Echo 1 is amusing. You see how it looks like it's just a giant mirrored balloon?
That's because THAT'S EXACTLY WHAT IT IS!
It was the first communication satellite, and it was completely passive: There's no electronics for the communications. Ground-based stations just aimed a radio signal at it and the signal would bounce right off and come back to earth, where it could be picked up again, on the other side of the country.
(There were some electronics in the balloon: a radio transmitter & some solar panels, but those were just used to track where the balloon was, so you knew where to aim your antennas)
Later active communications satellites have a radio system on board, where they receive the signal and then rebroadcast it amplified and directed, but it turns out if you just have something to bounce a radio wave off, you can do transcontinental radio signals with just a big balloon.
It stayed up there for nearly 8 years.
Fun fact: this is the first communication satellite used, but not the first launched. The "Echo 1" is actually "Echo 1A". The original Echo 1 was on a Thor-Delta that had a faulty Delta stage, so it launched into the Atlantic ocean.
And even before Echo, they tried a prototype on a "Shotput" rocket. That one launched to the intended altitude just fine, but had a problem with the balloon inflating, so that it just exploded. Apparently it was visible for the entire East Coast of the US, since the reflective mylar pieces glittered in the sunlight.
In fact, all the Echo balloons (There was a bigger Echo 2 launched in 1964) were very visible. They were big silvery balls orbiting in a relatively low orbit, so once it got dark (but the sun was still hitting the balloon) you could see them with the naked eye. The only picture I can find for that is this one:
That's a long exposure showing the satellite passing over NASA's Jet Propulsion Lab in Pasadena, California. This picture is from the day it launched!
JPL was one of the stations testing it, and they successfully bounced a signal off it that was picked up in New Jersey. That's 2430 miles/3910km as the cow flies.
A very cool day for space science... and it had a secondary effect that was even better.
So the signal was very weak, as you might expect. They're bouncing it off a balloon that's a thousand miles (1600km) up. To be able to pick up the reflected signal, the receiving location had to have a MASSIVE antenna.
So they built one! it's 50 feet (15m) long, and can rotate in two axises, to let it aim at all the sky. I don't think it was motorized, but it's got a lot of low-friction bearing so a couple of people working together could rotate it by hand.
So this is where the bounced Echo 1 (really Echo 1A) signal was received, but that's not the most important thing this antenna did. See, when it wasn't being used for satellite tests, it was also a radio telescope being used to study the more distant universe... and in 1965 two scientists named Arno Penzias and Robert Wilson discovered the Cosmic Microwave Background Radiation.
The CMBR (or CMB) is microwave radiation that fills all space in the universe. Even in the gaps between stars, where there shouldn't be any radiation, there's the thin CMBR: This was the proof needed to validate the Big Bang theory, because it shows that early in the universe's life, it was filled with a dense hot plasma which slowly cooled into the current universe.
So a side effect of THIS FUCKING BALLOON provided the evidence we needed to determine that The Big Bang was the correct theory of the early universe. Quite a lot of science from 400lb (180kg) of mylar!
