Communications Technology Satellite Research Articles

Experimental direct broadcast reception of 12GHz television signals from the Canadian Communications Technology Satellite

In order to gain practical experience of reception of television from satellites, a long-term experiment has been set up in Canada. The ground receiving station equipment and the monitoring arrangements are described.

Canada: New breed

Canada's space programme was back on the nation's front page and television screens again briefly last month when the United States launched her neighbour's latest satellite, the CTS (communications technology satellite). David Spurgeon reports from Ottawa

A perspective on the Canadian satellite program

During a period of 17 years Canada's space program has evolved from the Alouette I scientific satellite to the more complex observatory-type ISIS scientific satellites and subsequently to the ANIK commercial system and the Communications Technology Satellite (CTS). Many new and diverse engineering problems have been solved both in the space and ground segments of these systems. This paper provides a history of the program and an assessment of the current level of Canadian capability in satellite-related engineering.

Communications Technology Satellite: A Variable Conductance Heat Pipe Application

A variable-conductance heat pipe system (VCHPS) has been designed to provide thermal control for a transmitter experiment package (TEP) to be flown on the Communications Technology Satellite. The VCHPS provides for heat rejection during TEP operation and minimizes the heat leak during power down operations. The VCHPS described features a unique method of aiding priming of arterial heat pipes and a novel approach to balancing heat pipe loads by staggering their control ranges.

Some proposed experiments with the Communications Technology Satellite

The satellite (CTS), a system jointly sponsored and financed by the National Aeronautics and Space Administration (U. S. A.) and the Department of Communications (Canada), 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, to be undertaken under the sponsorship of the Ontario Educational Communications Authority. 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 725000 km 2 (inhabited largely by native people) are extremely limited. It is expected to assess the extent to which: (а) a satellite communications system might resolve the communications deficiency, (b) the native people will use the experimental facility, (c) health and general educational programmes, especially utilizing the interactive mode, will be viable. Since the design of the experiments is in a comparatively early stage the paper is speculative insofar as such central (for political and cultural reasons) questions as the active participation of the native peoples and the relative weights given to the educational, health and recreational programmes are concerned.

Multidisciplinary Applications of Communication Systems in Teleconferencing and Education

This paper describes a laboratory facility and the multidisciplinary research that has been carried out in it relevant to the application of communications technology in such areas as teleconferencing and education. This facility at Carelton University, Ottawa, Canada, provides multichannel multipoint audio and video communications, and information storage and control facilities to simulate a wide variety of uses. The research program, conducted by communication technologists, systems engineers, and social psychologists, is outlined and the results of a number of teleconferencing and educational experiments are presented. The forthcoming communications technology satellite (CTS) Stanford-Carleton Universities Curriculum-Sharing Experiment is described, as are the preparations for a project in the educational applications of communications technology.

Small Earth Stations for Broadcasting Satellite Systems

Typical parameters for individual and community earth stations capable of receiving TV transmission from a Communications Technology Satellite (CTS) (which is to use a 200-W traveling-wave tube) are considered in order to determine what is now feasible and what may become so over the coming decade. The state of the art in broadcasting-satellite ground receivers is reviewed in regard to antennas, microwave integrated circuits, surface-acoustic-wave devices, field-effect transistors and parametric amplifiers. Receiver models considered are of a type suitable for Canadian application, i.e. one or two television channels selectable by tuning, plus one of two audio channels (switched) in the case of individual receivers, and up to six simultaneous television channels, each with two audio, in the case of community receivers. It is concluded that, for economic reasons, direct-to-home broadcasting from satellites will not be a commercial proposition by the early 1980s although some forms of satellite-to-community broadcasting could be operating.

Magnetic-solar hybrid attitude control of satellites in near-equatorial orbits

Nutation damping using the Earth's magnetic field for spin-axis and solar radiation pressure for pitch control is studied for spacecraft in near-synchronous altitudes. The nonlinear, nonautonomous, coupled equations of motion involving a large number of parameters are only amenable to a numerical approach. The response data, presented as functions of the system parameters, show the controller's effectiveness in damping the most severe disturbances in a few degrees of the satellite's orbital travel. The controller provides versatility to the satellite, enabling it to change its preferred orientation in orbit and, hence, undertake diverse missions. The effectiveness of the system even in presence of rotor spin decay promises an increased satellite lifespan. An illustrative example using the inertia properties of Anik and the proposed Canadian Communications Technology Satellite demonstrates the feasibility of the concept in the geostationary orbit.

Attitude Dynamics of Satellites with Flexible Appendages- A Brief Review

E demand on precise orientation of satellite, relative to an inertial or an orbiting frame of reference, has resulted in whole new area of scientific endeavor referred to as attitude dynamics. In the early stages of space exploration when spacecraft tended to be small, mechanically simple, and essentially inflexible, the elastic deformations were relatively insignificant. Numerous investigations involving active and passive stabilization procedures and accounting for internal as well as external forces have been carried out assuming satellites to be rigid.* However, in modern space vehicle carrying lightweight deployable members, which are inherently flexible, this is no longer true. Motivations for this trend are many. 1) Every satellite goes through a brief interval of vigorous acceleration and vibration during boost, followed by prolonged functioning in quiescent mode of operation characterized by extremely small loads and acceleration. The universal solution to this dilemma has been to design large members (solar panels, booms, antennas, etc.) as flexible bodies that can be stored in compact fashion (and hence behave like rigid bodies) during the launch but emerge like butterfly from its cocoon after the boost terminates. 2) In response to demanding mission requirements, satellite configurations have become increasingly complex to maintain delicate balance between diverse constraints of space, weight, performance, control, and their optimum realization. For example, ever-increasing demand on power for operation of the on board instrumentation, scientific experiments, communications systems, etc., has been reflected in the size of the solar panels. It has increased to point where their flexibility can no longer be neglected. For example, the proposed Canadian Communications Technology Satellite (CTS), to be launched in 1975, is designed to carry two solar panels, 3.75 ft x 24 ft each, to generate 1.2 kw. ~ 8 3) Use of larger members may be essential in some missions. For example, Radio Astronomy Explorer (RAE) Satellite' used four 750 ft antennas for detecting low-frequency signals. 4) Certain multipurpose missions, particularly those requiring simultaneous relative measurements from points appreciably apart, may find elastically supported or the recently proposed cable connected multibody systems attractive. 5) Modular construction leading to gigantic space station through elastic linkages can no longer be considered fantasy. In this connection, studies of far-reaching significance by Roberson, Wittenburg, and others are of particular relevance. 6) For longer life span, passive or at least semi-passive attitude control procedures are ideal. They normally involve use of long booms, large radiation reflectors, or aerodynamic flaps. The structural flexibility may interact with attitude control systems of spacecraft in variety of ways. A NASA special report focuses attention on the significance of this problem through discussion of the anomalous behavior of several spacecraft. Besides citing useful references, it represents, with several others,' excellent review of the work in this area and puts current and anticipated problems in proper perspective. Furthermore, there are few recommended procedures for analysis, simulation, and design. A paper by Noll et al. effectively summarizes the NASA document. Experience to date suggests that in most cases problems arise not because of lack of available analytical/numerical design procedures but because of failure on our part to recognize and appreciate the mechanism of the attitude control/structural flexibility interactions. The review papers just mentioned serve as an ideal introduction to the subject. They effectively summarize dynamical problems through illustration of several past and projected configurations where flexibility played or is likely to play an important role. The problem of flexibility is neither of recent origin nor is it restricted to spacecraft. Missile, aircraft, and surface vehicle designers have long been dealing with it. As pointed out by Ashley, several of the techniques are directly applicable here. In many ways, however, spacecraft differ from other dynamical systems and require development of modified approaches specifically suited to the emerging field of astroelasticity. However,

Military Satellite Communications Using Small Earth Terminals

Satellite communications technology has reached the stage at which it is feasible to develop a reliable military tactical communications system using small transportable Earth terminals. This paper discusses the design considerations involved for a multiple-access system, with particular reference to the Earth terminals.

Reliability assurance of individual semiconductor components

Where small numbers of highly reliable semiconductor devices are required, conventional methods of procurement are found to have deficiencies. An approach to procurement is proposed which is cost effective, accommodates new device types, and assures reliability in the individual device. Although principally applied to silicon planar transistors, the approach can be extended to other semiconductor types. A critical evaluation is made of the manufacturer and his technology. The devices obtained from each diffused wafer are grouped into separate lots. Selected tests are performed on these lots in order to discover possible failure mechanisms. Tests may involve simple electrical measurements or detailed techniques such as scanning electron microscopy and X-ray microprobe analysis. The Canadian/U.S.A. Communications Technology Satellite (CTS) program has adopted this procurement procedure.

The Use of a Spinning Dissipator for Attitude Stabilization of Earth-Orbiting Satellites

This paper considers a novel attitude stabilizing system which acts both as a passive nutation damper and a momentum source for an Earth-orbiting satellite. The system may be designed to use four identical wheels mounted coaxially with and at the ends of the arms of a cruciform structure. The structure may then be spun about the axis perpendicular to the arms to provide angular momentum along the spacecraft spin axis. The wheels experience torques produced by inertial forces. The necessary damping and restoring (spring) torques are provided by means of a torsional arrangement built around the center of each wheel. The performance characteristics of the proposed stabilizing unit are evaluated by considering spacecraft parameters used in one phase of development of the Communications Technology Satellite (CTS). The results obtained for a specific design of the stabilizer indicate that global stability of the desired attitude motion of the spacecraft can be guaranteed with associated damping time constant as low as one second.

Satellite Communications in Japan

This paper describes recent research and development of satellite communication technology in Japan together with the future prospects. Newly developed earth station facilities for both commercial and experimental purposes are described first. New satellite communication systems, such as STAR, SMAX, TTT, SSB-PM, and SSRA, which originated and/or have been studied extensively in Japan, are described briefly. Recent developments of microwave and millimeter-wave antennas, parametric amplifiers, high-power tubes, etc., are surveyed. Brief descriptions are also given of radio-wave propagation studies and development plans for Japanese communication satellites.

Large deformation, deep penetration theory for a compressible strain-hardening target material

1 lorillo, A. J., Damping Dynamics of Axisymmetric Rotor Stabilized Satellites, ASME Winter Meeting, Chicago, 111., Nov. 1959. 2 Likins, P. W., Criteria for Dual Spin Journal of Spacecraft and Rockets, Vol. 4, No. 12, Dec. 1967, pp. 1638-1643. 3 Mingori, D. L., Effects of Energy Dissipation on the Attitude of Dual-Spin Satellites, AIAA Journal, Vol. 7, No. 1, Jan. 1969, pp. 20-27. 4 Pringle, R., Jr., Stability of the Force-Free Motions of a Dual-Spin AIAA Journal, Vol. 7, No. 6, June 1969, pp. 1054-1063. 5 Velman, J. R., Simulation Results for a Dual-Spin Proceedings of the Symposium on Attitude Stabilization and Control of Dual-Spin Spacecraft, Aug. 1-2, 1967, Rept. SAMSOTR-68-191, Nov. 1967, U. S. Air Force. 6 Johnson, C. R., Tacasat I Nutation Dynamics, to be published in AIAA Progress in Astronautics and Aeronautics: Communications Satellite Technology for the 70' s, Vol. 25, edited by N. E. Feldman and C. M. Kelly, MIT Press, Cambridge, 1971.

Satellite Communnications: A Case Study of Technolog's Impact on Politics

One of the challenges which democracies face is to preserve the essential liberties of their citizenry while undergoing continual, even drastic, economic and technological development. Mario Einaudi has described the New Deal as an effort to translate eighteenth-century agrarian democracy into twentiethcentury industrial democracy without evacuating the unique values which the Founding Fathers wished to be transmitted. Since the days of FDR, the United States of America has created a distinct “social breakthrough” by being the first nation to enter the postindustrial age of nuclear energy, computers, television, rockets, missiles, wonder drugs, psychedelic techniques, fertility control techniques, and supersonic jet travel. That political processes cannot be divorced from the wider environmental matrix of sociotechnological innovations is a proposition which is gaining in acceptance. Acknowledging the incidence of technological invention on the political process, we have singled out for case study the history of the communications satellite technology, the creation of an unprecedented “chosen instrument” to establish a global system of communications satellites, and the subsequent formation of an international consortium whose members have codominion over the space segment of the global system. What interests us in this study is how technological leadership becomes converted into other forms of power such as economic, political, and commercial.