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Space Pollution - what is it and why should you care

Since humans started space exploration in 1957 with the first artificial satellite - Sputnik 1 - a total of 9,300 tonnes worth of rockets, spaceships, and satellites have been launched into space. Most of these were launched with no plan of being brought back upon their end-of-life (EOL) - and with no full knowledge of the implications of sending such materials into space. These 6,050 launches have resulted in around 56,450 tracked objects in orbit, of which about 28,160 remain in space and are regularly tracked by the US Space Surveillance Network. Only a small fraction of the total hardware in space (about 4,000) are intact, operational satellites.


If you have seen Wall-E, you probably remember the orbital debris graveyard as the spaceship returns to Earth, and this is not far from the truth. According to the ESA, there are currently around 900,000 objects over one centimetre in size and 34,000 larger than 10 centimetres that have no use orbiting the Earth. This debris moves at more than 28,000 kilometres per hour, turning them into real projectiles able to significantly damage larger apparatus - even when small-sized.



While representing a liability for future missions having to plan around debris and potential interference with terrestrial communications, the topic of space pollution also brings the perspective of environmental responsibility beyond the Earth and has many geopolitical ramifications considering the increased competition in the space race.


What is space debris and where is it?

Space debris represents any piece of waste left behind by humans in space, and comes in many sizes and shapes.  There are two primary debris fields: the ring of objects in geosynchronous orbit (GSO) and the cloud of objects in low Earth orbit (LEO). Causes for the multiplication of this debris are varied, including defunct satellites, rocket stages, missing equipment, and anti-satellite weapons.

Stylised representation or orbital debris (National Geographic)

The ESA distinguishes between three object types:

  • Payload: Satellites and fragments from wear and tear and collisions, for example, paint flakes.

  • Rockets: Remains of stages to send rockets into orbit, including wear and tear and fragments.

  • Mission-related objects: For example, dropped tools and materials.

Count evolution by object type in space (ESA)

Why does it matter and how does it affect us?

The overcrowding of space and its resulting debris have several tangible implications representing a societal concern toward sustainable development. Indeed, achieving the UN’s Sustainable Development Goals (SDGs) directly relies on earth observation satellite data (e.g. for climate predictions, and environmental monitoring) that is threatened by residual flammable fuels, radioactive chemicals, waste micrometeorites, and direct collisions - the latter with far-reaching consequences, also known as the Kessler syndrome.


Coined in 1978 by NASA scientist Donald J. Kessler, the Kessler syndrome is a scenario where the density of objects in LEO due to space pollution is numerous enough that collisions between objects could cause a cascade in which each collision generates space debris that increases the likelihood of further collisions, acting as a vicious circle. For another cinematographic reference, the Kessler syndrome is the premise of the 2013 film Gravity by Alfonso Cuarón, where Russia’s attempt to shoot down an old satellite creates an apocalyptic cascade of collisions.


More than 560 in-orbit fragmentation events have been recorded since 1961, mostly due to explosions of spacecraft and upper stages from residual fuel. So far, only 7 direct collisions have been recorded, the most serious being the one from the operational US-built satellite Iridium 33 with the inactive Russian military Kosmos 2251 in 2009. However, with the current race to space and lack of EOL consideration, the ESA expects that collisions will become the dominant source of space debris in the future.


What are current initiatives to clean it up?

Consequently, the timely application of mitigation and remediation measures on an international scale is needed to prevent further damage to existing satellites. To not produce more space waste, new satellites increasingly use different strategies, including:

  • Orbit changes: As space gets more crowded, very low Earth orbit (VLEO) is increasingly seen as a critical domain for Earth Observation.

  • Self-destruction: Programming a satellite to leave its orbit at the end of its useful life and be eliminated when coming in contact with the atmosphere. For example, NOAA’s three Polar Operational Environmental Satellites (POES) can decommission themselves if life-ending conditions arise, a feature recently added to the POES satellite fleet and called autonomous decommissioning control (ADC).

  • Passivisation: Removal of any internal energy contained in the vehicle at the end of its useful life (e.g. fuel).

  • Reuse: Returning to Earth intact, with leading companies including SpaceX.

  • Laser: Stopping fragments by vaporising their surface with a powerful laser stopping them and making them fall.

  • Debris removal missions: For example, ESA's Clean Space initiative or private companies like Astroscale using innovative robotic arms.

ESA's proposed e.Deorbit mission's robotic arm (ESA)

Space sustainability and governance in the international discourse

Designers of new vehicles or satellites are frequently required by the  UN's specialised agency for ICTs (ITU) to demonstrate that they can be safely disposed of at the end of their life, for example by use of a controlled atmospheric reentry system or a boost into a graveyard orbit. In the US, government regulations require a plan to dispose of satellites after the end of their mission, whether through atmospheric re-entry, movement to a storage orbit, or direct retrieval. For an overview of worldwide regulations, this website provides some more background information.


However, space legislation has yet to benefit from an extensive consideration of international environmental law for outer space. Current legislation surrounding space sustainability includes:

  1. Outer Space Treaty (OST): Adopted by the United Nations in 1967, the Outer Space Treaty is a fundamental international agreement that establishes the principles governing the exploration and use of outer space. It emphasises peaceful use, prohibits the placement of weapons of mass destruction in orbit, and establishes liability for damage caused by space objects.

  2. Registration Convention: This treaty, also from 1975, requires parties to register objects launched into space with the United Nations, aiming to enhance transparency and assist in the identification of space objects.

  3. Space Debris Mitigation Guidelines: The United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) has issued guidelines on space debris mitigation. These guidelines provide recommendations for the design, operation, and disposal of space objects to minimise the creation of space debris.

  4. Guidelines for Long-term Sustainability of Outer Space Activities: COPUOS has developed guidelines to address the long-term sustainability of outer space activities. These guidelines cover various aspects, including space debris mitigation, space traffic management, and the preservation of the space environment.

Despite these efforts, there are challenges and gaps in space sustainability regulations. First, while guidelines and treaties are in place, enforcement mechanisms are often weak. There is a need for stronger mechanisms to ensure compliance and accountability for space activities. Second, with an increasing number of satellites and space activities, effective space traffic management becomes crucial. There is a need for clearer regulations and international collaboration in this area to prevent collisions and minimise space debris. Moreover, as companies and countries explore the possibility of mining asteroids or extracting resources from celestial bodies, there is a lack of clear international regulations governing these activities. Finally, the current liability regime for space activities may need refinement to address new challenges, including those associated with mega-constellations (e.g. light pollution) and commercial space operations (e.g. space tourism).


Discussions on whether an 18th SDG on space is missing are increasingly growing. The World Meteorological Organization (WMO), UNOOSA, and ITU opened the conversation for a just and unified approach to space governance in recent years. Space is yet to benefit from a more central consideration of social and environmental justice factors. Indeed, the sovereign and commercial use of airspace has long been concentrated within a few dominant countries (USA, China, Russia). However, more developing countries and private companies are entering the field and demanding their share of spatial orbit for their economic and sustainable development - the number of countries operating at least one satellite in orbit has gone from 50 to 87 in the last decade. Still, over 100 UN member states are missing out on the “transformative power of space assets” according to UNOOSA Director Simonetta Di Pippo. For a  peaceful use of outer space, the challenge lies in ensuring that countries are subject to the same regulations and have equitable access to orbits and frequencies without creating an orbital “Wild West”

Consequently, for successful orbital management, environmental modelling will be a crucial field for decision-making on orbital use, as well as a switch from a per-mission environmental planning to a spatial landscape approach. According to Space News, the following four steps are needed to achieve a future with capacity-aware use of LEO: 

  1. Develop consensus around technical definitions for space sustainability and reasonable modelling assumptions

  2. Mature community confidence in open-source, accessible environmental modelling tools, as well as the capability to use those tools.

  3. Build consideration of orbital capacity into regulatory processes.

  4. Work towards adaptive management and adaptive governance.

With the ESA pledging to tbe debris neutral by 2030, whether countries and companies fully take responsibility for their environmental impact in outer space and collaborate in a timely manner will need to be closely monitored in the next few years and determine whether crucial orbital regions will become unusable. 

Food for thought

I hope you enjoyed this article, and leave you with some questions for food for thought:

  • What is the role of social and environmental sciences in space?

  • How can space protection be added to a global agenda?

  • Are you aware of your country's spatial agenda and space sustainability commitments? 

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