The 40 Year Anniversary of the NASA Disco Ball

40 years ago, NASA put a giant disco ball in space. This disco ball has been revolving around the Earth for forty years and will continue to hang there for millions more. This NASA satellite was named LAGEOS and has transformed the ways that scientists explored and gathered data about Earth using relatively simple technology. According to Space.com, The 900-pound (408-kg) satellite has no onboard sensors, electronics or moving parts; it's simply a brass core surrounded by an aluminum shell that's covered in 426 retroreflectors. 

An important part of this laser satellite is the retroreflectors. Space.com further notes that the  retroreflectors, which reflect light with minimal scattering, made LAGEOS the first NASA orbiter to use a technique called laser ranging to take measurements. By sending light to LAGEOS and measuring how much time it took that light to bounce off the reflectors and make it back to Earth, NASA scientists could make measurements to millimeter-level precision of how far away LAGEOS was from the ground. Those measurements over time revealed how the ground stations were moving relative to Earth's center of mass. 

Previous satellites could only measure about 3 miles but this satellite could measure over 3,000 miles above the Earth within half an inch. Over the past 40 years, NASA has used LAGEOS to measure the movement of Earth's tectonic plates, detect irregularities in the rotation of the planet, weigh the Earth and track small shifts in its center of mass via tiny changes in the satellite's orbit and distance from Earth.