The Satellites that Surround Earth
			
		
		
		
			Thousands of 
satellites orbit the Earth.  
Costing billions of dollars, this swarm of 
high altitude robots is now vital to 
communication, 
orientation, and imaging both 
Earth and space.  
One common type of 
orbit is geostationary where a satellite will appear to 
hover above one point on Earth's equator.  
Geostationary orbits 
are very high up -- over five times the radius of the 
Earth -- 
and possible only because the satellite 
orbital period is exactly one day.  
It is usually cheaper to place a 
satellite in low Earth orbit, around 500 kilometers, 
just high enough to avoid the effect of 
Earth's atmosphere.  
The above animated sequence starts by showing the halo of 
Earth's satellites, including the ring at geostationary, and finishes by zooming 
in on the only one currently hosting humans: the 
International Space Station.