Border Points: Each cluster has a limited number of defined "border points" – these are the gateways in and out of the cluster.
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This almost certainly won’t happen to the ISS. At the same time, it’s a far more extreme version of the only way an American space station has ever come down. In 1979, after years spent vacant in orbit, Skylab, the US’s first space station, started sinking toward the atmosphere, where it threatened to fall and drop molten spacecraft parts on Earth. At that point, NASA officials had to remotely wake up its computers and, with only limited control of the station, direct it over a location that would endanger the fewest humans.