Project Echo

Project Echo was the first passive communications satellite experiment. Each of the two American spacecraft, launched in 1960 and 1964, was a metalized balloon satellite acting as a passive reflector of microwave signals. Communication signals were bounced off them from one point on Earth to another.

Echo 1

NASA's Echo 1 satellite was built by Gilmore Schjeldahl's G.T. Schjeldahl Company in Northfield, Minnesota. The balloon satellite functioned as a reflector, not a transceiver, so that after it was placed in a low Earth orbit, a signal would be sent to it, reflected or bounced off its surface, and then returned to Earth.

During ground inflation tests, 40,000 pounds (18,000 kg) of air was needed to fill the balloon, but while in orbit, several pounds of gas were all that was required to fill the sphere. At launch, the balloon weighed 156.995 pounds (71.212 kg) which included 33.34 pounds (15.12 kg) of sublimating powders of two types. The first weighing 10 pounds (4.5 kg) with a very high vapor pressure, the second with a much lower vapor pressure. According to NASA, "To keep the sphere inflated in spite of meteorite punctures and skin permeability, a make-up gas system using evaporating liquid or crystals of a subliming solid were incorporated inside the satellite."