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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Environmental projects. Volume 12: Friable asbestos abatement, GDSCC

The Goldstone Deep Space Communications Complex (GDSCC) is part of the NASA Deep Space Network, one of the world's largest and most sensitive scientific telecommunications and radio navigation networks. Activities at the GDSCC are carried out in support of six large parabolic dish antennas. These activities may give rise to a variety of environmental hazards, particularly the danger of exposure of GDSCC personnel to asbestos fibers that have been shown to be responsible for such serious ailments as asbestosis, lung cancer, and mesothelioma. Asbestos-containing materials (ACM's) were used in the construction of many of the approximately 100 buildings and structures that were built at the GDSCC during a 30-year period from the 1950s through 1980s. The friable asbestos-abatement program at the GDSCC is presented which consists of text, illustrations, and tables that describe the friable asbestos abatement carried out at the GDSCC from December 21, 1988 through May 11, 1989.

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NASA NTRS1990

Thermal balance testing of the Anik-E spacecraft

Spar Aerospace, Ltd. of Canada has recently completed the first of two infrared thermal balance/thermal vacuum tests on Canada's next generation of telecommunication satellites: Anik-E. Anik-E is a two spacecraft program using a three axis stabilized GE 5000 series bus as the vehicle for its payload. The infrared test setup consists of the mechanical hardware required to support the spacecraft within the thermal vacuum chamber and the infrared rig which supports the spacecraft. Spar developed a software package which calculated the lamp positions to provide the necessary uniform heat flux, based on the required heat inputs on the various isothermal zones of the spacecraft for the different phases of the tests. Infrared heat sensors, radiometers, were installed on the spacecraft surfaces. These were connected to the facility data processing system and continually monitored the flux absorbed by the various spacecraft surfaces. The test set up had distinct advantages. It enabled testing to progress directly from the thermal balance to thermal vacuum. Waveguide runs were installed for the communications portion of the testing prior to pumpdown. This precluded the requirement to return to ambient to reconfigure the setup.

Golob, Alex↗
NASA NTRS1991

SHARP: Automated monitoring of spacecraft health and status

Briefly discussed here are the spacecraft and ground systems monitoring process at the Jet Propulsion Laboratory (JPL). Some of the difficulties associated with the existing technology used in mission operations are highlighted. A new automated system based on artificial intelligence technology is described which seeks to overcome many of these limitations. The system, called the Spacecraft Health Automated Reasoning Prototype (SHARP), is designed to automate health and status analysis for multi-mission spacecraft and ground data systems operations. The system has proved to be effective for detecting and analyzing potential spacecraft and ground systems problems by performing real-time analysis of spacecraft and ground data systems engineering telemetry. Telecommunications link analysis of the Voyager 2 spacecraft was the initial focus for evaluation of the system in real-time operations during the Voyager spacecraft encounter with Neptune in August 1989.

Atkinson, David J.↗
NASA NTRS1991

Expert operator's associate: A knowledge based system for spacecraft control

The Expert Operator's Associate (EOA) project is presented which studies the applicability of expert systems for day-to-day space operations. A prototype expert system is developed, which operates on-line with an existing spacecraft control system at the European Space Operations Centre, and functions as an 'operator's assistant' in controlling satellites. The prototype is demonstrated using an existing real-time simulation model of the MARECS-B2 telecommunication satellite. By developing a prototype system, the extent to which reliability and effectivens of operations can be enhanced by AI based support is examined. In addition the study examines the questions of acquisition and representation of the 'knowledge' for such systems, and the feasibility of 'migration' of some (currently) ground-based functions into future spaceborne autonomous systems.

Nielsen, Mogens↗
NASA NTRS1990

Time and frequency comparisons in Europe by means of ECS 5 geostationary satellite

A time synchronization experiment between some European laboratories using the passive television method applied to the signals broadcasted by Eutelsat I-F5 telecommunication satellite was completed in 1990. The results obtained in the last period, when also range measurements from a Telespazio ground station were performed, are analyzed to evaluate the accuracy level of the time comparisons corrected for the effect of the satellite movement with position data obtained either from the European Space Agency (ESA) or from orbit determination with range data entered into GEODYN program of NASA/GSFC.

Cordara, Franco↗
NASA NTRS1990

Application of high stability oscillators to radio science experiments using deep space probes

The microwave telecommunication links between the earth and deep space probes have long been used to conduct radio science experiments which take advantage of the phase coherency and stability of these links. These experiments measure changes in the phase delay of the signals to infer electrical, magnetic and gravitational properties of the solar system environment and beyond through which the spacecraft and radio signals pass. The precision oscillators, from which the phase of the microwave signals are derived, play a key role in the stability of these links and therefore the sensitivity of these measurements. These experiments have become a driving force behind recent and future improvements in the Deep Space Network and spacecraft oscillators and frequency and time distribution systems. Three such experiments which are key to these improvements are briefly discussed and relationship between their sensitivity and the signal phase stability is described. The first is the remote sensing of planetary atmospheres by occultation in which the radio signal passes through the atmosphere and is refracted causing the signal pathlength to change from which the pressure and the temperature of the atmosphere can be derived. The second experiment is determination of the opacity of planetary rings by passage of the radio signals through the rings. The third experiment is the research for very low frequency gravitational radiation. The fractional frequency variation of the signal is comparable to the spatial strain amplitude the system is capable of detecting. A summary of past results and future possibilities for these experiments are presented.

Kursinski, Emil R.↗
NASA NTRS1990

International two-way satellite time transfers using INTELSAT space segment and small Earth stations

The satellite operated by the International Telecommunications Satellite Organization (INTELSAT) provides new and unique capabilities for the coordinates of international time scales on a world wide basis using the two-way technique. A network of coordinated clocks using small earth stations collocated with the scales is possible. Antennas as small as 1.8 m at K-band and 3 m at C-band transmitting powers of less than 1 W will provide signals with time jitters of less than 1 ns existing spread spectrum modems. One way time broadcasting is also possible, under the INTELSAT INTELNET system, possibly using existing international data distribution (press and financial) systems that are already operating spread spectrum systems. The technical details of the satellite and requirements on satellite earth stations are given. The resources required for a regular operational international time transfer service are analyzed with respect to the existing international digital service offerings of the INTELSAT Business Service (IBS) and INTELNET. Coverage areas, typical link budgets, and a summary of previous domestic and international work using this technique are provided. Administrative procedures for gaining access to the space segment are outlined. Contact information for local INTELSAT signatories is listed.

Veenstra, Lester B.↗
NASA NTRS1991

Ka-band MMIC microstrip array for high rate communications

In a recent technology assessment of alternative communication systems for the space exploration initiative (SEI), Ka-band (18 to 40 GHz) communication technology was identified to meet the mission requirements of telecommunication, navigation, and information management. Compared to the lower frequency bands, Ka-band antennas offer higher gain and broader bandwidths; thus, they are more suitable for high data rate communications. Over the years, NASA has played an important role in monolithic microwave integrated circuit (MMIC) phased array technology development, and currently, has an ongoing contract with Texas Instrument (TI) to develop a modular Ka-band MMIC microstrip subarray (NAS3-25718). The TI contract emphasizes MMIC integration technology development and stipulates using existing MMIC devices to minimize the array development cost. The objective of this paper is to present array component technologies and integration techniques used to construct the subarray modules.

Lee, R. Q.↗
NASA NTRS1990

The NASA radiowave propagation program

The objectives of the NASA radiowave Propagation Program are to enable new satellite communication applications and to enhance existing satellite communication networks. These objectives are achieved by supporting radio wave propagation studies and disseminating the study results in a timely fashion. Studies initiated by this program in the 1980s enabled the infant concept of conducting mobile communications via satellite to reach a state of relative maturity in 1990. The program also supported the satellite communications community by publishing and revising two handbooks dealing with radio wave propagation effects for frequencies below and above 10 GHz, respectively. The program has served the international community through its support of the International Telecommunications Union. It supports state of the art work at universities. Currently, the program is focusing on the Advanced Communications Technology Satellite (ACTS) and its propagation needs. An overview of the program's involvement in the ACTS project is given.

Davarian, Faramaz↗
NASA NTRS1990

Publications of the Jet Propulsion Laboratory 1989

This bibliography describes and indexes by primary author the externally distributed technical reporting, released during 1989, that resulted from scientific and engineering work performed, or managed, by JPL. Three classes of publications are included: JPL publications in which the information is complete for a specific accomplishment; articles from the quarterly Telecommunications and Data Acquisition (TDA) Progress Report; and articles published in the open literature.

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NASA NTRS1991

Millimeter wavelength communications applications for the SEI

The potentially complex missions of the Space Exploration Initiative (SEI) require advanced lunar communications, navigation, and information systems to provide voice, data, and image transmissions. The objectives here are to determine which SEI telecommunications applications will benefit from millimeter wave technology, assess the state of the art in millimeter wave technology, and describe the technology development shortfalls with respect to potential mission time frames. The assumptions for the analysis as well as other non-performance related issues are also presented.

Ponchak, Denise S.↗
NASA NTRS1990

Magellan space flight operations

This paper describes the Magellan spacecraft designed to collect information from the surface of Venus while orbiting this planet. Special attention is given to the attitude and articulation control of the spacecraft; the command, data, and data storage; the thermal control; and instrumentation. The operations at Venus, which will include Venus orbit insertion and in-orbit checkout and to both routine and nonroutine (at a period when Venus will be in superior conjunction, and the solar plasma will drive Magellan's telecommunications signal-to-noise ratio to a very high value) mapping of the surface, are discussed. Also discussed are operations on earth, carried out by the new Space Flight Operations Control Center.

Doody, Dave↗
NASA NTRS1990

Mars global network mission

The status of a program aimed at placing a global network of small surface landers on Mars for direct surface and subsurface measurements is reviewed. A possible baseline mission concept to establish a global network is discussed with particular reference to mission and system requirements, lander entry design considerations, and orbit design. The principal lander subsystems are described, including attitude control, power, command and data handling, telecommunications, and thermal subsystems.

Mostert, R. N.↗
NASA NTRS1990

A technology assessment of alternative communications systems for the space exploration initiative

Telecommunications, Navigation, and Information Management (TNIM) services are vital to accomplish the ambitious goals of the Space Exploration Initiative (SEI). A technology assessment is provided for four alternative lunar and Mars operational TNIM systems based on detailed communications link analyses. The four alternative systems range from a minimum to a fully enhanced capability and use frequencies from S-band, through ka-band, and up to optical wavelengths. Included are technology development schedules as they relate to present SEI mission architecture time frames.

Ponchak, Denise S.↗
NASA NTRS1990

Telemetry advances in data compression and channel coding

Addressed in this paper is the dependence of telecommunication channel, forward error correcting coding and source data compression coding on integrated circuit technology. Emphasis is placed on real time high speed Reed Solomon (RS) decoding using full custom VLSI technology. Performance curves of NASA's standard channel coder and a proposed standard lossless data compression coder are presented.

Miller, Warner H.↗
NASA NTRS1990

The Tracking and Data Relay Satellite System - The next decade

As currently envisioned, NASA's Tracking and Data Relay Satellite System (TDRSS) will support the tracking and telecommunications requirements of LEO user satellites until the late 1990s, when existing TDRSS satellites will reach the end of their service lives. Spacecraft replacement is conceived as inseparable from network expansion for the accommodation of user population growth and the improvement of user services. The objective is to achieve a cost-effective/low-risk transition from TDRSS to Advanced TDRSS without interruption of user support. Attention is presently given to Advanced TDRSS architectural candidates studied and the choices which have emerged through technical tradeoff assessments.

Guion, William S.↗
NASA NTRS1990

Observed mid-to-high latitude interchange of atmospheric angular momentum and some implications

Graphic illustration of midlatitude interchange of atmospheric angular momentum between distant regions is presented. An examination is conducted of the global distribution of atmospheric angular momentum during 1977-1978 and 1982-1983 in order to identify evidence of prominent short-term interchanges of relavitive atmospheric angular momentum between mid and high latitude zones in both hemispheres. Thirty-day detrended angular momentum time series, prepared from the NMC global zonal wind data, are examined in latitude bands. The results confirm that momentum can be selectively redistributed between tropical, temperate, and high latitudes in patterns indicative of the development and dissipation of interacting regions, described variously in studies on the index cycle, seesaws, and telecommunications.

Taylor, H. A., Jr.↗
NASA NTRS1990

The Cambridge encyclopedia of space (revised edition)

A comprehensive and intensively illustrated development history is presented for spaceflight, ranging over its basic concepts' speculative and fictional origins, the historical roots of rocket-related technologies, and the scientific accomplishments of earth orbit and interplanetary missions to date. Attention is given to propulsion systems, spaceflight launch centers, satellite systems, and solar system exploration by the U.S. and the Soviet Union. Current space-related activities encompass the meteorology, remote sensing, telecommunications and direct broadcasting, and navigation functions of unmanned satellites, as well as such manned spacecraft roles as medical and materials science research. The military uses of space, and increasingly important space industrialization concepts, are discussed as well.

D'Allest, Frederic↗