Satellites from Sputnik to SATCOM

Satellites From Sputnik to SATCOM By Jim Sparks June 1999 It all began on October 4, 1957 with a crescendo of sound and light as Sputnik 1 rocketed into earth's orbit. A steel ball, weighing 184 pounds with a 23-inch diameter...


Satellites

From Sputnik to SATCOM

By Jim Sparks

June 1999


It all began on October 4, 1957 with a crescendo of sound and light as Sputnik 1 rocketed into earth's orbit. A steel ball, weighing 184 pounds with a 23-inch diameter, and carrying a radio transmitter, was to be a watershed in modern history. Much of today's meteorology, communications, surveillance, and navigation are dependent upon a network of 4,000 satellites circling our planet.

Prior to 1956, capabilities for transatlantic voice communications were limited to radiotelephones and were often limited by atmospheric conditions. When the first cables were strung across the ocean floor in 1956, it soon became apparent they could not handle the rapidly increasing volume of calls. At that time, scientists decided to look skyward for a solution. The age of airborne telecommunications began in the early 1960's with the launch of TELSTAR 1 and has been advancing ever since. In 1962, the United States formed COMSAT (Communication Satellite Corporation) with the intent of developing a worldwide stellar communications network. Two years later, this turned into a global endeavor with eleven nations joining to form INTELSAT (International Telecommunications Satellite Organization). Today more than 130 nations participate.

Early Communications Satellites
Early communications satellites did not operate in a geosynchronous orbit (that is they did not remain above one specific place on earth), which would result in periodic drifting out of the range of ground stations. For example, the early TELSTAR satellite could only communicate with ground stations on an average of four hours per day.

The Hughes Aircraft Company working with NASA developed SYNCOM a high altitude geostationary satellite in 1963. This new technology enabled 24-hour communications with stations on the ground. Several other SYNCOM-type devices have been launched since the mid-1980's using the space shuttle as a delivery tool. The early INTELSAT network included 20 satellites that circled the earth in a geosynchronous orbit, meaning each satellite will remain over a particular point on the earth's surface and could receive and transmit signals from relay stations on the ground. Each satellite contained a receiver and an amplified transmitter, which were used to hand off messages. These "early bird" devices were used for about three and a half years and appeared as metal cylinders just over 2-feet wide and 1 1/2-feet high, encased in solar cells, and could handle 240 telephone lines or one television channel at any given time.

INTELSAT 4 revolutionized the industry in the early 1970's with a physical dominance over all previous models. Standing a towering 16 feet in height with antennae extended it was the only device of its day capable of carrying color television signals along with 6,000 telephone channels.

In the 1980's, the "spinning drum" technology of earlier years was cast aside and new models with outcast wings of solar panels were deployed. The extra power generated was employed to enable 15,000 telephone calls at any given time. Thirteen of these satellites were delivered from 1980 to 1989. The more recent INTELSAT 7 can handle up to 22,500 telephone calls and three television channels at any given time and are expected to last between ten and fifteen years in orbit.

With the high degree of mobility required in today's economy a service was required to provide communications with land vehicles, ships and aircraft. INMARSAT is an international organization whose purpose is to establish, operate and maintain a worldwide satellite network that complies with standards developed by the International Civil Aviation Organization (ICAO). Service includes two-way voice, fax and data for aircraft operating in most areas around the globe.

SATCOM
The INMARSAT satellite communications (SATCOM) system consists of three components:

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