A satellite's trajectory
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Put simply, an orbit is the sequence of positions in space of a star or artificial satellite in motion around another more massive star. An orbit’s trajectory is not random, but dictated by the laws of universal gravitation. |
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Consider the example of an artificial satellite orbiting Earth. Its trajectory depends first of all on the velocity and direction imparted by the launch vehicle. Once the satellite is released into space, it is subjected only to the Earth’s gravity, which causes it to adopt a regular, plane-curve trajectory. It is then said to be in orbit, or gravitating, about Earth.
| Experiment |
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Circular motion and satellites Draw a disc on a blackboard. Fix one end of a length of fishing line to its centre with a drawing pin. Then attach a piece of chalk to the other end. If you raise the chalk above the disc and then let it go, it falls vertically. However, if you throw the chalk outwards away from the centre, it revolves around the disk and is pulled toward its centre by the line. This phenomenon is similar to the orbital motion of satellites. |
Illustrated by Jean-Pierre Penot (CNES) and Bernard Nicolas, illustrated by Bernard Nicolas
The satellite moves within a specific plane passing through the centre of the Earth and containing the velocity vector imparted by the launcher.
An orbit may be equatorial (in the plane of the equator), polar (passing above or near the poles) or inclined with respect to the equatorial plane.
These general characteristics of a satellite orbit apply irrespective of the attracting celestial body.
