• 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.
    • Spacecraft Minicomputer for Control of a Communications Payload

      Rhodes, Russell R.; Semprucci, Marilyn D.; Massachusetts Institute of Technology (International Foundation for Telemetering, 1979-11)
      The paper describes the design, use and testing of a spacecraft minicomputer. The minicomputer was designed as a controller for the communications payload of a Communications Satellite with about 100 communications channels. Each of the channels has very flexible control including variable data rate, Doppler offset, and flexible routing.
    • Principles of Direct Detection Optical Communication

      Eastwood, Lester F., Jr.; Maynard, John A.; Green, Samuel I.; McDonnell Douglas Astronautics Company; McDonnell Douglas Corporation (International Foundation for Telemetering, 1979-11)
      This paper describes principles of direct detection laser communications link design. As background, it reviews the status of communication systems operating at McDonnell Douglas. It summarizes key modulation techniques, describing how they have been implemented at data rates up to one gigabit per second (Gbps) and how minor component changes can support eight Gbps. The paper describes, in detail, methods for calculating performance of important direct detection modulation schemes: pulse gated, pulse polarization, and pulse delayed binary modulations; pulse quaternary modulation; and pulse interval modulation. It also compares results of these calculations with measurements. Finally, it presents an example of end-to-end communications link analysis.
    • Control of Large Communication Satellites

      Gran, Richard; Proise, Michael; Zislin, Alex; Grumman Aerospace Corporation (International Foundation for Telemetering, 1979-11)
      Control of large communication satellites becomes most difficult when the structure gets large enough that the structural motion severely impacts the ability to stabilize the RF antennas. This structural/control interaction means that the control engineer can no longer use "benign neglect" of the structural vibrations, but must design a control that has a bandwidth that exceeds the lowest structural vibratory frequency. This in itself is not a problem as long as the sensors and actuators are colocated. Eventually, the antennas have to be controlled independently and the assumption of colocated sensors and actuators is no longer reasonable. This begins the problem. In this paper, the various approaches that have been proposed for controlling large flexible spacecraft when the structural frequencies and the control frequencies overlap will be described. A new approach to the design of such systems will be described, and a reasonably complex example of a large satellite control will be described. The presentation will show a movie that was produced to illustrate the control of this structure and the consequence of using the approach described in the paper.
    • On Board Satellite Communications Configuration Control Via Communication Channel

      MacPhee, Joseph V.; Coomber, David B.; Massachusetts Institute of Technology (International Foundation for Telemetering, 1979-11)
      Features of the design of the telemetry and command system for the LES-8 and LES-9 experimental communications satellites are described. Particular emphasis is placed on access to command and telemetry functions for the communications user community. Features described are: 1. Telemetry and command access through a communications channel in addition to dedicated telemetry and command channels. 2. The sets of telemetry and command functions for the communications user and for the satellite ground control center. Command set structure to allow for separable command sets. 3. Methods of display and control to provide for user control of the telemetry and command functions. In addition, extrapolation of user control of satellites by an experimental test community to a more general user community is projected.
    • The Problem --- Is It Hardware or Is It Software

      Olson, Roland E.; EMR Data Systems (International Foundation for Telemetering, 1979-11)
      The hardware design and development manager with all of his infinite wisdom, knowledge, and years of experience has always had to be on his toes to know when a hardware design is "good enough" to meet the requirement. Add to this duty, the management of software development which is relatively new which makes it difficult to decide if the software is "good enough" to meet the requirements and you have a manager faced with a man sized task. For example, ask him to decide when a computer problem occurs, if the problem is due to hardware or software, especially when both the hardware and software designers claims his system to be working okay --- this manager is in high demand because only a select few have experience with both hardware and software development and integration. So what about the rest of us? This paper provides the computer system manager such evaluation criteria, questions to ask and decision making rules to follow, when the hardware and software designers say to you --- "My system works fine, the problem is his."
    • Time Response Simulation of the Guidance and Control System of an Automatically Steered Wire-Following Vehicle

      Mukhopadhyay, Asok K.; Dobrotin, Boris M.; Jet Propulsion Laboratory (International Foundation for Telemetering, 1979-11)
      The purpose of the multi-mode evasive vehicle, as defined by the U.S. Army Armored Vehicle Command, is to provide an automatically steered moving platform for a target silhouette which will be used for tank gunnery evaluation. The vehicle, as well as its guidance and control systems, must be rugged enough to withstand battle conditions, rough terrain, hostile weather conditions, and the impact of dummy shells on its superstructure. The vehicle's steering and speed control are accomplished remotely by signals sent via a guide wire laid on the ground. The Army Wire-Following-Vehicle (WFV) represents new technology in the area of automatic vehicle guidance and has a host of potential applications, both military (such as a target drone) and civilian (such as underground mining and rescue as well as surface mass transit on electronic guide ways). For an high-order non-linear system, such as the WFV with its guidance and speed control subsystems, the final design must be generated and verified by non-linear time-response simulation. This paper describes the time-response simulation studies undertaken by the authors in support of the development and validation of the guidance/steering subsystem of the WFV (including the vehicular motion on some sample guided courses). Such simulation is the cheapest and quickest way to determine the design tolerances and hence, the field worthiness of the WFV. The WFV guidance system hardware design based on the continuous time-response simulation reported in this study has resulted in successful accomplishment of desired performance goals.
    • U. S. Domestic Communication Satellite Systems

      Martin, D. H.; The Aerospace Corporation (International Foundation for Telemetering, 1979-11)
      Domestic communication satellite (domsat) systems in the United States have a history of 14 years. Currently, several systems are in operation and another will be in early 1981. In recent years, many papers have been published, each describing certain details of a specific system. In contrast, this paper presents an overview and comparison of all the systems. As a background to this survey, the U. S. domsat history is briefly reviewed. The system overview then begins with a look at the satellites. Their basic designs are compared pictorially and through tabular data. Communication subsystems are also compared. The survey then goes on to the terminals, the terrestrial parts of the systems. Representative terminal characteristics are discussed. Finally, the various communication services offered by these systems are described.
    • Novel S and C Band TT and C Antennas for Satellite Applications

      Torres, J.; Patel, D. C.; Instituto Nacional de Tecnica Aerospacial; European Space Agency (International Foundation for Telemetering, 1979-11)
      Full spherical coverage from a single antenna cannot be provided at microwave frequencies on a normal satellite because of blockage by the satellite itself. However, cardioid coverage is sufficient. Achieving such coverage from a single antenna minimises the complexity of the on-board TT and C subsystem and so optimises both cost and reliability. Accordingly, investigations have been made into the feasibility of such an antenna in both S and C band versions. The design is a cylindrical waveguide, propagating a rotating TE mode, terminated in a circumferential array of axial slots and a short-circuiting plate into which an aperture is cut. A short metallic skirt can be added to the outside of the antenna if it is desired to reduce the coverage from the maximum achievable. The design has the advantage of being 'dual mode', i.e. it has two isolated Rf connectors providing identical pattern coverage. Thus two separate transponders can be 'hard-wired' on for reliability. The paper deals with the design, main development stages, an performance - including environmental testing results - of the antenna, and includes the results of investigations into a 'fill in' antenna intended to complete the spherical coverage if desired.
    • Control Aspects of Multibeam or Multielement Spacecraft Antennas

      Foldes, Peter; General Electric Company, Space Division (International Foundation for Telemetering, 1979-11)
      With the rapid development of spacecraft systems the trend is toward more sophisticated and larger on-board antennas. Many of these antennas employ an array of radiating elements, either as part of a feed system illuminating a larger aperture optics or as the direct radiators. The main purpose of using multiple radiators instead of a radiator in conjunction with a large aperture is to introduce a much larger degree of freedom in achieving desirable antenna characteristics. If an antenna system contains n independent radiating elements then the amplitude and phase of each of these elements can be selected for desirable results.
    • Reconstructing Pulse-Code Modulation Telemetry Data with Dropouts

      Hull, M. L.; Mote, C. D., Jr.; Lamoreux, L. W.; University of California, Davis; University of California, Berkeley (International Foundation for Telemetering, 1979-11)
      A data handling system was developed which transfers serial pulse-code modulation (PCM) telemetry data from an analog tape to a digital tape for analysis on a digital computer. The PCM data were collected from field experiments in snow skiing which measured the excitation between the ski boot and the ski. PCM data were FM transmitted and stored on an analog tape recorder. In the laboratory, data were decoded from the tape and parallel input to a Nova minicomputer which buffered the data and wrote tapes compatible with a CDC 6400 computer. A custom-built PCM decoder provided control and status commands to drive the minicomputer interrupt logic. The data transfer rate was 50 kbits/s. Special consideration was given to the problem of information losses. Lost data frames were not stored by the minicomputer and the data time series on the digital tape is discontinuous at each loss point. Spectral analysis of data with discontinuities produces erroneous results. Fourier coefficients and power spectra were computed for both continuous and discontinuous signals. Discontinuities caused significant reductions in amplitude and increase in bandwidth of spectrum estimates. Unique software eliminated data discontinuities by reconstructing the original time-base with linearly interpolated pseudo-data. Results are presented which show the enhanced accuracy obtained in spectrum estimates with the reconstructed data.
    • Hardware Compressor Reduces Computer Loading

      Strock, O. J. "Jud"; EMR-Telemetry (International Foundation for Telemetering, 1979-11)
      A hardware Compressor examines measurement data prior to computer entry, discards redundant or otherwise uninteresting words, and passes the appropriate information with tags to a computer. Continuous rates of 100,000 to 1,000,000 words per second are accepted. Under some conditions, 95% to 98% of the data can be discarded while passing every measurement which is of value in real-time analysis.
    • MMS Command and Data Handling

      Kelley, R. L.; Raymond, H. A.; Fairchild Space and Electronics Company (International Foundation for Telemetering, 1979-11)
      The Command and Data Handling System which is part of the NASA Multi-mission Modular Spacecraft (MMS) represents a versatile time division multiple access approach to processing spacecraft commands and retrieving data on real-time, delayed or preprogrammed basis. This paper traces the command signals from operator keyboard to execution within the spacecraft and telemetry/data signals from on-board spacecraft measurement to display on the operator's CRT page. Key technical features throughout this end-to-end signal processing loop are described and discussed.
    • Landsat D High Density Tape Recorders

      Montgomery John H.; Martin Marietta Corporation (International Foundation for Telemetering, 1979-11)
      High density tape recorders are being provided by Martin Marietta Corporation to facilitate Landsat D data acquisition and processing. High rate data form the Landsat D Thematic mapper and from the multispectrial scanner are to be stored on high density recorders of 42, 28, and 14 track configurations. Successive stages of data processing will utilize higher error-free reproduce techniques and tape systems will provide ease of operation with a variety of differing record and reproduce data rates. The design and implementation of these recorders will be discussed.
    • 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.
    • Estimating Time to Develop Software

      International Foundation for Telemetering, 1979-11
      The most devastating task ever given to the computer system manager, is that of estimating the manpower and time to develop software. Software development has become almost completely out of control in terms of estimating the manpower and time needed for the complete job, from interpretation of the requirements to the operational readiness date. Just as the hardware design engineer never reaches the ultimate design and thus never concludes his job, so goes the software designer. The difference is, hardware design managers have grown up in this environment and therefore know the pitfalls and stopping points of producing a good, reliable product. The software design manager is less qualified because the field is relatively new, it is very complex, and computer hardware technology is expanding so rapid that software designers cannot catch up. This paper is designed to provide the software development manager categories and rules of thumb for estimating time and manpower requirements for each category of software development. In addition to establishing the standard milestones such as requirements definition, specification, design, coding, checkout, verification and validation, consideration is given on how to keep the Ford requirement from turning into a Cadillac capability.
    • The Woe's of the Computer System Manager

      International Foundation for Telemetering, 1979-11
      The software has been designed, coded, and entered into the computer -- now comes the big task of verification and validation. This paper develops several system approaches, technical evaluation criteria, and key milestones for managing the progress, technical excellence and completion of this process. This is the phase of software development that becomes very difficult if a good design and design review has not been performed. In short, a well intentioned capability now becomes a "fair" design with patches installed to make it work. It is the number and type of patches to make it work that causes the software package to rapidly get out of hand. These problems will be discussed.
    • Development of a Seven Channel Telemetry Transmitter

      Seeley, R. L.; Long, F. M.; Pauley, J. D.; Weeks, R. W.; Naval Ocean Systems Center; University of Wyoming; University of Colorado Medical Center (International Foundation for Telemetering, 1979-11)
      Study of electroencephalograms (EEG) under normal behavior conditions required the development of a small, reliable telemetry system. Here two hybrid ceramic packages were attached face to face to provide a hermetically sealed seven channel telemetry transmitter with glass to metal seals around the seven differential pairs of input leads and the power supply leads. The transmitter's antenna is enclosed in the package by using two loops of gold substrate etched in a pattern around the other circuitry. The package measures .8 x 2.2 x 2.4 cm and weighs 8.5 gms. Input noise level is below 1 microvolt (rms) and dynamic range is from 1 to 250 microvolts (rms) with a frequency response (6 dB down) of 1 Hz to 150 Hz. Power requirements are 2.1 to 3.6 ma at 2.0 and 3.3 vdc., respectively, with at least 80% (3.3 and 9.5 mw, respectively) going to the radio frequency stage. Data are time multiplexed for pulse position modulation of an 88 to 108 MHz carrier. Maximum measured range of transmission with a 3 volt battery has been 10 m in air. This transmitter is well suited for the study of any animal large enough to carry the package and a battery. Other biopotentials such as EMG and ECG can be telemetered by increasing multiplexor rates and/or attenuating input signal levels.
    • Error Control Strategies for High Rate High Density Recording

      Montgomery, R. C.; Sangamo-Weston, Inc. (International Foundation for Telemetering, 1979-11)
      Current trends in digital magnetic recording are expected to lead to increases in speed, linear density and track density. These increases generate conflicting requirements on error control hardware. This paper discusses the conflicts expected and current and future methods of solution.
    • What The System Link Budget Tells the System Engineer or How I Learned to Count in Decibels

      Sklar, Bernard; The Aerospace Corporation (International Foundation for Telemetering, 1979-11)
      Because it is analytically straightforward, link budget analysis often takes a back seat in engineering curricula, yet this technique represents one of the most important tools available to communications engineers and managers. This paper presents a tutorial examination of link budget development, with an emphasis on satellite communications systems, and catalogues the typical sources of loss and noise. In addition, it treats the concepts of the range equation, free space, antenna gain and effective area, system temperature, and digital versus analog parameters. This paper also illustrates a typical budget and tradeoffs using a communication satellite example.