On 13 May 1960, a NASA Thor-Delta rocket carried the agency’s new Echo 1 satellite into a 1,000 mile orbit around the Earth. It was a 156.995 pound metalized sphere 100 feet in diameter, essentially an enormous, shiny balloon made of the same mylar as party balloons of today. It required forty thousand pounds of air to fully inflate the sphere at sea level, but in the rarefied atmosphere in orbit it only required a few pounds of gas.
Echo 1 was a passive satellite, used to reflect transcontinental and intercontinental telephone, radio, and television signals. It was so large and so reflective that it was easily visible to the naked eye for much of the Earth. It was expected to remain in orbit until sometime in 1964, but it survived much longer, and did not burn up in the atmosphere until 24 May 1968, eight years after its launch.
Its sister “satelloon” Echo 2 was even larger at 135 feet in diameter, therefore it was even more conspicuous while it was in orbit from 1964-1969. Both balloons were sufficiently large and lightweight that they experienced detectable pressure from the solar wind, providing support for the concept of a solar sail. They also secretly served as an early rudimentary GPS system, using the balloons’ positions and instruments to calculate the exact location of Moscow for America’s intercontinental ballistic missiles.