The Road to Successful Satellite Communications
With the first launching of a satellite into orbit by the Soviet Union in 1957, the real development work on satellite communications began. By 1960 Project Echo had proved that signals could be reflected off a man-made satellite and received several thousand miles away. And, in 1962, Project Telstar demonstrated to the whole world that an active repeater satellite could send telephone calls, data, and television across the ocean.
Bringing satellite communications almost to reality has required more than putting a man-made satellite into orbit around the earth. Just as important have been the invention and development of many remarkable new devices: the transistor, the solar cell, the traveling wave tube, the horn-reflector antenna, the waveguide, the solid-state maser, and the electronic computer—to mention only some of the more important. Without them it would still be impossible to find a tiny speeding object miles out in space, send signals to it, amplify them billions of times, and then return them to distant points on the earth.
Some of the new devices that help make satellite communications possible
horn-reflector antenna
traveling-wave tube
transistor
solar cell
solid-state maser
When you look back at it, we have seen remarkable progress in satellite communications—and work is still continuing at a fast pace. Some of the milestones have been these:
OCTOBER 1945 Arthur C. Clarke publishes “Extra-Terrestrial Relays—Can Rocket Stations Give World-Wide Radio Coverage?” in Wireless World, suggesting the use of satellites for communications.
JANUARY 11, 1946 Project Diana of the U. S. Army Signal Corps bounces microwave radar signals off the moon and back to the earth, proving that relatively low power can transmit signals over very long distances.
APRIL 1955 John R. Pierce publishes “Orbital Radio Relays” in Jet Propulsion, pointing out the requirements for a satellite communications system.
JULY 29, 1958 Congress passes the National Aeronautics and Space Act, setting up the National Aeronautics and Space Administration (NASA), with satellite communications experimentation as one of its interests.
DECEMBER 18, 1958 Score, the first communications satellite, is launched by the U. S. Air Force. It is equipped with tape recorder units that transmit prerecorded messages back to the earth upon receipt of signals. On December 19 a Christmas greeting to the world recorded by President Eisenhower—the first message from a satellite to the earth—is transmitted. Score continues to transmit for 12 days before its batteries become too weak for further use.
NOVEMBER 23, 1959 Live voice transmission is accomplished from Bell Telephone Laboratories in Holmdel, New Jersey, via the moon to Jet Propulsion Laboratories in Goldstone, California. This is the first of 17 tests in Project Moonbounce, all using the moon as a reflector.
JULY 8, 1960 The Bell System proposes to the Federal Communications Commission a detailed plan for a world-wide communications system using active repeater satellites to provide telephone circuits and facilities for transmitting television to various parts of the world.
AUGUST 12, 1960 Echo I is launched into orbit by NASA. Project Echo carries on a large number of communications experiments and, most important, proves that it is practical to use a man-made satellite to reflect two-way telephone conversations across the United States. Echo also dramatizes the possibilities of satellites for communications. Since it is a 100-foot inflated balloon made from aluminum-coated Mylar, it is large enough to be seen by the naked eye. People throughout the world see Echo I sail on schedule across the sky in its 1000-mile-high circular orbit. Three years later, although it is now wrinkled and deflated, the balloon is still in orbit.
Project Echo provided valuable data for future work in satellite communications. It demonstrated that a passive satellite—that is, one that simply reflects the microwave signals it receives from an earth station back to another point—would work. Two-way conversations of good quality were sent between the Bell Laboratories Holmdel station and Jet Propulsion Laboratories in Goldstone, and successful transmission was made to other points in the United States and Europe. A scaled-up horn-reflector antenna proved itself. A method of receiving microwave signals that had been little used until then, known as frequency modulation with feedback (FMFB), performed very well. New types of low-noise amplifiers using solid-state masers gave excellent results. And tracking of the satellite by electronic computers, by radar, and by telescope proved to be extremely reliable.
OCTOBER 4, 1960 Courier I-B is launched by the Army Signal Corps into a 500- to 650-mile-high orbit. A sphere weighing 500 pounds and measuring 51 inches in diameter, the Courier satellite is powered by 20,000 solar cells and contains four receivers, four transmitters, and five tape recorders. It is designed to demonstrate the possibility of using active repeaters for delayed transmission of messages. Signals are received, stored on the tapes, and then retransmitted back to earth when the satellite has moved on. After 18 days in orbit, technical difficulties ended Courier’s ability to send signals, but it received and retransmitted 118 million words during its active life.
JANUARY 19, 1961 The American Telephone and Telegraph Company is authorized by the Federal Communications Commission to establish an experimental satellite communications link across the Atlantic. Two 170-pound satellites are to be launched by NASA but will be designed, built, and paid for by AT&T. This project is later given the name “Telstar.”
MAY 18, 1961 NASA selects the Radio Corporation of America to design and build the Relay satellite, which will be used to test the feasibility of transoceanic telephone, telegraph, and television communications.
AUGUST 11, 1961 NASA awards the Hughes Aircraft Corporation a contract to build Syncom, an experimental active satellite to be placed into a 22,300-mile-high orbit that will be synchronous with the rotation of the earth. (See [page 37] for definitions of various kinds of satellite orbits.)
DECEMBER 20, 1961 The United Nations adopts a resolution on the peaceful uses of outer space that includes a request for world cooperation in developing a system of communications satellites. Both the United States and the Soviet Union sign the resolution.
FEBRUARY 7, 1962 President Kennedy asked Congress to pass a bill setting up a corporation to operate a satellite communications system. The proposed corporation would be owned jointly by the public at large and the country’s communications common carriers.
JULY 10, 1962 Project Telstar is successful. For the first time, voice communications and live television are transmitted across the Atlantic via a man-made satellite that picks up signals sent from one continent, amplifies them, and retransmits them to another continent. (On pages [21] to [33] we talk at further length about Project Telstar.)
AUGUST 31, 1962 President Kennedy signs the Communications Satellite Act, establishing a private corporation under government regulation—the Communications Satellite Corporation—which will plan, own, and operate a commercial satellite communications system.
DECEMBER 13, 1962 Relay I is launched by NASA. Similar in many ways to the Telstar satellite, it is an active repeater device that picks up telephone, television, and other electronic signals and retransmits them to a distant point. Relay also provides the first satellite communications link between North and South America. The satellite is a tapered cylinder 33 inches long weighing 172 pounds. A mast-like antenna at one end is used to receive and transmit a single television broadcast or 12 simultaneous two-way telephone conversations. Four whip antennas at the other end of the cylinder handle control, tracking, and telemetry—turning experiments on and off and sending information on the behavior of its components and on the amount of radiation it encounters in space. Relay is powered by nickel-cadmium storage batteries that are charged by more than 8,000 solar cells mounted on its eight sides. It contains two identical receiving, amplifying, and transmitting systems called transponders, each with an output of 10 watts.
Relay I is traveling in an orbit that ranges from 820 to 4,612 miles high, and circles the earth about every 185 minutes. Soon after it is launched, Relay’s telemetry reports trouble in the voltage regulator of one of the transponders, which causes excessive power drain. On January 3, 1963, the alternate transponder is switched on, and a successful series of tests—including live television broadcasts between the United States and Europe—begins.
JANUARY 4, 1963 The Telstar I satellite, which for almost two months could not be turned on to transmit communications signals, is reactivated by Bell Laboratories engineers. (The story of this ingenious electronic detective work is told in detail on pages [78] to [85].)
FEBRUARY 14, 1963 The first Syncom satellite is launched by NASA, but its communications systems do not operate. It is the first satellite to try for a synchronous path, revolving around the earth once every 24 hours and thus appearing to hover continuously over the same longitude. Syncom is a short cylinder 28 inches in diameter and 15½ inches long, and weighs 86 pounds. Like Telstar and Relay, it is powered by a combination of solar cells and nickel-cadmium batteries, but it is designed to handle only one two-way telephone conversation and cannot transmit television.
MAY 7,1963 The Telstar II satellite is launched for the Bell System by NASA. (See [page 31].)