Laser geodetic satellites: a high-accuracy scientific tool

Satellite Laser Ranging (SLR) began in the mid-1960s on satellites of opportunity with retro-reflectors intended as a part of intercomparison tests of satellite tracking techniques. Shortly thereafter, data from these satellites began to work their way into geodetic solutions and dedicated geodesy experiments. By early 1970s when future requirements for centimeter accuracy were envisioned, planning began for dedicated, spherical retro-reflector geodetic satellites. Built with high mass-to-area ratios, these satellites would have important applications in gravity field modeling, station geolocation and fiducial reference systems, Earth rotation, and fundamental physics. Early geodetic satellites were Starlette, launched in 1975 by Centre National d’Etudes Spatiales (CNES), and LAGEOS in 1976 by the National Aeronautics and Space Administration (NASA). Recent geodetic satellites include LARES, launched in 2012, and LARES-2 under development, both by the Italian Space Agency (ASI). Today, a complex of these ‘geodetic satellites’ from low to high altitude Earth orbits supports many space geodesy requirements. This paper will discuss the evolution of the geodetic satellites from the early days, through current programs and out to future needs as we approach our goal for millimeter accuracy.