRS1989

Operational aspects of CASA UNO '88-The first large scale international GPS geodetic network

For three weeks, from January 18 to February 5, 1988, scientists and engineers from 13 countries and 30 international agencies and institutions cooperated in the most extensive GPS (Global Positioning System) field campaign, and the largest geodynamics experiment, in the world to date. This collaborative eperiment concentrated GPS receivers in Central and South America. The predicted rates of motions are on the order of 5-10 cm/yr. Global coverage of GPS observations spanned 220 deg of longitude and 125 deg of latitude using a total of 43 GPS receivers. The experiment was the first civilian effort at implementing an extended international GPS satellite tracking network. Covariance analyses incorporating the extended tracking network predicted significant improvement in precise orbit determination, allowing accurate long-baseline geodesy in the science areas.

Neilan, Ruth E.↗