Space Hazard / Accident
A space accident is any accident involving space objects that cause damage (adapted from UNGA, 1971).
Primary reference(s)
UNGA, 1971. Resolution 2777 (XXVI). 1998th plenary meeting, 29 November 1971. United Nation’s General Assembly (UNGA). Accessed 2 April 2025.
Annotations
Additional scientific description
The term 'damage' refers to 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 organisations. The term 'space objects' includes component parts of a space object as well as its launch vehicle and parts thereof (UNGA, 1971: Article I).
Space debris are all human- made objects including fragments and elements thereof, in Earth orbit or re-entering the atmosphere, that are non-functional. During the operational phases, a spacecraft or orbital stage can be considered as functional (IADC, 2025)
In addition, there is also the risk of damage on the ground, if debris survives Earth's atmospheric re-entry. The prompt implementation of appropriate debris mitigation measures is therefore considered a prudent and necessary step towards preserving the outer space environment for future generations (UN OOSA, 2010).
Noting concerns about an increased risk even for nominally controlled re-entries, IADC considers that if a spacecraft or orbital stage is to be disposed of by re-entry into the atmosphere, debris that survives to reach the surface of the Earth should not pose an undue risk to people or property (IADC, 2025). Using 10-4 as the upper limit for the expected number of human casualties per re-entry is recommended. This may be accomplished by limiting the amount of surviving debris or confining the debris to uninhabited regions, such as broad ocean areas. Also, ground environmental pollution, caused by radioactive substances, toxic substances or any other environmental pollutants resulting from on-board articles, should be prevented or minimised in order to be accepted as permissible (IADC, 2025)
The Inter-Agency Space Debris Coordination Committee (IADC) and other studies have demonstrated that accidental collisions will drive the future space debris population increase in the environment. In developing the design and mission profile of a spacecraft or orbital stage, a program or project should estimate and limit the probability of accidental collision with known objects during the spacecraft or orbital stage's orbital lifetime. If reliable orbital data and conjunction assessments are available, avoidance manoeuvres for spacecraft during all operational phases and co-ordination of launch windows for launch vehicle orbital stages should be considered. After the end of all operational phases of a spacecraft or orbital stage, the integrated collision risk during the remaining orbital lifetime should be minimised commensurate with post-mission disposal measures. Spacecraft design should also limit the probability of collision with small debris which could cause a loss of control, thus preventing post-mission disposal and passivation (IADC, 2025)
Spacecraft or orbital stages, in particular those that present challenges for space surveillance networks, should enhance their trackability by adding on-board active and/or passive components to the design and consider operational procedures which facilitate use thereof (IADC, 2025).
The IADC has found that observed annual rates of explosive break-ups are not compatible with limiting the space debris environment. During the design of spacecraft or orbital stages, each program or project should demonstrate, using failure mode and effects analyses or an equivalent analysis, that there is no probable failure mode leading to accidental explosive break-ups. If such failures cannot be excluded, the design or operational procedures should minimise the probability of their occurrence. The probability of occurrence during all operational phases should be at least below 10-3in order to have a noticeable effect on the space debris environment (IADC, 2025).
During the operational phases, a spacecraft or orbital stage should be periodically monitored to detect malfunctions that could lead to a break-up or loss of control function. In the case that a malfunction is detected, adequate recovery measures should be planned and conducted; otherwise, post-mission disposal and passivation measures for the spacecraft or orbital stage should be planned and conducted (IADC, 2025)
In all operational orbit regimes, spacecraft and orbital stages should be designed not to release debris during normal operations. Where this is not feasible any release of debris should be minimised in number, area and orbital lifetime. Any program, project or experiment that will release objects in orbit should not be planned unless an adequate assessment can verify that the effect on the space environment, and the hazard to other operating spacecraft and orbital stages, is acceptably low in the long-term (COPUOS, 2025)
Metrics and numeric limits
The current cumulative annual global casualty expectancy for uncontrolled re-entries of orbital stages and spacecraft is of the order of 10−2. Hence, the corresponding individual risk is still extremely low, if compared with the hazards commonly faced in everyday life, with a probability of being personally injured of the order of 1 in 800 billion per year. However, this risk is increasing, due to the rapid growth of space launch activities and to the rise in world population. Moreover, during the last decades, there has been a growing consensus, at the international level, in considering a casualty expectancy of 10−4. as the risk limit not to be exceeded for any individual uncontrolled re-entry, while the introduction of collective risk limits is currently considered for large space systems, like mega-constellations (Pardini & Anselmo, 2024).
Key relevant UN convention / multilateral treaty
The Convention on International Liability for Damage Caused by Space Objects (Liability Convention) 1972 was considered and negotiated by the Legal subcommittee from 1963 to 1972. Agreement was reached in the General Assembly in 1971 (UNGA, 1971), and the Convention entered into force in September 1972 (UN OOSA, 1972). Elaborating on Article 7 of the Outer Space Treaty, the Liability Convention provides that a launching State shall be absolutely liable to pay compensation for damage caused by its space objects on the surface of the Earth or to aircraft, and liable for damage due to its faults
Drivers
Spacecraft and launch vehicle orbital stages that have terminated their operational phases in orbits that pass through the LEO region should be removed from orbit in a controlled fashion. If this is not possible, they should be disposed of in orbits that avoid their long-term presence in the low earth orbit (LEO) region. When making determinations regarding potential solutions for removing objects from LEO, due consideration should be given to ensuring that debris that survives to reach the surface of the Earth does not pose an undue risk to people or property, including through environmental pollution caused by hazardous substances (UNOOSA, 2010).
Impacts
Any debris left on orbit is a hazard in view of the relative velocity with other space object in case of collision. Therefore, restrictions, in the possible release of debris in terms of number, size, source, and risk compatibly to the state-of-the-art technology are necessary (ESA, 2023). Additionally, from a space accident, harm to space craft and astronauts is a risk. ESA (2017) reports that re-entry poses hazards to human health, the Earth’s environment, and damages to assets, associated to the re-entry of a space system, can be caused by: impacting fragments, floating fragments, pressurized or explosive fragments, hazardous chemical substances, and radioactive substances. Impacts following an accident may include ground environmental pollution, caused by radioactive substances, toxic substances or any other environmental pollutants resulting from on-board articles, should be prevented or minimised (IADC, 2025).
Multi-hazard context
The figure below summarises common interactions between geomagnetic disturbance and other hazards. This information should be used with caution and not be solely relied upon in Disaster Risk Management, particularly as some interactions may not have been included. Note that hazardous events occurring together or locally in space or time may not necessarily cause, amplify or be otherwise related to each other. Specific examples of multi-hazard context can be found in the ‘Hazard drivers’ and ‘Impacts’ sections above.
Multi-hazard diagram
Risk Management
If a spacecraft or orbital stage is to be disposed of by re-entry into the atmosphere, debris that survives to reach the surface of the Earth should not pose an undue risk to people or property. Using 10-4 as the upper limit for the expected number of human casualties per re-entry is recommended. This may be accomplished by limiting the amount of surviving debris or confining the debris to uninhabited regions, such as broad ocean areas. Also, ground environmental pollution, caused by radioactive substances, toxic substances or any other environmental pollutants resulting from on-board articles, should be prevented or minimised in order to be accepted as permissible (COPUOS, 2025)
ISO 24113:2023 is the top-level standard in a family of standards addressing space debris mitigation and defines the primary space debris mitigation requirements applicable to all elements of unmanned systems launched into, or passing through, near-Earth space, including launch vehicle orbital stages, operating spacecraft and any objects released as part of normal operations (ISO, 2023).
IADC recommend that in order to limit the risk to other spacecraft and orbital stages from accidental break-ups after the completion of mission operations, all on-board sources of stored energy of a spacecraft or orbital stage, such as residual propellants, batteries, high-pressure vessels, self-destructive devices, flywheels and momentum wheels, should be depleted or made safe when they are no longer required for mission operations or post-mission disposal (IADC, 2025). Depletion should occur as soon as this operation does not pose an unacceptable risk to the payload. Mitigation measures should be carefully designed not to create other risks.
- Residual propellants and other fluids, such as pressurant, should be depleted as thoroughly as possible, either by depletion burns or venting, to prevent accidental break-ups by over-pressurisation or chemical reaction.
- Batteries should be adequately designed and manufactured, both structurally and electrically, to prevent break-ups. Pressure increase in battery cells and assemblies could be prevented by mechanical measures unless these measures cause an excessive reduction of mission assurance. At the end of operations battery charging lines should be de-activated.
- High-pressure vessels should be vented to a level guaranteeing that no break-ups can occur. Leak-before-burst designs are beneficial but are not sufficient to meet all passivation recommendations of propulsion and pressurisation systems. Heat pipes may be left pressurised if the probability of rupture can be demonstrated to be very low.
- Self-destruct systems should be designed not to cause unintentional destruction due to inadvertent commands, thermal heating, or radio frequency interference.
- Power to flywheels and momentum wheels should be terminated during the disposal phase.
- Other forms of stored energy should be assessed, and adequate mitigation measures should be applied (IADC, 2025)
The International Association for the Advancement of Space Safety (IAASS) is an association that seeks internationally to advance space safety through advancing the science and application of space safety. The IAASS website contains numerous resources on the topic (IAASS, no date).
Monitoring
There are many national and international organisations involved in monitoring. As an example of monitoring, the NASA Orbital Debris Program officially began in 1979 in the Space Sciences Branch at the Johnson Space Center (JSC) in Houston, Texas. The program looks for ways to create fewer orbital debris, and designs equipment to track and remove the debris already in space (NASA, no date).
References
COPUOS, 2025. IADC Space Debris Mitigation Guidelines Committee on the Peaceful Uses of Outer Space Scientific and Technical Subcommittee (COPUOS). Accessed 2 April 2025.
ESA. 2023. ESA Space Debris Mitigation Requirements. European Space Agency (ESA). Accessed 2 April 2025.
ESA, 2017. ESA Re-entry Safety Requirements. European Space Agency (ESA). Accessed 2 April 2025.
IADC, 2025. 02-01 Space Debris Guidelines Rev 4 Inter-Agency Space Debris Coordination Committee (IADC). Accessed 2 April 2025.
IAASS, no date. International Association for the Advancement of Space Safety. Accessed 2 April 2025.
ISO, 2023. International organization for standardization, space systems Space systems — Space debris mitigation requirements (edition 4), Internat. Standard ISO 24113, 2023. International Organization for Standardization (ISO). Accessed 2 April 2025.
NASA, no date. Space Debris. National Aeronautics and Space Administration (NASA). Accessed 2 April 2025.
Pardini C., & Anselmo L., The risk of casualties from the uncontrolled re-entry of spacecraft and orbital stages, Journal of Space Safety Engineering, Volume 11, Issue 2, 2024, Pages 181-191, ISSN 2468-8967. DOI: 10.1016/j.jsse.2024.02.002 Accessed 2 April 2025.
UNGA, 1971. Resolution 2777 (XXVI). 1998th plenary meeting, 29 November 1971. United Nation’s General Assembly (UNGA). Accessed 2 April 2025.
UN OOSA, 1972. Convention on International Liability for Damage Caused by Space Objects (Liability Convention), 1972. Accessed 2 April 2025.
UN OOSA, 2010. Space Debris Mitigation Guidelines of the Committee on the Peaceful Uses of Outer Space. United Nations Office for Outer Space Affairs (UN OOSA). Accessed 2 April 2025.