We depend on communications satellites. These space-based relay stations are more active than we realize, receiving signals from the ground, filtering them, changing their frequencies, and amplifying them before sending them back to specific spots on Earth. But the first communications satellites were passive, simply reflecting signals back to a specific point Earth. They were the “Echo satellites” — the first launched in 1960 and the second launched just over 50 years ago on January 25, 1964.
The Echo program began in 1956 as a National Advisory Committee for Aeronautics experiment. The large, balloon-inspired satellites were designed primarily to test the effects the upper atmosphere on large lightweight orbital structures. But a second use for a reflective body in space soon occurred to John Robinson Pierce and Rudolf Kompfner, two researchers with AT&T’s Bell Telephone Laboratories. Already interested in using satellites for communications, they realized the Echo was a perfect passive communications test bed. The satellite couldn’t do much, but it would be a great body off which to bounce signals, sending them from one point on Earth to another. When the NACA was dissolved and replaced by NASA, Echo became a NASA project.
The first Echo satellites were designed and built by engineers at NASA’s Langley Research Center. The first version called Echo 1 (properly Echo 1A after Echo 1 was destroyed during a failed launch attempt) was a 100-foot-diameter balloon with a mylar polyester skin just 0.0127 millimeters thick. And though it weighed just 150 pounds, in space it needed just a few pounds of gas to stay inflated. On board was a set of beacon transmitters for telemetry data that were powered by five nickel-cadmium batteries. The batteries were in turn charged by 70 solar cells mounted on the balloon.
Echo 1 launched on Aug. 12, 1960, and enabled some important firsts in satellite communications. It saw the first live satellite-based voice communication; a radio message delivered by President Eisenhower; the first satellite-transferred image; an image of the President; and the first transcontinental satellite phone call was made between two researchers. It was also one among the first satellites to feel the effects of solar wind. Like a solar sail, Echo 1 responded to the pressure of photons that pushed it around and distorted the satellite’s orbit.
Echo 2 followed four years later, another passive communications satellite larger than its predecessor. Although it had a similar battery-powered beacon telemetry system on board to provide a tracking signal, monitored the balloon’s skin temperature, and managed its internal pressure to keep it inflated, Echo 2 was more advanced than its predecessor in a few ways. For one, it was larger with a nearly 135-foot diameter. It featured a better inflation system, which meant that once it was inflated in orbit the balloon’s skin was smoother and its overall shape more spherical. As a secondary aim, Echo 2 helped scientists gather more data about the dynamics of large spacecraft in orbit and about the shape and size of large areas of the Earth.
Echo 2 marked the end of NASA’s investigation into passive communications satellites. These balloons were massive compared to the active communications satellites and far less sophisticated. At the same time that Echo 1 was scoring firsts for the nascent world of space-based communications, AT&T was developing the active communications satellite called Telstar. Echo 1A reentered on May 24, 1968. Echo 2 followed on June 7, 1969.
Source: Discovery News