Note: Single-source report; awaiting corroboration.
Launched on May 4, 1976, the Laser Geodynamics Satellite (LAGEOS) is a two-foot-wide spherical satellite covered with 426 retroreflectors that reflect laser light back to Earth-based stations for precise distance measurements. Its dense brass core and spherical shape provide a stable orbit ideal for satellite laser ranging, enabling calculations accurate to within a few millimeters due to the precision of the speed of light.
For over fifty years, LAGEOS data have been instrumental in tracking tectonic plate movements, monitoring subtle crustal shifts, and measuring fault line motions. The satellite’s measurements have also enhanced understanding of Earth's shape and improved models of the planet’s gravity field.
Beyond its Earth science contributions, LAGEOS has helped confirm predictions of Einstein’s theory of general relativity, specifically the effects on orbits of massive bodies around Earth. In 1992, a second satellite, LAGEOS II, built by the Italian Space Agency and nearly identical to the original, was launched to allow even more precise comparative measurements.
Despite being one of the oldest scientific satellites still operational, LAGEOS continues to function due to its simple, maintenance-free design and minimal atmospheric drag from its high orbit. It is expected to remain in orbit for millions of years, maintaining its role as a long-term benchmark for Earth science.