LAGEOS (Laser Geodetic Satellite) was a very dense (high mass-to-area ratio) laser retroreflector satellite which provided a permanent reference point in a very stable orbit for such precision earth-dynamics measurements as crustal motions, regional strains, fault motions, polar motion and earth-rotation variations, solid earth tides, and other kinematic and dynamic parameters associated with earthquake assessment and alleviation. The performance in orbit of LAGEOS was limited only by degradation of the retroreflectors, so many decades of useful life can be expected. The high mass-to-area ratio and the precise, stable (attitude-independent) geometry of the spacecraft, together with the orbit, made this satellite the most precise position reference available. Because it is visible in all parts of the world and has an extended operation life in orbit, LAGEOS can serve as a fundamental standard for decades.
In conjunction with appropriate laser-tracking systems, LAGEOS permitted extreme precision-ranging measurements for both geometric mode (multilateration) and orbital dynamic mode determinations of positions of points on the earth. It was the first spacecraft dedicated exclusively to high-precision laser ranging and provided the first opportunity to acquire laser-ranging data that were not degraded by errors originating in the target satellite. The high-accuracy range measurements from this permanent-orbiting reference point were used to accomplish many extreme precision earth-dynamics measurements required by the earthquake hazard assessment and alleviation objectives of the Earth and Ocean Physics Applications Program (EOPAP). References: 1 , 2 , 5 , 6 .