Several Low-Earth-Orbit (LEO) networks were proposed, but only one got off the ground: the Iridium system. The original Iridium proposal called for a "constellation" of 77 satellites, which gave the plan its name: the element iridium has atomic number 77, meaning that an iridium atom has 77 orbiting electrons. Before the satellites were launched, the constellation was scaled back to 66 active satellites, but no one wanted to change the name to Dysprosium.
A NASA astronaut, forced to retire years earlier so he could save his family farm, has never given up his dream of space travel and looks to build his own rocket, despite the government's threats to stop him.
The contents of the city's images which are referable to physical forms can conveniently be classified into five types of elements: paths, edges, districts, nodes, and landmarks.
Paths are the channels along which the observer customarily, occasionally, or potentially moved.
Edges are the linear elements not used or considered as paths by the observer. They are the boundaries.
Districts are the medium-to-large sections of the city, conceived of as having two-dimensional extent.
Nodes are points, the strategic spots in a city into which an observer can enter, and which are the intensive foci to and from which they are traveling.
Landmarks are another type of point-reference, but in this case the observer does not enter within them, they are external. They are usually a rather simply defined physical object: building, sign, store, or mountain.