Space debris


Space debris are defunct human-made objects in spaceprincipally in Earth orbitwhich no longer serve a useful function. These include derelict spacecraft, mission-related debris, and particularly numerous in-Earth orbit, fragmentation debris from the breakup of derelict rocket bodies and spacecraft. In addition to derelict human-made objects left in orbit, space debris includes fragments from disintegration, erosion, or collisions; solidified liquids expelled from spacecraft; unburned particles from solid rocket motors; and even paint flecks. Space debris represents a risk to spacecraft.
Space debris is typically a negative externality. It creates an external cost on others from the initial action to launch or use a spacecraft in near-Earth orbit, a cost that is typically not taken into account nor fully accounted for by the launcher or payload owner.
Several spacecraft, both crewed and un-crewed, have been damaged or destroyed by space debris. The measurement, mitigation, and potential removal of debris is conducted by some participants in the space industry.
, the European Space Agency's Space Environment statistics reported 40,230 artificial objects in orbit above the Earth regularly tracked by Space Surveillance Networks and maintained in their catalogue.
However, these are just the objects large enough to be tracked and in an orbit that makes tracking possible. Satellite debris that is in a Molniya orbit, such as the Kosmos Oko series, might be too high above the Northern Hemisphere to be tracked., more than 128 million pieces of debris smaller than, about 900,000 pieces of debris 1–10 cm, and around 34,000 of pieces larger than were estimated to be in orbit around the Earth. When the smallest objects of artificial space debris are grouped with micrometeoroids, they are together sometimes referred to by space agencies as MMOD.
Collisions with debris have become a hazard to spacecraft. The smallest objects cause damage akin to sandblasting, especially to solar panels and optics like telescopes or star trackers that cannot easily be protected by a ballistic shield.
Below, pieces of debris are denser than meteoroids. Most are dust from solid rocket motors, surface erosion debris like paint flakes, and frozen coolant from Soviet nuclear-powered satellites. For comparison, the International Space Station orbits in the range, while the two most recent large debris events, the 2007 Chinese antisatellite weapon test and the 2009 satellite collision, occurred at altitude. The ISS has Whipple shielding to resist damage from small MMOD. However, known debris with a collision chance over 1/10,000 are avoided by maneuvering the station.
According to a report published in January 2025, scientists are encouraging vigilance around closing airspace more often to avoid collisions between airline flights and space debris reentering the earth's atmosphere amid an increasing volume of both. Following a destructive event, the explosion of SpaceX's Starship Flight 7 on January 16, 2025, the US Federal Aviation Administration slowed air traffic in the area where debris was falling. This prompted several aircraft to request diversion because of low fuel levels while they were holding outside the Debris Response Area.

History

Space debris began to accumulate in Earth orbit with the launch of the first artificial satellite, Sputnik 1, launched into orbit in October 1957. But even before this event, humans might have produced ejecta that became space debris, as in the August 1957 Pascal B test. Space debris for example was ejected in 1957 purposefully from an Aerobee launch system in a likely failed attempt to reach for the first time escape velocity from Earth, and therefore space beyond Earth. Going back further, natural ejecta from Earth has entered orbit.
After the launch of Sputnik, the North American Aerospace Defense Command began compiling a database of all known rocket launches and objects reaching orbit, including satellites, protective shields and upper-stages of launch vehicles. NASA later published modified versions of the database in two-line element sets, and beginning in the early 1980s, they were republished in the CelesTrak bulletin board system.
NORAD trackers who fed the database were aware of other objects in orbit, many of which were the result of in-orbit explosions. Some were deliberately caused during anti-satellite weapon testing in the 1960s, and others were the result of rocket stages blowing up in orbit as leftover propellant expanded and ruptured their tanks. More detailed databases and tracking systems were gradually developed, including Gabbard diagrams, to improve the modeling of orbital evolution and decay.
When the NORAD database became publicly available during the 1970s, techniques developed for the asteroid-belt were applied to the study of known artificial satellite objects.
Time and natural gravitational/atmospheric effects help to clear space debris. A variety of technological approaches have also been proposed, though most have not been implemented. A number of scholars have observed that systemic factors, political, legal, economic, and cultural, are the greatest impediment to the cleanup of near-Earth space. There has been little commercial incentive to reduce space debris since the associated cost does not accrue to the entity producing it. Rather, the cost falls to all users of the space environment who benefit from space technology and knowledge. A number of suggestions for increasing incentives to reduce space debris have been made. These would encourage companies to see the economic benefit of reducing debris more aggressively than existing government mandates require. In 1979, NASA founded the Orbital Debris Program to research mitigation measures for space debris in Earth orbit.

Debris growth

During the 1980s, NASA and other US groups attempted to limit the growth of debris. One trial solution was implemented by McDonnell Douglas in 1981 for the Delta launch vehicle by having the booster move away from its payload and vent any propellant remaining in its tanks. This eliminated one source for pressure buildup in the tanks which had previously caused them to explode and create additional orbital debris. Other countries were slower to adopt this measure and, due especially to a number of launches by the Soviet Union, the problem grew throughout the decade.
A new battery of studies followed as NASA, NORAD, and others attempted to better understand the orbital environment, with each adjusting the number of pieces of debris in the critical-mass zone upward. Although in 1981 the number of objects was estimated at 5,000, new detectors in the Ground-based Electro-Optical Deep Space Surveillance system found new objects. By the late 1990s, it was thought that most of the 28,000 launched objects had already decayed and about 8,500 remained in orbit. By 2005 this was adjusted upward to 13,000 objects remaining in orbit, and a 2006 study increased the number to 19,000 as a result of an ASAT and a satellite collision. In 2011, NASA said that 22,000 objects were being tracked.
A 2006 NASA model suggested that if no new launches took place, the environment would retain the then-known population until about 2055, when it would increase on its own. Richard Crowther of Britain's Defence Evaluation and Research Agency said in 2002 that he believed the cascade would begin about 2015. The US National Academy of Sciences, summarizing the professional view, noted widespread agreement that two bands of LEO space900 to and were already past critical density.
In the 2009 CEAS European Air and Space Conference, University of Southampton researcher Hugh Lewis predicted that the threat from space debris would rise 50 percent in the next decade and quadruple in the next 50 years., more than 13,000 close calls were tracked weekly.
A 2011 report by the US National Research Council warned NASA that the amount of orbiting space debris was at a critical level. According to some computer models, the amount of space debris "has reached a tipping point, with enough currently in orbit to continually collide and create even more debris, raising the risk of spacecraft failures." The report called for international regulations limiting debris and research of disposal methods.

Debris history in particular years

  • By mid-1994 there had been 68 breakups or debris "anomalous events" involving satellites launched by the former Soviet Union/Russia and 18 similar events had been discovered involving rocket bodies and other propulsion-related operational debris.
  • , 19,000 pieces of debris over were tracked by the United States Space Surveillance Network.
  • , estimates of more than 170 million pieces of debris smaller than, about 670,000 pieces 1–10 cm, and approximately 29,000 larger pieces were in orbit.
  • , nearly 18,000 artificial objects were orbiting above Earth, including 1,419 operational satellites.
  • , nearly 20,000 artificial objects were in orbit above the Earth, including 2,218 operational satellites.

    Characterization

Size and numbers

there were estimated to be over 128 million pieces of debris smaller than, and approximately 900,000 pieces between 1 and 10 cm. The count of large debris was 34,000 in 2019, and at least 37,000 by June 2023. The technical measurement cut-off is c..
, there were 8,000 metric tons of debris in orbit, a figure that is expected to increase.

Low Earth orbit

In the orbits nearest to Earthless than orbital altitude, referred to as low-Earth orbit there have traditionally been few "universal orbits" that keep a number of spacecraft in particular rings. There is currently 85% pollution in LEO. This was beginning to change in 2019, and several companies began to deploy the early phases of satellite internet constellations, which will have many universal orbits in LEO with 30 to 50 satellites per orbital plane and altitude. Traditionally, the most populated LEO orbits have been a number of Sun-synchronous satellites that keep a constant angle between the Sun and the orbital plane, making Earth observation easier with consistent sun angle and lighting. Sun-synchronous orbits are polar, meaning they cross over the polar regions. LEO satellites orbit in many planes, typically up to 15 times a day, causing frequent approaches between objects. The density of satellitesboth active and derelictis much higher in LEO.
Orbits are affected by gravitational perturbations, and collisions can occur from any direction. The average impact speed of collisions in Low Earth Orbit is 10 km/s with maximums reaching above 14 km/s due to orbital eccentricity. The 2009 satellite collision occurred at a closing speed of, creating over 2,000 large debris fragments. These debris cross many other orbits and increase debris collision risk.
It is theorized that a sufficiently large collision of spacecraft could potentially lead to a cascade effect, or even make some particular low Earth orbits effectively unusable for long term use by orbiting satellites, a phenomenon known as the Kessler syndrome. The theoretical effect is projected to be a theoretical runaway chain reaction of collisions that could occur, exponentially increasing the number and density of space debris in low-Earth orbit, and has been hypothesized to ensue beyond some critical density.
Crewed space missions are mostly at altitude and below, where air drag helps clear zones of fragments. The upper atmosphere is not a fixed density at any particular orbital altitude; it varies as a result of atmospheric tides and expands or contracts over longer time periods as a result of space weather. These longer-term effects can increase drag at lower altitudes; the 1990s expansion was a factor in reduced debris density. Another factor was fewer launches by Russia; the Soviet Union made most of their launches in the 1970s and 1980s.