The ability of a satellite to stay in orbit is dependent on its velocity and the gravitational pull from the planet that the satellite is orbiting. The closer the satellite is to a planet, the faster it has to travel to maintain its orbit.
The orbit principles of Johann Kepler are the basis for the understanding of satellite orbit. Kepler was the first to describe the orbital shape of planets in a mathematical sense. He determined that Earth had an eliptical orbit around the Sun rather than the previous theory which stated that all planets orbited in a perfect circle. Kepler theorized that for an object to orbit the Earth, it must carry enough speed to maintain its path around the planet. Kepler's work helped scientists determine that the closer an object orbits the Earth, the stronger the gravitational pull on the object. Velocity must be increased or else the object would crash to Earth under the weight of the force of attraction.
Artificial satellites are launched into different levels of orbit. The most common satellite orbit is called geosynchronous orbit. Geosynchronous orbit means that it takes the satellite 24 hours to orbit the Earth. This type of orbit is used for communications and television satellites because the satellite remains in the same place over the Earth.
Orbiting satellites can be natural or man-made. The moon is a natural satellite of the earth. In turn, the earth orbits the sun and therefore is also considered to be a satellite of the sun.
All orbits are elliptical, moving closer to what they orbit at different points in their path. Some are circular, while others are oval in shape. When a satellite is nearest the sun, it is called the perihelion. The aphelion is the farthest point in the orbit around the sun .
Man-made satellites orbit the earth at different heights depending upon their purpose. The International Space Station orbits in the first 100 to 200 miles of space. Other satellites orbit approximately 23,000 miles above the equator in a path called a geosynchronous orbit. Some orbital paths pass over or near the poles and are called polar orbits.