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At least 865 records · Page 48

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NASA NTRS1982

Microwave noise temperature and attenuation of clouds - Statistics of these effects at various sites in the United States, Alaska, and Hawaii

The microwave attenuation and noise temperature effects of clouds can result in serious degradation of telecommunications link performance, especially for low-noise systems presently used in deep-space communications. Although cloud effects are generally less than rain effects, the frequent presence of clouds will cause some amount of link degradation a large portion of the time. This paper presents a general review of cloud types and their water particle densities, attenuation and noise temperature calculations, and basic link signal-to-noise ratio calculations. Tabular results of calculations for 12 different cloud models are presented for frequencies in the range 10-50 GHz. Curves of average-year attenuation and noise temperature statistics at frequencies ranging from 10 to 90 GHz, calculated from actual surface and radiosonde observations, are given for 15 climatologically distinct regions in the contiguous United States, Alaska, and Hawaii. Nonuniform sky cover is considered in these calculations.

Slobin, S. D.↗

NASA NTRS1983

Low cost planetary science missions

The use of existing earth-orbiting satellite technology represents a potential way of fulfilling important planetary exploration goals at greatly reduced cost, at least within the region between Venus and the inner asteroid belt. The present paper reports three studies of options for such missions to near-earth asteroids, the moon and Mars. The asteroid mission projected would be that of a rendezvous with either Anteros or Eros for purposes of resource determination, using an adaptation of the Tiros-N weather satellite. Two parallel studies were done on geoscience orbiters intended to provide detailed composition mapping from low polar orbit of the moon and Mars based on the modification of the same spacecraft design: the FLTSATCOM spacecraft, and the Atmospheric Explorer/Dynamics Explorer (later changed to Tiros for combined moon-Mars missions). Studies have shown the major modifications required to involve the telecommunications, data handling, power, propulsion and attitude control subsystems, and have demonstrated concept feasibility.

French, J. R.↗

NASA NTRS1981

Future satellite systems - Market demand assessment

During 1979-80, a market study was performed regarding the future total demand for communications services, and satellite transmission service at the 4/6 GHz, 12/14 GHz, and 20/30 GHz frequencies. Included in the study were a variety of communications traffic characteristics as well as projections of the cost of C and Ku band satellite systems through the year 2000. In connection with the considered study, a total of 15 major study tasks and subtasks were undertaken and were all interrelated in various ways. The telecommunications service forecasts were concerned with a total of 21 data services, 5 voice services, and 5 video services. The traffic volumes within the U.S. for the three basic services were projected for three time periods. It is found that the fixed frequency allocation for domestic satellites combined with potential interference from adjacent satellites means a near term lack of orbital positions above the U.S.

Reiner, P. S.↗

NASA NTRS1983

Remote ground-based observations of terrestrial airglow emissions and thermospheric dynamics at Calgary, Alberta, Canada

The article discusses the automated optical observatory at Calgary, Alberta, Canada at which three sophisticated optical instruments are operated unattended via telecommunications between the laboratory and observatory computers. These instruments are a single-etalon, 15-cm Fabry-Perot interferometer with six filter channels, a tilting filter with four filter channels, and a 1-m Ebert-Fastie spectrophotometer. The instrumental control computer is a LSI-11 microcomputer packaged with dual floppy disk drives. The observatory has been operating with good results since September 1981.

Meriwether, J. W., Jr.↗

NASA NTRS1983

Comparative analysis of large antenna spacecraft using the ideas system

A Land Mobile Satellite System (LMSS), capable of providing mobile communications for commercial and government applications in nonmetropolitan areas of the continental U.S. and Canada as an augmentation to existing and planned terrestrial systems, is being studied. The satellite system would provide 'narrow band' telecommunications services such as mobile radio, telephone, dispatch, safety, and special radio services, and thin-route fixed telephone and data services in the 806-890 MHz band and continuous emergency beacon monitoring in the 406-406.1 MHz band. A single Shuttle launch with an upper stage orbital transfer system would place the LMSS spacecraft in geosynchronous orbit over the continental U.S. in 1995 with a 10-year lifetime. The present investigation has the objective to evaluate, compare, and rank selected spacecraft concepts, to suggest design improvement to the individual concepts, and to identify technology needs.

Garrett, L. B.↗

NASA NTRS1983

The future of the U.S. aviation system

The growth of the aviation system of the U.S. over the last twenty years is described. Long-term and short-term causes of air travel are analyzed, showing the interaction of economic activity, airline yields and quality of service. Future trends in general aviation, aircraft technology, and telecommunications are described. Potential future scenarios for the airline industry are presented.

Ausrotas, R. A.↗

NASA NTRS1982

Weight and structural analysis of four structural concepts for a land mobile satellite system

The present study is concerned with a Land Mobile Satellite System (LMSS) which can provide mobile communications for commercial and government applications in nonmetropolitan areas of the continental U.S. and Canada as an augmentation to existing and planned terrestrial systems. The satellite system would provide 'narrow band' telecommunications services, thin-route fixed telephone and data services in the 806-890 MHz band, and continuous emergency beacon monitoring in the 406-406.1 MHz band. It is pointed out that a satellite system operating in concert with terrestrial cellular systems could provide truly ubiquitous mobile communications services in the U.S. and Canada. A single shuttle shuttle launch could place the LMSS spacecraft in geosynchronous orbit over the continental U.S. in 1995 with a 10-year lifetime. Attention is given to the structural concepts, a weight analysis, and a structural analysis.

Ferebee, M. J.↗

NASA NTRS1983

Beam forming networks for mm-wave satellite communications

Technology features of a beam forming network (BFN) employing ferrite devices to provide multiple beam antenna pattern control for satellites used in telecommunications are described. The BFN produces the phase and amplitude distribution for each horn in an antenna array, with the number of horns in the array being equal to the number of outputs in the BFN. One configuration involves microwave switches and permits illumination of a single feed horn at a time using ferrite latching circulators that function by reversing the circulation direction. A more flexible version, yielding a variable amplitude distribution across the feed horn array to accommodate changing traffic patterns or serving a TDMA system, includes the capability of forming nulls in the system with a variable phase shifter in the input ports. The antenna scan angles in phased arrays can be limited to 8 deg from center. Acceptable insertion losses have been demonstrated in BFN with hundreds of ports and switching rates as high as 10 kHz.

Sharon, T. E.↗

NASA NTRS1983

Communications satellites - The experimental years

Only eight years after the launc of Sputnik-1 by the Soviet Union, the first commercial satellite, 'Early Bird', entered service. In just twelve years commercial satellite service extended around the earth and became profitable. The reasons for the successful development of the communications satellite services in a comparatively short time are considered. These reasons are related to the presence of three ingredients, taking into account technology to create the system, communications requirements to form a market, and a management structure to implement the system. The formation of the concept of using earth orbiting satellites for telecommunications is discussed. It is pointed out that the years from 1958 to 1964 were the true 'experimental years' for satellite communications. The rapid development of technology during this crucial period is described, giving attention to passive satellites, active systems, and development satellites.

Edelson, B. I.↗

NASA NTRS1983

New approaches to planetary exploration - Spacecraft and information systems design

Approaches are recommended for use by the NASA Solar System Exploration Committee (SSEC) in lowering the costs of planetary missions. The inclusion of off-the-shelf hardware, i.e., configurations currently in use for earth orbits and constructed on a nearly assembly-line basis, is suggested. Alterations would be necessary for the thermal control, power supply, telecommunications equipment, and attitude sensing in order to be serviceable as a planetary observer spacecraft. New technology can be developed only when cost reduction for the entire mission would be realized. The employment of lower-cost boost motors, or even integrated boost motors, for the transfer out of earth orbit is indicated, as is the development of instruments that do not redundantly gather the same data as previous planetary missions. Missions under consideration include a Mars geoscience climatology Orbiter, a lunar geoscience Orbiter, a near-earth asteroid rendezvous, a Mars aeronomy Orbiter, and a Venus atmospheric probe.

Diaz, A. V.↗

NASA NTRS1982

Satellite communications for the Pacific islands. Second year report

Requirements, options and costs for use of communications satellites in underserved areas of the Pacific Basin are described with emphasis on extended utilization of INTELSAT. The economic structures within and among Pacific Basin entities are examined, particularly the relationship between the growth of regional trade and telecommunications potential for the region. Suitable satellite services are recommended and the financial implications for extended utilization of communications satellites in the Pacific Basin are considered.

Young, E.↗

NASA NTRS1983

Publications of the Jet Propulsion Laboratory 1982

A bibliography of articles concerning topics on the deep space network, data acquisition, telecommunication, and related aerospace studies is presented. A sample of the diverse subjects include, solar energy remote sensing, computer science, Earth resources, astronomy, and satellite communication.

Source record↗

NASA NTRS1984

Determination of the key parameters affecting historic communications satellite trends

Data representing 13 series of commercial communications satellites procured between 1968 and 1982 were analyzed to determine the factors that have contributed to the general reduction over time of the per circuit cost of communications satellites. The model by which the data were analyzed was derived from a general telecommunications application and modified to be more directly applicable for communications satellites. In this model satellite mass, bandwidth-years, and technological change were the variable parameters. A linear, least squares, multiple regression routine was used to obtain the measure of significance of the model. Correlation was measured by coefficient of determination (R super 2) and t-statistic. The results showed that no correlation could be established with satellite mass. Bandwidth-year however, did show a significant correlation. Technological change in the bandwidth-year case was a significant factor in the model. This analysis and the conclusions derived are based on mature technologies, i.e., satellite designs that are evolutions of earlier designs rather than the first of a new generation. The findings, therefore, are appropriate to future satellites only if they are a continuation of design evolution.

Namkoong, D.↗

NASA NTRS1984

Practical Applications of a Space Station

The potential uses of a special station for civil and commercial applications is examined. Five panels of experts representing user-oriented communities, and a sixth panel which dealth with system design considerations, based their studies on the assumption that the station would be a large platform, capable of housing a wide array of diverse instruments, and could be either manned or unmanned. The Earth's Resources Panel dealt with applications of remote sensing for resource assessment. The Earth's Environment Panel dealt with the Earth's atmosphere and its impact on society. The Ocean Operations Panel looked at both science and applications. The Satellite Communications Panel assessed the potential role of a space station in the evolution of commercial telecommunication services up to the year 2000. The Materials Science and Engineering panel focused on the utility of a space station environment for materials processing.

Source record↗

NASA NTRS1984

Prospects for the Voyager extra-planetary and interstellar mission

An advance study has been conducted to examine the trajectory characteristics of Voyager 1 and 2 as they depart from the solar system and traverse interstellar space. A survey of the extraplanetary phase, commencing with completion of the final planetary encounters and ceasing with loss of spacecraft communication, considers the trajectory aspects attendant to a heliospheric investigation and possible sensing of a trans-Neptunian massive body. An analysis of departure telecommunications capability attempts to bound the inevitable time of communication loss. A study of the interstellar phase examines closest approaches of the spacecraft to the sun's stellar neighbours. A covariance analysis is provided to illustrate the statistical effect of stellar state uncertainties on these approaches. In addition to the Voyager spacecraft, data for Pioneers 10 and 11 are provided where appropriate.

Cesarone, R. J.↗

NASA NTRS1984

Lasers, their development, and applications at M.I.T. Lincoln Laboratory

A historical account of the work on lasers at MIT Lincoln Laboratory is presented. Highlighted are the efforts that led to the coinvention of the semiconductor laser and the Laboratory's later role in establishing the feasibility of GaInAsP/InP semiconductor lasers for use in fiber telecommunications at 1.3-1.5 micron wavelengths. Descriptions of other important developments include tunable lead-salt semiconductor and solid-state lasers for spectroscopy and LIDAR applications, respectively, as well as ultrastable CO2 lasers for coherent infrared radar.

Rediker, R. H.↗

NASA NTRS1984

Earth orbiter into planetary orbiter - What's the problem?

A recent series of competitive design studies appears to have yielded positive results about the efficacy of adapting earth-orbiting spacecraft to perform planetary missions. The purpose of this paper is twofold: (1) to show the intrinsic attributes required to adapt an earth orbiter into a Martian orbiter compatible with the scientific requirements, and (2) to show the minimum requisite changes needed to make the adaptation. It is shown that major deficiencies of such conversion for earth-orbiting satellites lie in the not-unexpected inability of its telecommunications system to operate at Martian distances and its lack of an autonomous recovery system from anomalous performance. Since these deficiencies can be overcome without too great a financial or schedule penalty, the study shows that the adaptation can be made cost effectively.

Brodsky, R. F.↗

NASA NTRS1984

Natural radio noise - A mini-review

Natural radio noise in telecommunication systems can be accounted for by the contribution which it makes to antenna noise temperature. Attenuation due to water vapor and oxygen, clouds, and precipitation is accompanied by thermal noise which further degrades the applicable signal-to-noise ratio. Extraterrestrial noise may be of thermal or nonthermal origin and may cover a continuum of frequencies or occur at discrete frequencies. The spectral index n (the exponent giving the variation of noise power density with wavelength) is -2 for a black body and between 0 and -2 for thermal emission in general. The mechanism responsible for much of the extensive nonthermal extraterrestrial noise is synchrotron radiation, characterized by a positive spectral index.

Flock, W. L.↗