Communications satellites can be grouped into two broad categories. Passive vehicles reflect signals from one ground station to another. Active satellites accept ground signals and either amplify and rebroadcast them immediately or record messages for later transmission.

The Echo satellite balloons typified the passive category of communications spacecraft. These satellites “bounced” radio signals from one ground station to another. Uninflated Echo payloads were carried into orbit packed in special storage containers. When released in space, the balloon was inflated by chemicals packed inside which subliminated to produce inflating gas. The mylar plastic skin of the satellite was sandwiched between two layers of aluminum foil. Echo 2—on display—included a system for releasing gas over a long period of time to maintain the satellite’s spherical shape. Launched January 25, 1964, Echo 2 was the first satellite used for communication experiments between the United States and the Soviet Union.

Project West Ford, launched May 9, 1963, was a unique experiment in passive satellite communications. It was not a solid vehicle, but a series of 400-million tiny individual copper filaments called dipoles. The dipoles formed a reflective layer some 64,300 kilometers (40,000 miles) long, 32 kilometers (20 miles) thick, and 32 kilometers (20 miles) wide. The distance between the individual dipoles averaged 536 meters (one-third mile). The West Ford experiment proved disappointing, and advances in the design of active communications satellites made further experiments of this nature unnecessary.

Oscar 1 (Orbital Satellite Carrying Amateur Radio) was conceived, designed, and constructed by American amateur radio “hams.” Launched as a “piggyback” satellite on December 12, 1963, Oscar transmitted a series of Morse code dots spelling “hi.” The message was picked up by 5000 operators in 28 nations during the 18 days of transmission. Oscar investigated radio propagation phenomena in space on that portion of the radio frequency spectrum allocated to amateur radio (144-146 megaherz).

Testing the use of a “delayed-repeater” satellite in global military communications, Courier 1-B was placed in a high-altitude orbit on October 4, 1960. The craft accepted and stored messages as it passed over one ground station, then replayed them on command.

Relay, another active repeater satellite, was placed in orbit on December 13, 1962. Relay carried communications experiments to test a variety of relay equipment—including that for photofacsimile, teleprinter, and data transmission. During its 25-month lifespan, Relay 1 introduced the nations of the world to satellite communication. A second, improved Relay was launched in 1964.

The world’s first commercial communications satellite was called “Early Bird,” or INTELSAT 1. Built a decade ago by Hughes Aircraft Company for Communications Satellite Corporation (COMSAT), Early Bird could transmit simultaneously on 240 two-way channels for telephone, telegraph, or data transmission. Transatlantic telephone circuit capability increased by 50 percent once Early Bird went into orbit on April 6, 1965. Although the craft had a life expectancy of 18 months, it operated satisfactorily in full-time service for more than three and one-half years.

INTELSAT 2 introduced multipoint communications between earth stations in the Northern and Southern hemispheres. With almost twice the power of Early Bird, INTELSAT 2 proved particularly important as communications support for the Apollo missions to the Moon.

INTELSAT 2 established a global network of three satellites that was effective in linking two-thirds of the world’s people in one communications chain. The first of the series was launched on January 11, 1967. These spacecraft were designed and manufactured by the Hughes Aircraft Company for Intelsat, Inc., and had a design lifetime of three years.

INTELSAT 3 was a series of five communications satellites which provided global coverage for the first time. This INTELSAT had a capacity of 2400 voice, data, facsimile, and telegraph circuits, plus four television channels and had a design lifetime of five years.

The satellite featured a de-spun antenna which remained pointed at a particular area of the globe, while the body of the satellite spun around it. It was the first commercial satellite capable of transmitting voice and television broadcasts simultaneously.

INTELSAT 3 satellites were manufactured by TRW Systems, Inc., for Intelsat, Inc.

Echo 2, Courier 1-B, and Relay are from the National Aeronautics and Space Administration; OSCAR 1 is from Project Oscar, Inc.; INTELSAT 1, INTELSAT 2, and INTELSAT 3 are from the International Telecommunications Satellite Organization.