Near-Earth orbits are becoming congested as a result of an increase in the number of objects in space-operational satellites as well as orbital space debris. The risk of collisions between satellites and space debris is also growing. Controlling the production of debris is crucial to the sustainable use of space. This article presents background information on space debris, including number, size, spatial distribution, source, and the threat to satellites. It also discusses international efforts to control the debris population, including the development of debris mitigation measurements, active removal of space debris, and space traffic management. KEYWORDS: space debris, collision risk, debris mitigation.
SINCE THE LAUNCH OF THE FIRST ARTIFICIAL SATELLITE, SPUTNIK 1, ON October 4, 1957, over four thousand rockets have sent more than six thousand payloads into orbit, greatly improving the world's capacity to retrieve, transmit, and share information. Unfortunately, space activities have produced large quantities of discarded equipment, rocket upper stages, defunct satellites, bolts, and other hardware released during the deployment of satellites, as well as fragments from the breakup of satellites and rocket upper stages. These objects are moving at high speed at different altitudes and inclination of orbit.As a result, the impact risk to existing space systems is increasing.
Space debris is a growing concern, as even small particles can be very destructive in a collision due to their high orbital speed. Objects in orbit must travel at extremely high speeds in order to resist the pull of gravity and remain in space. Orbital speeds in low-Earth orbit (LEO, defined as the region between altitudes of 200 and 2,000 km), are greater than 7 km/second (km/s), and the average relative speed of a piece of debris and a satellite in a collision is 10 km/s. The damage from such a hypervelocity impact has been widely studied through tests and numerical simulations. Shielding has been designed to protect some critical devices on satellites, but can only protect against small debris (<1 cm) and greatly increases the cost. In a catastrophic collision, enormous pieces of debris are produced, posing short-term and long-term threats to satellites in nearby orbits. Recent studies have shown that at some altitudes in LEO, collisions will become the dominant debris generation mechanism, and the debris generated would then feed back to the environment and induce more collisions (Kessler 2000; Kessler and Anz-Meador 2001; Liou and Johnson 2007). Space debris is a global problem that all spacefaring nations should take seriously.
This article considers why space debris is a problem, how space debris is distributed, what risks space debris poses to satellites, what international communities have done to ameliorate the problem, and what we should do in the future.
Damage to Spacecraft from Space Debris
The consequences of debris impacts on spacecraft can range from small surface pits due to micrometer-size impactors, via clear hole penetrations for millimeter-size objects, to mission-critical damage for projectiles larger than 1 cm.Any impact of a 10-cm catalog object on a spacecraft or orbital stage will most likely entail a catastrophic disintegration of the target. Figure 1 shows the results of a laboratory test impact between a small sphere of aluminum travelling at approximately 6.8 km/s and a block of aluminum 18 cm thick. This destructive energy is a consequence of high-impact velocities that are greater than 7 km/s in LEO, and the average relative speed of a piece of debris and a satellite in a collision is 10 km/s. For the extremely high relative velocity, the impact between space debris and spacecraft could be classified as hypervelocity impact, which is much different in physical phenomena compared to low-velocity and high-velocity impact.
Experimental tests or numerical simulation methods are the main tools used to understand the damage patterns to space structures from hypervelocity impacts of orbit debris. …