4. Orbits - Geostationary

This is an orbit that allows the satellite to appear stationary in the sky.

It works because it is traveling at just the right speed to keep it above the same spot on Earth all the time.

The geostationary orbit is about 22,000 miles (37,000 Km) above the Earth and it is very popular with communication satellite companies. It is ideal for television broadcasting as customers can use a fixed antenna on the side of their house to point at the satellite.

However, there are some issues with this orbit

• Every country wants to use it but it can only support a limited number of satellites. Otherwise they interfere with one another.
• International organisations have been set up to allow a fair share of the orbit and to allocate satellite frequency bands to avoid interference.
• Time delay is a basic issue. For television, the 1/4 second delay is no problem as no-one is sending a message back. Telephone companies use it, and customers put up with the longish delay. However, as an Internet connection, the delay means it is no good for real-time games or time-sensitive communication.

Just like a torch shines a light on a certain spot, satellites can do the same - they can be designed to illuminate only certain parts of the Earth. This is called the satellite footprint and it is shaped to cover the customers it is designed to serve. This also helps reduce the satellite crowding problem.