Why NASA sends giant disco balls into space

Imagine a journey through space where you encounter an enormous disco ball. What would you do? Surprisingly, you soon after discover that this shiny sphere holds significant information about ancient civilizations. While it may sound like a tale from science fiction, it could soon become a reality. In the 1970s, NASA and the Italian Space Agency (ASI) jointly launched a giant disco ball into space. Its purpose? Teaching the humans of today and the civilizations of tomorrow about Earth.

On May 4, 1976, satellite LAGEOS-1 was launched into space. A few decades later, its younger sibling LAGEOS-2,  followed on October 22, 1992. Both of them carry brass and aluminum plaques adorned with depictions of Earth's continents as they appeared during their launch years. These historical markers preserve a snapshot of the world at a specific moment in time. But these satellites don’t just serve as cosmic time capsules, they also helped discover the very information they carry with them.

The primary purpose of these cosmic mirror balls is to serve as a high-precision target for laser ranging experiments. LAGEOS boasts a precise spherical shape, and is covered in 426 cube-corner retroreflectors. These retroreflectors reflect light or laser beams directly back to their source, aiding in accurate distance measurements. By precisely measuring the time it takes for a laser beam to travel to the satellite and back, scientists can accurately determine the satellite's distance from Earth.

These disco balls also hold the record for the longest-lived satellite in orbit dedicated to Earth observations. LAGEOS-1 has been circling the Earth for over 46 years, and LAGEOS-2 for over 30 years. As LAGEOS silently observes Earth's geophysical changes, its data has been instrumental in studying tectonic plate movements, Earth's rotation, and even the distribution of mass within our planet. And they will continue to do so, while also holding valuable knowledge for whoever it might find millions of years from now.