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At least 451 records · Page 25

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NASA NTRS1971

Communication system modeling

This report presents the results of work on communications systems modeling and covers three different areas of modeling. The first of these deals with the modeling of signals in communication systems in the frequency domain and the calculation of spectra for various modulations. These techniques are applied in determining the frequency spectra produced by a unified carrier system, the down-link portion of the Command and Communications System (CCS). The second modeling area covers the modeling of portions of a communication system on a block basis. A detailed analysis and modeling effort based on control theory is presented along with its application to modeling of the automatic frequency control system of an FM transmitter. A third topic discussed is a method for approximate modeling of stiff systems using state variable techniques.

Holland, L. D.↗

NASA NTRS1972

Communications systems checkout study

The results and conclusions of an engineering study of Space Station communications subsystem checkout are reported. The primary purpose of the study is to recommend specific guidelines and constraints for the design and utilization of the communications subsystem leading to a practical and effective means of onboard checkout implementation. Major study objectives are as follows: (1) identify candidate communications subsystem checkout concepts, (2) determine implementation impacts of feasible concepts, (3) evaluate practicality and effectiveness of alternative concepts, (4) propose baseline modifications to accommodate preferred concepts, and (5) recommend areas for additional investigation. In addition, study results are interpreted, where appropriate, in terms of their applicability to checkout of Shuttle-Orbiter communications subsystem.

Ginter, W. G.↗

NASA NTRS1972

Apollo experience report: Communications system flight evaluation and verification

Flight tests of the synergetic operation of the spacecraft and earth based communications equipment were accomplished during Apollo missions AS-202 through Apollo 12. The primary goals of these tests were to verify that the communications system would adequately support lunar landing missions and to establish the inflight communications system performance characteristics. To attain these goals, a communications system flight verification and evaluation team was established. The concept of the team operations, the evolution of the evaluation processes, synopses of the team activities associated with each mission, and major conclusions and recommendations resulting from the performance evaluation are represented.

Travis, D.↗

NASA NTRS1972

Apollo experience report: Lunar module communications system

The development of the lunar module communications system is traced from the initial concept to the operational system used on manned lunar missions. The problems encountered during the development, the corrective actions taken, and recommendations for similar equipment in future programs are included. The system was designed to provide communications between the lunar module and the manned space flight network, between the lunar module and the command and service module, and between the lunar module and the extravehicular crewmen. The system provided the equipment necessary for voice, telemetry, and television communications; ranging information; and various communications links.

Dietz, R. H.↗

NASA NTRS1972

Study of optimum methods of optical communication

Optimum methods of optical communication accounting for the effects of the turbulent atmosphere and quantum mechanics, both by the semi-classical method and the full-fledged quantum theoretical model are described. A concerted effort to apply the techniques of communication theory to the novel problems of optical communication by a careful study of realistic models and their statistical descriptions, the finding of appropriate optimum structures and the calculation of their performance and, insofar as possible, comparing them to conventional and other suboptimal systems are discussed. In this unified way the bounds on performance and the structure of optimum communication systems for transmission of information, imaging, tracking, and estimation can be determined for optical channels.

Harger, R. O.↗

NASA NTRS1972

A digital simulation of message traffic for natural disaster warning communications satellite

Various types of weather communications are required to alert industries and the general public about the impending occurrence of tornados, hurricanes, snowstorms, floods, etc. A natural disaster warning satellite system has been proposed for meeting the communications requirements of the National Oceanic and Atmospheric Administration. Message traffic for a communications satellite was simulated with a digital computer in order to determine the number of communications channels to meet system requirements. Poisson inputs are used for arrivals and an exponential distribution is used for service.

Hein, G. F.↗

NASA NTRS1972

A high-power communications technology satellite for the 12 and 14 GHz bands.

Description of the mission, subsystems and communication capabilities of a joint Communications Technology Satellite (CTS) scheduled for launch in 1975 by the Canadian Department of Communications in cooperation with NASA. The principal objectives of the mission are TV transmission at 12 GHz to low-cost ground terminals, up-link TV transmission at 14 GHz transportable terminals, and flight tests of spacecraft subsystems and components for future communications satellites. The major advanced spacecraft subsystems are a novel superefficiency TWT design, a 0.4 mlb Mercury Bombardment ion engine for north-south station keeping, a 3-axis stabilization system to maintain a high antenna boresight pointing accuracy, a liquid metal slip ring experiment, and a lightweight extendible solar array with an initial power output greater than 1 kW.

Franklin, C. A.↗

NASA NTRS1972

Employee Communication at the NASA Langley Research Center

The means of employee communication at the NASA Langley Research Center are reported, and their effectiveness evaluated. The history, purpose, and structure of the organization as well as the employee educational background and salary status are discussed. Some of the approaches used by Langley Research Center management in communicating with their men are addressed and compared with recommendations of experts in employee communication. The results of personal interviews involving both employee and management assessment of management-employee communication are presented and evaluated. Employees need a great deal more recommunication from management providing rationale behind the cancellation of existing projects or the disapproval of proposed research projects. Also NASA management needs to establish a policy and guidelines for the rapid and simultaneous dissemination of all non-restricted information to employees during organizational activities having potential adverse effects on large numbers of personnel. Finally some improvements should be made in employee orientation procedures.

Bendura, R. J.↗

NASA NTRS1972

The pseudonoise test set: Communication system's performance evaluation based upon RMS error testing

A pseudonoise (PN) test set was built to provide a relatively easy means of accurately determining the end-to-end rms error introduced by a communication system when subjected to wideband data. It utilizes a filtered pseudorandom sequence generator as a wideband data source, providing a convenient means for digitally delaying the input reference signal for comparison with the distorted test communication system output. In addition to providing a means to measure the end-to-end rms error and the average delay of a communication system, the PN test set also provides a means to determine the tested system's impulse response and correlation function. The theory of PN testing is discussed in detail along with the most difficult aspects of implementation, the building of matched filter pairs. Both analytical and empirical results are reported which support the contentions that this is an accurate and practical way to acquire figures of merit for complete communication systems.

Wallace, G. R.↗

NASA NTRS1972

Satellite communication and navigation for mobile users

Efforts made to utilize space technology for solving communication and navigation problems faced by mobile users in earth orientated situations are outlined. Applications include transoceanic airline communications, reliable long range ship-shore communications, emergency communications in regions with rough terrain, and military operations.

Bernstein, S. L.↗

NASA NTRS1972

A new device for communication systems

A communication device and modulation capability were developed for the transmission of digital data or voices from point to point. This device is a fast-switching phase coherent frequency synthesizer. When this synthesizer is appropriately incorporated in a communication system it can provide interference resistance, multiple-user capability, user identification, ranging, navigation, Doppler correction, and digitized communication (voice and data). The application of this device to aircraft/airport complex and law enforcement communications is discussed.

Beck, R. R.↗

NASA NTRS1973

Technology forecasting for space communication

A study was conducted to determine techniques for application to space communication. The subjects considered are as follows: (1) optical communication systems, (2) laser communications for data acquisition networks, (3) spacecraft data rate requirements, (4) telemetry, command, and data handling, (5) spacecraft tracking and data network antenna and preamplifier cost tradeoff study, and (6) spacecraft communication terminal evaluation.

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NASA NTRS1974

MSFC Skylab instrumentation and communication system mission evaluation

An evaluation of the in-orbit performance of the instrumentation and communications systems installed on Skylab is presented. Performance is compared with functional requirements and the fidelity of communications. In-orbit performance includes processing engineering, scientific, experiment, and biomedical data, implementing ground-generated commands, audio and video communication, generating rendezvous ranging information, and radio frequency transmission and reception. A history of the system evolution based on the functional requirements and a physical description of the launch configuration is included. The report affirms that the instrumentation and communication system satisfied all imposed requirements.

Adair, B. M.↗

NASA NTRS1973

The effect of communications and traffic situation displays on pilots awareness of traffic in the terminal area

The Air Traffic Control (ATC) system is evolving under a general plan specified by the Federal Aviation Administration. Among the developments being considered is the Discrete Address Beacon System (DABS). The use of this system, although relieving congestion on the communications frequencies, would eliminate information about other aircraft because the party line communications now in use would be lost. One alternative to restore this lost information is an Airborne Traffic Situation Display (TSD). Experienced airline and military pilots participated in a factorial design to evaluate two types of communication (discrete address, party line) and two types of displays (TSD, no TSD). A stop-action quiz was used to evaluate their knowledge of other aircrafts' position, altitude, speed, heading, rate of climb, identity, and landing sequence number. Significant differences between conditions were detected, primarily in the position variables. Workload, as measured by a spare capacity side-task, showed a main effect of displays and a significant interaction between displays and communications. The data are summarized by plotting each display/communication condition configuration in the plane defined by information and workload index. A limited number of blunders by other aircraft were included in the simulations with a significant, but not entirely satisfactory, improvement in blunder detection attributed to the TSD.

Melanson, D.↗

NASA NTRS1975

Alternative communication network designs for an operational Plato 4 CAI system

The cost of alternative communications networks for the dissemination of PLATO IV computer-aided instruction (CAI) was studied. Four communication techniques are compared: leased telephone lines, satellite communication, UHF TV, and low-power microwave radio. For each network design, costs per student contact hour are computed. These costs are derived as functions of student population density, a parameter which can be calculated from census data for one potential market for CAI, the public primary and secondary schools. Calculating costs in this way allows one to determine which of the four communications alternatives can serve this market least expensively for any given area in the U.S. The analysis indicates that radio distribution techniques are cost optimum over a wide range of conditions.

Mobley, R. E., Jr.↗

NASA NTRS1975

A review of the theory of interstellar communication

The probability is analyzed that intelligent civilizations capable of interstellar communication exist in the galaxy. Drake's (1960) equation for the prevalence of communicative civilization is used in the calculations, and attempts are made to place limits on the search range that must be covered to contact other civilizations, the longevity of the communicative phase of such civilizations, and the possible number of two-way exchanges between civilizations in contact with each other. The minimum estimates indicate that some 100,000 civilizations probably coexist within several tens of astronomical units of each other and that some 1,000,000 probably coexist within 10 light years of each other. Attempts to detect coherent signals characteristic of intelligent life are briefly noted, including Projects Ozma and Cyclops as well as some Soviet attempts. Recently proposed American and Soviet programs for interstellar communication are outlined.

Billingham, J.↗

NASA NTRS1975

Some proposed experiments with the Communications Technology Satellite

The satellite (CTS) is tentatively scheduled to be launched in January 1976. It will be available for educational and societal experimentation early in 1977. This paper will outline some of the educational experiments involving the CTS. The major object of the experiments is to assess the communications and educational implications of the CTS in northern Ontario; the existing communications facilities for this region of approximately 725,000 sq km (inhabited largely by native people) are extremely limited. It is expected to assess the extent to which: (1) a satellite communications system might resolve the communications deficiency, (2) the native people will use the experimental facility, and (3) health and general educational programs, especially utilizing the interactive mode, will be viable.

Porter, A.↗

NASA NTRS1976

Communications technology satellite

A description of the Communications Technology Satellite (CTS), its planned orbit, its experiments, and associated ground facilities was given. The communication experiments, to be carried out by a variety of groups in both the United States and Canada, include tele-education, tele-medicine, community interaction, data communications and broadcasting. A historical summary of communications satellite development was also included.

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