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Welcome to The COMSAT Legacy Project, Advanced Communication Technology Satellite (ACTS) Program.

COMSAT Labs' research is part of the Advanced Communications Technology Satellite program-ACTS, for short. ACTS is a NASA project aimed at developing an experimental satellite that will combine for the first time a number of advanced technologies which have developed independently.

COMSAT Labs serves as a subcontractor to RCA, the program's prime contractor. Also on the team are TRW and Motorola. COMSAT Corporation's role, according to Bill Schmidt, associate director of the Labs' ACTS Program management office, is to design, build and install the "brains" of the system. The Labs' ACTS staff of 77 full-time employees draws on expertise from across the Labs, including the Microwave Technology, Network Technology and System Development Divisions and elements of the Design and Fabrication Center. Irv Dostis, ACTS PMO director, heads up the program within COMSAT Corporation. To appreciate COMSAT Corporation's contribution , it helps to understand generally how the new satellite will work.

Picture two satellites perched sideby-side, 23,000 miles over the United States. One uses today's technology, the other is the ACTS satellite. Satellites don't emit light, but to visualize how the two would work, try to imagine their energy as light. In this scenario, today's satellite is equipped with a single floodlight shining across the entire United States. Its light is quite dim, but it reaches every corner of the country. allowing earth stations with sufficient power to operate with it. Much of its energy is wasted: it is covering areas that don't need satellite service and its energy is constant instead of being used only when needed. Continuing the example , the ACTS satellite is equipped with a number of powerful spotlights. Instead of blanketing the entire country with dim light, the ACTS satellite concentrates its energy into powerful beams, each of which focuses on a single area at a time. The satellite serves the entire country, but it does so by moving its beams rapidly across the landscape, stopping only for a thousandth of a second to send and receive messages from earth stations below. In fact, the satellite wastes no time searching around for messages. It is programmed to target its beams to a particular area only on a demand basis-that is, when there are messages to be delivered or picked up. The ACTS satellite, then, uses both energy and time efficiently, enabling it to handle many more transmissions than today's relatively inefficient models. As Schmidt explains it, if the satellite were equipped with four spot beams-one for each time zone, for example-it would have four times the capacity of today's satellite that blankets the entire nation with one beam, because the precious frequency spectrum is used four times. Several different technologies will be tested through the ACTS program, Schmidt says. The satellite itself will allow researchers to experiment with use of the higher-frequency Ka-band, which operates at 30/20 GHz and offers twice as much capacity as the Ku- and C'-band frequencies combined. On board the satellite, two different systems for sending and receiving messages will be tested. One will handle "high burst rate" transmissions to and from larger, more powerful earth stations, interconnecting the correct tip-link and down-link spot-beams by analog switches. The other, called a baseband processor, will handle what are called "low burst rate" transmissions from smaller, less powerful earth stations. The baseband processor, according to Schmidt, is often described as the "heart" of the system. He compares it to an earth station in the sky. Its job is to take analog signals it receives from the ground, convert them to a digital format, sort then according to destination, store them until there is an available time slot to their destination, retransmit them to earth stations by routing them to the appropriate down-line, and amplifying them as required. A central part of COMSAT Labs' role, Schmidt says, is to provide the ground-based computer controls-the hardware and software that will choreograph the movement of the satellite's spot-beams and direct the baseband processor. In fact, the Labs' contribution to the project will ensure that the satellite operates at optimum efficiency, using available capacity by placing its energy where it is needed only when it is needed. Ultimately, COMSAT Corporation's ground controls will he located at the NASA Lewis Research Center in Cleveland, Ohio. For now, the preliminary design of the system's complex controls are contained in a three volume report. Exactly when those steps will begin to be implemented remains uncertain, according to Schmidt. When NASA began funding ACTS in 1984, plans called for a 1989 launch date. Congress recently decided to provide $77 million in funding for 1987, assuring the program's completion. The launch date, however, may be delayed until 1991-92. Beyond the launch date, several years of testing will precede any commercial application of the experimental ACTS satellites. COMSAT Labs' participation in the design of the ACTS satellite represents a valuable investment in the company's future. Once satellites similar to ACTS are ready for commercial duty, COMSAT Corporation will have a leg up in understanding the capacities of the technology and applying them to the marketplace.

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Advanced Communication Technology Satellite (ACTS) Program Gallery





Steven L. Teller
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COMSAT Legacy Archives
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Email: teller@comsatlegacy.com
Phone: (301) 892-6256
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