Above: A map of the geostationary arc (and a bunch of other satellites too).
The arc is a ring of satellites in the most prized of all orbits, geostationary orbit. Here a satellite will take 24 hours to orbit the Earth once – so, in effect, it hangs motionless in Earth’s sky. That’s a pretty useful property to have, whether your space platform's job is communication, navigation, surveillance, weather monitoring, or… well, anything.
Above: The view from one point on the arc, the Echostar 11 satellite.
True, it’s a bit of a cheat: The belt isn’t a single, solid structure – although it’s members do hold a constant pattern. But then, many things we regard as structures aren’t one piece: The stones of stone circles don’t all connect to each other, nor do all the houses in a city or all the trees in the forest. And the GEO ring is definitely going to last to last as long as any stone circle: With no weather, nor oxidising atmosphere to attack them, and orbits that stay up for millions of years, the satellites in the ring will be a permanent trace of our civilisation – perhaps for far longer than our civilisation will exist…