Introduction

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

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:

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:

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, 2010–2018; 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).

Conclusion

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.