NASA has developed a satellite called LAGEOS and placed it in orbit in such a way that it can be seen from ground stations all over the world. The satellite is covered with special reflectors that are made to reflect laser beams sent by stations on the ground. Scientists measure the time between the transmission of the light from the ground and its reception by the satellite to determine the distance between the satellite and the station. The long-term data they obtain from these measurements is used to follow the movement of the tectonic plates, to calculate the gravitational field of the Earth and for other scientific research.
The ground stations that track LAGEOS are found all over the world. There are stations in the USA, China, France, Poland, Italy, Japan, Australia, Mexico and Peru. The satellite is set to crash land and decay in 8 million years and it carries a special message for the beings that will then be inhabiting the Earth. The message includes three different maps of the planet – one from 268 million years ago, one from present days and an impression of the future, when the satellite is about to be demolished.