Satellites remain in orbit because the momentum of the satellite and the pull of earth's gravity are balanced. Gravity is an attraction toward the center of the earth. Momentum is the speed or velocity at which an object moves. If the pull of the earth's gravity and the momentum of the object are unbalanced, the object either falls back to Earth or spins off into outer space.
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.