LAGEOS: An Earth Science Mission Built for Enduring Precision

On May 4, 1976, a spacecraft resembling a disco ball entered orbit almost 3,700 miles (6,000 kilometers) above Earth. This shiny, two‑foot‑wide (60‑centimeter) sphere called the Laser Geodynamics Satellite, or LAGEOS, is covered with 426 retroreflectors—small mirrored prisms designed to bounce laser light directly back to where it came from. Beneath its aluminum exterior sits a dense brass core that makes LAGEOS incredibly heavy (900 pounds or 400 kilograms) for its size. …