• Computer Controlled Testing of Telemetry Ground Stations

      Law, Eugene L.; Pacific Missile Test Center (International Foundation for Telemetering, 1978-11)
      The testing of telemetry ground stations by manual methods can be very time consuming. The test time can be reduced by using an automated test system. A minicomputer controlled test system is described and is shown to provide accurate, repeatable results and to reduce the test time to about one-fifth of the manual test time.
    • A Concept for a Transparent Data Acquisition and Distribution System for Spaceflight Applications

      Greene, Edward P.; NASA/Goddard Space Flight Center (International Foundation for Telemetering, 1978-11)
      The emergence of "smart" sensors onboard space missions is forcing a reexamination of the procedures by which NASA acquires, multiplexes, transmits, annotates, and distributes sensor data to the user community. Increasingly we find that "smart" sensors are being planned for future space missions which will search for specific unusual phenomena and, when present, record these phenomena in great detail. This gives rise to the need for a widely varying bandwidth requirement from each instrument in response to the occurrence of phenomena that cannot be anticipated in advance. An asynchronously multiplexed packet telemetry concept is described which, within broad limits, permits instruments to acquire and transmit information at the rate appropriate for the experimental phenomena being observed. Data from a single instrument, along with the necessary ancillary data (typically time, position, and attitude), will be assembled into self-contained packets and will be subsequently transmitted over various communications links (i.e., space telemetry channel, ground communications circuits, etc.) to the experimenter's facility in near real time. Reliable error control coding will be included in each link transmission to protect the integrity of the data packets. A major objective is to make the entire data acquisition and distribution process completely transparent to the experimenter in the sense that the output terminal of the distribution system will be physically, logically, and electrically identical to that of the experiment output channel. To provide greater inter-mission portability of instruments and to reduce the instrument interfacing costs, the emerging national and international telecommunications standards (ADCCP/HDLC/SDLC, X.25, etc.) will be utilized as the instrument interface standards wherever practical. Except for the time delay imposed by propagation and nominal queueing considerations, the experimenters will observe an interface identical to that which would occur if the instrument were physically located at their facilities.
    • Considerations in AJ System Development, Operation and Definitions

      Goldman, H. B.; Hughes Aircraft Company (International Foundation for Telemetering, 1978-11)
      The conventional communication system is designed to work over a worst-case propagation environment with sufficient performance so that the probability of mission success is cost-effectively achieved. Conventional systems have been in a state of evolution and refinement since the early part of the 20th century. Their anomalies are well known. The jam-resistant communications system, however, with additional emphasis on low probability of intercept and exploitation (LPI, LPE) present a whole new list of uncertainties that affect deployment, operation and definitions of what AJ and LPI are in terms of performance against propagation anomalies, the jammer and the intercept system threat.
    • Correlation Tracking for a Planetary Pointing and Tracking System

      Assefi, Touraj; California Institute of Technology (International Foundation for Telemetering, 1978-11)
      The Planetary Pointing and Tracking System (PPTS) being developed at Jet Propulsion Laboratory is intended to provide precision pointing for science platforms on future autonomous planetary spacecraft. Future missions will impose very stringent platform pointing requirements due to low light levels and very high ground tracking rates. An integral part of PPTS is the correlation tracker, which has the potential to revolutionize autonomous guidance. The tracker provides two-axis pointing information concerning the position of the target body. It consists of a large-area charge-coupled device (CCD) imager and a microprocessor to control the CCD scanning function and data processing. The correlation tracker has three modes of operation: track, acquire and map. The track mode performs precision tracking of a target object. This is initiated after a target has been acquired. The map mode determes the centroidal coordinates, magnitude and size of bodies within the optical field of view. To improve precision pointing, various power spectra, such as shot noise and dark current, are derived. The probability of acquiring a target body is a function of signal-to-noise ratio and the noise equivalent angle. Derivations illustrating the application of these concepts are given. A discussion of mission analysis with the Uranian system as a representative example is provided.
    • Data Asymmetry Analysis for Space Shuttle Communications Link

      Simon, M. K.; Tu, K.; Batson, B. H.; Jet Propulsion Lab; Lockheed Electronics Company; NASA Lyndon B. Johnson Space Center (International Foundation for Telemetering, 1978-11)
      This paper systematically analyzes the signal-to-noise ratio degradations which can potentially occur due to data asymmetry in digital transmission systems. Suitable asymmetry models are developed and error probability performance for two types of data detectors (integrate-and-dump filter, and gated-integrate-and-dump filter) is derived. Although this work was done to resolve problems being encountered in the Shuttle Kuband return link design, specifically for the 50 Mbps convolutionally encoded channel (NRZ format), generalizations are made which provide results for other cases of interest (other Ku-band return link channels, or other systems entirely). This paper therefore considers Manchester data formats (in addition to NRZ) and uncoded transmission (in addition to convolutionally coded transmission).
    • A Data Formatter and Control Unit for the SEASAT-A Synthetic Aperture Radar Ground Support Network

      Elder, B. M.; Oden, S. F.; Buchholz, D. E.; John Hopkins University (International Foundation for Telemetering, 1978-11)
      The Applied Physics Laboratory has developed special ground station equipment for NASA that recovers the video radar returns and timing reference signals from the SEASAT-A spacecraft synthetic aperture radar (SAR), digitizes the video data, and combines video and engineering data into a format compatible with a high-speed digital tape recorder. This paper describes the design and implementation of the SAR data formatter, which performs the video digitizing and data formatting functions for tape recording, and the formatter control unit, which uses stored commands from the station control center to direct operation of a special downlink demodulator during satellite passes.
    • Defense Satellite Communication System

      Donovan, Andrew R., Jr.; Def. Comm. Eng. Center (International Foundation for Telemetering, 1978-11)
      This paper will present an overview of the Defense Satellite Communication System (DSCS) with emphasis on its current capabilities and future planning. The DSCS is DoD's strategic satellite communications system providing unique and vital worldwide service to the National Command Authorities (NCAs), Worldwide Military Command and Control System (WWNCCS), the White House Communications Agency (WHCA), the Defense Communication System, NATO-Allied nations and other special users. The DSCS will soon expand to encompass the Army/Air Force Ground Mobile Forces SHF-Tactical applications and the Advanced Airborne Command Post (AABNCP).
    • Design of the DSCS III Software for Multiple Beam Antenna Control and Pattern Analysis

      Laurelli, Carmen Joseph, III; Miller, Scott F.; General Electric Company (International Foundation for Telemetering, 1978-11)
      This report describes the software capabilities developed by the General Electric Company Space Division for the real-time command, control and analysis of the multiple beam antennas (MBA) for the Defense Satellite Communication System Phase III (DSCS III). A broad description is provided which traces the generation of MBA commands by the Communications Configuration Program (CCP) through the transmission of the command data to the spacecraft and its subsequent command verification by means of telemetry data using portions of the real-time Telemetry and Command Program (TCP). A detailed description is provided of the related portions of the TCP and the CCP which are utilized to analyze requirements and generate control information for the two nineteen beam transmit MBA's and the sixty-one beam receive MBA. CCP is the key element which provides the operator the capability to merge the requirements of the user community and the MBA characteristics to provide an optimal user gain distribution. Block diagrams are employed to depict the data flow through the DSCS system and the interaction of the operator with the software. Samples of the graphic display capability of the CCP software are included to demonstrate the flexibility afforded the operator as an analysis tool for operations planning. Comparison of actual range measured antenna patterns with CCP generated patterns demonstrates the overall accuracy of simulating the receive and transmit MBA's. The CCP software is a multifaceted computer program which forms an integral part of the planning, analysis and command determination function when interfaced with the operator and analyst at the operational DSCS III ground stations.
    • Detection of Moving Optical Objects

      Burczewski, R. M.; Mohanty, N. C.; Rockwell International (International Foundation for Telemetering, 1978-11)
      This paper deals with the detection of a moving optical object in the presence of background, sensor or star and other noise. The algorithms are derived to estimate noise statistics, and its extrapolation, signal statistics, and the criterion for detecting the moving objects. The performance of the algorithm has also been derived.
    • A Distributed Microcomputer Telemetry System for Spacecraft Applications

      Lord, Donald D.; California Institute of Technology (International Foundation for Telemetering, 1978-11)
      Three significant difficulties exist in using a set of microcomputers (or any computers) as an integral part of an on-board telemetry system. The difficulties arise in providing for: a) the precise timing required by a telemetry system, including accurate time-tagging of data samples; b) the interconnection of several (many) computers in a controlled, organized, understandable manner; c) the capability to allow computer controlled science instruments to operate relatively autonomously with minimum software interactions with other computers. The three items listed above are desirable features and are achievable with proper telemetry system architecture designs. This paper will address each of the three items and present an architecture that provides the desired features.
    • A Distributed Shortest - Path Algorithm

      Humblet, Pierre A.; Massachusetts Institute of Technology (International Foundation for Telemetering, 1978-11)
      The problem of routing in a data network is often treated by assigning traffic dependent lengths to the links of the network and routing traffic from node i to node j along the shortest path from i to j . We present a distributed algorithm in which the nodes cooperate to find all shortest paths. It runs asynchronously in every node and does not require the network topology, or even the number of nodes in the network, to be known a priori by the nodes.
    • DSCS III Communications Satellite Performance

      Weinrich, A. W.; Horvath, A.; Harcar, A.; GE Space Division (International Foundation for Telemetering, 1978-11)
      The DSCS III satellite is the third generation space segment of the Defense Satellite Communication System. This satellite is unique compared to earlier DSCS satellites in that it has a six channel transponder designed for both FDMA and TDMA operation and realtime commendable uplink and downlink multibeam antennas. The antenna suit is designed to provide uplink anti-jam discrimination and selective coverage with a 61 element multibeam antenna 45 inches in diameter. The transmit antenna suit includes two 19 element multibeam antennas 28 inches in diameter that provide flexible selective coverage to maximize EIRP allocation and hence optimize satellite traffic thruput. The flexibility in antenna coverage and antenna - transponder interconnectivity allows the system operator to respond rapidly to wide variations in the deployment of forces precipitated by changing world events. This paper describes the overall DSCS III system in which the satellite functions and presents typical antennas patterns obtained with the DSCS III hardware built during the development phase of the program. In addition, overall program status is described and critical hardware elements are shown.
    • An Efficient Multichannel FFT Demodulator

      von der Embse, U. A.; Austin, M. C.; Hughes Aircraft Company (International Foundation for Telemetering, 1978-11)
      A multichannel binary FSK demodulator for spaceborne application has been implemented using an efficient preweighted and thinned fast Fourier transform (FFT) algorithm. Theory, configuration, and performance are described and compared with the analog unit which performs the same functions. Being able to perform the first base 16 pass with add-only operations following preweighting, provided the complexity reduction which made it feasible to use the FFT to perform the channelization and predetection filtering.
    • End-To-End Information System Design at the NASA Jet Propulsion Laboratory

      Hooke, Adrian J.; NASA Jet Propulsion Laboratory (International Foundation for Telemetering, 1978-11)
      Recognizing a pressing need of the 1980's to optimize the two-way flow of information between a ground-based user and a remote space-based sensor, an end-to-end approach to the design of information systems has been adopted at the Jet Propulsion Laboratory. The objectives of this effort are to ensure that all flight projects adequately cope with information flow problems at an early stage of system design, and that cost-effective, multimission capabilities are developed when capital investments are made in supporting elements. This paper reviews the End-to-End Information System (EEIS) activity at the Laboratory, and notes the ties to the NASA End-to-End Data System program.
    • Engineering of a Multifunction Spread Spectrum System

      Winterkorn, John H.; The Aerospace Corporation (International Foundation for Telemetering, 1978-11)
      In the past ten years there have been dramatic strides in the spread spectrum communications system area. The knowledge of spread spectrum systems has progressed from a fragmented understanding of the techniques and their characteristics to the point where spread spectrum communication techniques are well documented and their characteristics are well understood. Thus, spread spectrum has progressed from analytical investigation into practical application. This presentation will provide a brief tutorial on spread spectrum techniques in the RF, modulation detection, and coding areas. The characteristics of these techniques will be addressed and related to specific communication functions. The presentation will address the application of spread spectrum techniques to a communication system design and will emphasize the suitability of spread spectrum for multiple applications in a given system. Specific examples of multiple spread spectrum usage will be given and a generalized approach to spread spectrum engineering will be presented. The application of this system approach to spread spectrum engineering results in spread spectrum taking on functions beyond its primary purpose of existence and becoming an integral part of a communication system rather than being an add-on, necessary but undesirable, appendage.
    • Experimental 2 GBPS MM Wave System and 4 GBPS QASK Modulator

      Horwood, D. F.; Luke, R. T.; Lee, G. E.; Des Brisay, G. S., Jr.; Hughes Aircraft Company (International Foundation for Telemetering, 1978-11)
      A 2 GBPS QPSK modulator and demodulator were developed and BER performance was evaluated over a millimeter wave data channel. The error rate measurements taken with the breadboard equipment showed system performance to be less than 2 dB from theoretical at an error rate of 10⁻⁵. Additionally, a second QPSK modulator was constructed and combined with the first to generate 4 GBPS QASK data for future evaluation.
    • Experimental Evaluation of MSK and Offset Keyed QPSK Through Satellite Channels

      Horwood, D. F.; Angello, P. S.; Hughes Aircraft Company (International Foundation for Telemetering, 1978-11)
      Laboratory test measurements show nearly equivalent error rate performance of MSK and OKQPSK modulation formats for channels having bandwidths approximately equal to the bit rate bandwidth and typical associated phase delay characteristics. High quality MSK and OKQPSK transmitters and a versatile modular receiver have been designed and constructed to eliminate differences associated with varying degrees of hardware quality when the performance of the various modulation formats is compared. The selection of a modulation format should, therefore, be strongly directed by considerations other than error rate, such as complexity, sensitivity to alignment, and compatibility with differential coding.
    • A Fast Complex Integer Convolution Using a Hybrid Transform

      Reed, I. S.; Truong, T. K.; University of Southern California; California Institute of Technology (International Foundation for Telemetering, 1978-11)
      In this paper it is shown that the cyclic convolution of complex values can be performed by a hybrid transform. This transform is a combination of a Winograd transform, and a fast complex integer transform developed previously by the authors. This new hybrid algorithm requires fewer multiplications than any previously known algorithm.
    • Fast Fourier Transform Algorithm Formulation

      Thong, Tran; General Electric Company (International Foundation for Telemetering, 1978-11)
      A new unified formulation of the fast Fourier transform based on the unwrapping of a multi-dimensional array is presented. The decimation in time FFT algorithms is treated in detail. The decimation in frequency algorithms is then discussed.
    • FET Amplifiers for Communications Applications

      Kennedy, W. Keith, Jr.; Watkins-Johnson Company (International Foundation for Telemetering, 1978-11)
      The Field Effect Transistor (FET) is revolutionizing microwave communications with both its low noise performance and high dynamic range. This paper emphasizes developed amplifier hardware available today for both ground and satellite applications. The focus is on the noise figures and output powers available from 4 to 15 GHz.