DK Space: Satellites
A spacecraft that travels in a steady path, or orbit, around Earth is called a satellite. Satellites receive and send on communication and navigation signals, watch the weather, survey the land, and study space.
Satellites stay in orbit because of their speed. A satellite in orbit about 190 miles (300 km) above Earth must travel at a speed of 17,500 mph (28,200 km/h) to stay in space. This speed is called its orbital velocity. There are several types of SATELLITE ORBIT.
Satellites travel around Earth in elliptical (oval) orbits, over the equator, over the poles, or on paths in between.
Low-flying satellites may fall back to Earth after only a few months because they pass through traces of air in the upper atmosphere, which slow them down. High-flying satellites can stay in space forever.