LAGEOS was the first spacecraft dedicated exclusively to high-precision laser ranging. LAGEOS-2, based on the original LAGEOS design, was built by the Italian Space Agency and launched in 1992. Looking like 900-pound golf balls, this pair of satellites with no sensors, electronics, or moving parts, but dimpled with hundreds of reflecting prisms, have helped scientists measure the movement of Earths tectonic plates, detect irregularities in the rotation of the planet, weigh it, and track small shifts in its center of mass.