(79K)Echo was NASA's first communications satellite project, launched on August 12, 1960. Echo was a passive satellite that reflected radio waves back to the ground. Earlier in the 1950's, the Navy had used the Moon as a passive reflector.
The Echo spacecraft was a 100 ft. diameter balloon made of aluminized polyester that was inflated after it was put in a 800-900 nmi. orbit. Radio waves could be bounced off the smooth aluminum surface. The frequencies used for Echo 1 were 960 and 2390 MHz. Two-way voice links "of good quality" were set-up between Bell Laboratories in Holmdel, NJ and the NASA station at Goldstone, CA. Some transmissions from the U. S. were received in England.
In the ground stations, the frequency modulation (FM) receivers used feedback (FMFB), phase-lock loops, and low noise amplifiers using solid state masers. Echo demonstrated satellite tracking and ground station technology that would be used in later active systems.
Leonard Jaffe, the director of the communications program at NASA Headquarters, wrote:
Numerous experiments were conducted with Echo I in the early months involving practically all of the types of communications. Echo I not only proved that microwave transmission to and from satellites in space was understood and there would be no surprised but it dramatically demonstrated the promise of communications satellites. The success of Echo I had more to do with the motivations of following communications satellite research than any other single event. [Jaffe, pg 80]
Echo II was launched on January 25, 1964. It had an improved inflation system to improve the balloon's smoothness and sphericity. Echo II investigations were concerned less with communications and more with the dynamics of large spacecraft.
The U. S. Navy had begun communications experiments bouncing radio signals off the Moon in 1954. The world's first operational space communications system, called Communication by Moon Relay (CMR), was used between 1959 and 1963 to link Hawaii and Washington, DC.
The first active communications satellite, Project SCORE, had been launched almost two years before Echo 1 by the Department of Defense (DoD). SCORE stands for Signal Communication by Orbiting Relay Equipment. It was an active system that received radio signals from the ground and retransmitted them.
Another passive system, called West Ford, was launched by the DoD in 1963. In this system the reflector consisted of a belt of 480 million of hair-thin copper filaments each about 3/4 inch long. West Ford was developed by MIT Lincoln Laboratory.
After Echo II, NASA abandonded passive communications systems in favor of the superior performance of active satellites.
Echo 1 was built by Schjeldahl (balloon) and Grumman (dispenser) for NASA's Langley Research Center. Echo 2 was managed by NASA's Goddard Space Flight Center.