Space debris describes particulates in the vacuum of outer space, specifically particles originating from human activity that remain in geocentric orbit around the Earth. The International Association of Astronauts define space debris as "any man-made Earth orbiting object which is non-functional with no reasonable expectation of assuming or resuming its intended function or any other function for which it is or can be expected to be authorized, including fragments and parts thereof".
Space debris is classified by size and operational purpose, and divided into four main subsets: inactive payloads, operational debris, fragmentation debris and microparticulate matter. Inactive payloads refer to any launched space objects that have lost the capability to reconnect to its corresponding space operator; thus, preventing a return to Earth. In contrast, operational debris describes the matter associated with the propulsion of a larger entity into space, which may include upper rocket stages and ejected nose cones. Fragmentation debris refers to any object in space that has become dissociated from a larger entity by means of explosion, collision or deterioration. Microparticulate matter describes space matter that typically cannot be seen singly with the naked eye, including particles, gases, and spaceglow.
In response to research that concluded that impacts from Earth orbital debris could lead to greater hazards to spacecraft than the natural meteoroid environment, NASA began the orbital debris program in 1979, initiated by the Space Sciences branch at Johnson Space Center (JSC). Beginning with an initial budget of $70,000, the NASA orbital debris program began with the initial goals of characterizing hazards induced by space debris and creating mitigation standards that would minimize the growth of the orbital debris environment. By 1990, the NASA orbital debris program created a debris monitoring program, which included mechanisms to sample the low Earth orbit (LEO) environment for debris as small as 6mm using the Haystack X-band ground radar.