Rendezvous is the procedure by which space vehicles in differing flight paths and orbits can be placed into the same orbital space, with relative zero velocity, at a preselected location and time. Various types of rendezvous maneuvers have been developed, but all depend on orbital mechanics. Fundamentally, a satellite in orbit moves in an elliptical path created by the gravitational force of a celestial body such as a planet. The speed of the satellite is inversely proportional to the square root of the radius of the orbit (or more strictly the semimajor axis of the orbit). This means that larger orbits have slower speeds than smaller orbits. For example, a satellite orbiting 8,000 kilometers (4,960 miles) from the center of Earth (about 1,500 kilometers [930 miles] above the surface) moves twice as fast as a satellite in an orbit with a radius of 32,000 kilometers (19,840 miles; about 25,500 kilometers [15,810 miles] above the surface.)

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