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Aviation History
1962
1962 - 0106.PDF
106 FLIGHT International, 18 January !%•) Missiles and Spaceflight Project Advent Example of intermediate "walking" or "drift" orbit for Advent. The satellite drifts eastward to the desired longitude, when its hot-gas propulsion system imports the extra velocity to achieve circular orbit at the correct height for a 24-hour period THE United States communication satellite programme embraces five major projects—the National Aeronautics and Space Administration's Rebound, Relay, Syncom and (in association with American Telephone and Telegraph Co) Telstar; and the Defense Department's Advent. Of these, Syncom and Advent are '"stationary" satellite systems employing 24hr synchronous orbits. The military system is outlined in this article, and details of Syncom were given in our issue of November 16, 1961. The Defense Department's programme began in May 1958 with the establishment of a communication satellite committee within the Advanced Research Projects Agency. In December of that year a development plan was prepared jointly by the Air Force and the Army Signal Corps, and by May 1959 the programme had evolved into three separate projects—Steer (SAC polar system). Tackle (advanced polar system), and Decree (stationary global system). In February 1960 these were reorganized to form the inter-Service programme known as Project Advent. The purpose of the Advent programme is to test the feasibility of achieving a reliable global microwave system for surface-to- surface communication, using active repeater satellites in syn chronous orbits. Current work is concerned primarily with test planning and with the design of satellites, boosters, communications equipment, ground stations and other subsystems, with orbital flights due to begin this year. The essential characteristics of the Advent system will be (1) a multi-channel, wide-band capacity for a large volume of com munications, (2) anti-jamming provision for communications, (3) the ability to place a satellite in orbit at any longitude along the equator, and (4) a "mean time to failure" for the satellites of at least one year. The anti-jamming requirements involve special equipment at ground stations as well as aboard the satellite, and the ability to place the satellite at any chosen longitude is an essen tial feature stated to be dictated by the worldwide responsibilities of the armed forces. Overall management of research and development in Project Advent is handled by the Department of the Army, and in particular by the US Army Advent Management Agency at Fort Monmouth. New Jersey. The Air Force Special Systems Division is responsible for system engineering and technical direction of the booster, satell ite. tracking and telemetry aspects (this work has been contracted to the Aerospace Corporation, with companies such as General Electric. Convair, Lockheed, Philco, Rocketdyne and Burroughs responsible for hardware). System engineering and technical direction for the communication subsystems of the satellite and its ground stations is the responsibility of the US Army Signal Research and Develop ment Laboratory (main contractors Bendix and Sylvania respect ively) and the US Navy's Bureau of Ships is engaged on system engineering and technical direction in the provision of a shipbome communication terminal (using Bendix equipment). The following description of the Advent satellite is based on an American Rocket Society paper The Advent Communication Satellite Program by Brig-Gen William M. Thames, commander of the Army Advent Management Agency, and Mr George E. Mueller. vice-president of Space Technology Laboratories. The complete Advent satellite will have fixed to its body a horn antenna for receiving communication signals from the surface stations and a separate paraboloidal antenna for relaying them back to Earth. It will have four one-way radio-frequency channels (that is, two two-way channels), and will be able to handle information at the rate of half-a-million bits per second on each RF channel: alternatively it will provide twelve voice channels on each HF channel. The satellite will rebroadcast the messages at a power level of one watt per RF channel. The power for operating the repeater and other equipment, as v. ell as for charging the battery, will come from solar cells mounted on
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