Physics Narrative for 11-14
Geostationary and polar orbits
Satellites can operate in several different types of Earth orbit. A geostationary orbit is one in which the satellite is always in the same position with respect to the rotating Earth. The satellite orbits at an elevation of approximately 35 831 km, because that produces an orbital period (time for one orbit) equal to the period of rotation of the Earth (23 hour, 56 minute, 4.09 second).
By orbiting at the same rate, in the same direction as the Earth (synchronous with respect to the rotation of the Earth), the satellite appears stationary from the Earth's surface. The big problem with geostationary satellites is that there is only one distance from the Earth where they can orbit while maintaining the same position above the Earth's surface. Given that there are now over 22 000 satellites in orbit around the Earth, this geostationary orbit is getting highly crowded and there is great competition for space.
Other satellites are in polar orbits. On every circuit of the Earth, a polar satellite travels over both the North and South poles. Polar satellites do not remain above the same spot on the Earth's surface and the data they provide is usually only updated once per orbit as they pass across the ground control station on the Earth – approximately once every 90 minutes in most cases.