Overview of key space sustainability issues under consideration.
Space sustainability aims to maintain the safety and health of the space environment, as well as planetary environments. Similar to sustainability
initiatives on Earth, space sustainability seeks to use the environment
of space to meet the current needs of society without compromising the
needs of future generations. It usually focuses on space closest to Earth, Low Earth Orbit (LEO), since this environment is the one most used and therefore most relevant to humans. It also considers Geostationary Equatorial Orbit (GEO) as this orbit is
another popular choice for Earth-orbiting mission designs.
The issue of space sustainability is a new phenomenon that is gaining more attention in recent years as the launching of satellites and other space objects has increased. These launches have resulted in more space debris
orbiting Earth, hindering the ability of nations to operate in the
space environment while increasing the risk of a future launch-related
accident that could disrupt its proper use. Space weather also acts as an outstanding factor for spacecraft failure. The current protocol for spacecraft disposal at end-of-life has, at
large, not been followed in mission designs and demands extraneous
amounts of time for disposal.
Precedent created through prior policy initiatives has
facilitated initial mitigation of space pollution and created a
foundation for space sustainability efforts. To further mitigation, international and transdisciplinary consortia
have stepped forward to analyze existing operations, develop standards,
and incentivize future procedures to prioritize a sustainable approach. A shift towards sustainable interactions with the space environment is
growing in urgency due to the implications of climate change and
increasing risk to spacecraft as time presses on.
Fundamentals
Space sustainability requires all space participants to have three
consensuses. The space field should be used peacefully, jointly protect
the space field from harm, and maximize space utilization through
environmental, economic, and security exploration of space. These consensuses also clarify the relationship between space
sustainability and international security, that states and individuals
explore space for various purposes. Their reliance on space needs to be
guided by rules, order, and policies and obtain more benefits without
negatively affecting the space environment and space activities.
However, striking an agreement remains challenging even with such
demands in place. In the discussions between countries on long-term
sustainability, technical improvements are given more importance than
introducing and applying new legal regimes. Specifically, technical approaches to space debris have been proposed, such as debris removal. Specific data on space debris is also being explored to help study its
impact on sustainability and promote further cooperation between
countries.
Current state
Space sustainability comes into play to address the pressing current
state of near-Earth orbits and its high amounts of orbital debris. Spacecraft collisions with orbital debris, space weather, overcrowding
in low Earth orbit (LEO) makes spacecraft susceptible to higher rates of
failure. The current end-of-life protocol for spacecraft exacerbates the space
sustainability crisis; many spacecraft are not properly disposed, which
increasing the likelihood of further collisions.
Orbital debris
A computer-generated animation by the European Space Agency representing space debris in low earth orbit at the current rate of growth compared to mitigation measures being taken.
Orbital debris is defined as unmanned, inoperative objects that exist in space. This orbital debris breaks down further as time progresses as a result
of naturally occurring events, such as high-velocity collisions with micrometeoroids, and forced events, such as a controlled release of a launch vehicle. In LEO, these collisions can take place at speeds anywhere between an
average velocity of 9 kilometers per second (km/s) and 14 km/s relative
to the debris and spacecraft. In GEO, however, these high-speed collisions are a much lower risk as
the average relative velocity between the debris and spacecraft is
typically between 0 km/s and 2.5 km/s. As of 2012, the United States Joint Space Operations Center tracked
21,000 pieces of orbital debris larger than 10 cm in Earth's nearby
orbits (LEO, GEO, and Sun-synchronous), where 16,000 of these pieces are catalogued. Space debris can be categorized into three categories: small, medium, and large. Small debris is for pieces that are less than 10 centimeters (cm). Medium-sized debris is for pieces larger than 10 cm, but not an entire spacecraft. Large-sized debris has no official classification, but typically refers
to entire spacecraft, such as an out of use satellite or launch
vehicle. It is difficult to track small-sized debris in LEO, and challenging to track small and medium-sized debris in GEO. Yet this statement is not to discount the abilities of LEO and GEO
tracking capabilities, the smallest piece of tracked debris can weigh as
low as ten grams. If the size of the debris prohibits it from being tracked, it also
cannot be avoided by the spacecraft and does not allow the spacecraft to
lower its risk of collisions. The likelihood of the Kessler syndrome,
which essentially states that each collision produces more debris,
grows larger as the amount of orbital debris multiplies, increasing the
amount of further collisions until space cannot be used entirely.
Space weather
Space weather poses a risk to satellite health, consequently, resulting in greater amounts of orbital debris. Space weather impacts satellite health in a variety of ways. Firstly,
surface charging from the Sun's surface facilitates electrical
discharges, damaging on-orbit electronics, posing a threat to mission
failure. Single Event Upsets (SEUs) can also damage electronics. Dielectric charging and bulk charging can also occur, causing energy problems within the spacecraft. Additionally, at altitudes less than one thousand kilometers, atmospheric drag can increase during solar storms by increasing the altitude of the spacecraft, only adding more drag onto the spacecraft. These factors degrade performance over the spacecraft's lifetime,
leaving the spacecraft more susceptible to further system and mission
failures.
Overcrowding
There has been a dramatic increase in the use of LEO and GEO orbits
over the last sixty years since the first satellite launch in 1957. To
date, there have been approximately ten thousand satellite launches,
whereas only approximately 2000 are still active. These satellites can be used for a variety of purposes, which are
telecommunications, navigation, weather monitoring, and exploration.
Within the coming decade, companies like SpaceX are predicted to launch an additional fifteen thousand satellites into LEO and GEO orbits. Microsatellites built by universities or research organizations have
also increased in popularity, contributing to the overcrowding of near
earth orbits. This overcrowding of LEO and GEO orbits increases the likelihood of
potential collisions among satellites and orbital debris, contributing
further to the large amount of orbital debris present in space.
End of life protocol
The current end of life protocol is that at the end of mission, spacecraft are either added to the graveyard orbit or at a low enough altitude that drag will allow the spacecraft to burn up upon reentry and fall back to Earth. Approximately twenty satellites are put into the graveyard orbit each year. There is no current process to return satellites to Earth after entering the graveyard orbit. The process of a spacecraft returning to Earth via drag can take between ten and one hundred years. This protocol is critical to reduce overcrowding in near-Earth orbits.
Mega constellation and space debris
The impact of constellations on the space environment has also been
studied, such as the probability of collisions of mega constellations in
the presence of large amounts of space debris.
Although studies have shown that the predictors of mega constellations
are highly variable, specific information related to mega constellations
is not transparent.
But any catastrophic collision, as in the case of Kessler syndrome,
has consequences for people and the environment. Putting this thinking
into mega constellations, their existence may have potential benefits,
but it will not bring adequate help to the governance of space debris. At the same time, the space debris situation cannot be underestimated
or ignored because of the existence of mega constellations.
Atmospheric entry mass by spacecraft accounted for 3% compared to
entries by meteoroids in 2019, but in a scenario in which large amounts
of proposed satellite internet constellations are realized, artificial entries would make up 40% compared to meteoroid entries. The impact of spacecraft burning up in the atmosphere during artificial
atmospheric entry is different to meteors due to the spacecraft's
generally larger size and different composition. The atmospheric
pollutants produced by artificial atmospheric burning-up have been
traced in the atmosphere and identified as reacting and possibly
negatively impacting the composition of the atmosphere and particularly
the ozone layer.
Considering space sustainability in regard to atmospheric impact of re-entry is by 2022 just developing and has been identified in 2024 as suffering from "atmosphere-blindness", causing global environmental injustice. This is identified as a result of the current end-of life spacecraft management, which favors the station keeping practice of controlled re-entry. This is mainly done to prevent the dangers from uncontrolled atmospheric entries and space debris.
Suggested alternatives are the use of less polluting materials and by in-orbit servicing and potentially in-space recycling.
Space environment
The existence of orbital debris has caused great trouble to the
conduct of space activities. The development of space sustainability has
not given sufficient political attention, although some warnings and
discussions have made this abundantly clear. Debris management is still voluntary on the part of the state, and
there are no laws mandating debris management practices, including the
amount of debris to be managed. Although the UN Space Debris Mitigation Guidelines were promulgated in
2007 as an initial measure of space debris governance, there is still no
broad consensus or action on further limits on space debris after that.
The difficulties for individuals wishing to participate in debris
management initiatives cannot be ignored. Any individual or sector
desiring to participate in space debris operations needs to obtain
permission from the launching state, which is difficult for the
launching state to do. This is because the process of space debris management inevitably has a
negative impact on other space objects, and there is a lot of
subsequent liability in terms of financial consumption. Therefore, the launching state would argue that space debris management requires the joint efforts of all states. However, it is difficult to determine what actions can be taken to gain acceptance between countries.
Regulations
Current space sustainability efforts rely heavily on the precedent
set by regulatory agreements and conventions of the twentieth century. Much of this precedent is included in or is related to the Outer Space Treaty of 1963, which represented one of the initial major efforts by the United Nations to create legal frameworks for the operation of nations in space.
Pre-Outer Space Treaty
The international community has had concerns about space contamination since the 1950s prior to the launch of Sputnik I. These concerns stemmed from the idea that increasing rates of
exploration into further areas of outer space could lead to
contamination capable of damaging other planetary bodies, resulting in
limitations to human exploration on these bodies and potential harm to
the Earth. Efforts to combat these concerns began in 1956 with the International Astronautical Federation (IAF) and the United Nations Committee on the Peaceful Uses of Outer Space (COPUOUS). These efforts continued to 1957 through the National Academy of Sciences and International Council for Science (ICSU). Each of these organizations aimed to study space contamination and
develop strategies for how to best address its potential consequences. The ICSU went on to create the Committee on Contamination by
Extraterrestrial Exploration (CETEX) that put forward recommendations
leading to the establishment of the Committee on Space Research (COSPAR). COSPAR continues to address outer space research on an international scale today.
Outer Space Treaty
Relevant regulations of international space law to sustainability in space can be found in the Outer Space Treaty, which was adopted by the UN General Assembly in 1963. The Outer Space Treaty contains seventeen articles designed to create a
basic framework for how international law can be applied in outer
space. Basic principles of the Outer Space Treaty include the provision in
Article IX that parties should "avoid harmful contamination of space and
celestial bodies;" definitions of "harmful contamination" are not provided.Other articles of relevance to space sustainability include articles I,
II, and III that concern the fair and inclusive international use of
space in a manner free from sovereignty, ownership, or occupation by any
nation. In addition, articles VII and VIII protect ownership by their
respective countries of any objects launched to space while attributing
responsibility for any damages to the property or personnel of other
countries by those objects to said countries. Descriptions or definitions for what these damages may entail are not provided.
COSPAR Planetary Protection Policy
Principles of Article IX provided the basis for the Committee of Space Research (COSPAR) Planetary Protection Policy guidelines, which are generally well-regarded among scientific experts. Such guidelines, however, are non-binding and often described as "soft-law," as they lack legal mandate. The Planetary Protection Policy is primarily concerned with providing
information regarding best practices to avoid contamination of the space
environment during space exploration missions. COSPAR believes that the prevention of such contamination is in the
best interest of humanity as it may impede scientific progress,
exploration, and the mission of a search for life. In addition, the argument is made that cross-contamination of the Earth
can be potentially harmful to its environment due to the largely
unknown nature of potential space contaminants.
Other relevant regulations
Regulatory clarifications concerning the Outer Space Treaty of 1963
of relevance to space sustainability were made in subsequent years. The
1967 Return Agreement relates mainly to the return of lost astronauts to
their appropriate nations, but also requires Outer Space Treaty signing
nations to assist other nations with the return of objects that return
to Earth from orbit to their proper owners The 1972 Liability Convention
attributes liability for damages from space objects to the nation that
launched the object, regardless of whether that damage occurred in space
or on Earth. Other clarifications include the 1975 registration convention that
attempted to create mechanisms for nations to identify space objects,
and the 1979 Moon Agreement that established protections for the
environments of the Moon and other nearby planetary bodies. These agreements and conventions represented attempts to improve the
initial Outer Space Treaty as space exploration continued to grow in
importance throughout the 20th century.
Attitudes
Countries and major international institutions
Both the state and space agencies are working to improve the laws and
regulations that facilitate the long-term sustainability of space. For
example, the European Code of Conduct for Space Debris Mitigation signed
by France, the UK and other countries in 2016. China, Brazil, Mexico and others have legal background and methodological measures under long-term space sustainability.However, the main problem is that until the concept of space
sustainability is agreed between countries, inter-regional efforts are
not working well.
Currently, the Committee on the Peaceful Uses of Outer Space
(COPUOS) encourages states to incorporate the space debris mitigation
guidelines developed by bodies such as the Inter-Agency Space Debris
Coordination (IADC) into their national legislation, thereby regulating
state behavior. Some countries have responded positively to this, such as Switzerland,
the Netherlands and Spain. However, there are still some countries that
do not consider debris management approaches in their national
legislation, such as Japan and Australia. Many delegates at the COPUOS meeting expressed their reasons for doing
so, arguing that space debris management is closely linked to technology
and funding. Technology is dynamic and constantly evolving. Therefore,
the incorporation of debris governance guidelines into national law is
not an immediate priority at this time.
Scientific attitudes
A study outlined rationale for governance that regulates the current free externalization of true costs and risks, treating orbital space around the Earth as an "additional ecosystem" or a common "part of the human environment" which should be subject to the same concerns and regulations like oceans on Earth.
While scientists may not have the means to make and enforce global laws
themselves, the study concluded in 2022 that it needs "new policies,
rules and regulations at national and international level".
Mitigation
Sustainability mitigation efforts include but are not limited to
design specifications, policy change, removal of space debris, and
restoration of orbiting semi-functional technologies. Efforts begin by regulating the debris released during normal
operations and post-mission breakups. Due to the increased awareness
of high-velocity collisions and orbital debris in the previous decades,
missions have adapted design specifications to account for these risks. For example, the RADARSAT
program implemented 17 kilograms of shielding to their spacecraft,
which increased the program's predicted success rate to 87% from 50%. Another effort in mitigation is restoring semi-functional satellites,
which allows a spacecraft classified as "debris" to be reclassified as
"functional." Space debris mitigation focuses on limiting debris release during normal operations, collisions and intentional destruction. Mitigation also includes reducing the possibility for post-mission
breakups due to stored energy and/or operations phases, as well as
addressing procedure for end of mission disposal for spacecraft.
Space Sustainability Rating
One example leading the regulatory sustainability measures is the
Space Sustainability Rating (SSR), which is an instigator for industry
competitors to incorporate sustainability into spacecraft design. The Space Sustainability Rating was first conceptualized at the World
Economic Forum Global Future Council on Space Technologies designed by
international and transdisciplinary consortia. The four leading organizations are the European Space Agency, Massachusetts Institute of Technology, University of Texas at Austin, and BryceTech with the goal to define the technical and programmatic aspects of the SSR. The SSR represents an innovative approach to combating orbital debris
through incentivizing the industry to prioritize sustainable and
responsible operations. This response entails the consideration of potential harm to the space
environment and other spacecraft, all while maintaining mission
objectives and high-quality service. The rating takes inspiration from other standards, like leadership in
energy and environmental design (LEED) for the building sector. Several
of the factors emphasized in the rating were extracted from LEED design
considerations like the incorporation of feedback and public comments,
or the rating's advocacy to influence policy, such as orbit
fragmentation risks, collision avoidance capabilities, trackability, and
adoption of international standards.
Tracking
Tracking is one of the main Space Sustainability Rating modules'
efforts. The module "Detectability, Identification and Tracking" (DIT)
consists of standardizing the comparison of satellite missions to
encourage satellite operators to improve their satellite design and
operational approaches for the observer to detect, identify, and track
the satellites. Tracking presents challenges when the observer seeks to monitor and predict the spacecraft behavior over time. While the observer may know the name, owner, and instantaneous location
of the satellite, the operator controls the full knowledge of the
orbital parameters. The Space Situational Awareness (SSA) is one the tools geared towards
solving the challenges presented when tracking orbiting satellites and
debris. The SSA continuously tracks objects using ground-based radar and
optical stations so the orbital paths of debris can be predicted and
operations avoid collisions. It feeds data to 30 different systems like satellites, optical
telescopes, radar systems, and supercomputers to predict risk of
collision days in advance. Other efforts in tracking orbital debris are made by the US Space Surveillance Network (SSN).
Removal
Under the "External Services" module of the SSR, the rating offers
commitment to use or demonstration of use of end-of-life removal
services. Space debris mitigation measures are found to be inadequate to
stabilize debris environments with an actual current compliance of
approximately sixty percent. Moreover, a low compliance rate of approximately thirty percent of the
103 spacecraft that reached end of life between 1997 and 2003 were
disposed of in a graveyard orbit. Since policy has not caught up to ensure the longevity of LEO for
future generations, actions like Active Debris Removal (ADR) are being
considered to stabilize the future of LEO environment. Most famous removal concepts are based on directed energy, momentum
exchange or electrodynamics, aerodynamic drag augmentation, solar sails,
auxiliary propulsion units, retarding surfaces and on-orbit capture. As ADR consists of an external disposal method to remove obsolete satellites or spacecraft fragments. Since large-sized debris objects in orbit provide a potential source
for tens of thousands of fragments in the future, ADR efforts focus on
objects with high mass and large cross-sectional areas, in densely
populated regions, and at high altitudes; in this instance, retired
satellites and rocket bodies are a priority. Other practical advancements toward space debris removal include missions like RemoveDEBRIS, ClearSpace-1, and End-of-Life Service (ELS-d).
Growing urgency
The growth of all tracked objects in space over time
The previous reduced state of regulation and mitigation on space debris and rocket fuel emissions is aggravating the Earth's stratosphere through collisions and ozone depletion, increasing the risk for spacecraft health through its lifetime.
Inaccessibility to LEO
Due to the increase of satellites being launched and the growing amount of orbital debris in LEO, the risk of LEO becoming inaccessible over time (in accordance with the Kessler syndrome)
is increasing in likelihood. The mitigation policies for creating space
debris fall under an area of voluntary codes by the states, although it
has been disputed whether the Article I Outer Space Treaty or the
Article IX Outer Space Treaty protects the space environment from
deliberate harm, which has yet to be upheld. In 2007, an inactive Chinese satellite was purposefully destroyed by
the Chinese government as a part of their anti-satellite weapon test
(ASAT), spreading nearly 2800 objects of space debris five centimeters
or larger into LEO. An analysis concluded that about eighty percent of the debris will remain in LEO nine years after this destruction. In addition, the destruction increased the collision likelihood for
three Italian satellites that launched the same year as the Fengyun-1C
destruction. The increase in collision ranged between ten and sixty percent. However, there were no legal consequences against the Chinese government.
Rocket fuel emissions
When rockets are launched into space, parts of their fuel enter the
stratosphere of the Earth. Rocket fuel emissions are made up of carbon
dioxide, water, hydrochloric acid,
alumina and soot particles. The most concerning emissions from rocket
fuel are chlorine and alumina particles from solid rocket motors (SRMs)
and soot from kerosene fueled engines. When the hydrochloric acid from
the engine exhaust dissociates, the free chlorine roams freely in the
stratosphere. The chemical reaction between these chlorine and alumina causes ozone
depletion. In addition, the soot particles form over a black umbrella
over the stratosphere which can cause the temperature of the Earth's
surface to lower and further depleting the ozone layer, an unintentional
form of geoengineering. The nature of geoengineering
has been disputed as a form of mitigating global warming and has the
possibility of being banned and holding rockets accountable for the soot
particles they distribute to the stratosphere. New types of engines and
fuels are emerging, mainly the liquid oxygen (LOX) and
monomethylhydrazine engine, but there is minimal research on their
impact on the environment besides their emission of hydroxide and
nitrogen oxide compounds, two molecules that have significant impact on
the ozone layer. Currently, rocket fuel emissions have been deemed insignificant when it
comes to their consequences to Earth's environment and LEO. However, emissions will increase in the coming years, making rocket
fuel's contribution to global warming much more significant.
Beyond LEO
Space environment issues are not confined to LEO, which is part of
the wider space environment. There are different issues, like geostationary orbital space management, due to its limited space, and lunar orbit
has been discussed as the next environment to consider. In the context
of the presence of space debris in LEO, it is normal to speculate that
lunar orbit also possesses space debris. Space debris measures similar
to those in LEO related to space sustainability have been discusse.
Space debris (also known as space junk, space pollution, space waste, space trash, space garbage, or cosmic debris) are defunct human-made objects in space – principally in Earth orbit – which no longer serve a useful function. These include derelict spacecraft
(nonfunctional spacecraft and abandoned launch vehicle stages),
mission-related debris, and fragmentation debris from the breakup of
derelict rocket bodies and spacecraft. In addition to derelict
human-made objects left in orbit, space debris includes fragments from
disintegration, erosion, or collisions;
solidified liquids expelled from spacecraft; unburned particles from
solid rocket motors; and even paint flecks. Space debris represents a
risk to spacecraft.
Space debris is typically a negative externality.
It creates an external cost on others from the initial action to launch
or use a spacecraft in near-Earth orbit, a cost that is typically not
taken into account nor fully accounted forby the launcher or payload owner.
Several spacecraft, both crewed and un-crewed, have been damaged
or destroyed by space debris. The measurement, mitigation, and potential
removal of debris is conducted by some participants in the space industry.
As of April 2025, the European Space Agency's Space Environment statistics reported 40,230 artificial objects in orbit above the Earth regularly tracked by Space Surveillance Networks and maintained in their catalogue.
However, these are just the objects large enough to be tracked
and in an orbit that makes tracking possible. Satellite debris that is
in a Molniya orbit, such as the Kosmos Oko series, might be too high above the Northern Hemisphere to be tracked. As of January 2019,
more than 128 million pieces of debris smaller than 1 cm (0.4 in),
about 900,000 pieces of debris 1–10 cm, and around 34,000 of pieces
larger than 10 cm (3.9 in) were estimated to be in orbit around the
Earth. When the smallest objects of artificial space debris (paint flecks, solid rocket exhaust particles, etc.) are grouped with micrometeoroids, they are together sometimes referred to by space agencies as MMOD (Micrometeoroid and Orbital Debris).
Collisions with debris have become a hazard to spacecraft. The smallest objects cause damage akin to sandblasting, especially to solar panels and optics like telescopes or star trackers that cannot easily be protected by a ballisticshield.
Below 2,000 km (1,200 mi), pieces of debris are denser than meteoroids. Most are dust from solid rocket motors, surface erosion debris like paint flakes, and frozen coolant from Soviet nuclear-powered satellites. For comparison, the International Space Station (ISS) orbits in the 300–400 kilometres (190–250 mi) range, while the two most recent large debris events, the 2007 Chineseantisatellite weapon test and the 2009 satellite collision, occurred at 800 to 900 kilometres (500 to 560 mi) altitude. The ISS has Whipple shielding to resist damage from small MMOD. However, known debris with a collision chance over 1/10,000 are avoided by maneuvering the station.
According to a report published in January 2025, scientists are
encouraging vigilance around closing airspace more often to avoid
collisions between airline flights and space debris reentering the
earth's atmosphere amid an increasing volume of both. Following a destructive event, the explosion of SpaceX's Starship Flight 7
on January 16, 2025, the US Federal Aviation Administration (FAA)
slowed air traffic in the area where debris was falling. This prompted
several aircraft to request diversion because of low fuel levels while
they were holding outside the Debris Response Area.
Space debris began to accumulate in Earth orbit with the launch of the first artificial satellite, Sputnik 1,
launched into orbit in October 1957. But even before this event, humans
might have produced ejecta that became space debris, as in the August
1957 Pascal B test. Space debris for example was ejected in 1957 purposefully from an Aerobee launch system in a likely failed attempt to reach for the first time escape velocity from Earth, and therefore space beyond Earth. Going back further, natural ejecta from Earth has entered orbit.
Gabbard
diagram of almost 300 pieces of debris from the disintegration of the
five-month-old third stage of the Chinese Long March 4 booster on 11
March 2000
NORAD trackers who fed the database were aware of other objects in orbit, many of which were the result of in-orbit explosions. Some were deliberately caused during anti-satellite weapon
(ASAT) testing in the 1960s, and others were the result of rocket
stages blowing up in orbit as leftover propellant expanded and ruptured
their tanks. More detailed databases and tracking systems were gradually
developed, including Gabbard diagrams, to improve the modeling of
orbital evolution and decay.
When the NORAD database became publicly available during the 1970s, techniques developed for the asteroid-belt were applied to the study of known artificial satellite objects.
Time and natural gravitational/atmospheric effects help to clear
space debris. A variety of technological approaches have also been
proposed, though most have not been implemented. A number of scholars
have observed that systemic factors, political, legal, economic, and
cultural, are the greatest impediment to the cleanup of near-Earth
space. There has been little commercial incentive to reduce space debris
since the associated cost does not accrue to the entity producing it.
Rather, the cost falls to all users of the space environment who benefit
from space technology and knowledge. A number of suggestions for
increasing incentives to reduce space debris have been made. These would
encourage companies to see the economic benefit of reducing debris more
aggressively than existing government mandates require. In 1979, NASA founded the Orbital Debris Program to research mitigation measures for space debris in Earth orbit.
Debris growth
NASA computer-generated image of growth of space debris
During the 1980s, NASA and other US groups attempted to limit the growth of debris. One trial solution was implemented by McDonnell Douglas in 1981 for the Delta launch vehicle by having the booster move away from its payload and vent any propellant remaining in its tanks. This eliminated one source for pressure buildup in the tanks which had
previously caused them to explode and create additional orbital debris. Other countries were slower to adopt this measure and, due especially to a number of launches by the Soviet Union, the problem grew throughout the decade.
A new battery of studies followed as NASA, NORAD, and others
attempted to better understand the orbital environment, with each
adjusting the number of pieces of debris in the critical-mass zone
upward. Although in 1981 (when Schefter's article was published) the
number of objects was estimated at 5,000, new detectors in the Ground-based Electro-Optical Deep Space Surveillance
system found new objects. By the late 1990s, it was thought that most
of the 28,000 launched objects had already decayed and about 8,500
remained in orbit. By 2005 this was adjusted upward to 13,000 objects remaining in orbit, and a 2006 study increased the number to 19,000 as a result of an ASAT and a satellite collision. In 2011, NASA said that 22,000 objects were being tracked.
A 2006 NASA model suggested that if no new launches took place,
the environment would retain the then-known population until about 2055,
when it would increase on its own. Richard Crowther of Britain's Defence Evaluation and Research Agency said in 2002 that he believed the cascade would begin about 2015. The US National Academy of Sciences, summarizing the professional view,
noted widespread agreement that two bands of LEO space – 900 to
1,000 km (620 mi) and 1,500 km (930 mi) – were already past critical
density.
In the 2009 CEAS European Air and Space Conference, University of Southampton
researcher Hugh Lewis predicted that the threat from space debris would
rise 50 percent in the next decade and quadruple in the next 50 years.
As of 2009, more than 13,000 close calls were tracked weekly.
A 2011 report by the US National Research Council
warned NASA that the amount of orbiting space debris was at a critical
level. According to some computer models, the amount of space debris
"has reached a tipping point, with enough currently in orbit to
continually collide and create even more debris, raising the risk of
spacecraft failures." The report called for international regulations
limiting debris and research of disposal methods.
Objects in Earth orbit including fragmentation debris, November 2020, NASA: ODPO
Debris history in particular years
By mid-1994 there had been 68 breakups or debris "anomalous
events" involving satellites launched by the former Soviet Union/Russia
and 18 similar events had been discovered involving rocket bodies and
other propulsion-related operational debris.
As of July 2013, estimates of more than 170 million pieces of debris
smaller than 1 cm (0.4 in), about 670,000 pieces 1–10 cm, and
approximately 29,000 larger pieces were in orbit.
As of July 2016, nearly 18,000 artificial objects were orbiting above Earth, including 1,419 operational satellites.
As of October 2019, nearly 20,000 artificial objects were in orbit above the Earth, including 2,218 operational satellites.
Characterization
Size and numbers
As of January 2019 there were estimated to be over 128 million pieces
of debris smaller than 1 cm (0.39 in), and approximately 900,000 pieces
between 1 and 10 cm. The count of large debris (defined as 10 cm across
or larger) was 34,000 in 2019, and at least 37,000 by June 2023. The technical measurement cut-off is c. 3 mm (0.12 in).
As of 2020, there were 8,000 metric tons of debris in orbit, a figure that is expected to increase.
Low Earth orbit
Debris density in low Earth orbit
In the orbits nearest to Earth – less than 2,000 km (1,200 mi) orbital altitude,
referred to as low-Earth orbit (LEO) – there have traditionally been
few "universal orbits" that keep a number of spacecraft in particular
rings (in contrast to GEO, a single orbit that is widely used by over 500 satellites).
There is currently 85% pollution in LEO (Low Earth Orbit). This was
beginning to change in 2019, and several companies began to deploy the
early phases of satellite internet constellations,
which will have many universal orbits in LEO with 30 to 50 satellites
per orbital plane and altitude. Traditionally, the most populated LEO
orbits have been a number of Sun-synchronous satellites that keep a constant angle between the Sun and the orbital plane, making Earth observation easier with consistent sun angle and lighting. Sun-synchronous orbits are polar,
meaning they cross over the polar regions. LEO satellites orbit in many
planes, typically up to 15 times a day, causing frequent approaches
between objects. The density of satellites – both active and derelict –
is much higher in LEO.
Orbits are affected by gravitational perturbations
(which in LEO include unevenness of the Earth's gravitational field due
to variations in the density of the planet), and collisions can occur
from any direction. The average impact speed of collisions in Low Earth
Orbit is 10 km/s with maximums reaching above 14 km/s due to orbital eccentricity. The 2009 satellite collision occurred at a closing speed of 11.7 km/s (26,000 mph), creating over 2,000 large debris fragments. These debris cross many other orbits and increase debris collision risk.
It is theorized that a sufficiently large collision of spacecraft
could potentially lead to a cascade effect, or even make some
particular low Earth orbits effectively unusable for long term use by orbiting satellites, a phenomenon known as the Kessler syndrome. The theoretical effect is projected to be a theoretical runaway chain reaction
of collisions that could occur, exponentially increasing the number and
density of space debris in low-Earth orbit, and has been hypothesized
to ensue beyond some critical density.
Crewed space missions are mostly at 400 km (250 mi) altitude and below, where air drag helps clear zones of fragments. The upper atmosphere is not a fixed density at any particular orbital altitude; it varies as a result of atmospheric tides and expands or contracts over longer time periods as a result of space weather. These longer-term effects can increase drag at lower altitudes; the 1990s expansion was a factor in reduced debris density. Another factor was fewer launches by Russia; the Soviet Union made most of their launches in the 1970s and 1980s.
Higher altitudes
Illustration of a satellite breaking up into multiple pieces at higher altitudes
At higher altitudes, where air drag is less significant, orbital decay takes longer. Slight atmospheric drag, lunar perturbations, Earth's gravity perturbations, solar wind, and solar radiation pressure can gradually bring debris to lower altitudes (where it decays), but at very high altitudes this may take centuries. Although high-altitude orbits are less commonly used than LEO and the
onset of the problem is slower, the numbers progress toward the critical
threshold more quickly.
Many communications satellites are in geostationary orbits
(GEO), clustering over specific targets and sharing the same orbital
path. Although velocities are low between GEO objects, when a satellite
becomes derelict (such as Telstar 401) it assumes a geosynchronous orbit; its orbital inclination
increases about 0.8° and its speed increases about 160 km/h (99 mph)
per year. Impact velocity peaks at about 1.5 km/s (0.93 mi/s). Orbital perturbations cause longitude drift of the inoperable spacecraft and precession of the orbital plane. Close approaches (within 50 meters) are estimated at one per year. The collision debris pose less short-term risk than from a LEO
collision, but the satellite would likely become inoperable. Large
objects, such as solar-power satellites, are especially vulnerable to collisions.
Although the ITU
now requires proof a satellite can be moved out of its orbital slot at
the end of its lifespan, studies suggest this is insufficient. Since GEO orbit is too distant to accurately measure objects under 1 m
(3 ft 3 in), the nature of the problem is not well known. Satellites could be moved to empty spots in GEO, requiring less maneuvering and making it easier to predict future motion. Satellites or boosters in other orbits, especially stranded in geostationary transfer orbit, are an additional concern due to their typically high crossing velocity.
Despite efforts to reduce risk, spacecraft collisions have occurred. The European Space Agency telecom satellite Olympus-1 was struck by a meteoroid on 11 August 1993 and eventually moved to a graveyard orbit. On 29 March 2006, the Russian Express-AM11 communications satellite was struck by an unknown object and rendered inoperable; its engineers had enough contact time with the satellite to send it into a graveyard orbit.
Vanguard 1 is expected to remain in orbit until at least the year 2250.
In 1958, the United States launched Vanguard I into a medium Earth orbit (MEO). As of October 2009,
it, the upper stage of Vanguard 1's launch rocket and associated piece
of debris, are the oldest surviving artificial space objects still in
orbit and are expected to be until after the year 2250. As of May 2022, the Union of Concerned Scientists listed 5,465 operational satellites from a known population of 27,000 pieces of orbital debris tracked by NORAD.
Occasionally satellites are left in orbit when they are no longer useful. Many countries require that satellites go through passivation at the end of their life. The satellites are then either boosted into a higher, graveyard orbit
or a lower, short-term orbit. Nonetheless, satellites that have been
properly moved to a higher orbit have an eight-percent probability of
puncture and coolant release over a 50-year period. The coolant freezes
into droplets of solid sodium-potassium alloy, creating more debris.
Despite the use of passivation, or prior to its standardization,
many satellites and rocket bodies have exploded or broken apart in
orbit. In February 2015, for example, the USAFDefense Meteorological Satellite Program
Flight 13 (DMSP-F13) exploded in orbit, creating at least 149 debris
objects, which were expected to remain in orbit for decades. Later that same year, NOAA-16, which had been decommissioned after an anomaly in June 2014, broke apart in orbit into at least 275 pieces. For older programs, such as the Soviet-era Meteor 2 and Kosmos
satellites, design flaws resulted in numerous break-ups – at least 68
by 1994 – following decommissioning, resulting in more debris.
Lost equipment
Space debris includes a glove lost by astronaut Ed White on the first American spacewalk (aka EVA), a camera lost by Michael Collins near Gemini 10, a thermal blanket lost during STS-88, garbage bags jettisoned by Soviet cosmonauts during Mir's 15-year life, a wrench, and a toothbrush. Sunita Williams of STS-116 lost a camera during an EVA. During an STS-120 EVA to reinforce a torn solar panel, a pair of pliers was lost, and in an STS-126 EVA, Heidemarie Stefanyshyn-Piper lost a briefcase-sized tool bag.
Spent upper stage of a Delta II rocket, photographed by the XSS 10 satellite
A significant portion of debris is due to rocket upper stages (e.g. the Inertial Upper Stage) breaking up due to decomposition of unvented fuel. The first such instance involved the launch of the Transit-4a satellite in 1961. Two hours after insertion into orbit, the Ablestar upper stage exploded. Even boosters that do not break apart can be a problem. A major known impact event involved an intact Ariane booster.
Although NASA and the United States Air Force
now require upper-stage passivation, other launchers – such as the
Chinese and Russian space agencies – do not. Lower stages, like the
Space Shuttle's solid rocket boosters or the Apollo program's Saturn IB launch vehicles, do not reach orbit.
Examples:
Two Japanese H-2A rockets broke up in 2006.
A Russian Briz-M booster stage exploded in orbit over South Australia on 19 February 2007. Launched on 28 February 2006 carrying an Arabsat-4Acommunications satellite,
it malfunctioned before it could use up its propellant. Although the
explosion was captured on film by astronomers, due to the orbit path the
debris cloud has been difficult to measure with radar. By 21 February
2007, over 1,000 fragments were identified. A 14 February 2007 breakup was recorded by Celestrak.
Another Briz-M broke up on 16 October 2012 after a failed 6 August Proton-M launch. The amount and size of the debris was unknown.
The second stage of the Zenit-2, called the SL-16 by western governments, along with the second stages of the Vostok and Kosmos launch vehicles, make up about 20% of the total mass of launch debris in Low Earth Orbit (LEO). An analysis that determined the 50 "statistically most concerning"
debris objects in low Earth orbit determined that the top 20 were all
Zenit-2 upper stages.
A Delta II rocket used to launch NASA's 1989 COBE spacecraft
exploded on December 3, 2006. This occurred even though its residual
fuel had already been vented to space.
In 2018–2019, three different Atlas VCentaur second stages broke up.
In December 2020, scientists confirmed that a previously detected
near-Earth object, 2020 SO, was rocket booster space junk launched in 1966 orbiting Earth and the Sun.
At least eight Delta rockets have contributed orbital debris in the
Sun-synchronous low Earth orbit environment. The variant of the Delta
upper stage that was used in the 1970s was found to be prone to in-orbit
explosions. Starting in 1981, depletion burns – to get rid of excess
propellant – became standard and no Delta Rocket Bodies launched after
1981 experienced severe fragmentations afterward, but some of those
launched prior to 1981 continued to explode. In 1991, the Delta
1975-052B fragmented, 16 years after launch, demonstrating the
resilience of the propellent.
In addition to the accidental creation of debris, some has been made
intentionally through the deliberate destruction of satellites. This has
been done as a test of anti-satellite or anti-ballistic missile
technology, or to prevent a sensitive satellite from being examined by a
foreign power. The United States has conducted over 30 anti-satellite weapons tests (ASATs), the Soviet Union/Russia has performed at least 27, China has performed 10 and India has performed at least one. The most recent ASATs were the Chinese interception of FY-1C, Russian trials of its PL-19 Nudol, the American interception of USA-193 and India's interception of an unstated live satellite.
A former source of debris was anti-satellite weapons (ASATs) testing by the US and Soviet Union during the 1960s and 1970s. North American Aerospace Defense Command (NORAD) only collected data for Soviet tests, and debris from US tests were identified subsequently. By the time the debris problem was understood, widespread ASAT testing had ended. The US Program 437 was shut down in 1975.
The US restarted their ASAT programs in the 1980s with the Vought ASM-135 ASAT.
A 1985 test destroyed a 1-tonne (2,200 lb) satellite orbiting at 525 km
(326 mi), creating thousands of pieces of debris larger than 1 cm
(0.39 in). At this altitude, atmospheric drag decayed the orbit of most
of the debris within a decade. A de facto moratorium followed the test.
Known orbit planes of Fengyun-1C debris one month after the weather satellite's disintegration by the Chinese ASAT
China's government was condemned for the military implications and the amount of debris from a 2007 anti-satellite missile test, the largest single space debris incident in history (creating over
2,300 pieces golf-ball size or larger, over 35,000 1 cm (0.4 in) or
larger, and one million pieces 1 mm (0.04 in) or larger). The target
satellite orbited between 850 km (530 mi) and 882 km (548 mi), the
portion of near-Earth space most densely populated with satellites. Since atmospheric drag is low at that altitude, the debris is slow to return to Earth, and in June 2007 NASA's Terra environmental spacecraft maneuvered to avoid impact from the debris. Brian Weeden, a US Air Force officer and Secure World Foundation staff
member, noted that the 2007 Chinese satellite explosion created more
than 3,000 separate objects of orbital debris that then required
tracking.
On 20 February 2008, the US launched an SM-3 missile from the USS Lake Erie to destroy a defective US spy satellite thought to be carrying 450 kg (1,000 lb) of toxic hydrazine propellant. The event occurred at about 250 km (155 mi). The missile was aimed to minimize the amount of debris, which
(according to Pentagon Strategic Command chief Kevin Chilton) had
decayed by early 2009.
On 27 March 2019, Indian Prime Minister Narendra Modi
announced that India shot down one of its own LEO satellites with a
ground-based missile. He stated that the operation, part of Mission Shakti, would defend the country's interests in space. Afterwards, US Air Force Space Command announced they were tracking 270 new pieces of debris but expected the number to grow as data collection continues.
On 15 November 2021, the Russian Defense Ministry destroyed Kosmos 1408 orbiting at around 450 km, creating "more than 1,500 pieces of
trackable debris and hundreds of thousands of pieces of un-trackable
debris" according to the US State Department.
Collision
on Launch Avoidance lead to delayed spacecraft launches to avoid
potential conjunctions/collisions during launch. Seen here is a
Collision Avoidance analysis that mandated a four-minute delay for the
launch of SPADEX in 2024.
Space junk can be a hazard to active satellites and spacecraft. It has been suggested that Earth orbit could even become impassable if the risk of collision becomes too great, a phenomenon known as Kessler syndrome.
However, since the risk to spacecraft increases with exposure to
high debris densities, it is more accurate to say that LEO would be
rendered unusable by orbiting craft. The threat to craft passing through LEO to reach a higher orbit would be much lower owing to the short time span of the crossing.
Uncrewed spacecraft
View of an orbital debris hole made in the panel of the Solar Max satellite
Although spacecraft are typically protected by Whipple shields, solar panels, which are exposed to the Sun, wear from low-mass impacts. Even small impacts can produce a cloud of plasma which is an electrical risk to the panels.
Satellites are believed to have been destroyed by micrometeorites
and small orbital debris (MMOD). The earliest suspected loss was of Kosmos 1275,
which disappeared on 24 July 1981, a month after launch. Kosmos
contained no volatile fuel, therefore, there appeared to be nothing
internal to the satellite which could have caused the destructive
explosion. However, the case has not been proven and another hypothesis
forwarded is that the battery exploded. Tracking showed it broke into
300 objects.
Many impacts have been confirmed since. For example, on 24 July 1996, the French microsatelliteCerise was hit by fragments of an Ariane 1 H-10 upper-stage booster which exploded in November 1986. On 29 March 2006, the Russian Ekspress-AM11 communications satellite was struck by an unknown object and rendered inoperable. On 13 October 2009, Terra
suffered a single battery cell failure anomaly and a battery heater
control anomaly which were subsequently considered likely the result of
an MMOD strike. On 12 March 2010, Aura lost power from one-half of one of its 11 solar panels which was attributed to an MMOD strike. On 22 May 2013, GOES 13
was hit by an MMOD which caused it to lose track of the stars that it
used to maintain an operational attitude. It took nearly a month for the
spacecraft to return to operation.
The first major satellite collision occurred on 10 February 2009. The 950 kg (2,090 lb) derelict satellite Kosmos 2251 and the operational 560 kg (1,230 lb) Iridium 33 collided, 500 mi (800 km) over northern Siberia. The relative speed of impact was about 11.7 km/s (7.3 mi/s), or about 42,120 km/h (26,170 mph). Both satellites were destroyed, creating thousands of pieces of new
smaller debris, with legal and political liability issues unresolved
even years later.
On 22 January 2013, BLITS (a Russian laser-ranging satellite) was struck by debris suspected to be from the 2007 Chinese anti-satellite missile test, changing both its orbit and rotation rate.
Satellites sometimes perform Collision Avoidance Maneuvers
and satellite operators may monitor space debris as part of maneuver
planning. For example, in January 2017, the European Space Agency
altered the orbit of one of its three Swarm mission spacecraft, based on data from the US Joint Space Operations Center, to lower the risk of collision from Cosmos-375, a derelict Russian satellite.
Crewed spacecraft
Crewed flights are particularly vulnerable to space debris
conjunctions in the orbital path of the spacecraft. Occasional avoidance
maneuvers or longer-term space debris wear have affected the Space Shuttle, the MIR space station, and the International Space Station.
Space Shuttle missions
Space ShuttleEndeavour had a major impact on its radiator during STS-118. The entry hole is about 5.5 mm (0.22 in), and the exit hole is twice as large.
From the early shuttle missions, NASA used NORAD
space monitoring capabilities to assess the shuttle's orbital path for
debris. In the 1980s, this consumed a large proportion of NORAD
capacity. The first collision-avoidance maneuver occurred during STS-48, in September 1991; a seven-second thruster burn to avoid debris from the derelict satellite Kosmos 955. Similar maneuvers were executed on missions 53, 72 and 82.
One of the earliest events to publicize the debris problem occurred on Space ShuttleChallenger's second flight, STS-7. A fleck of paint struck its front window, creating a pit over 1 mm (0.04 in) wide. On STS-59 in 1994, Endeavour's front window was pitted about half its depth. Minor debris impacts increased from 1998.
Window chipping and minor damage to thermal protection system tiles
(TPS) were already common by the 1990s. The Shuttle was later flown
tail-first to take a greater proportion of the debris load on the
engines and rear cargo bay, which are not used in orbit or during
descent, and thus are less critical for post-launch operation. When
flying attached to the ISS, a shuttle was flipped around so the better-armoured station shielded the orbiter.
A NASA 2005 study concluded that debris accounted for approximately half of the overall risk to the Shuttle. An executive-level decision to proceed was required if the catastrophic
impact was more likely than 1 in 200. On a normal (low-orbit) mission
to the ISS, the risk was approximately 1 in 300, but the Hubble telescoperepair mission
was flown at the higher orbital altitude of 560 km (350 mi) where the
risk was initially calculated at a 1-in-185 (due in part to the 2009
satellite collision). A re-analysis with better debris numbers reduced
the estimated risk to 1 in 221, and the mission went ahead.
Debris incidents continued on later Shuttle missions. During STS-115 in 2006, a fragment of circuit board bored a small hole through the radiator panels in the US space shuttle Atlantis cargo bay. On STS-118 in 2007, debris blew a bullet-like hole through the US space shuttle Endeavour radiator panel.
Mir
Debris impacts on Mir's
solar panels degraded their performance. The damage is most noticeable
on the panel on the right, which is facing the camera with a high degree
of contrast. Extensive damage to the smaller panel below is due to
impact with a Progress spacecraft rather than space debris.
Impact wear was notable on the Soviet space station Mir, since it remained in space for long periods with its original solar module panels.
International Space Station
The ISS also uses Whipple shielding to protect its interior from minor debris. However, exterior portions (notably its solar panels)
cannot be protected easily. In 1999, the ISS panels were predicted to
degrade approximately 0.23% in four years due to the "sandblasting"
effect of impacts with small orbital debris. An avoidance maneuver is typically performed for the ISS if "there is a
greater than a one-in-10,000 chance of a debris strike". As of January 2014, there have been sixteen maneuvers in the fifteen years the ISS had been in orbit. By 2019, over 1,400 meteoroid and orbital debris (MMOD) impacts had been recorded on the ISS.
As another method to reduce the risk to humans on board, ISS operational management asked the crew to shelter in the Soyuz
on three occasions due to late debris-proximity warnings. In addition
to the sixteen thruster firings and three Soyuz-capsule shelter orders,
one attempted maneuver was not completed due to not having the several
days' warning necessary to upload the maneuver timeline to the station's
computer. A March 2009 event involved debris believed to be a 10 cm (3.9 in) piece of the Kosmos 1275 satellite. In 2013, the ISS operations management did not make a maneuver to avoid any debris, after making a record four debris maneuvers the previous year.
Growth of tracked objects in orbit and related events; efforts to manage outer space global commons have so far not reduced the total amount of debris or the growth of objects in orbit.
The Kessler syndrome, proposed by NASA scientist Donald J. Kessler in 1978, is a theoretical scenario in which the density of objects in low Earth orbit
(LEO) is high enough that collisions between objects could cause a
cascade effect where each collision generates space debris that
increases the likelihood of further collisions. He further theorized that one implication, if this were to occur, is
that the distribution of debris in orbit could render space activities
and the use of satellites in specific orbital ranges economically impractical for many generations.
The growth in the number of objects as a result of the late-1990s
studies sparked debate in the space community on the nature of the
problem and the earlier dire warnings. According to Kessler's 1991
derivation and 2001 updates, the LEO environment in the 1,000 km (620 mi) altitude range should be
cascading. However, only one major satellite collision incident
occurred: the 2009 satellite collision between Iridium 33 and Kosmos
2251. The lack of obvious short-term cascading has led to speculation
that the original estimates overstated the problem. According to Kessler in 2010, however, a cascade may not be obvious until it is well advanced, which might take years.
Saudi officials inspect a crashed PAM-D module in January 2001.
Although most debris burns up in the atmosphere, larger debris
objects can reach the ground. According to NASA, an average of one
cataloged piece of debris has fallen back to Earth each day for the past
50 years. Despite their size, there has been no significant property
damage from the debris. Burning up in the atmosphere contributes to air pollution. Numerous small cylindrical tanks from space objects have been found, designed to hold fuel or gasses.
Infographic showing the space debris situation in different kinds of orbits around Earth
Tracking from the ground
Radar and optical detectors such as lidar
are the main tools for tracking space debris. Although objects under
10 cm (4 in) have reduced orbital stability, debris as small as 1 cm can
be tracked,however determining orbits to allow re-acquisition is difficult. Most debris remain unobserved. The NASA Orbital Debris Observatory tracked space debris with a 3 m (10 ft) liquid mirrortransit telescope. FM Radio waves can detect debris, after reflecting off them onto a receiver. Optical tracking may be a useful early-warning system on spacecraft.
The US Strategic Command keeps a catalog of known orbital objects, using ground-based radar
and telescopes, and a space-based telescope (originally to distinguish
from hostile missiles). The 2009 edition listed about 19,000 objects. Other data come from the ESA Space Debris Telescope, TIRA, the Goldstone, Haystack, and EISCAT radars and the Cobra Danephased array radar, to be used in debris-environment models like the ESA Meteoroid and Space Debris Terrestrial Environment Reference (MASTER).
Returned space hardware is a valuable source of information on the
directional distribution and composition of the (sub-millimetre) debris
flux. The LDEF satellite deployed by mission STS-41-CChallenger and retrieved by STS-32Columbia spent 68 months in orbit to gather debris data. The EURECA satellite, deployed by STS-46Atlantis in 1992 and retrieved by STS-57Endeavour in 1993, was also used for debris study.
The solar arrays of the Hubble space telescope were returned by missions STS-61Endeavour and STS-109Columbia, and the impact craters were studied by the ESA to validate its models. Materials returned from Mir were also studied, notably the Mir Environmental Effects Payload (which also tested materials intended for the ISS).
Gabbard diagrams
Gabbard diagram of debris from the disintegration of the third stage of a Chinese Long March 4 booster
A debris cloud resulting from a single event is studied with scatter plots known as Gabbard diagrams, where the perigee and apogee of fragments are plotted with respect to their orbital period.
Gabbard diagrams of the early debris cloud prior to the effects of
perturbations, if the data were available, are reconstructed. They often
include data on newly observed, as yet uncatalogued fragments. Gabbard
diagrams can provide insights into the features of the fragmentation,
the direction and point of impact.
Dealing with debris
Space debris identified as WT1190F, burning up in a fireball over Sri Lanka
An average of about one tracked object per day has been dropping out of orbit for the past 50 years, averaging almost three objects per day at solar maximum (due to the heating and expansion of the Earth's atmosphere creating more drag), but one about every three days at solar minimum, usually five and a half years later. In addition to natural atmospheric effects, corporations, academics and
government agencies have proposed plans and technology to deal with
space debris, but as of November 2014, most of these are theoretical, and there is no business plan for debris reduction.
In May 2024, a NASA report from the Office of Technology, Policy,
and Strategy introduced new methods for addressing orbital debris. The
report, titled Cost and Benefit Analysis of Mitigating, Tracking, and Remediating Orbital Debris, provided a comprehensive analysis comparing the cost-effectiveness of
over ten different actions, including shielding spacecraft, tracking
smaller debris, and removing large debris. By evaluating these measures
in economic terms, the study aims to inform cost-effective strategies
for debris management, highlighting that methods like rapid deorbiting
of defunct spacecraft can significantly reduce risks in space.
National and international regulation
After reentry, Delta 2 second stage pieces were found in South Africa.
There is no international treaty minimizing space debris. However, the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) published voluntary guidelines in 2007, using a variety of earlier national regulatory attempts at developing
standards for debris mitigation. As of 2008, the committee was
discussing international "rules of the road" to prevent collisions
between satellites. By 2013, a number of national legal regimes existed, typically instantiated in the launch licenses that are required for a launch in all spacefaring nations.
The US issued a set of standard practices for civilian (NASA) and military (DoD and USAF) orbital-debris mitigation in 2001. The standard envisioned disposal for final mission orbits in one of
three ways: 1) atmospheric reentry where even with "conservative
projections for solar activity, atmospheric drag will limit the lifetime
to no longer than 25 years after completion of mission;" 2) maneuver to
a "storage orbit:" move the spacecraft to one of four very broad parking orbit
ranges (2,000–19,700 km (1,200–12,200 mi), 20,700–35,300 km
(12,900–21,900 mi), above 36,100 km (22,400 mi), or out of Earth orbit
completely and into any heliocentric orbit; 3) "Direct retrieval: Retrieve the structure and remove it from orbit as soon as practicable after completion of mission." The standard articulated in option 1, which is the standard applicable
to most satellites and derelict upper stages, has come to be known as
the "25-year rule". The US updated the Orbital Debris Mitigation Standard Practices in
December 2019, but made no change to the 25-year rule even though
"[m]any in the space community believe that the timeframe should be less
than 25 years." There is no consensus however on what any new timeframe might be.
In 2002, the European Space Agency (ESA) worked with an
international group to promulgate a similar set of standards, also with a
"25-year rule" applying to most Earth-orbit satellites and upper
stages. Space agencies in Europe began to develop technical guidelines
in the mid-1990s, and ASI, UKSA, CNES, DLR and ESA signed a "European Code of Conduct" in 2006, which was a predecessor standard to the ISO international standard work
that would begin the following year. In 2008, ESA further developed
"its own "Requirements on Space Debris Mitigation for Agency Projects"
which "came into force on 1 April 2008."
Germany and France have posted bonds to safeguard property from debris damage. The "direct retrieval" option (option no. 3 in the US "standard
practices" above) has rarely been done by any spacefaring nation
(exception, USAF X-37)
or commercial actor since the earliest days of spaceflight due to the
cost and complexity of achieving direct retrieval, but the ESA has
scheduled a 2026 demonstration mission (ClearSpace-1) to do this with a single small 94 kg (207 lb) satellite (PROBA-1) at a projected cost of €120 million not including the launch costs.
By 2006, the Indian Space Research Organization (ISRO) had
developed a number of technical means of debris mitigation (upper stage
passivation, propellant reserves for movement to graveyard orbits, etc.)
for ISRO launch vehicles and satellites, and was actively contributing
to inter-agency debris coordination and the efforts of the UN COPUOS
committee.
In 2007, the ISO began preparing an international standard for space-debris mitigation. By 2010, ISO had published "a comprehensive set of space system
engineering standards aimed at mitigating space debris. [with primary
requirements] defined in the top-level standard, ISO 24113." By
2017, the standards were nearly complete. However, these standards are
not binding on any party by ISO or any international jurisdiction. They
are simply available for use in voluntary ways. They "can be adopted
voluntarily by a spacecraft manufacturer or operator, or brought into
effect through a commercial contract between a customer and supplier, or
used as the basis for establishing a set of national regulations on
space debris mitigation."
A computer-generated animation by the European Space Agency representing space debris in low earth orbit at the current rate of growth compared to mitigation measures being taken
The voluntary ISO standard also adopted the "25-year rule" for the
"LEO protected region" below 2,000 km (1,200 mi) altitude that has been
previously (and still is, as of 2019) used by the US, ESA, and UN
mitigation standards, and identifies it as "an upper limit for the
amount of time that a space system shall remain in orbit after its
mission is completed. Ideally, the time to deorbit should be as short as
possible (i.e., much shorter than 25 years)".
Holger Krag of the ESA states that as of 2017 there is no binding
international regulatory framework with no progress occurring at the
respective UN body in Vienna.
Spatial density of LEO space debris by altitude, according to 2011 a NASA report to the United Nations Office for Outer Space AffairsSpatial
density of space debris by altitude according to ESA MASTER-2001,
without debris from the Chinese ASAT and 2009 collision events
As of the 2010s, several technical approaches to the mitigation of
the growth of space debris are typically undertaken, yet no
comprehensive legal regime or cost assignment structure is in place to
reduce space debris in the way that terrestrial pollution has reduced
since the mid-20th century.
International mitigation guidance has been published to reduce
the creation of new debris, including recommendations to minimize debris
released during normal operations, prevent on-orbit breakups, and
perform post-mission disposal and collision-avoidance planning. NASA has also published detailed engineering guidance for limiting
orbital debris as part of its technical standards documentation.
To avoid excessive creation of artificial space debris, many –
but not all – satellites launched to above-low-Earth-orbit are launched
initially into elliptical orbits with perigees inside Earth's atmosphere so the orbit will quickly decay and the satellites then will be destroyed upon reentry into the atmosphere. Other methods are used for spacecraft in higher orbits. These include passivation
of the spacecraft at the end of its useful life; as well as the use of
upper stages that can reignite to decelerate the stage to intentionally
deorbit it, often on the first or second orbit following payload
release; satellites that can, if they remain healthy for years, deorbit
themselves from the lower orbits around Earth. Other satellites (such as
many CubeSats) in low orbits below approximately 400 km (250 mi)
orbital altitude depend on the energy-absorbing effects of the upper
atmosphere to reliably deorbit a spacecraft within weeks or months.
Increasingly, spent
upper stages in higher orbits – orbits for which low-delta-v deorbit is
not possible, or not planned for – and architectures that support
satellite passivation, are passivated at end of life. This removes any
internal energy contained in the vehicle at the end of its mission or
useful life. While this does not remove the debris of the now derelict
rocket stage or satellite itself, it does substantially reduce the
likelihood of the spacecraft destructing and creating many smaller
pieces of space debris, a phenomenon that was common in many of the
early generations of US and Soviet spacecraft.
Upper stage passivation (e.g. of Delta boosters)
achieved by releasing residual propellants reduces debris from orbital
explosions; however even as late as 2011, not all upper stages implement
this practice. SpaceX used the term "propulsive passivation" for the final maneuver of their six-hour demonstration mission (STP-2) of the Falcon 9 second stage for the US Air Force in 2019, but did not define what all that term encompassed.
With a "one-up, one-down" launch-license policy for Earth orbits,
launchers would rendezvous with, capture, and de-orbit a derelict
satellite from approximately the same orbital plane. Another possibility is the roboticrefueling of satellites. Experiments have been flown by NASA, and SpaceX is developing large-scale on-orbit propellant transfer technology.
Another approach to debris mitigation is to explicitly design the mission architecture to leave the rocket second-stage in an ellipticalgeocentric orbit with a low-perigee, thus ensuring rapid orbital decay
and avoiding long-term orbital debris from spent rocket bodies. Such
missions will often complete the payload placement in a final orbit by
the use of low-thrust electric propulsion or with the use of a small kick stage
to circularize the orbit. The kick stage itself may be designed with
the excess-propellant capability to be able to self-deorbit.
Self-removal
Although the ITU requires geostationary satellites to move to a
graveyard orbit at the end of their lives, the selected orbital areas do
not sufficiently protect GEO lanes from debris. Rocket stages (or satellites) with enough propellant may make a direct,
controlled de-orbit, or if this would require too much propellant, a
satellite may be brought to an orbit where atmospheric drag would cause
it to eventually de-orbit. This was done with the French Spot-1 satellite,
reducing its atmospheric re-entry time from a projected 200 years to
about 15 by lowering its altitude from 830 km (516 mi) to about 550 km
(342 mi).
The Iridium constellation
– 95 communication satellites launched during the five-year period
between 1997 and 2002 – provides a set of data points on the limits of
self-removal. The satellite operator – Iridium Communications
– remained operational over the two-decade life of the satellites
(albeit with a company name change through a corporate bankruptcy during
the period) and, by December 2019, had "completed disposal of the last
of its 65 working legacy satellites." However, this process left 30 satellites with a combined mass of
(20,400 kg (45,000 lb), or nearly a third of the mass of this
constellation) in LEO orbits at approximately 700 km (430 mi) altitude,
where self-decay is slow. Of these satellites, 29 simply failed during
their time in orbit and were thus unable to self-deorbit, while one –
Iridium 33 – was involved in the 2009 satellite collision with the derelict Russian military satellite Kosmos-2251. No contingency plan was laid for the removal of satellites that were
unable to remove themselves. In 2019, the CEO of Iridium, Matt Desch,
said that Iridium would be willing to pay an active-debris-removal
company to deorbit its remaining first-generation satellites if it were
possible for an unrealistically low cost, say "US$10,000
per deorbit, but [he] acknowledged that price would likely be far below
what a debris-removal company could realistically offer. 'You know at
what point [it is] a no-brainer, but [I] expect the cost is really in
the millions or tens of millions [of dollars], at which price I know it
doesn't make sense.'"
Passive methods of increasing the orbital decay rate of spacecraft debris have been proposed. Instead of rockets, an electrodynamic tether could be attached to a spacecraft at launch; at the end of its lifetime, the tether would be rolled out to slow the spacecraft. Other proposals include a booster stage with a sail-like attachment and a large, thin, inflatable balloon envelope.
In late December 2022, ESA successfully carried out a demonstration of a breaking sail-based satellite deorbiter, ADEO,
which could be used by mitigation measures and is part of ESA's Zero
Debris Initiative. Around one year earlier, China also tested a drag
sail.
External removal
A variety of approaches have been proposed, studied, or had ground
subsystems built to use other spacecraft to remove existing space
debris.
A consensus of speakers at a meeting in Brussels, Belgium in
October 2012, organized by the US think tank Secure World Foundation and
the French International Relations Institute, reported that removal of the largest debris would be required to
prevent the risk to spacecraft becoming unacceptable in the foreseeable
future (without adding to the inventory of dead spacecraft in LEO). As
of 2019, removal costs and legal questions about ownership and the
authority to remove defunct satellites have stymied national or
international action. Current space law retains ownership of all
satellites with their original operators, even debris or spacecraft
which are defunct or threaten active missions.
Multiple companies made plans in the late 2010s to conduct external removal of their satellites in mid-LEO orbits. For example, OneWeb
planned to use onboard self-removal as "plan A" for satellite
deorbiting at the end of life, but if a satellite were unable to remove
itself within one year of end of life, OneWeb would implement "plan B"
and dispatch a reusable (multi-transport mission) space tug to attach to
the satellite at an already built-in capture target via a grappling
fixture, to be towed to a lower orbit and released for re-entry.
Remotely controlled vehicles
A well-studied solution uses a remotely controlled vehicle to rendezvous with, capture and detumble, and return debris to a central station. One such system is Space Infrastructure Servicing (SIS), a commercially developed
refueling depot and service spacecraft for communications satellites in
geosynchronous orbit originally scheduled for a 2015 launch. The SIS would be able to "push dead satellites into graveyard orbits." The Advanced Common Evolved Stage family of upper stages is being designed with a high leftover-propellant margin (for derelict capture and de-orbit) and in-space refueling capability for the high delta-v required to de-orbit heavy objects from geosynchronous orbit. A tug-like satellite to drag debris to a safe altitude for it to burn up in the atmosphere has been researched. When debris is identified the satellite creates a difference in
potential between the debris and itself, then using its thrusters to
move itself and the debris to a safer orbit.
A variation of this approach is for the remotely controlled vehicle to rendezvous with debris, capture it temporarily to attach a smaller de-orbit satellite and drag the debris with a tether to the desired location. The "mothership" would then tow the debris-smallsat combination for atmospheric entry or move it to a graveyard orbit. One such system is the proposed Busek ORbital DEbris Remover, which would carry over 40 SUL (satellite on umbilical line) de-orbit satellites and propellant sufficient for their removal.
In December 2019, the ESA awarded the first contract to clean up space debris. The €120 million mission dubbed ClearSpace-1 (a spinoff from the EPFL project) is slated to launch in 2026. It aims to remove the 94 kg PROBA-1 satellite from orbit. A "chaser" will grab the junk with four robotic arms and drag it down to Earth's atmosphere where both will burn up.
Laser methods
The laser broom uses a ground-based laser to ablate the front of the debris, producing a rocket-like thrust that slows and detumbles the object. With continued application, the debris would fall enough to be influenced by atmospheric drag. During the late 1990s, the US Air Force's Project Orion was a laser-broom design. Although a test-bed device was scheduled to launch on a Space Shuttle
in 2003, international agreements banning powerful laser testing in
orbit limited its use to measurements. The 2003 Space Shuttle Columbia disaster
postponed the project and according to Nicholas Johnson, chief
scientist and program manager for NASA's Orbital Debris Program Office,
"There are lots of little gotchas in the Orion final report. There's a
reason why it's been sitting on the shelf for more than a decade."
The momentum of the laser-beam photons
could directly impart a thrust on the debris sufficient to move small
debris into new orbits out of the way of working satellites. NASA
research in 2011 indicates that firing a laser beam at a piece of space
junk could impart an impulse of 1 mm (0.039 in) per second, and keeping
the laser on the debris for a few hours per day could alter its course
by 200 m (660 ft) per day. One drawback is the potential for material degradation; the energy may break up the debris, adding to the problem. A similar proposal places the laser on a satellite in Sun-synchronous
orbit, using a pulsed beam to push satellites into lower orbits to
accelerate their reentry. A proposal to replace the laser with an Ion Beam Shepherd has been made, and other proposals use a foamy ball of aerogel or a spray of water, inflatable balloons, electrodynamic tethers, electroadhesion, and dedicated anti-satellite weapons.
Nets
On 28 February 2014, Japan Aerospace Exploration Agency (JAXA) launched a test "space net" satellite. The launch was an operational test only. In December 2016 the country sent a space junk collector via Kounotori 6 to the ISS by which JAXA scientists experimented to pull junk out of orbit using a tether. The system failed to extend a 700-meter tether from a space station resupply vehicle that was returning to Earth.On 6 February the mission was declared a failure and leading researcher
Koichi Inoue told reporters that they "believe the tether did not get
released".
Between 2012 and 2018, the ESA was working on the design of a
mission to remove large space debris from orbit using mechanical
tentacles or nets. The mission, e.Deorbit, had an objective to remove debris heavier than 4,000 kilograms (8,800 lb) from LEO. Several capture techniques were studied, including a net, a harpoon, and a combination robot arm and clamping mechanism, which also serve as detumbling devices. Funding of the mission was stopped in 2018 in favor of the ClearSpace-1 mission, which is under development.
Harpoon
The RemoveDEBRIS
mission plan is to test the efficacy of several ADR technologies on
mock targets in low Earth orbit. In order to complete its planned
experiments, the platform is equipped with a net, a harpoon, a laser
ranging instrument, a dragsail, and two CubeSats (miniature research satellites). The mission was launched on 2 April 2018.
Recycling space debris
Metal processing technologies to melt space debris and transform it into other useful form factors are developed by CisLunar Industries. Their system uses electromagnetic heating to melt metal and shape it into metal wire, sheet metal, and metal fuel.
Reusing space debris
A propulsion system dubbed the Neumann Drive has been developed in Adelaide, South Australia, and first sent into space in June 2023. Metal space junk is converted into fuel rods,
which can be plugged into the Neumann Drive, "basically converting the
solid metal propellant into plasma". The Drive is intended to be used by
American space companies which already carry nets or robotic arms to
capture orbital waste. The thruster would enable these satellites to
return to Earth with the waste they have collected, allowing it to be
melted down to make more fuel.
Barriers to dealing with debris
With the rapid development of the computer and digitalization
industries, more countries and companies have engaged in space
activities since the turn of the 21st century. The tragedy of the commons
is an economic theory referring to a situation where maximizing
self-interest through using a shared resource can lead to the resource
degradation shared by all. Based on the theory, individuals' rational action in space will lead to
an irrational collective result: orbits crowded with debris. As a common-pool resource, the Earth's orbits, especially LEO and GEO that accommodate most satellites, are nonexcludable and rivalrous.
To address the issue and ensure space sustainability,
many technical approaches have been developed. In terms of governance
mechanisms, a top-down centralized one is less suitable to tackle the
complex debris problem due to the increasing number of space actors. Instead, a polycentric form of governance developed by Elinor Ostrom has been proposed although the promotion of the polycentric network has not been fully developed.
Incomplete data of space debris
As orbital debris is a global problem affecting both spacefaring and
non-spacefaring nations, it is necessary to be handled in a worldwide
context. Because of the complexity and dynamics of object movements like
spacecraft, debris, meteorites, etc., many countries and regions
including the United States, Europe, Russia, and China have developed
their space situational awareness (SSA) to avoid potential threats in space or plan actions in advance. To an extent, SSA plays a role in tracking space debris. In order to
build a powerful SSA system, there are two prerequisites: international
cooperation and exchange of information and data. However, limitations exist in spite of the improving data quality over
the past decades. Some space powers are not willing to share the
information that they have collected, and those, such as the US, that
have shared the data keep parts of it secret. Instead of joining in a coordinated way, a many SSA programs and
national databases run parallel to each other with some overlaps,
hindering the formation of a collaborative monitoring system.
Some private actors are also trying to establish SSA systems. For
example, the Space Data Association (SDA) formed in 2009 is a
non-governmental entity. It currently consists of 21 global satellite
operators and 4 executive members: Eutelsat, Inmarsat, Intelsat, and SES.
SDA is a non-profit platform, aiming to avoid radio interference and
space collisions through pooling data from operators independently. Researchers suggest that it is essential to establish an international
center for exchanging information on space debris because SSA networks
do not completely equal debris tracking systems – the former ones focus
more on active and threatening objects in space. In terms of debris populations and defunct satellites, few operators have provided data.
In a polycentric governance network, a resource that cannot be holistically monitored is less likely to be well managed. Both insufficient transnational cooperation and information sharing
bring resistance to addressing the debris problem. There is a long way
to go to build a global network that covers complete data and has strong
interconnection and interoperability.
Insufficient participation of private actors
With the commercialization of satellites and space, the private
sector is getting more interested in space activities. For example, SpaceX is creating a network of around 12,000 small satellites that can transmit high-speed internet to any place in the world. The proportion of commercial spacecraft has increased from 4.6% in the 1980s to 55.6% in the 2010s. Despite the high participation rate of commercial entities, UN COPUOS once deliberately excluded them from having a voice in discussions unless being formally invited by a member state. Ostrom said that the involvement of all relevant stakeholders in the
rule-design and implementation process is one of the critical elements
of successful governance. The exclusion of private actors largely reduces the effectiveness of
the UN committee's role in making collective-choice arrangements that
reflect the interests of all space users.
The limited engagement of private actors slows the process of addressing space debris. Ties between dissimilar stakeholders in the governance network offer access to diverse resources. Different competence among stakeholders can help allocate the tasks
more reasonably. In that case, the expertise and experience of private
operators are critical to help the world achieve space sustainability. The complementary strengths of different stakeholders enable the
governance network to be more adaptable to changes and reach common
goals more effectively. In recent years, many private actors have seen commercial opportunities
for eliminating space debris. It was estimated in 2018 that by 2022 the
global market for debris monitoring and removal would generate a
revenue of around $2.9 billion. For example, in 2021, Astroscale had contracted with European and Japanese space agencies to develop the capacity of removing orbital debris. Despite that, they are still in small quantity compared to the number of those who have placed satellites in space. Privateer Space, a Hawaiian-based startup company by American engineer Alex Fielding, space environmentalist Moriba Jah, and Apple co-founder Steve Wozniak, announced plans in September 2021 to launch hundreds of satellites into orbit in order to study space debris. However, the company stated it is in "stealth mode" and no such satellites have been launched.
Fortunately, space exploration is not completely driven by
competition, and there exists an opportunity for dialogues and
cooperation among all stakeholders in both developed and developing
countries, to reach an agreement on tackling space debris and assure an
equitable and orderly exploration. Besides private actors, network governance
does not necessarily exclude the states from playing a role. Instead,
the different functions of states might promote the governance process. To improve the polycentric governance network of space debris,
researchers suggest: encourage data-sharing among different national and
organizational databases at the political level; develop shared
standards for data collection systems to improve interoperability; and
enhance the participation of private actors through involving them in
national and international discussions.
On other celestial bodies
Perseverance's backshell sitting upright on the surface of Jezero Crater
The issue of space debris has been raised as a mitigation challenge
for missions around the Moon with the danger of increasing space debris
around it.
It is thought that on 4 March 2022, for the first time, human space debris – most likely a spent rocket body, Long March 3C third stage from the 2014 Chang'e 5 T1 mission – unintentionally hit the lunar surface, creating an unexpected double crater.
In 2022, several elements of space debris were found on Mars: Perseverance's backshell was found on the surface of Jezero Crater, and a piece of a thermal blanket which may have come from the descent stage of the rover.
As of February 2024, Mars
is littered with about seven tons of human-made debris. Most of it
consists of crashed and inactive spacecraft as well as discarded
components.
In popular culture
Until the End of the World
(1991) is a French sci-fi drama set under the backdrop of an
out-of-control Indian nuclear satellite, predicted to re-enter the
atmosphere, threatening vast populated areas of the Earth.
Wall-E (2008) features a future Earth that is full of garbage and abandoned by humanity.
As the titular robot leaves the planet and as the humans come back to Earth, they collide with derelict satellites.
In the 2009 Walt Disney Pictures film G-Force, the antagonist, Speckles (voiced by Nicolas Cage)
orchestrates a plot to destroy humanity with a massive, planet-wide
bombardment of space debris to make the Earth's surface uninhabitable.
Gravity, a 2013 survival film directed by Alfonso Cuaron, is about a disaster on a space mission caused by Kessler syndrome.
In season 1 of Love, Death & Robots
(2019), episode 11, "Helping Hand", revolves around an astronaut being
struck by a screw from space debris which knocks her off a satellite in
orbit.
Manga and anime Planetes tells a story about a crew of Space Debris station that collects and disposes of space debris.
Beside space debris as an issue of science-fiction stories other
stories feature it as a reservoir for the story, as in stories about
space junk scavengers like Space Sweepers (2021), or as a result or environment of the story.
The episode Conflict from Gerry and Sylvia Anderson's U.F.O.
sci-fi TV series shows how small alien spaceships could use terrestrial
space debris such as orbital boosters to become undetectable by SHADO's orbital Space Intruder Detector.
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