• Future Modular Data Handling Concepts for Large Space Platforms

      Thompson, G. P.; ESA/ESTEC (International Foundation for Telemetering, 1979-11)
      With the ever-increasing competition for geostationary orbital positions, designers of applications satellites are looking more and more to the use of large multipurpose platforms to fly simultaneously a variety of payloads. This paper looks at the challenges these platforms provide in the field of data handling for individually launched and docking satellites, and reviews current European concepts and technologies which are being developed to meet these challenges.
    • The LEASAT Communications Satellite

      Dutcher, G. L.; Lankford, J. G.; Hughes Aircraft Company (International Foundation for Telemetering, 1979-11)
      Beginning in 1982 communication services will be provided to the U.S. Navy by a series of UHF communications satellites known as LEASAT. The communications payload will be carried on a new spacecraft bus developed as an optimum bus for space shuttle launches; the program is the first of its kind to take advantage of the full 15 foot shuttle payload bay diameter. Several new spacecraft design concepts are employed in this optimized bus. The communications payload incorporates transponders in the UHF and SHF regimes. Four distinct types of transponders are employed: wideband, narrowband, relay, and fleet broadcast. The functional characteristics of each type is described in detail. The frequency plan leads to a significant potential for passive generation of intermodulation products, and intermodulation considerations are an integral part of the spacecraft design.
    • Super High Bit Rate Recording

      Wood, Tracy G.; Ampex Corporation (International Foundation for Telemetering, 1979-11)
      A radically different magnetic recording approach is proposed to solve the very high density and very high data rate requirements of the 1980's. In direct contrast to the industry's traditional approach of head-per-track longitudinal recording is a multi-track rotary helical recorder using narrow tracks. This technique is described. These narrow tracks, in conjunction with a novel development called "Automatic Scan Tracking" (AST), make possible the development of a family of recorders with data rates up to one (1) gigabits per second with user packing densities of five (5) megabits per square inch and a bit error rate performance better than one (1) part in a million (106) without aid of error detection and correction codes.
    • Decentralized Control for Large Communication Satellites by Model Error Sensitivity Suppression

      Sesak, John R.; Bowman, Robert M.; General Dynamics Convair Division (International Foundation for Telemetering, 1979-11)
      The rapid growth in world demand for satellite telecommunications and the limited number of positions in the geostationary arc are leading inexorably to larger, higher capacity communications satellites. This trend, coupled with the projected weight and volume capability of the Space Transportation System (STS), will lead to satellites in the 80s weighing 5000 kg and measuring 50 to 100 feet across. By the end of the century these figures could increase again by an order of magnitude. Such large, low-density structures tend to have closely spaced, low-frequency dynamic modes. At the same time, multibeam-frequency reuse antennas (MBFRA) projecting narrow-spotbearns require pointing stability within a hundredth of a degree or so. The combination of low structural natural frequency and more stringent pointing requirements imposes the need for an entirely fresh approach to dynamic control of communications satellites. This paper outlines such an approach. A modern optimal control methodology is advanced that provides decentralized modular control for large communication satellites. The fundamental property of the control algorithm is its ability to stabilize certain subsets of vibration modes without disturbing others. This decoupling action allows the control task to be implemented in a modular or building block fashion so that different modal subsets are stabilized by separate controllers. Decentralization according to functional task is also possible such that noninteracting rigid body and elastic body control is achieved. Thus, the technique provides a solution for the problem of rigid body control in the presence of low frequency elastic modes that are in the rigid body controller bandwidth. The design methodology, termed Model Error Sensitivity Suppression (MESS), is a derivative of modern optimal control and estimation theory. Several examples illustrate the capability of the design algorithm.
    • An Overview of TDRSS Ground Station

      Morran, Peter C.; Bebb, Joan E.; TRW DSSG (International Foundation for Telemetering, 1979-11)
    • Intersatellite Link Tracking Antenna Pointing Requirements

      Srinivas, D. N.; COMSAT Laboratories (International Foundation for Telemetering, 1979-11)
      Intersatellite links (ISLs) appear advantageous for future communications satellite systems. This paper considers satellites spaced 10° apart on the geostationary orbit. Based on proposed communications performance goals, it discusses applicable ISL antenna acquisition and tracking system requirements and cites limitations on the initial ISL antenna pointing accuracy and the required size of the antenna scan. Also examined are particular antenna configurations (single or 2-antenna), implementation concepts, and influences on spacecraft subsystems such as structure, power, and thermal considerations.
    • Convolutional Error Detection on an Additive White Gaussian Noise Channel

      King, Maurice A., Jr.; The Aerospace Corporation (International Foundation for Telemetering, 1979-11)
      Concatenated coding schemes involving a convolutional inner code and a block outer code have occasionally been used in communication systems that are very intolerant of errors. In these schemes the vast majority of channel errors are corrected by the convolutional decoder while the block outer code is used to detect convolutional decoder errors. Block code words containing detected errors are erased. Soft decision Viterbi convolutional decoders operate by comparing path metrics and selecting the path with the largest metric (the maximum likelihood path). There is a substantial amount of information in the path metrics that is not used in this pick-thelargest decision. It is proposed that some of this information be used in a probabilistic decoding error detection scheme. Such a detection scheme would obviate the use of the block outer code. The result is a bandwidth savings at the cost of some additional processing of the convolutional code metrics.
    • Fundamentals of Heterodyne Detection in Laser Communications

      Goodwin, Frank E.; Hughes Aircraft Company (International Foundation for Telemetering, 1979-11)
      The use of optical heterodyne detection in a communication system requires a local oscillator laser beam to be coincident with the incoming signal on the detector. After detection, the signal behaves in every way like a classical microwave or radio signal which has been detected with a heterodyne receiver. This discussion of the use of optical heterodyne detection in laser communications thus includes consideration of modulation formats as well as the special geometrical requirements of combining the local oscillator and signal. Modulation formats of interest are amplitude modulation, frequency modulation and phase modulation, and both heterodyne and homodyne detection techniques are considered. The physical and geometric treatment of optical heterodyne detection is given. General equations are derived for the signal to noise ratio of a coherent receiver in terms of the distribution functions of the signal and local oscillator fields and the size of the detector. The most efficient local oscillator field distribution function is when it exactly matches that of the signal field distribution over the detector surface. A special case of interest is when the signal field is an Airy function and the local oscillator field is uniform. This special case is shown to be feasible with a small penalty in heterodyne mixing efficiency. An analysis of the heterodyne NEP includes factors from geometrical mixing efficiency, thermal noise, dark current, and electrical load mismatch. The degree of degradation is then a function of the amount of local oscillator power. Practical limits on heterodyne NEP's are established.
    • Performance Analysis of Noncoherent AGC for Signal Presence Detection and Autotrack Signal Extraction

      Carpenter, Daniel D.; TRW Defense and Space Systems (International Foundation for Telemetering, 1979-11)
      The acquisition of a communication satellite data signal starts with a spatial search for the incoming direction of arrival. As the antenna scans the received signal level builds up as this direction is approached. This level builds up according to the antenna gain pattern. Once detected, this level can be used to determine when the pull-in range is reached. This allows the automatic tracking, or the autotrack system to take over and maintain the pointing control. An AGC control voltage can provide an indication of signal level, gain, and thus the pointing error. A non-coherent AGC can be used to provide both a signal presence indication and tracking error signal, if a single channel autotrack signal with AM or AM-PM modulation is used. This includes five horn and dual mode feed systems.
    • A Microcomputer Interface for Transfer of Data Between Multiple Computer Systems

      Smith, B. L.; Vandenberg Air Force Base (International Foundation for Telemetering, 1979-11)
      An interface was required for transmitting telemetered inertial guidance data from any one of twelve SEL 32/55 computers to an IBM 360-65 and a CDC 3300 computer. A flexible interface was designed to meet this requirement. The interface is comprised of several nested microcomputer systems and a fiber optic data transmission system for accomplishing the control and data transmission functions. A unique approach was used to transmit the data asynchronously and make it appear to be synchronous at the response of the computers receiving the data. A description of the approach and system operation will be discussed.
    • Optimum Digital Data Storage on Magnetic Tape

      Hedeman, W. R., Jr.; Law, E. L.; Pacific Missile Test Center (International Foundation for Telemetering, 1979-11)
      An instrumentation magnetic tape recorder, free of tape drop-outs, wow and flutter, is simulated by filters and a chromatic noise source. At a fixed bit error probability the capacity of the link is measured as a function of rms signal-to-noise ratio for NRZ-L, Manchester and Miller codes. Two operating regions are observed: (1) noise limited at low values of SNR and (2) band limited at high values of SNR. In the noise limited region doubling the data rate requires a 6 dB increase in SNR; in the band limited region an increase of approximately 12 dB is required to produce the same result. The conclusion is that, for baseband recording of digital data, operation should be in the noise limited region slightly below the transition to the band limited region. If SNR margin is available at this operating point more data per square of tape can be stored by increasing the number of tracks rather than increasing the storage per track. The theoretical penalty of 3.5 dB for the Miller code bit detector should, and does, result in a data rate decrease to .67 of the data rate with the NRZ-L code at the same SNR in the noise limited region. For the Manchester code the transition to the band limited region occurs at a lower SNR than for either NRZ-L or Miller codes. It is concluded that the Manchester code would result in approximately the same data storage per square of tape as NRZ-L, and more than Miller, if the number of tracks is doubled.
    • Serial PCM Recording Standard

      Law, E. L.; Hedeman, W. R., Jr.; Pacific Missile Test Center (International Foundation for Telemetering, 1979-11)
      This standard includes recommendations for pre-detection PCM recording, post-detection PCM recording, and serial high density digital recording using IRIG analog wideband recorder/ reproducers. The serial high density digital standard, based on studies conducted at the Pacific Missile Test Center, recommends the BI∅/-L code for packing densities up to 15 kilobits per inch and the randomized NRZ-L code (with 15-stage register length for packing densities up to 25 kilobits per inch. The signals are recorded using bias and the standard IRIG record levels. The minimum recommended reproduce rate (without special electronics) for randomized NRZ-L is 200 kilobits per second.
    • Dual Beam Single Axis Tracking Antenna for Tracking Telemetry Instrumented Airborne Vehicles

      Sullivan, Arthur; Electra Magnetic Processes, Inc. (International Foundation for Telemetering, 1979-11)
      A dual-beam, single-axis, tracking antenna capable of receiving and tracking telemetry data from an instrumented airborne vehicle is described. The dual-beam, single-axis, tracking antenna system consists of both a high-gain and a low-gain antenna positioned by the same antenna pedestal/servo electronics. Automatic switching between the high-gain and the low-gain antennas, based on received signal strength, permits tracking from maximum range (using the high-gain antenna) to close-in nearly overhead passes (using the low-gain antenna) by exploiting the wide-beam characteristics of the low-gain antenna when space losses are at a minimum. The wide beamwidth of the low-gain antenna permits its use as an acquisition aid for the high-gain antenna during initial acquisition, while its wide beamwidth also precludes locking on to a side lobe. The use of only one tracking axis rather than two reduces cost and improves reliability.
    • Millimeter-Wave Technology Overview

      Wiltse, James C.; Georgia Tech (International Foundation for Telemetering, 1979-11)
      Millimeter-wave technology has progressed rapidly during the past several years. A summary is given of the state-of-the-art in components, devices, and techniques and their uses in several system applications. Although present systems activity includes work on radar, guidance, remote sensing, radio astronomy and spectroscopy, the applications to communications are emphasized.
    • Millimeter-Wave Solid State Transmitter Components

      Sun, C.; Hughes Aircraft Company (International Foundation for Telemetering, 1979-11)
      Recent trends in millimeter-wave solid state transmitter components are reviewed. Specifically, the progress of the developments of IMPATT and Gunn Oscillators, Power Combiners, phase and injection locking techniques and upconverters are presented.
    • Solar Power Satellites - The Present and the Future

      Arndt, C. D.; NASA-Johnson Space Center (International Foundation for Telemetering, 1979-11)
      The concept of using large satellites in neosynchronous orbit to collect solar energy for earth use, first proposed in 1968, is being evaluated by the Department of Energy and the National Aeronautics and Space Administration. A reference system has been defined to provide a basis for evaluating alternate technical approaches and for assessing environmental impacts. This reference system is described with emphasis on the microwave subsystems and possible alternatives. Other considerations, including study guidelines, system sizing tradeoffs, mass and cost projections, and environmental factors, are discussed. An outline of a ground-based exploratory development program which could follow the present evaluation study (now scheduled for completion in 1980) and answer key technological issues is given. Several space technology projects as further steps towards developing an SPS system are also discussed.
    • Tunable Millimeter-Wave Communications

      Becker, Stanley; AIL Division of Eaton Corporation (International Foundation for Telemetering, 1979-11)
      A communication link operating at 5 millimeters can be designed to take advantage of the properties of the oxygen absorption band to provide relatively interference free and secure communications. A tunable transmitter and receiver were developed to demonstate the adaptability of such a link to varying propagation and potentially hostile EMI conditions.
    • Millimeter-Wave Receiver Components

      Bernues, F.; Pusateri, P.; Hughes Aircraft Co. (International Foundation for Telemetering, 1979-11)
      This paper presents an overview of the state-of-the-art performance of mm-wave receiver front-end components. Topics covered include filters, diplexers, mixers (broadband and narrowband) and local oscillators (free-running and phase-locked). Examples of mm-wave receiver front-end configurations are given and performance tradeoffs are discussed.
    • A Review of the Public Broadcast Service TV Distribution System and Plans for the National Public Radio System

      Kellow, Robert S.; Rockwell International (International Foundation for Telemetering, 1979-11)
      Nationwide Television Programming for the Public Broadcasting Service is now being carried by the largest integrated network of Earth Stations ever constructed by a single turn-key contractor. The 165 station network, including 5 remote origination transmit terminals, was completed significantly ahead of a schedule established two years before. Such an accomplishment required carefully orchestrated efforts between customer and contractor in the areas of system and equipment design and qualification, site selection and design, frequency coordination, equipment scheduling, on site construction, site installation and test effort mobilization. Unusual and unexpected constraints were often encountered, requiring resourceful and innovative solutions. Performance records since early 1978 when initial operations began indicate the reliability, availability and cost improvement goals of the system have been exceeded by a significant margin. A similar system for the National Public Radio, involving 205 stations (15 with transmit capability) is currently in the early stages of implementation.
    • The Application of Frequency Offset Advantage (FOA) in Frequency Coordination

      Raghavan, Srini; Armes, Jerry; Spectrum Analysis & Frequency Engineering (International Foundation for Telemetering, 1979-11)
      A major telecommunications growth area at this time is narrowband digital transmissions via satellites. With the availability of low cost 5 and 10 meter earth stations, and readily available digital ground equipment, this trend can be expected to continue for some time. With the degree of frequency congestion which exists currently in the 6 GHz band, the frequency coordination of these earth stations will become more and more difficult. Since the data rate is generally 56 KBPS or 1.544 MBPS, the satellite uplink carrier frequency is often selected to give a degree of isolation from standard frequency plans used by the terrestrial common carriers. The amount of offset advantage in db to be conceded from a given frequency separation between satellite and terrestrial carriers is a matter of controversy however. This paper describes a computer program written to provide the necessary calculations, the underlying models, and results in the form of parametric curves which can be used directly to obtain the offset advantage for a given carrier separation.