A tiny flake of paint orbiting Earth can strike a spacecraft with the force of a bullet.

Objects in Low Earth Orbit (LEO) travel at approximately 7.8 kilometers per second, which is about 17,500 miles per hour. Kinetic energy is calculated as half the mass times the velocity squared, meaning that as speed increases, the destructive potential grows exponentially. A paint chip just a few millimeters wide traveling at these speeds can hit with the same impact energy as a 40-caliber bullet.NASA and the European Space Agency (ESA) have documented numerous instances of such damage. In 1983, a tiny 0.2-millimeter paint flake hit the windshield of the Space Shuttle Challenger, creating a pit nearly 4 millimeters wide. This impact forced NASA to replace the entire window for safety reasons. Similar incidents have occurred on the International Space Station (ISS), including a 2016 strike that left a 7-millimeter crack in a window of the Cupola module.To protect against these high-velocity impacts, the ISS uses Whipple shields. These consist of two layers of metal with a gap between them. The first layer breaks the debris into a cloud of smaller particles, and the second layer absorbs the remaining energy. For larger objects, the U.S. Space Surveillance Network tracks over 27,000 pieces of orbital debris to help spacecraft perform evasive maneuvers.The threat is growing due to the 'Kessler Syndrome,' a theory proposed by NASA scientist Donald Kessler in 1978. He suggested that the density of objects in LEO could eventually become high enough that collisions create a chain reaction of more debris. This would make certain orbits unusable for generations, highlighting the critical need for active debris removal technologies.