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NASA NTRS1983

Test results of the STI GPS time transfer receiver

Global time transfer, or synchronization, between a user clock and USNO UTC time can be performed using the Global Positioning System (GPS), and commercially available time transfer receivers. This paper presents the test results of time transfer using the GPS system and a Stanford Telecommunications, Inc. (STI) Time Transfer System (TTS) Model 502. Tests at the GPS Master Control Site (MCS) in Vandenburg, California and at the United States Naval Observatory (USNO) in Washington, D.C. are described. An overview of GPS, and the STI TTS 502 is presented. A discussion of the time transfer process and test concepts is included.

Hall, D. L.↗

NASA NTRS1983

Telemetry Modulation and Coping

Digital telemetry has supplanted analog telemetry for deep space communications. With digital telemetry, the telecommunications systems design engineer may use error correcting codes. This allows increased error protection at the cost of increased bandwidth. All science telemetry returned from the Voyager and Galileo spacecraft are protected by error correcting codes. Both the modulation and coding of digital telemetry for the deep space channel are considered. The descriptions include relative performance of some competing schemes. However, the treatment given here is, of necessity, cursory. A small class of modulation schemes has proven to be best for the deep space channel. The digital telemetry is either phase-shift-keyed onto a squarewave subcarrier and then phase modulated onto the carrier or the digital telemetry is directly phase modulated onto the carrier.

Kinman, P. W.↗

NASA NTRS1983

Command

The Command System provides the means by which a project controls the activities of its spacecraft from the Earth. An overview of the Multimission Command (MMC) System is presented. The major components within the MMC System are discussed, with emphasis on the telecommunications related implementations. Two versions of the spacecraft command detection system the Viking Heritage command detector and the NASA standard command detector are summarized. The former prevails in the existing flight projects and the latter will likely be adopted by the missions of the near future. The preparation of Design Control Tables for the control of command link performance between Deep Space Stations and the spacecraft is also discussed.

Burow, N. A.↗

NASA NTRS1983

New Directions: 1982-2000

The major objective of the Deep Space Network in the period 1983-2000 is the fulfillment of the extremely diverse telecommunications requirements of the known and anticipated users. Deep space exploration projects will continue to occupy a dominant role, although in the mid-1980s, with the completion of the Networks Consolidation Program, high Earth orbiter projects will become substantial users of the Network. Also playing an increasingly important role in the Network of the next decade will be non-flight projects, such as Geodynamics, Radio Astronomy, Radar Astronomy, and the Search for Extraterrestrial Intelligence (SETI). The major challenge in meeting the primary Network objective of the next decade will be that of providing increased performance as required by users at costs which can be borne by NASA in an environment of limited resources. Emphasis will be on increased commonality, flexibility, and automation to reduce maintenance and operations costs, and lower mission costs.

Renzetti, N. A.↗

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.

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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.

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