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date: 29 November 2020

Space Law and Hazardous Space Debrisfree

  • Martha Mejía-KaiserMartha Mejía-KaiserInternational Institute of Space Law


International space law is a branch of public international law. Norms of treaty law and customary law provide a foundation for the behavior of the subjects of international law performing space activities. Five multilateral space treaties are in effect, which are complemented by important recommendations of international organizations such as United Nations (UN) General Assembly Resolutions and International Telecommunication Union (ITU) Regulations.

The Inter-Agency Space Debris Mitigation Coordination Committee (IADC), a non-governmental body composed of several space agencies (for instance, the European Space Agency, the United States National Aeronautics and Space Administration, the Japanese Aerospace Exploration Agency, the Russian Federal Space Agency), issued its Space Debris Mitigation Guidelines in 2002. The IADC defines “space debris” as “all man-made space objects including fragments and elements thereof, in Earth orbit or re-entering the atmosphere, that are non-functional” (IADC, 2002, Revision 1, 2007, 3.1. Space Debris). Although the term “space debris” was not included in any space treaty, the drafters of the space treaties considered space objects as “hazardous” because “component parts of a space object as well as its launch vehicles and parts thereof” detach in course of normal launching operations, because space objects can fragment during an attempted launch, and because space objects that re-enter Earth’s atmosphere and survive friction have the potential to cause damage. In addition, radioactive and chemical substances on board space objects may represent a hazard to populations and the environment on the Earth.

Besides the threats to aircraft in flight and to persons and property on the surface of the Earth, space debris in orbit is increasing alarmingly and poses a threat to manned space missions and non-manned space objects. While the Convention on International Liability for Damages Caused by Space Objects (Liability Convention, 1972) considers the threats of space objects during launch, in outer space, and when entering the Earth’s atmosphere, there have been efforts to minimize the generation of space debris in orbit, outside the framework of the space treaties.

The IADC Space Debris Mitigation Guidelines are a comprehensive list of recommendations to launching states, owners, and operators of space objects. They are increasingly recognized by states through the creation of codes of conduct, national legislation, recommendations of international organizations, and state practice. Furthermore, non-governmental institutions, like the International Organization for Standardization, are providing more detailed technical instructions for the implementation of the Space Debris Mitigation Guidelines, which are a breakthrough for the application of the guidelines by states of different economic and technical standing.

Even though states are reluctant to accept new obligations through treaties, recommendations and state practice are becoming powerful instruments to avert the dangers of hazardous space debris that may create damage on the Earth or in orbit. Space debris also is becoming one of the drivers for the initiatives of the United Nations on the long-term sustainability of outer space activities to promote the existing mitigation guidelines and to formulate new guidelines for clearing outer space of debris.


After the Soviet Union launched the first space object in 1957, the United States and other states followed, although at that time only a few states were financially and technically fit to reach outer space.

In this framework, representatives of states gathered in the United Nations and negotiated the first rules for the activities in outer space. The UN General Assembly (UNGA) created the Committee on the Peaceful Use of Outer Space (COPUOS) by act of Resolution 1348 (UNGA, 1958), initially composed of representatives of eighteen states. In this forum, delegates discussed the ongoing developments of space activities, foresaw possible advances, and considered their concerns and hopes. This was the place where five space treaties were drafted and adopted, becoming legally binding for those states that ratified them. The Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies (Outer Space Treaty, 1967) was the first space treaty that entered into force; as of 2019 it had been ratified by 109 states (COPUOS, 2019a).

The Outer Space Treaty highlights that space activities should be conducted for the benefit and in the interest of all countries, regardless of their economic or technical standing. Article IX of this Treaty calls upon states to avoid harmful contamination of outer space when performing space activities (Marchisio, 2009, pp. 176–177).

Many provisions in the space treaties were visionary at the time of their drafting. However, nobody foresaw that an increasing number of states engaging in the exploration and use of outer space and a growing number of launches would create higher risks to persons and property on Earth, to humans working in outer space and also to operational space objects. Though no more space treaties have been drafted, the UN General Assembly has approved several resolutions that help to interpret concepts contained in space treaties and address topics not included therein.

This is an interdisciplinary area that connects space physical sciences, technologies, systems and operations with policy and law, and is of importance for the whole international community (UN Secretary-General, 1999).

Hazardous Space Debris

Space debris can be divided into two categories: (a) space debris falling to the Earth, either generated during a launch in the Earth’s atmosphere or re-entering the Earth’s atmosphere from outer space; and (b) space debris in orbit. The latter category is known as “orbital space debris” (IAA, 2005, p. 6).

Regarding the term “hazardous,” there is no internationally agreed definition. It has been defined as “involving danger; perilous; risky; involving risk of loss” in Blacks’ Law Dictionary (Nolan & Nolan-Halley, 1991). The terms “hazardous” and “hazard” appear in the Agreement on the Rescue of Astronauts, the Return of Astronauts, and the Return of Objects Launched Into Outer Space (Rescue Agreement, 1968, Art. 5(4)), in the Convention on Registration of Objects Launched into Outer Space ( Registration Convention, 1974), Art. VI), and in the UNGA Resolution Principles Relevant to the Use of Nuclear Power Sources in Outer Space (UNGA, 1992, NPS Resolution 47/68, Principle 3(1)(a)). The nuclear power sources (NPS) resolution puts its focus on radiological hazards and calls for the protection of “individuals, populations and the biosphere”.

Outside of the scope of the legal and political instruments for space activities, the Draft Articles on Prevention of Transboundary Harm from Hazardous Activities, prepared by the UN International Law Commission (ILC), do not contain a definition of the term “hazardous,” but the document’s commentary considers that “[t]he harm must lead to a real detrimental effect on matters such as, for example, human health, industry, property, environment or agriculture in other states” (ILC, 2001, p. 152).

The hazards posed by space debris do not mean that debris will with certainty cause damage, but that there is a high risk that damage can be caused and therefore measures to mitigate such hazard need to be taken.

Once a space object has been considered as hazardous, it would make sense that the “launching state” for that space object should be responsible to mitigate the hazard. The launching state is the state “which launches or procures the launching of a space object [and a] State from whose territory or facility a space object is launched” (Liability Convention, 1972, Art. I(c)). Since space treaties neither define space debris, nor expressly address it, the way how states should manage the different sorts of hazards need to be identified under their existing obligations and relevant recommendations of space law.

Hazardous Space Debris During Launch and Re-Entry Into the Earth’s Atmosphere

Kinetic Hazard

During the debates at COPUOS for the drafting of space treaties, concerns were expressed that launch vehicles and detached parts thereof of one state could cause damage to another state during normal launch operations. Launch failures were also considered as a hazard, and therefore the term “attempted launching” was included in the definition of “launching” of Article I of the Liability Convention (COPUOS, 1969a, A/AC.105/58, p. 8; Smith & Kerrest, 2013, p. 106).

Launch systems are a prerequisite for placing a space object in outer space, and they usually consist of several stages. In order to reduce the exposure of hazards to populated areas resulting from spent stages that separate from the parent body during nominal launch, and also in order to reduce damage risks in case of launch failures (Harland & Lorenz, 2005, pp. 47–58, 137), launches of space objects are usually performed from coastal installations or installations in non-populated areas (Clark, 2016). However, some installations have a launch corridor over populated areas in the same country of launch, as in China or Kazakhstan, where, from time to time, spent stages cause injury or death of persons, damage to property of nationals of those states or damage to the environment (Cooper, 2018; Space Safety Magazine, 2015).

Rocket stages and other released objects that reach outer space and become orbital space debris (released as part of normal launch operations, because of malfunctions, or as result of a fragmentation event), are mainly under the gravitational influence of the Earth that pulls them to re-enter the atmosphere. Most of these debris objects disintegrate during atmospheric re-entry, but massive space debris, or hard metals contained therein, can survive atmospheric re-entry (IAA, 2005, p. 24; Lindinger, 2013). Uncontrolled re-entries of space debris into the Earth’s atmosphere represent a hazard to the population. There is an increasing number of such space debris objects reaching the surface of the Earth (Space Safety Magazine, n.d.; UNOOSA, n.d.b). For instance, the US Skylab re-entered the atmosphere in 1979. Although NASA attempted to reduce risks to the population by applying some de-orbiting maneuvers, some fragments fell onto Australian territory, where no damage was reported (Hanes, 2018; Sweeney, Oliver, & Leech, 1988). In 1991, the Soviet Salyut-7 space station dismembered during its re-entry in the atmosphere and many fragments reached Argentinian soil, where no serious damage was reported (Lyall & Larsen, 2018, p. 108; Reuters, 1991). The Russian Mir Station (COPUOS, 2001, A/AC.105/759) had a controlled atmospheric re-entry (Klinkrad, 2001, p. 513), while the Chinese Tiangong-1 Station (COPUOS, 2017, A/AC.1150/Add.1) had an uncontrolled re-entry (Berging & Barbosa, 2018; Vellutini et al., 2018, p. 2). Both space stations reached the ocean—Pacific and Atlantic respectively—without causing any harm.

While there is no international legal instrument that imposes a duty on states to “seek to avoid a potential terrestrial impact by [their] re-entrant object” (Lyall & Larsen, 2018, p. 109), states will often apply orbital maneuvers to diminish the hazard, if the spacecraft is still in a condition that it can be maneuvered. The situation is different with space debris that re-enters the Earth’s atmosphere in an uncontrolled way. Space debris objects in outer space are under the influence of many natural factors and hence do not have a repeatable orbit, so the trajectory of a space object “can only be estimated statistically” (Finkleman, 2015). This results in uncertainty in predictions of the moment of atmospheric re-entry and of the location of the point of impact on the surface of the Earth.

States have no duty to inform of upcoming atmospheric re-entries. Only through the NPS Resolution (UNGA, 1992, NPS Resolution 47/68, Principle 5) are launching states recommended to notify states that may be in danger of the atmospheric re-entry of a space object containing radioactive materials. Some states issue public communications about massive space debris without nuclear materials when they consider that the debris may survive atmospheric friction (Lyall & Larsen, 2018, p. 106). Some private institutions provide regular information about re-entries to the public (Aerospace Corporation, n.d.; Satview, n.d.). In order to reduce the hazard of impact with aircraft in flight, authorities of states under the path of re-entering hazardous space debris may use such information to take measures such as closing their air space to aircraft. Since the point of impact is only known with limited precision and with a short lead-time (Sgobba, 2013), evacuation of the possible impact area is very unlikely; hence, states lack timely and effective protective measures. Drafters of the space treaties were aware that kinetic hazards during launch and re-entry could not completely be avoided (Cheng, 1979, pp. 83–84). They also knew that states would nevertheless continue launching space objects (just in 2018, 114 launches sent 469 spacecraft into outer space; Bryce Report, 2018), so they sought agreement on liability for damage through the Outer Space Treaty and the Liability Convention.

Article VII of the Outer Space Treaty mandates that a state

that launches or procures the launching of an object into outer space, . . . and . . . from whose territory or facility an object is launched, is internationally liable for damage to another State Party to the Treaty or to its natural or juridical persons by such object or its component parts on the Earth, in air space or in outer space

(Outer Space Treaty, 1967).

This article implicitly also includes damage resulting from kinetic energy stored in component parts of the space object (e.g., momentum wheels).

Mechanisms for compensation of damage caused by space objects are widely elaborated in the Liability Convention. “Damage” is defined in this international legal instrument as “loss of life, personal injury or other impairment of health; or loss of or damage to property of States or of persons, natural or juridical, or property of international intergovernmental organizations” (Liability Convention, 1972, Art. I(a)). For the application of this treaty, it is necessary to prove the causal connection between the space object and the damage caused on “the surface of the Earth or to aircraft in flight.” The launching state is then “absolutely liable” and has the obligation to pay compensation (Art. II).

Nuclear Hazard

Several events motivated government representatives at COPUOS to discuss the matter of hazard due to the use of nuclear power sources. One of these events was the sinking of the service module of Apollo 13 with its plutonium power source into the Pacific Ocean in 1970 (NASA, 2019; Cheng, 1979, pp. 83–84). Another event was the Soviet satellite Cosmos-954, which used uranium 235 as a source of electrical power, that de-orbited in 1978, re-entered the Earth’s atmosphere, disintegrated over Canadian territory, and scattered several thousand fragments over a large area (COPUOS, 1978, A/AC.105/236).

Although the definition of damage of Article I of the Liability Convention does not specify the inclusion of nuclear damage, representatives of states agreed during the drafting of this treaty that the scope of the Liability Convention should be extended to cover nuclear damage (Cheng, 1979, p. 115; COPUOS, 1969b, A/AC.105/C.2/SR.118, p. 82).

The Rescue Agreement (1968) and the Liability Convention (1972) were already in force at the time of the Cosmos-954 atmospheric re-entry. The Rescue Agreement provides the steps to be followed in case a space object of one state is discovered in the territory of another, and clarifies the rights and obligations of the involved parties. Article 5(2) of this treaty stipulates that the launching state of a space object or its component parts discovered in the territory of another state, has the right to request the return of the such space object (Rescue Agreement, 1968), but the Soviet Union did not make use of this right. Article 5 of the Rescue Agreement indicates that the state of the territory on which the space object was found may notify the launching authority in case the space object “is of a hazardous or deleterious nature,” that the launching State shall “immediately take effective steps, under the direction and control of the said Contracting Party, to eliminate possible danger or harm,” and that the expenses for the recovery and return shall be borne by the launching authority. The Canadian government duly notified the Soviet authorities on the “intrusion into Canadian air space of a Soviet space object, the Cosmos 954 satellite, and the deposit on Canadian territory of hazardous radioactive debris from the satellite” (USSR, 1978), but it did not ask the Soviet Union to engage in the recovery of the fragments. Canada, with the assistance of the United States, engaged in an expensive search and recovery action of the fragments. The Soviet Union showed no interest in the return of fragments and stated that “the Canadian side can continue to dispose of them at its own discretion” (USSR, 1978). Canada invoked the Liability Convention by submitting a claim to the Soviet Union for the costs of the operation, yet the Canadian government did not report any death, injuries or damage to property (Canada, 1978, NO. FLA-268; Cohen, 1984). The Soviet Union paid only part of the costs after diplomatic negotiations, outside the framework of the Liability Convention or of any other space treaty (UNOOSA, 1981), which was considered by Terekhov (1992) to be an ex gratia settlement. In the same year of the Cosmos 954 accident, in a paragraph of UN Resolution 33/16, the General Assembly requested launching states to inform concerned states when a space object with nuclear power source malfunctions and bears the risk of re-entering the Earth’s atmosphere (UNGA, 1978, Resolution 33/16, para. 9).

Some years later, the UN General Assembly adopted a resolution dedicated to the use of NPS in space objects (UNGA, 1992, NPS Resolution 47/68). In its preamble, the resolution states that safety assessments should be undertaken to reduce “the risk of accidental exposure of the public to harmful radiation or radioactive material,” and that the principles apply only to nuclear power sources that generate electrical power on board the spacecraft for non-propulsive purposes. The NPS Principles furthermore recommend that the use of NPS is restricted to “space missions which cannot be operated by non-nuclear energy sources in a reasonable way,” and that only highly enriched uranium 235 is used (NPS Principle 3) (Goh Escolar, 2015, pp. 219–226). This specific radioactive material is not suitable for use in weapons and, if it is stored in a safe containment system, does not explode even in case of a rocket explosion or when it is exposed to stress during atmospheric re-entry (NPS Principles 3(2)(e) and 3(3)(b); see Fischer, 1998, pp. 64–65).

The NPS Principles recommend restricting the operation of nuclear reactors on board spacecraft to those on interplanetary trajectories, in very high orbits where space debris have a long-lasting lifetime before their natural de-orbiting, and in low earth orbit (LEO) provided they are raised into a high orbit at their end-of-life (NPS Principle 3(2)).

Regarding interplanetary spacecraft, there are concerns about radiological exposure of the population and the environment in the event of a launch failure and of close approximations of the spacecraft to our planet, when the gravitational pull of the Earth is being used to accelerate and direct the space objects onto a desired interplanetary trajectory. The latter was the case of the US Galileo space probe to Jupiter which carried plutonium pellets to serve as power source for the instruments on board (Broad, 1989). Several months after launch, the Galileo probe came close to the Earth for a swing-by maneuver to put the spacecraft onto its path towards Jupiter. The US Cassini spacecraft, to explore Saturn and its Moons, also carried NPS on board and made a swing pass close to the Earth. Several groups in the United States initiated legal proceedings to stop the launch of both space probes, addressing the hazard of rocket failure at the moment of launch, and the hazard in case of failure during the swing-by maneuvers, either of which could result in a re-entry into the Earth’s atmosphere. The courts dismissed the claims and both spacecraft were cleared to launch (Florida Coalition for Peace and Justice v. Bush, 1989; Gorove, 1996, pp. 12–14; Hawai‘i County Green Party v. Clinton,1997).

Several hazardous space debris with NPS in Earth orbits have been transferred into so-called “nuclear safe orbits” (NSO), at altitudes where it is expected that the space debris will have about 300 years to naturally decay before re-entering the Earth’s atmosphere (Bennett, 2003). Between 1967 and 1988 the Soviet Union operated radar satellites “RORSAT” with NPS. In order to reduce the hazard of nuclear contamination in case of atmospheric re-entry, several radioactive cores of Soviet satellites were ejected into outer space, with the intention of causing them to fully disintegrate by air friction (Wiedemann et al., 2005, p. 478).

For malfunctioning space objects with NPS that bear the risk of re-entering the Earth’s atmosphere, the NPS Resolution recommends launching states to issue a notification of such events to “States concerned” (NPS Principle 5). States, other than the launching state, and international organizations with technical capabilities are called upon to contribute with timely information from space monitoring and tracking systems “to allow States that might be affected to assess the situation and take any precautionary measures deemed necessary” (NPS Principle 7). It is also recommended that the launching state aids the affected state “to eliminate actual and possible harmful effects” and to perform the retrieval of fragments and clean-up of the affected area (NPS Principle 7(2)(a)).

The NPS Resolution calls upon launching states to conduct safety assessments, to safely use the NPS, to consider all possible scenarios and to take measures to reduce the hazard as much as possible.

Outside of the scope of the space treaties, the Convention on Early Notification of a Nuclear Accident aims to minimize transboundary radiological consequences of an accident, including radiological hazards due to NPS on board space objects (Convention on Early Notification, 1986, Art. 1(2)(f)). This instrument entered into force on October 27, 1986 and has been ratified by more than 100 states (IAEA, n.d.).

Chemical Hazards

Space debris objects may pose hazards to the population and the environment not only by nuclear materials, but also by fuel remnants, gases (Cooper, 2018), chemicals for pyrotechnic mechanisms, and other toxic, explosive, or energy-charged materials.

The Japanese Hayabusa asteroid sample space probe made a controlled landing in Australia. After landing, during the retrieval of the sample canister from the space object, Japanese technicians neutralized the hazard of explosion “by cutting cables leading to pyrotechnic mechanisms that were used to jettison the heat shield” (JAXA, 2010). The asteroid sample recovery was a successful cooperation between the governments of Japan and Australia (de Zwart, 2016, pp. 66–67).

In 2008, the US authorities announced that its satellite USA-193 had malfunctioned and had a full tank of hydrazine on board. It was claimed that the space object was quickly de-orbiting and posed a hazard. The United States destroyed the satellite intentionally in orbit with a missile launched from Earth. US authorities claimed this action to be an effort of eliminating hazards to the population and the environment (Oberg, 2008).

Similar to the actions to avert nuclear hazards, the steps for the mitigation of chemical hazards of space debris after launch or re-entry are encompassed in Article 5 of the Rescue Agreement. Compliance with the procedures for the mitigation of hazards reduces the liability risk of states under the Liability Convention, which applies when damage is caused.

Outside of the scope of space treaties, states parties to the 1972 London Convention and the 1996 Protocol on the Prevention of Marine Pollution by Dumping of Wastes discuss how to cope with the dangers to marine environment due to increasing jettisoned material during space launches, and also consult with COPUOS on the matter (IMO, Consultative Meeting of Contracting Parties, 2018).

Hazardous Space Debris in Orbit

Launchers that lift space objects into outer space usually consist of several stages (boosters, upper stages, apogee kick motors). Some of these detach when they are still in the Earth’s atmosphere, while others propel space objects into orbit. If no orbital correction is performed, the orbits of space objects naturally decay. Objects in very low Earth orbits re-enter the Earth’s atmosphere in some hours, days, months or few years. Objects in higher orbits will take longer. Launch stages and other non-functional space objects contribute to an accumulation of about 30,000 space debris objects larger than 1 meter in orbits around the Earth and many more of centimeter, millimeter and sub-millimeter size (ESA, 2018).

Orbital space debris consists of spent stages of launchers, component parts that detach during deployment of space objects as part of normal launch operations, space objects that reach their end of life, objects that malfunction, fragments that result from explosions or collisions and many small space objects such as screws, screw eyes, fragments of aluminum, paint flakes, aluminum oxide particles ejected from motor boosters, and sodium–potassium droplets (Wiedemann et al., 2005, p. 478).

Orbital space debris may collide and dismember in numerous smaller parts. In 1978, researchers Kessler and Cour-Palais studied the evolving accumulation of orbital space debris and forecast that a collision cascading effect will take place when the amount of space debris in a particular orbit reaches a critical mass, even if no further new space objects arrive in this orbit (Kessler & Cour-Palais, 1978; NASA, 2016). This process, known as the “Kessler Syndrome,” describes the process of colliding space debris, their fragmentation and the production of further smaller space debris in a chain reaction. Whilst no cascade process has been observed among space debris larger than 1 meter in cross-section, Kessler comments “[t]he cascade process can be more accurately thought of as continuous and as already started, where each collision or explosion in orbit slowly results in an increase in the frequency of future collisions” (Gini, 2012).

At present, there are about 2000 operational space objects around the Earth, including manned space objects (ESA, 2019a). All these operational space objects are at risk of being damaged, and humans working in outer space are at risk of being injured or killed by a collision in outer space, which is more likely to occur with space debris, which by far outnumbers operational space objects. Although most of the operational space objects have maneuvering systems to avoid collisions, some space objects do not have this capability, such as the Hubble Space Telescope, and very small satellites (IAA, 2005, p. 16).

In case of damage in outer space, the Liability Convention merely provides that a launching state that causes damage “shall be liable only if the damage is due to its fault or the fault of persons for whom it is responsible” (Liability Convention, 1972, Art. III). Since there is no norm that forbids leaving space debris in orbit, it is difficult to attach liability to the launching state of a space object that has transformed into space debris and creates damage.

In addition, Article IX of the Outer Space Treaty stipulates that “States Parties to the Treaty shall . . . conduct exploration [of outer space and celestial bodies] so as to avoid their harmful contamination . . .” This provision has been considered by some researchers to be a basis for the environmental protection of outer space (Marchisio, 2009, p. 176), but it falls short to establish a legally binding obligation for all launching states to avoid the generation of space debris, to minimize the associated risks of orbital space debris (for instance, by de-orbiting) or actively remove them, and thus to avert any hazard to operational space objects and humans in outer space.

This situation demands practical and regulatory measures to handle the growing number of space debris objects and the finding of ways to reduce it.

Efforts to Mitigate Hazardous Orbital Space Debris

Looking at the increase of orbital space debris, space researchers at the IADC convened to discuss how to tackle the problem of increasing space debris and the pollution of Earth orbits. Given the vast area of outer space around the Earth, they decided to concentrate their efforts on two areas: low earth orbit (LEO), reaching from the surface of the Earth up to 2000 kilometers altitude, and the geostationary orbit (GEO), located at about 36,000 kilometers altitude with an additional area of 200 km above and 200 km below the geostationary line, and 15° inclination north and south, projected from the Earth’s center. The IADC then dedicated its efforts to compiling a list of guidelines to diminish the generation of space debris.

In 2002 the IADC published its Space Debris Mitigation Guidelines (IADC, 2002, Revision 1, 2007), which can be summed up as follows:


Reduce the release of component parts during normal launch operations to a minimum.


In order to minimize break-ups of launch vehicles or payloads, if a condition is detected that may lead to a failure during the operation of such space objects, all energy carried on board should be released (e.g., dumping residual propellants, disconnecting batteries from solar panels).


Evade collisions with other space objects.


Refrain from intentionally destroying space objects and from other harmful activities affecting the integrity of space objects.


For space objects approaching their end of life in the LEO region, use the last kilograms of propellant for reducing their altitude (de-orbiting) and thus accelerate their re-entry into the atmosphere. This measure intends to assure that space debris is not left for a long period in the LEO protected region.


Reduce the post-mission break-ups of space objects at the end of life by releasing all energy carried on board.


For space objects in the GEO approaching their end-of-life, use the last kilograms of fuel to propel them into orbits outside the protected region.

In the framework of COPUOS, a Working Group (COPUOS, 2004, A/AC.105/823, p. 41) discussed and drafted over a period of several years a set of recommendations, largely based on the IADC Mitigation Guidelines, which were later adopted by COPUOS as the Space Debris Mitigation Guidelines of the Committee on the Peaceful Uses of Outer Space (COPUOS, 2007). The United Nations General Assembly endorsed the COPUOS Space Debris Mitigation Guidelines (UNGA, 2007, Resolution 62/217).

The International Organization for Standardization (ISO) provides detailed technical instructions for the implementation of the Space Debris Mitigation Guidelines. One of them is ISO 24113:2011, the Space Debris Mitigation Requirements standard (ISO, 2011, updated in 2019). These detailed technical recommendations represent a breakthrough for the application of the IADC Mitigation Guidelines by states of different economic and technical standing.

Despite the non-binding nature of these guidelines and standards, an increasing number of states follow the IADC guidelines, have implemented codes of conduct (Mejía-Kaiser, 2009), and have issued national legislation and regulations. Examples are:

Austria (2011), Outer Space Act, § 5;

Canada (2017), Licensing of Space Stations, Art. 3.3.3;

China (2005, revised in 2015), National Industry standard QJ3221-2005—Requirements for Orbital Debris Mitigation; and (2015) Measures on Space Debris Mitigation and Management and Protective Management;

Denmark (2016), Outer Space Act, Art. 6.(1)(4);

Finland (2018), Act on Space Activities, Sec. 5(3) & Sec. 10;

France (2011), Technical Regulations, Art. 34;

Germany (2018), Administrative Provision on Satellite Systems, Part B, Art. 5.7;

Japan (2016), Act on the Launching and Control of Spacecraft, Art. 22;

Ukraine (1996), Ordinance on Space Activity, Art. 9;

United Kingdom (1986, as of 2018), Outer Space Act, Art. 5;

United States, Code of Federal Regulations (n.d.), Title 47, § 25.114 (14).

The IADC and UN Guidelines, Standards of ISO and other organizations, and national legislation use different language and levels of regulation or compliance. Despite this, a growing state practice is observed by which states implement space debris-mitigation measures (Johnson, 1999, 2007; Mejía-Kaiser, 2006). This practice of spacefaring states is already a contribution to diminish the hazards resulting from orbital space debris. Some authors consider that an opinio iuris and state practice are evolving to crystallize some of the IADC guidelines into norms of international customary law. It is also considered that the state practice relating to some of these mitigation guidelines will establish a minimum standard of care for determining fault (Mejía-Kaiser, 2009). Consequently, damage caused due to the lack of following mitigation guidelines may be considered as “fault” and lead to liability for orbital collisions under the Liability Convention (Mejía-Kaiser, 2012).

Even though only part of the states which operate space objects follow to some extent the IADC guidelines, they still keep generating space debris (IAA, 2016, pp. 121–122). Other states do not follow the IADC guidelines at all. The release of component parts during normal launch operations will also continue, though it is a declining practice. Further space debris will result from unavoidable incidents like the malfunctioning of spacecraft and launchers, and fragmentation events. A vast increase of space debris population must also be expected following the forthcoming deployment of mega-constellations of small satellites in LEO (Liou, Matney, Vavrin, Manis, & Gates, 2018; Oltrogge, 2018, p. 18).

Negotiations are taking place under the auspices of the United Nations Office for Outer Space Affairs on guidelines for the long-term sustainability of outer space activities (UNOOSA, n.d.a). In 2018, the delegates agreed on a preamble and 21 guidelines (COPUOS, 2018, A/AC.105/C1/L.366). In 2019, COPUOS adopted the Guidelines for the Long-term Sustainability of Outer Space Activities (COPUOS, 2019b, A/AC.105/L. 318/Add.6). Some of these guidelines relate to the reduction of hazards resulting from space debris, promote the existing IADC guidelines, and formulate new guidelines for clearing outer space from space debris.

Space agencies and researchers are working on recommendations for removing orbital space debris (ESA, 2019b; IAA, n.d., 2019; IAC, 20102018; NASA & DARPA, 2009). Proposed methods include: capturing space debris and affixing augmentation devices to reducing their orbital life; targeting space debris objects with laser beams to reduce their altitude and accelerate their atmospheric re-entry; capturing large space debris objects and removing them from protected regions. Some experiments have been carried out to investigate the capability to capture simulated space debris in orbit (Clark, 2018). However, so far, no space debris object has been removed.

Since small space debris is mostly generated when detaching from larger space debris or as result of fragmentation events of larger space debris, it makes sense as a first step to start removing large space debris. A list of the 20 most hazardous large space debris objects in LEO was issued (Wiedemann et al., 2011). Four clusters of massive space debris in valuable LEO orbital areas have also been identified (McKnight, 2017). A list of the most hazardous space debris objects in the Geostationary Protected Region is still missing. There have been urgent calls to start with active removal of space debris, which would fall under the freedom of exploration and use of outer space promulgated in Article I of the Outer Space Treaty, but the costs and technological aspects represent an obstacle.

There is concern that a space debris removal mission, undertaken by the launching state of the space debris object or by another state(s), may result in an uncontrollable atmospheric re-entry that causes damage to a third state on the surface of the Earth or to aircraft in flight. In such cases, the launching state(s) of the space object(s) that caused the damage is/are absolutely liable and has/have the obligation to pay compensation. There are also concerns about potential failures of removal operations that may end in catastrophic collisions in outer space and result in more space debris objects. Any damage caused in outer space to another state would only raise liability of the state(s) performing the removal if fault can be demonstrated, as provided in Article III of the Liability Convention. Since there are no legally binding rules or internationally accepted minimum standards for space debris removal and damage arising to space assets and/or personnel of a state not involved in the operation, fault would arise only if negligent behavior or intention to cause damage can be proved. As with to other new launch and space technologies, the introduction of removal operations will bear risks that need to be expected and managed, because there is no other option to clear outer space.

It appears likely that those major spacefaring countries with adequate technological and financial means will perform the first removal operations of their own hazardous large space debris objects (Mejía-Kaiser, 2019). It is another question, if and how states without the necessary technological means but which procured the launch of a space objects that transformed into hazardous space debris, will bear the costs of removal operations that can only be performed by those who possess this technology. Since the existing space treaties do not address space debris, there is neither a legal obligation on states to remove their space debris nor to bear the cost for its removal. It needs to be seen if states that wish to maintain their sustainable access to space will engage in arrangements for the removal of space debris.

States, including spacefaring countries, which do not wish to cooperate in the removal of their hazardous space debris represent a legal challenge. According to Article VIII of the Outer Space Treaty, states that launch a space object obtain jurisdiction and control over the object. Jurisdiction and control “represent an aspect of sovereignty and incorporate the rights and powers to exercise legislative, judicial and administrative authority [on space objects in outer space]” (Vereshchetin, 1981, p. 33). The term “control” does not refer to the physical ability to maneuver a space object, but to “the exclusive right [of the state] and the actual possibility to supervise the activities of the space object” (Schmidt-Tedd & Mick, 2009, p. 157). The question arises how long this jurisdiction and control over a space object lasts. During the negotiations and the drafting of the space treaties, many definitions of the term “space object” were discussed. At the end, the drafters could only reach agreement on the lowest common denominator and the following wording was included in Article I of the Liability Convention and in Article I of the Registration Convention: “The term ‘space object’ includes component parts of a space object as well as its launch vehicle and parts thereof.”

Albeit this definition is succinct, the wording indicates an implicit inclusion of space debris. This is confirmed by the preparatory works during the drafting of this article. At that time, the concept of “space debris” did not yet exist and therefore this term was not considered by the drafters. However, discussions indicate that space debris was to be included in the term “space object” (Liability Convention: Texts of Documents, 1981). This means that the transformation of operational space objects into space debris has no impact on the jurisdiction and control of the launching state. Even if a space object is derelict, it cannot be captured, removed, or transferred to another orbit without the express permission of the state of jurisdiction and control. The question arises what to do when a state opposes the removal of its hazardous space debris object over which it still has jurisdiction and control.

The jurisdiction and control rights of states over their space debris are addressed in Article IX of the Outer Space Treaty: “In the exploration and use of outer space . . ., States Parties to the Treaty shall be guided by the principle of cooperation and mutual assistance and shall conduct all their activities in outer space . . ., with due regard to the corresponding interests of all other States Parties to the Treaty. States Parties to the Treaty shall . . . conduct exploration of [outer space] so as to avoid [its] harmful contamination [. . . and], shall adopt appropriate measures for this purpose.”

On one hand there is the right of a state to decide the fate of its space debris and to oppose to any removal. On the other hand, there are increasing hazards of collision and fragmentation in the closer outer space around our planet, which affect not only the states that operate space objects, but the whole international community that benefits from space technology (UNOOSA, n.d.a).

Although it is expected that experimental removals of space debris objects will take place in the future, states ought to start a discussion in international fora about a system to remove the hazardous space debris of non-cooperative states. States with jurisdiction and control over hazardous orbital space debris need to be encouraged, for instance, through the UN General Assembly or the Security Council, to perform or arrange removals of their hazardous space debris. Should these states not follow, new legal mechanisms need to be considered for removal, such as introducing a time limitation for the jurisdiction and control rights of non-cooperative states over hazardous space debris, and allowing the removal by other states.

Cooperation is essential between space agencies and institutions to aid each other in the planning, development, and assistance of each removal operation (including surveillance, tracking, and ITU-issued warnings). The establishment of an international fund (Prasad & Lochan, 2007, p. 8), and of insurance covering removal, would help to overcome the financial risks.

It has also been proposed for the far future, to operate debris removal as a commercial endeavor with a self-enforcing mechanism, similar to the Nairobi International Convention on the Removal of Wrecks (Nairobi Wreck Removal Convention, 2007; Mejía-Kaiser, 2010). States also need to pay attention to the deletion of small space debris objects, increasingly becoming a concern (Oltrogge, 2018, p. 1).


The space era opened new horizons for humankind in many fields. From the exploration of the Earth from outer space to the exploration of the deepest parts of our universe, many benefits of space activities have spread to many countries, even to those that do not possess their own space technology. However, the use and exploration of outer space also has its risks. Hazards to the population and the environment at the moment of launch, during atmospheric re-entry of space objects, or by radioactive or chemical substances on board space objects are only rudimentarily addressed in the space treaties and other international instruments. The increasing pollution of the orbits around our planet could transform it into a non-operable area, to the detriment of all states. The technological development in the exploration and the increasing use of outer space is leading to a point of time when urgent measures need to be taken. To maintain this common place operational and clear from hazards is not the responsibility of a few states only, but an endeavor that requires the cooperation of the whole international community.