What is Space Sustainability and Why is It Important?

What is Space Sustainability?

Space sustainability is a broad concept focused on preserving the utility and accessibility of the space environment for current and future generations. It’s about managing human activities in space, particularly in Earth orbit, to ensure that space remains a safe, stable, and usable domain. This isn’t just an environmental concern; it’s a practical necessity for our modern, interconnected world.

Our global economy, scientific endeavors, and national security are deeply reliant on space-based assets. Global Positioning System (GPS) satellites underpin everything from financial transactions and logistics to navigation and precision agriculture. Weather satellites provide the data needed for forecasts and climate monitoring. Communications satellites link remote communities and carry vast amounts of the world’s data. Space sustainability is the effort to protect this vital infrastructure from the threats we ourselves have created.

Defining the Challenge: A Crowded Frontier

For the first few decades of the space age, orbit was vast and empty. The risk of two objects colliding was statistically negligible. Today, the situation is entirely different. The orbital environment, especially Low Earth Orbit (LEO), has become a crowded frontier.

LEO, an area extending from about 160 to 2,000 kilometers above the planet, is desirable for its proximity to Earth, which allows for low-latency communications and high-resolution imaging. This has made it the destination of choice for thousands of new satellites, particularly the “megaconstellations” being launched for global internet service by companies like SpaceX with its Starlink network and OneWeb.

This rapid influx of satellites, combined with decades of accumulated “space junk,” has created a complex and hazardous environment. Every new object adds to the cumulative risk of collision. Managing this environment is the central challenge of space sustainability.

The Core Pillars of Sustainability in Orbit

Space sustainability rests on several interconnected pillars, much like its terrestrial counterpart.

Environmental Sustainability (Orbital Debris)

This is the most widely discussed pillar. It concerns the preservation of the orbital environment itself. The primary threat is orbital debris, or “space junk.” This includes everything from defunct satellites and spent rocket stages to tiny flecks of paint and fragments from past collisions. This debris travels at incredibly high speeds, turning even a small object into a ballistic threat capable of destroying an active satellite. Environmental sustainability focuses on mitigating the creation of new debris and, increasingly, on removing existing debris.

Economic Sustainability (A Viable Market)

Space must remain economically viable. If the risk of operating in orbit becomes too high, or the cost of insurance and protective measures becomes prohibitive, the business case for space collapses. Economic sustainability means ensuring that companies can continue to invest, innovate, and provide services from space. This involves creating clear, predictable regulations, fostering a competitive market for services like debris removal, and ensuring that the actions of one operator don’t impose catastrophic costs on others.

Social and Political Sustainability (Equitable Access)

This pillar addresses the human aspect of space. Space is legally defined as the “province of all mankind.” Sustainability means ensuring that all nations, not just the wealthiest, have access to the benefits of space. It also involves managing potential conflicts. As space becomes more congested, the potential for disputes over orbital “slots,” radio frequencies, and liability for collisions increases. Political sustainability requires robust diplomatic frameworks, transparent communication, and shared “rules of the road” to prevent space from becoming a lawless or weaponized domain. It also includes protecting the interests of science, such as preserving the dark sky for ground-based astronomy.

Why It Matters Now More Than Ever

The urgency of space sustainability stems from two factors: our growing dependence on space and the accelerating growth of objects in orbit. A failure in LEO would not be an isolated incident. It could trigger a cascading failure that disrupts global supply chains, cripples communication networks, compromises national security, and halts our ability to monitor climate change.

We are at a point where the orbits we rely on are a finite resource. They can be “polluted” just like oceans or the atmosphere. Without active management, we risk losing access to them, perhaps for generations.

Kessler Syndrome: The Tipping Point Scenario

The most dramatic warning of this risk is the Kessler Syndrome, a scenario proposed in 1978 by NASA scientist Donald J. Kessler.

He theorized that if the density of objects in LEO becomes high enough, a single collision could create a cloud of debris. Each of those debris fragments then becomes a projectile, increasing the probability of further collisions. This creates a chain reaction, a cascading series of impacts that shatters more and more objects, exponentially increasing the amount of debris.

If such a scenario were to unfold, it could render certain orbits unusable for centuries. The debris field would become so dense that any new satellite launched into it would have a very short lifespan before being destroyed. This is the “tipping point” that sustainability efforts are designed to prevent. We are not there yet, but experts warn that the proliferation of satellites and debris is pushing us in that direction.

The Analogy of the “Tragedy of the Commons”

The challenge of space sustainability is often described as a modern example of the “tragedy of the commons.” This is an economic theory where multiple independent actors, acting in their own rational self-interest, ultimately deplete a shared, limited resource, even when it is clear that doing so is not in anyone’s long-term best interest.

Orbit is a shared global commons. Each satellite operator has an incentive to launch as many satellites as possible to maximize their service and profit. However, each launch adds to the collective risk for everyone. The “cost” of that added risk (in the form of debris and collision potential) is shared by all operators, while the “benefit” of the launch is captured by just one.

Without regulation or co-operation, this leads to overuse and degradation of the resource. Space sustainability is the effort to create the rules, norms, and technologies needed to manage this commons effectively.

The Primary Threat: Orbital Debris

The most immediate and tangible threat to space sustainability is orbital debris. This “space junk” is the byproduct of more than 60 years of space exploration and operations. It represents a persistent, high-velocity hazard to all space-based infrastructure.

What Constitutes “Space Junk”?

Orbital debris is any human-made object in orbit that no longer serves a useful function. This junk comes in many forms, which are tracked and cataloged by organizations like the U.S. Space Surveillance Network.

Defunct Satellites

These are “dead” satellites that have reached the end of their operational life and are no longer controllable. They range in size from tiny CubeSats to massive, school-bus-sized satellites from the Cold War era. They will continue to orbit until their orbits naturally decay, which can take decades or even centuries depending on their altitude.

Rocket Bodies and Upper Stages

For many launches, the upper stage of the rocket, which pushes the payload into its final orbit, is abandoned after use. These large, cylindrical objects are some of the most massive pieces of debris. A single rocket body can weigh several tons. Because of their large mass and surface area, their fragmentation upon collision would be catastrophic.

Mission-Related Debris

This is a broad category of items “lost” during operations. It includes things like lens caps, tools dropped by astronauts during spacewalks, insulation blankets, and bolts from explosive separation mechanisms. While often small, these items are traveling at orbital speeds, giving them significant destructive potential.

Fragmentation Debris (The Most Dangerous)

This is the largest and most concerning category of debris. It consists of the millions of tiny, untrackable fragments created by on-orbit explosions or collisions.

There are two main causes:

1. Explosions: A defunct satellite or rocket body may still have unspent fuel or pressurized batteries on board. Over time, the harsh space environment can cause these components to degrade and explode, shattering the object into thousands of pieces.
2. Collisions: When two objects collide at orbital velocity, they don’t just “bump.” They vaporize and create a cloud of shrapnel.

This type of debris is the most dangerous because the majority of it – fragments smaller than 10 centimeters – is too small to be tracked by ground-based radar. However, an object as small as 1 centimeter can strike with the force of a bowling ball traveling at 100 miles per hour, capable of disabling a satellite. A fragment the size of a fleck of paint can pit a space station window, requiring its replacement.

The Physics of Orbital Debris

Understanding the threat requires understanding the environment. The danger doesn’t come from the debris itself, but from its relative velocity.

High-Velocity Impacts

In LEO, objects travel at speeds around 7.8 kilometers per second, or over 17,000 miles per hour. This is many times faster than a bullet. Because objects are in different orbital paths (different inclinations and altitudes), collisions can occur at even higher relative speeds, up to 15 kilometers per second.

At these velocities, impacts are “hypervelocity” events. The kinetic energy is so immense that solid objects behave like fluids. The impact doesn’t just make a hole; it creates a plasma-filled crater and sends a shockwave through the target, often causing it to shatter completely. This is why a 1-kilogram piece of debris can destroy a 1,000-kilogram satellite.

The Different Orbital Regimes

The debris problem is not uniform across all orbits. Different altitudes present unique challenges.

• Low Earth Orbit (LEO): This is the most congested region. It benefits from atmospheric drag, which is a natural cleansing mechanism. At altitudes below 600 kilometers, drag from the thin upper atmosphere will pull objects and debris down, causing them to burn up on re-entry within a few years. Above 800 kilometers drag is much weaker. An object released there can stay in orbit for centuries. The most “cluttered” altitudes are the “sun-synchronous” orbits, popular for Earth-observation satellites, around 700-900 kilometers.
• Medium Earth Orbit (MEO): This region, around 20,000 kilometers, is primarily used by navigation constellations like GPS, GLONASS, and Galileo. It is far less congested than LEO, and there is virtually no atmospheric drag. Objects left here will remain for thousands of years.
• Geostationary Orbit (GEO): This is a unique, single-ring orbit at 35,786 kilometers above the equator. Here, a satellite’s orbital period matches Earth’s rotation, making it appear “fixed” over one spot on the ground. This is invaluable for telecommunications and weather broadcasting. The “slots” in this orbit are a finite resource, managed by the International Telecommunication Union (ITU). Debris in GEO is a major problem because it will never deorbit. To manage this, operators are required to move their satellites into a “graveyard orbit” a few hundred kilometers higher at the end of their lives.

Notable Debris-Generating Events

A few key events are responsible for a disproportionately large amount of the most dangerous debris in orbit today.

The 2007 Chinese ASAT Test

In January 2007, China conducted an anti-satellite (ASAT) weapon test, destroying one of its own defunct weather satellites, Fengyun-1C. The satellite was in a high LEO orbit (around 865 km). The collision was catastrophic, creating the largest single debris cloud in history. It generated over 3,000 trackable pieces of debris and an estimated 150,000 untrackable fragments. Because of the high altitude, this debris will persist for decades, threatening all satellites in that popular orbital band.

The 2009 Iridium-Cosmos Collision

In February 2009, the first-ever accidental hypervelocity collision between two intact satellites occurred. The active Iridium 33 communications satellite (operated by Iridium Communications) collided with the defunct Russian military satellite Cosmos 2251. The collision, which happened at nearly 26,000 miles per hour, instantly destroyed both satellites. It created over 2,000 pieces of trackable debris and many thousands of smaller fragments, polluting a wide range of LEO altitudes. This event was a wake-up call, proving that the risk of collision was no longer just theoretical.

The 2021 Russian ASAT Test

In November 2021, Russia conducted its own ASAT test, destroying its defunct satellite Cosmos 1408. This event created over 1,500 pieces of trackable debris in an orbit that directly threatened the International Space Station (ISS). Astronauts on board the ISS, including American and Russian crews, were forced to shelter in their transport capsules in case a piece of debris punctured the station. This event was widely condemned for its reckless disregard for the safety of crews and the stability of the LEO environment.

To illustrate the impact of these events, the table below summarizes their contribution to the orbital debris problem.

Tracking the Threat: Space Situational Awareness (SSA)

You can’t avoid what you can’t see. The foundation of space sustainability is Space Situational Awareness (SSA), which is the practice of tracking and characterizing objects in orbit.

The Role of Ground-Based Radar and Optical Telescopes

The primary tools for SSA are on the ground.

• Radar: Phased-array radars, like the U.S. Space Force’s Space Fence, send beams of energy into space and listen for reflections. They are highly effective at tracking objects in LEO, regardless of weather or time of day. They can track objects down to the size of a marble.
• Optical Telescopes: For objects in higher orbits (MEO and GEO), radar is less effective. Here, ground-based optical telescopes are used. These telescopes track objects by observing the sunlight they reflect. This means they work best at dawn and dusk, when the telescope is in darkness but the satellite is still illuminated by the sun.

The U.S. Space Surveillance Network

For decades, the most comprehensive catalog of space objects has been maintained by the United States Department of Defense, and is now managed by the U.S. Space Force. This Space Surveillance Network (SSN) is a global network of over 30 radar and optical sensors.

The SSN maintains a catalog of all trackable objects, which is used to provide Collision Avoidance (COLA)warnings to all satellite operators, including commercial and international partners. When the system predicts a “conjunction” (a close approach) between two objects, it alerts the operators, who can then decide whether to move their satellite out of the way.

Commercial SSA Providers

In recent years, a new industry of commercial SSA has emerged. Companies like LeoLabs, ExoAnalytic Solutions, and COMSPOC have built their own private networks of radars and telescopes. They sell high-fidelity tracking data and analytics services to satellite operators, governments, and insurance companies. This commercial involvement is a major development, as it increases the amount of available tracking data, provides redundancy, and drives innovation in the field.

The Legal Foundation: International Treaties and Principles

The “rules of the road” in space are built on a framework of international treaties and principles developed at the United Nations during the Cold War. While visionary for their time, they are now being tested by the realities of a crowded, commercialized space environment.

The 1967 Outer Space Treaty: The Magna Carta of Space

The cornerstone of all space law is the Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies, known simply as the Outer Space Treaty. It was negotiated at the UN Committee on the Peaceful Uses of Outer Space (COPUOS) and entered into force in 1967.

Key Provisions

The treaty lays down the fundamental principles for space activities. Its most famous provisions state that:

• Space is the “province of all mankind,” free for exploration and use by all states.
• Space is not subject to national appropriation by claim of sovereignty (i.e., no one can “own” the Moon or an orbital slot).
• The Moon and other celestial bodies shall be used exclusively for peaceful purposes.

Article VI: State Responsibility

This is one of the most important articles for the modern era. It states that nations are responsible for all national space activities, whether carried on by governmental agencies or by non-governmental entities(i.e., private companies).

This means that the United States is responsible for the activities of SpaceX, and the United Kingdom is responsible for OneWeb. To fulfill this, states must authorize and provide “continuing supervision” for their private companies. This is the legal basis for national licensing regimes, such as those run by the Federal Communications Commission (FCC) and the Federal Aviation Administration (FAA) in the U.S.

Article IX: Due Regard and Harmful Contamination

Article IX is the primary legal basis for space sustainability. It has two key parts:

1. “Due Regard”: States must conduct their activities with “due regard to the corresponding interests of all other” states. This is a general “good neighbor” policy, implying that one country’s activities should not unduly interfere with another’s.
2. Harmful Contamination: States must avoid the “harmful contamination” of space and celestial bodies. This was originally intended to mean biological contamination (related to planetary protection), but it is increasingly being interpreted in a legal context to include the “contamination” of orbits with debris.

Other Key UN Treaties

Four other treaties were built upon the foundation of the Outer Space Treaty.

The Rescue Agreement (1968)

The Agreement on the Rescue of Astronauts, the Return of Astronauts and the Return of Objects Launched into Outer Space, known as the Rescue Agreement, expands on the idea of astronauts as “envoys of mankind” and requires states to assist in their rescue and return. It also requires states to help return space objects to their launching state.

The Liability Convention (1972)

The Convention on International Liability for Damage Caused by Space Objects, or Liability Convention, is a critical piece of space law. It establishes two standards of liability:

1. Absolute Liability: A launching state is “absolutely liable” for any damage caused by its space object on the surface of the Earth or to aircraft in flight. This is a very high bar; no fault needs to be proven. This was famously invoked by Canada against the Soviet Union when the nuclear-powered Cosmos 954satellite crashed in the Canadian Arctic in 1978.
2. Fault-Based Liability: For damage caused in space (e.g., one satellite hitting another), liability is based on fault. This is much harder to prove. The convention provides no mechanism for determining fault and has never been successfully used for an in-space collision.

The Registration Convention (1976)

The Convention on Registration of Objects Launched into Outer Space, or Registration Convention, requires states to maintain a national registry of their space objects and to provide that information to the United Nations Office for Outer Space Affairs (UNOOSA), which maintains a central, public register. This is intended to promote transparency and help identify objects.

The Moon Agreement (1979): A Treaty That Failed to Launch

The Agreement Governing the Activities of States on the Moon and Other Celestial Bodies, or Moon Agreement, was an attempt to regulate the exploration and exploitation of resources on the Moon. It proposed that these resources are the “common heritage of mankind” and that an international regime should be set up to govern their extraction. The major space-faring nations, including the U.S., Russia, and China, have not ratified this treaty, and it is largely considered a failure.

The Gaps in International Law

This 20th-century legal framework is struggling to address 21st-century problems. There are several significant gaps:

• Vague Definitions: The treaties do not define key terms. What constitutes “debris”? What is the legal threshold for “harmful interference”? This ambiguity makes enforcement nearly impossible.
• Lack of Enforcement: The treaties are agreements between nations. There is no “space police” or international court with the power to enforce them. Disputes are handled through state-to-state diplomacy or, in the case of the Liability Convention, a claims commission that has never been fully formed.
• The “Fault” Problem: For the Iridium-Cosmos collision, who was at fault? The Iridium satellite was active, but the Cosmos satellite was defunct. Does an active satellite have a greater duty to maneuver? The law is silent.
• Commercial Actors: The treaties place all responsibility on states. But what happens when a collision is predicted between two private companies from different countries? The legal and communication channels are complex and slow, whereas the need for a maneuver decision is immediate.
• No “Salvage” Law: On the high seas, there is a well-established law of salvage, allowing parties to recover and claim derelict vessels. No such law exists for space. You cannot legally “salvage” another country’s (or company’s) billion-dollar defunct satellite, even if it poses a threat to the environment. This is a major hurdle for active debris removal.

Because of these gaps, the international community has shifted its focus from binding treaties to a more flexible system of non-binding standards, guidelines, and best practices.

Guiding the Way: Standards and Best Practices

With international law providing only a high-level framework, the real, practical work of space sustainability is being driven by technical standards and operational best practices. These are developed by technical experts and, while often voluntary, are increasingly being adopted into national regulations.

The Inter-Agency Space Debris Coordination Committee (IADC)

The most important technical body for debris mitigation is the Inter-Agency Space Debris Coordination Committee (IADC). Founded in 1993, the IADC is an international forum of space agencies, including NASA, the European Space Agency (ESA), Roscosmos, JAXA (Japan), CNSA (China), and others.

Its purpose is to exchange information, coordinate research, and develop consensus guidelines on debris mitigation.

The IADC Space Debris Mitigation Guidelines

In 2002, the IADC published its landmark guidelines, which have become the global baseline for sustainable operations. The key guidelines include:

1. Limit Debris Release During Operations: Don’t jettison lens caps, separation bolts, or other non-functional objects.
2. Minimize On-Orbit Explosions: “Passivate” spacecraft and rocket stages at the end of their life. This involves venting leftover fuel, discharging batteries, and releasing any other stored energy to prevent a future explosion.
3. Post-Mission Disposal: Remove spacecraft from useful orbits in a timely manner.
4. Avoid Intentional Destruction: Do not intentionally destroy spacecraft in a way that creates long-lived debris (a direct response to ASAT tests).

The UN COPUOS “Long-term Sustainability” (LTS) Guidelines

The IADC’s technical guidelines were so successful that they were taken up by the UN Committee on the Peaceful Uses of Outer Space (COPUOS). After nearly a decade of diplomatic negotiations, COPUOS adopted a set of 21 “Guidelines for the Long-term Sustainability of Outer Space Activities” (LTS Guidelines) in 2019.

A Consensus-Based Approach

These guidelines are not legally binding, but they represent a powerful political consensus. They translate the IADC’s technical recommendations into a broader policy framework that all nations have agreed to promote. They cover a wide range of topics, including:

• Sharing information on space objects and operational status.
• Adopting debris mitigation standards.
• Co-operating on SSA and conjunction warnings.
• Improving the registration of space objects.
• Developing standards for designing spacecraft that are easier to track and remove.

National Standards and Regulations

The most effective way to enforce these guidelines is to turn them into binding national law. States are increasingly doing this as partof their “authorization and continuing supervision” responsibilities under the Outer Space Treaty.

The United States: NASA Standards and FCC Rules

The United States has long been a leader in this area. NASA has a robust set of internal standards for its own missions that are often stricter than the international baseline.

A more recent development has come from the Federal Communications Commission (FCC). Because every satellite needs a license to transmit radio frequencies, the FCC has a powerful licensing lever. In 2022, the FCC adopted a new rule that mandates a 5-year post-mission disposal rule for all new U.S.-licensed satellites in LEO. This is a dramatic tightening of the old “25-year” guideline and is intended to force operators to deorbit their satellites much more quickly.

Europe: The French Space Operations Act

In Europe, several countries have national space laws. The French Space Operations Act (FSOA) of 2008 is one of the most comprehensive. It requires all satellite operators under French jurisdiction to obtain a license. To get that license, they must submit a debris mitigation plan that proves they can and will dispose of their satellite safely at the end of its life, adhering to the 25-year rule.

Japan’s Regulatory Framework

Japan has also incorporated debris mitigation into its national space policy. The Japanese government, through its Cabinet Office, licenses commercial space activities and requires adherence to IADC guidelines. The Japan Aerospace Exploration Agency (JAXA) is also a world leader in developing technology for active debris removal.

The “25-Year Rule”: A Guideline Under Stress

For decades, the most well-known IADC guideline for LEO was the “25-year rule.” This was a recommendation that satellite operators should ensure their spacecraft will deorbit (either through a controlled maneuver or natural decay) within 25 years of mission completion.

What is the 25-Year Rule?

This was a compromise. In the 1990s, it was seen as a reasonable and low-cost way to prevent the long-term accumulation of debris. The 25-year timeframe was long enough that it didn’t impose significant fuel or design costs on satellite missions. The idea was that this would be “good enough” to keep the LEO environment stable.

Challenges in Implementation and Compliance

The 25-year rule has two major problems.

1. Poor Compliance: Studies have shown that compliance, especially for rocket bodies and commercial satellites, has been historically poor. Many operators simply ignored the guideline.
2. No Longer Sufficient: The guideline was designed for a world with a few hundred satellite launches per year. It is completely insufficient for an environment with thousands of new satellites being launched annually by megaconstellations. A satellite launched today into a crowded orbit could be involved in a collision long before its 25-year “clock” runs out.

This is why regulators like the FCC have moved to a much stricter 5-year rule, reflecting the new urgency of the LEO congestion problem.

Designing for Demise (D4D)

A key technical best practice is Design for Demise (D4D). When a satellite re-enters the atmosphere, it heats up and breaks apart. Most of it burns up, but some dense components – like fuel tanks made of titanium or steel, or optical lenses – can survive re-entry and impact the ground.

D4D is an engineering philosophy that involves designing satellites to break apart and burn up more completely. This can involve:

• Using materials with lower melting points (e.g., aluminum alloys instead of titanium).
• Designing joints and structures to break apart early in the re-entry process, exposing more components to heat.
• Avoiding the use of materials that are resistant to heat.

The goal is to reduce the “casualty risk” – the statistical probability of a piece of debris hitting a person on the ground – to an acceptable level (often cited as less than 1 in 10,000).

Passivation: Preventing On-Orbit Explosions

As noted, one of the main sources of fragmentation debris is the explosion of old spacecraft. Passivation is the simple, effective best practice of preventing this.

At the end of a satellite’s or rocket stage’s mission, operators perform a final set of actions to render it inert. This includes:

• Venting any remaining propellant or pressurized gases.
• Discharging batteries to prevent them from overheating and exploding.
• Turning off all transmitters to prevent radio frequency interference.

This practice is now a standard requirement for most launch providers and satellite operators.

Collision Avoidance (COLA) Maneuvers

This is the day-to-day work of space sustainability. Satellite operators constantly receive conjunction data from the U.S. Space Force and commercial SSA providers. Their teams analyze the risk of these close passes.

If the “probability of collision” (PoC) rises above a certain threshold (e.g., 1 in 10,000), the operator must make a decision. They can perform a Collision Avoidance (COLA) maneuver, firing the satellite’s thrusters for a few seconds to slightly change its orbit, speed, or altitude, ensuring it will safely miss the other object.

This process is becoming a major operational burden. Megaconstellation operators like SpaceX must perform thousands of such maneuvers per year. This consumes fuel (shortening the satellite’s life), temporarily interrupts the satellite’s service, and requires 24/7 staffing by trained operators.

Key Organizations Shaping Space Sustainability

A complex, global ecosystem of organizations is working on the problem of space sustainability, from high-level diplomacy to on-the-ground technical implementation.

Intergovernmental Organizations

These are organizations composed of member states that set the global rules and norms.

The United Nations Office for Outer Space Affairs (UNOOSA)

Based in Vienna, UNOOSA is the UN’s main body for space matters. It implements the decisions of COPUOS and works to promote international co-operation. A key function of UNOOSA is managing the Register of Objects Launched into Outer Space, where nations file information about their satellites in accordance with the Registration Convention.

The UN Committee on the Peaceful Uses of Outer Space (COPUOS)

COPUOS is the diplomatic forum where space law is made. It consists of a Scientific and Technical Subcommittee and a Legal Subcommittee. It was here that the Outer Space Treaty was born, and it is where the LTS Guidelines were negotiated. COPUOS operates on a consensus basis, meaning all member states must agree, which can make progress slow but ensures that its outcomes are globally supported.

The International Telecommunication Union (ITU)

The ITU, a specialized agency of the UN, is one of the most powerful organizations in space. It manages the global allocation of the radio frequency spectrum and geostationary orbital slots.

Satellites are useless if they can’t communicate with the ground, and they can’t do that if their signals interfere with each other. The ITU coordinates “filings” from countries, which are essentially applications to use a specific frequency in a specific orbit. This co-ordination role makes the ITU a de facto regulator. It has its own rules about bringing satellites into use, which helps prevent “paper satellites” where a country might claim an orbital slot it never intends to use.

National Space Agencies

The world’s space agencies are the primary drivers of research, innovation, and implementation of sustainability practices.

NASA (National Aeronautics and Space Administration)

NASA’s Orbital Debris Program Office at the Johnson Space Center is a world leader in debris research. It runs models to predict the future debris environment, develops mitigation technologies, and maintains its own set of stringent standards for NASA missions. NASA also co-operates with the Department of Defense to track debris and protect its high-value assets like the ISS.

ESA (European Space Agency)

The European Space Agency (ESA) has made space sustainability a central part of its mission. Its “Space Safety” program focuses on three main areas: orbital debris, space weather, and planetary defense. ESA has been a pioneer in funding active debris removal, commissioning the ClearSpace-1 mission. It also has its own SSA program and works to harmonize standards across its European member states.

JAXA (Japan Aerospace Exploration Agency)

JAXA is a key member of the IADC and a leader in developing technology for Active Debris Removal (ADR). It has funded several demonstration missions and is conducting research on innovative removal methods, such as electrodynamic tethers.

Roscosmos

The Russian space agency is a major space power and a key partner in the ISS. It operates its own SSA system and participates in the IADC, contributing to the development of mitigation guidelines.

China National Space Administration (CNSA)

The CNSA is one of the world’s most active space agencies, with its own space station (Tiangong), lunar program, and navigation system (BeiDou). As a major space-faring nation, China’s participation in the IADC and COPUOS is essential for developing any global sustainability consensus.

Non-Governmental and Academic Groups

A number of non-profit and academic organizations provide independent research, analysis, and a forum for co-operation.

The Space Generation Advisory Council (SGAC)

The Space Generation Advisory Council (SGAC) is a UN-affiliated non-profit that connects students and young professionals in the space industry. Its “Space Safety and Sustainability” project group plays an active role in policy discussions, bringing the perspective of the next generation to COPUOS and other forums.

The Secure World Foundation

The Secure World Foundation (SWF) is a private foundation dedicated to the long-term sustainability of space. It publishes extensive research, hosts dialogues, and engages with governments and private industry to promote co-operation and the development of effective policies. SWF’s reports and handbooks are highly respected resources in the space community.

The Space Safety Coalition

The Space Safety Coalition (SSC) is an industry-led group that publishes a “Best Practices for the Sustainability of Space Operations” document. It represents an effort by the commercial sector to self-regulate and establish norms of behavior that go beyond the minimum requirements of international guidelines. This includes transparency, data sharing, and co-ordination for collision avoidance.

The Rise of Commercial Influence

The most significant change in the organizational landscape is the new power of commercial companies.

SpaceX and Starlink

SpaceX operates Starlink, the world’s largest satellite constellation by far. With thousands of satellites in LEO, its operational choices have an outsized impact on the entire environment. SpaceX has published its own sustainability practices, such as launching satellites into very low orbits (where they decay quickly if they fail) and designing them for full “demisability.” The company has also developed an autonomous, automated collision avoidance system to manage its massive fleet.

OneWeb

OneWeb’s constellation, though smaller than Starlink, operates at a higher altitude (1,200 km), where debris persists for much longer. This has led OneWeb to take a “responsible space” approach, including equipping its satellites with a grappling fixture to make them easier to deorbit at the end of their life.

Planet Labs

Planet Labs, which operates the largest fleet of Earth-observation satellites, has also been a vocal advocate for sustainability. As a company whose business depends on clear, unobstructed views from LEO, it has a direct financial interest in keeping orbits clear.

Viasat

The satellite communications company Viasat has used legal and regulatory channels to challenge the expansion of megaconstellations. It has filed lawsuits and regulatory protests, arguing that the environmental impact of thousands of new satellites has not been properly assessed and that they pose an undue risk of collision and radio frequency interference. This represents a new front in the sustainability debate, where market competitors use sustainability arguments in legal and economic disputes.

Insurance and Finance

A final, powerful set of actors are those who finance and insure space missions.

• Space Insurers: Before a satellite is launched, it is typically insured against launch failure and on-orbit failure. Insurers are now looking closely at the sustainability practices of operators. An operator that ignores debris guidelines or has a poor track record of collision avoidance may be charged a much higher premium, or may be denied insurance altogether. This creates a powerful financial incentive for good behavior.
• Environmental, Social, and Governance (ESG) in Space: Investment firms are beginning to apply ESGcriteria to space companies. An investor may ask what a company is doing to mitigate its “environmental” (orbital) impact. This is pushing companies to adopt more transparent and sustainable practices to attract investment.

Active Solutions: The Field of Debris Removal and Servicing

Mitigation – preventing the creation of new debris – is essential. However, most experts agree it is no longer sufficient. The debris population in LEO is already so high that collisions between existing objects will continue to generate new debris, even if all launches stopped today.

This means we need remediation, or the Active Debris Removal (ADR). This has opened up a new field of technology known as On-Orbit Servicing, Assembly, and Manufacturing (OSAM).

Why Mitigation Isn’t Enough: The Need for Remediation

The Kessler Syndrome is driven by the density of objects. Models from NASA and ESA show that to stabilize the LEO environment, we must not only adhere to the 25-year rule (or the 5-year rule) but also begin actively removing 5 to 10 massive objects from orbit every single year.

These “high-priority” targets are typically large, defunct rocket bodies or satellites in crowded orbits. Removing a single one of these objects is far more effective than removing thousands of small pieces, as it prevents that object from becoming the source of a massive new debris cloud.

On-Orbit Servicing, Assembly, and Manufacturing (OSAM)

OSAM is a broad category of emerging capabilities that involve working on assets directly in space. ADR is one component of OSAM.

Refueling Satellites

Many satellites are retired not because their electronics fail, but because they run out of the propellant needed for station-keeping and collision avoidance. OSAM missions are being developed to rendezvous with these satellites and refuel them, extending their operational lives by years and delaying their transformation into debris.

Repairing and Upgrading Assets

It’s also possible to use a robotic servicing vehicle to repair a satellite with a stuck solar array, or even to install a new, upgraded processor or sensor package. This transforms satellites from disposable assets into serviceable ones, much like a car.

Key Missions: Northrop Grumman’s MEV

This is no longer science fiction. Northrop Grumman’s Mission Extension Vehicle (MEV) is the first commercially operational servicer. The MEV-1 and MEV-2 vehicles have successfully docked with two different Intelsat satellites in GEO. The MEV latches onto the client satellite and uses its own engines and fuel to provide all propulsion and attitude control. This has added years of life to otherwise healthy satellites. Northrop Grumman is also developing a system that can attach a small “propulsion pod” to a satellite and leave it there, freeing up the “tug” to service other clients.

Active Debris Removal (ADR) Concepts

ADR is the specific task of capturing and deorbiting a piece of uncooperative junk. This is much harder than servicing, as the target is not designed to be captured and may be tumbling uncontrollably. A variety of capture methods are in development.

Harpoons

One concept is to fire a harpoon into the target. The harpoon tethers the target to the “chaser” satellite, which can then use its engines to drag the combined stack into the atmosphere, where both will burn up. This method was successfully tested on the RemoveDEBRIS demonstration mission.

Nets

Another method, also tested by RemoveDEBRIS, is to fire a large net that entangles the target. The net can then be reeled in, or a tether can be used to pull the object to its disposal orbit. This is good for capturing objects with complex shapes or those that are tumbling.

Robotic Arms

This method involves using a sophisticated robotic arm to grab the target. This requires advanced autonomous navigation and control, as the chaser must precisely match the motion of the tumbling object. Once grabbed, the chaser can secure the object and perform a controlled deorbit.

Tethers (Electrodynamic and Momentum Exchange)

Tethers are a more exotic, propellant-less removal concept. An electrodynamic tether is a long, conductive wire. As it moves through Earth’s magnetic field, it generates a current, which in turn creates a tiny amount of drag. This drag can, over time, pull a satellite down from orbit without using any fuel. A momentum exchange tether is a spinning tether that could “catch” a piece of debris and then “throw” it down into a disposal orbit.

Lasers

A final concept involves using a powerful ground-based or space-based laser. The laser wouldn’t destroy the debris, but would instead be “ablating” its surface. Firing the laser at one side of an object would create a tiny plume of vaporized material, which acts as a small thruster, gently nudging the object’s orbit over time until it is pushed into a decay trajectory.

Notable ADR Demonstration Missions

Several companies and agencies are now moving from concept to hardware.

Astroscale’s ELSA-d

The Japanese company Astroscale is a global leader in the OSAM and ADR market. In 2021, it launched its ELSA-d mission. This consisted of two spacecraft: a “servicer” and a “client” (a mock piece of debris). The mission successfully demonstrated the servicer’s ability to autonomously rendezvous with the client and capture it using a magnetic docking mechanism. It is now testing more complex captures, such as capturing the client while it is tumbling.

ClearSpace-1 (An ESA-commissioned mission)

ESA has commissioned a mission from the Swiss startup ClearSpace. The ClearSpace-1 mission, planned for launch in the coming years, will be the first-ever mission to remove an actual piece of debris. Its target is a Vespa (Vega Secondary Payload Adapter), a 100-kg object left in orbit by an ESA launch in 2013. ClearSpace-1 will use a set of four robotic arms to capture the Vespa and then drag it down to a re-entry orbit.

The Economic and Legal Hurdles of ADR

While the technology is being proven, two massive hurdles remain for ADR.

Who Pays for Removal?

Cleaning up orbit is a public good, which makes it a difficult business. Why would one company pay millions to remove a piece of debris that benefits all of its competitors?

• Government Contracts: The first ADR missions (like ClearSpace-1) are being paid for by governments, who see it as developing a strategic capability.
• Mandates: Regulators could one day mandate that a company must pay for the removal of its defunct satellite, creating a market for removal services.
• Incentives: Governments could offer “bounties” or tax credits for each piece of debris removed.

Liability and “Salvage” Rights

As mentioned, the Outer Space Treaty makes it illegal to touch another nation’s space object without permission. This means Astroscale can’t just go and grab a defunct Russian rocket body. This requires new diplomatic agreements, standards for “due care,” and a legal framework for transferring liability. What if the removal mission fails and creates more debris? Who is responsible? These legal questions are just as challenging as the technical ones.

Emerging Challenges to Sustainability

Even as we develop solutions for old problems, new challenges are emerging that complicate the picture of space sustainability.

Large Constellations: A Paradigm Shift

The single biggest new challenge is the proliferation of large constellations in LEO. Companies are launching satellites not one by one, but by the thousands.

The Proliferation of Satellites

In 2010, there were roughly 1,000 active satellites in orbit. Today, there are over 10,000, and plans have been filed with the ITU for well over 100,000 more. This is a fundamental change to the orbital environment.

Increased Collision Risk and Maneuvering

These satellites are being launched into the most congested parts of LEO. This dramatically increases the number of conjunctions and the need for collision avoidance maneuvers. While operators like SpaceX have automated systems, the risk of a failure – a software bug, a loss of communication, or a dead satellite that can’t move – grows with every satellite added.

The Challenge of “Cumulative Effects”

The core problem is one of cumulative effects. A single constellation operator may have a “safe” design, with a low failure rate and a good disposal plan. But what happens when there are ten such constellations, all sharing the same “airspace”? The cumulative collision risk from all of them combined may be unacceptably high. Regulators and scientists are struggling with how to model and manage this “aggregate” risk.

Light Pollution and Radio Astronomy

Satellites don’t just create physical debris; they also create interference.

Streaks in the Sky: Impact on Optical Astronomy

Large constellations have created a new form of light pollution. Astronomers using sensitive ground-based telescopes, like the Vera C. Rubin Observatory, are finding their long-exposure images marred by bright streaks from sunlight reflecting off thousands of satellites. This threatens to degrade or even halt key areas of astronomical research, such as the search for potentially hazardous asteroids.

Radio Frequency Interference (RFI)

Radio telescopes, which “listen” for faint natural radio signals from the universe, are also at risk. The thousands of new internet satellites are all “shouting” in radio frequencies. While the ITU allocates specific bands, the “noise” from satellite side-lobes and reflections can bleed over and drown out the faint whispers from the cosmos.

Efforts to Mitigate: Darker Satellites and Software Fixes

This has led to an ongoing dialogue between astronomers and satellite operators. SpaceX has experimented with painting its satellites black and adding “visors” to block sunlight from reflecting off shiny components. Astronomers, in turn, are developing sophisticated software to “mask out” satellite streaks from their data. This represents a new conflict over the “commons” of the night sky.

Space Traffic Management (STM)

The current system of collision avoidance is ad-hoc. The U.S. Space Force sends out a warning, and operators e-mail or call each other to coordinate. This is not sustainable.

What is STM? (The “Air Traffic Control” for Space)

The solution is a global Space Traffic Management (STM) system, analogous to the air traffic control (ATC) system for aviation.

An STM system would:

• Ingest tracking data from all sources (military and commercial) into one unified catalog.
• Use advanced analytics to predict collisions with high confidence.
• Provide clear “rules of the road” (e.g., “who must move”).
• Automate and co-ordinate maneuver requests between operators.

The Need for a Global, Transparent System

For an STM system to work, it must be global and transparent. All operators must participate and trust the data. If different operators are using different catalogs or different risk models, they may make conflicting decisions (e.g., both maneuvering into the same “safe” spot).

Who Should Manage It? (Civil vs. Military vs. International)

The biggest debate is who should run this system.

• Military: The U.S. military has the best data, but many nations are uncomfortable with a military organization managing global “traffic.” Military data is also often classified.
• Civil: In the U.S., the Department of Commerce (via the Office of Space Commerce) has been tasked with creating a civil, open-data SSA and STM pilot program.
• International: Many argue that, like ATC (which is coordinated by the UN’s ICAO), a global STM system must be run by an international, neutral body, perhaps under the UN.

The Weaponization of Space

The most severe threat to sustainability is the prospect of conflict in space.

Anti-Satellite (ASAT) Weapons

As the ASAT tests of 2007 and 2021 proved, these weapons are “debris generators.” A war in space, even a limited one, would be an environmental catastrophe. The debris created by destroying just a few large satellites could trigger a Kessler Syndrome and close off LEO for everyone.

The Threat of “Dual-Use” Technologies

The new OSAM and ADR technologies are inherently “dual-use.” A satellite that can repair a friendly satellite can also, in theory, disable or damage an opponent’s satellite. A robotic arm for debris removal could also be used as a weapon. This creates a complex security dilemma, where even peaceful sustainability efforts can be viewed with suspicion.

How Conflict in Space Creates Uncontrollable Debris

This is why many nations are pushing for new norms of behavior, such as the UN-backed resolution to ban destructive, debris-generating ASAT tests. The long-term sustainability of space is fundamentally incompatible with its use as a warfighting domain.

Beyond Earth Orbit: Planetary Protection

Space sustainability is not just about Earth orbit. It also encompasses the scientific and ethical responsibility to protect other worlds, and our own, from biological contamination. This field is known as planetary protection.

Defining Planetary Protection

Planetary protection involves “the practice of protecting solar system bodies from contamination by Earth life, and protecting Earth from possible life forms that may be returned from other solar system bodies.” The international guidelines for this are set by the Committee on Space Research (COSPAR).

Forward Contamination: Protecting Other Worlds

This is the concern of “contaminating” other planets with microbes from Earth. The primary goal is to preserve the scientific integrity of “astrobiological” missions. If we are searching for life on Mars, we must be certain that any “life” we find isn’t just a hardy bacterium that hitched a ride from the clean room in Pasadena, California.

The COSPAR Categories

COSPAR classifies missions into five categories based on their destination and purpose.

• Category I: Missions to places with no direct interest for chemical evolution or the origin of life (e.g., the Sun). No protection required.
• Category IV: Missions that land on “biologically interesting” worlds. This is split into:
  • IVa: Missions to Mars that do not search for life. Rovers like Curiosity and Perseverance must be built in ultra-clean rooms and have their “bioburden” (number of microbes) strictly controlled.
  • IVc: Missions that land in “Special Regions” on Mars where liquid water is believed to exist. These missions would require full sterilization.
• Category V (Restricted): Missions that return samples to Earth.

Sterilizing Mars Rovers

Rovers like Perseverance undergo a process of “dry heat microbial reduction.” The entire spacecraft is “baked” at high temperatures for many hours to kill as many microbes as possible. This is a major engineering challenge, as the electronics must be designed to survive this baking.

The “Ocean Worlds” Dilemma (Europa, Enceladus)

The most sensitive targets are the “ocean worlds” like Jupiter‘s moon Europa and Saturn‘s moon Enceladus, which are believed to have liquid water oceans beneath their ice shells. These are the most likely places to find extraterrestrial life in our solar system.

Missions to these worlds are held to the highest standard. For example, the Galileo spacecraft, at the end of its mission, was intentionally deorbited and plunged into Jupiter’s atmosphere to ensure it could never, ever accidentally crash on Europa and contaminate it.

Backward Contamination: Protecting Earth

This is the other side of the coin: ensuring that any samples brought back from other worlds do not contain “extra-terrestrial replicating agents” that could be harmful to Earth’s biosphere.

Mars Sample Return

This is no longer a theoretical concern. The joint NASA-ESA Mars Sample Return (MSR) mission is underway. The Perseverance rover is currently drilling and caching rock samples on Mars. A future mission will retrieve these samples, launch them into Mars orbit, and bring them back to Earth.

Quarantine Protocols

These samples will be treated as “biohazardous” until proven safe. They will be returned in a “biocontainment” vessel designed to withstand any impact or failure. On Earth, they will be delivered to a specialized Sample Receiving Facility (SRF), a maximum-security (BSL-4) lab where they can be studied in total isolation, similar to how we handle the world’s most dangerous viruses. This is a modern-day quarantine protocol, just like the one used for the Apollo program astronauts returning from the Moon.

Planetary Protection and Commercial Missions

This entire field is being challenged by the rise of commercial spaceflight. The COSPAR guidelines were written for state-run space agencies. How do they apply to a company like SpaceX, which has stated its intention to land humans on Mars?

This is an open question. NASA has begun adapting its policies for “public-private partnerships,” but there is no global consensus on how to enforce planetary protection on commercial actors, who may be less willing to bear the high cost of sterilization.

The Economic Case for Sustainability

Ultimately, the most powerful driver for space sustainability may not be law or diplomacy, but economics. A “business case” for sustainability is emerging, based on both the cost of inaction and the opportunity for new markets.

The Cost of Inaction

The global space economy is worth hundreds of billions of dollars. The services it provides to the wider global economy – from navigation and timing to communications and climate data – are valued in the trillions.

If LEO were to become unusable due to debris, the economic consequences would be devastating.

• Insurance Costs: Premiums would skyrocket, making new space ventures un-bankable.
• Replacement Costs: Satellites would be destroyed faster than they could be replaced.
• Loss of Services: GPS networks could fail. Internet access would be disrupted. Weather forecasting would become less reliable.
• Innovation Stops: Investment in space-based services would dry up.

The cost of inaction – of not funding SSA, mitigation, and removal – is far higher than the cost of implementing sustainable practices.

The Business of Sustainability

This risk is also creating new business opportunities. The private sector is responding with market-based solutions.

Space Situational Awareness as a Service

Companies like LeoLabs and ExoAnalytic Solutions are selling SSA data as a commercial service. Satellite operators, governments, and insurers pay for this data because it is more precise, has lower latency, and is tailored to their specific needs. This is a new, multi-million-dollar market that exists only because of the sustainability challenge.

The Emerging Market for OSAM and ADR

Companies like Astroscale, ClearSpace, and Northrop Grumman are not just demonstration missions; they are the pioneers of a future market. They are betting that in the future, “end-of-life services” and “debris removal” will be a routine part of the space economy. A satellite operator will include the cost of a “deorbit service” in its original business plan, just as a shipping company includes the cost of fuel.

A “Circular Economy” in Space

The long-term vision for space sustainability is a circular economy. This is a shift away from the current model of “launch, use, and discard.”

Reusing and Recycling On-Orbit

In a circular space economy, resources are kept in use for as long as possible.

• Refueling: Satellites are refueled instead of being replaced.
• Servicing: Robotic servicers repair and upgrade existing assets.
• Recycling: In the more distant future, old satellites might be disassembled in orbit, and their raw materials (like aluminum and rare Earth metals) recycled to manufacture new components in space.

Sustainable Launch Practices

Sustainability also includes the launch itself. This involves not just minimizing debris from the launch vehicle but also considering the terrestrial environmental impact of launches, including carbon emissions and the atmospheric effects of rocket exhaust.

Summary

Space sustainability is a complex and urgent challenge, moving from a niche academic concern to a central strategic and economic issue. It is the recognition that the orbital environment is a finite, shared, and fragile resource that is vital to modern civilization.

The problem is defined by the physical threat of orbital debris, which travels at hypervelocity speeds and threatens a cascading chain reaction – a Kessler Syndrome – that could render key orbits unusable. This threat has been exacerbated by accidental collisions and irresponsible ASAT tests.

The solutions are multifaceted. They begin with the legal framework of the Outer Space Treaty, which establishes state responsibility, but this framework is insufficient for the modern era. The real progress is found in non-binding (but highly influential) technical guidelines from bodies like the IADC and the UN’s LTS Guidelines. These standards, such as passivation and post-mission disposal, are increasingly being written into binding national regulations, like the FCC’s 5-year rule.

A global web of organizations, from UNOOSA and ESA to commercial megaconstellation operators and SSA data providers, are the key actors. They are all grappling with new challenges, including the massive influx of satellites, the impact on astronomy, and the need for a global Space Traffic Management (STM) system.

Looking forward, the field is expanding. Mitigation alone is not enough, which has given rise to a new industry focused on Active Debris Removal (ADR) and On-Orbit Servicing (OSAM), with missions like ELSA-d and ClearSpace-1 proving the technology. The concept of sustainability also extends beyond Earth to include planetary protection – the scientific imperative to protect other worlds from our microbes and Earth from unknown samples.

Sustainability in space is not just an environmental good; it is an economic necessity. The cost of losing orbit is far too high to ignore. This economic reality is driving investment, creating new markets, and pushing all actors – public and private – toward a more responsible and co-operative management of this final frontier.