【英语时差8,16】地球同步卫星：速度和轨道-上

 A geostationary satellite orbits the planet at the same rate as the planet rotates, so the satellite is always over the same patch of ground. Cool! I’d like to have one of those about twenty feet over my house. Sadly, geos only work easily at one distance: 22,500 miles up. Other satellites can have different orbits, can’t they? Yes, they can. But that’s because they can also move at different speeds. A geo doesn’t have that option - by definition it must orbit at the same speed as the earth turns. And that speed determines how high it must be!