Space Debris

Space debris refers to the space junk or derelict human-made space objects in orbit around Earth. Space debris presents a hazard to astronauts, spacecraft, and large space facilities such as space stations.

Since the start of the space age in 1957, the natural meteoroid environment has been a design consideration for spacecraft. Meteoroids are an integral part of the interplanetary environment and sweep through Earth orbital space at an average speed of about 20 kilometers (km) per second. Space science data indicate that at any one moment, a total of approximately 200 kg of meteoroid mass is within some 2,000 km of Earth’s surface, the region of space (called low Earth orbit, or LEO) most frequently used. The majority of this mass is found in meteoroids about 0.01 cm diameter. However, lesser amounts of this total mass occur in meteoroid sizes both smaller and larger than 0.01 cm. The natural meteoroid flux varies in time as Earth travels around the Sun.

Human-made space debris is also called orbital debris and differs from natural meteoroids because it remains in Earth orbit during its lifetime and is not a transient phenomenon such as the meteoroid showers that occur as the Earth travels through interplanetary space around the Sun. The estimated mass of human-made objects orbiting the Earth within about 2,000 km of its surface is about 3 million kg, or about 15,000 times more mass than that represented by the natural meteoroid environment. These human-made objects are for the most part in high-inclination orbits and pass one another at an average relative velocity of 10 km per second. Most of this mass is contained in more than 3,000 spent rocket stages, inactive satellites, and a comparatively few active satellites. A lesser amount of space debris mass (some 40,000 kg) is distributed in more than 4,000 smaller-sized orbiting objects currently being tracked by space surveillance systems. The majority of these smaller space debris objects are the by-products of more than 130 on-orbit fragmentations (satellite breakup events). Recent studies indicate a total mass of at least 1,000 kg for orbital debris sizes of 1 cm or smaller and about 300 kg for orbital debris smaller than 0.1 cm. The explosion or fragmentation of a large space object also has the potential to produce a large number of smaller objects, objects too small to be detected by contemporary ground-based space surveillance systems. Consequently, this orbital debris environment is now considered more hazardous than the natural meteoroid environment to spacecraft operating in Earth orbit below an altitude of 2,000 km.

Two general types of orbital debris are of concern: (1) large objects (greater than 10 cm in diameter) whose population, while small in absolute terms, is large relative to the population of similar masses in the natural meteoroid environment, and (2) a much greater number of smaller objects (less than 10 cm in diameter), whose size distribution approximates the natural meteoroid population and whose numbers add to the “natural debris” environment in those size ranges. The interaction of these two general classes of space debris objects, combined with their long residence time in orbit, create further concern that new collisions producing additional fragments and causing the total space debris population to grow are inevitable.

Aerospace engineers consider the growing space debris problem when they design new spacecraft. In an attempt to make these new spacecraft as “litter-free” as possible, new spacecraft are designed with provisions for retrieval or removal at the end of their useful operations.

Questions to Ponder

•  What will happen if too much of space debris gets collected in the orbit?
• How does space debris harm our satellites?