What is Space Junk (Debris) and why is it a global threat?


  • Space debris, also known as space junk, is any piece of human-made objects in space—principally in Earth’s orbits—that no longer serves a useful function.
  • Only one human in history has been hit by orbital debris falling on Earth.
  • ESA’s Space Environment Report 2022 stated that the number of tracked pieces of space debris is now over 30,000. The population of debris objects larger than 1 cm in size is approximately 1 million.
  • Objects in low Earth orbit are estimated to be travelling between 17,500 and 18,000 miles per hour (7 and 8 km/s).
  • An impact from objects that are approximately or greater than 10 cm in diameter can be equivalent to a TNT blowing up. 
  • Space debris can remain in Earth’s orbit for centuries. Had the Romans launched a satellite to 1200 km about 2000 years ago, it would only have re-entered Earth now.
  • ESA highlights that passivation is an important part of the end-of-life disposal procedures which involves de-orbiting or deactivating spacecraft at the end of their mission.

There are over 100 trillion untracked pieces of space debris in low-Earth orbit. 

You read that right! 

A study titled ‘Protect Earth’s Orbit: Avoid high seas mistakes’ published in Science Journal reveals this startling number. Though a significant amount of debris burns up due to the severe heating that occurs during re-entry through Earth’s dense atmosphere, remnants that do survive fall into the oceans and other sparsely populated regions of the world. 

As the skies turn extremely crowded, just like the traffic on our regular roads, experts predict an increasing threat of space debris falling back on Earth. The National Aeronautics and Space Administration (NASA) while answering ‘Frequently Asked Questions on Space Debris’ on its website reveals that over the past 50 years, on average, one tracked piece of debris has fallen back to Earth each day. The SpaceTrack.Org data shows that approximately 1,600 pieces of debris re-entered in 2022. 

As per Guinness World Records, the first and only human in history to have been hit by orbital debris was Lottie Williams of Oklahoma, USA, while she was walking in a park on January 22, 1997, and was struck on her shoulder by a 5-inch-long (12.7 cm) piece of space debris from the second stage of a US-made Delta II rocket. She escaped unharmed. 

But worse is happening in the space above. 

First-Ever In-Orbit Collision Between Two Satellites

On February 10, 2009, the active Iridium 33 and the derelict Russian military Kosmos 2251, two communications satellites, accidentally collided at a speed of 11.7 km/s and an altitude of 789 km above Siberia. The Kosmos satellite had been dysfunctional since 1995. The collision generated more than 2300 trackable fragments, as per ESA. 

In another instance, NASA cited the first known collision between space debris and a functioning satellite in 1996, when a French satellite ‘CERIS’ got hit by debris from a French rocket that had exploded a decade earlier.

What worries the scientific community more is that these collisions beget collisions. ESA expects that in the future, collisions will become the dominant source of space debris. With the increasing density of objects in Earth’s orbit due to congestion in space leading to an increased amount of space debris, it may cause a chain reaction of collisions known as Kessler Syndrome. 

How serious is that? Well, to the point that it will make the low-Earth orbit unusable. 

Now, we are launching more than ever!

According to NASA’s Space Situational Awareness (SSA) program, as of March 8, 2023, there are an estimated 8,767 operational satellites in space. This number excludes defunct satellites and debris. If we look at the historical spike in the number of debris objects in space (till 2022) as shared by NASA’s Orbital Debris Office (Figure below), orbital debris has grown in number and total mass since the beginning of the space age.

Space Debris Objects in Space

As per the latest data from ESA’s Space Environment Report 2022, more than 30,000 pieces of space debris. It is no wonder that space agencies have to frequently conduct a collision avoidance maneuver (CAM) to change the trajectory of a spacecraft to avoid a collision with another object in space. 

The Indian Space Research Organization (ISRO) has been proactively taking steps to avoid collisions in outer space. In 2022, they conducted 22 maneuvres to prevent their satellites from colliding with other objects. The maximum number of threat objects were fragments from the Cosmos–Iridium collision (2009) and Fengyun 1C (Chinese ASAT test in 2007). The International Space Station (ISS) in LEO has performed 32 maneuvres between 1999-2022 to dodge these collisions. On average, the ESA has to carry out approximately 12 maneuvres in a year.

With the low-Earth orbit getting congested and polluted, the future of human space exploration is at risk. In the study, Melissa Quinn, Head of Spaceport Cornwall, said, “Satellites are vital to the health of our people, economies, security, and Earth itself. However, using Space to benefit people and the planet is at risk.”

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The question is, where does all that Space Junk come from? But first, let’s understand what is Space Junk or Space Debris. 

What is Space Debris?

(Above): An animation by ESA depicts different types of space debris of different sizes swirling around Earth’s orbit. (2019). Red: satellites (dead or active), Yellow: rocket bodies, Green: mission-related objects, Blue: Fragmentation-debris

Space debris, also known as space junk, is any piece of human-made objects in space—principally in Earth’s orbits—that no longer serves a useful function. This includes non-functional satellites, fragmentation debris due to collisions between satellites, payload and mission-related debris, and clutter from working satellites such as tiny flecks of paint released due to thermal stress. 

Payload and mission-related debris include separation bolts, hardware, optical instruments or astronaut tools, spent fuel tanks, batteries, abandoned launch vehicle stages, rocket bodies, spent rocket boosters, and some debris from anti-satellite tests.

Holger Krag, head of the ESA’s Space Safety Programme, explains, “The biggest contributor to the current space debris problem is explosions in orbit, caused by left-over energy – fuel and batteries – onboard spacecraft and rockets.”

The European Space Agency (ESA) highlights that since 1961, there have been more than 550 in-orbit fragmentation events. ESA estimates that 12 fragmentation events have happened every year for the past two decades.

“The greatest amount of space debris comes from ‘fragmentation events’ caused by propulsion elements, i.e., bits of spent launchers or fuel left inside inactive satellites,” tweeted ESA.


Q. What’s the main cause of #SpaceDebris?

A. The greatest amount of space debris comes from ‘fragmentation events’ caused by propulsion elements, i.e. bits of spent launchers or fuel left inside inactive satellites. See https://t.co/ZHyEXxCSGY pic.twitter.com/yeRdRvsFFq

— ESA (@esa)
March 20, 2021

Anti-Satellite Tests Added 25% To Space Debris

The former Soviet Union was the first nation to conduct an Anti-Satellite Test (ASAT) in space. Only the United States (US), Russia, China, and India have launched ASAT. The US has conducted over 30 ASATs, the Soviet Union/Russia have performed at least 27, China has performed 10, and India has performed at least one.

ESA report states, “The Chinese FengYun-1C engagement in January 2007 alone increased the trackable space object population by 25%”.

  On January 11, 2007, the People’s Republic of China conducted its ASAT test against its Fengyun-1C weather satellite, producing the largest number of tracked fragments in the history of satellite fragmentations—close to 3,000 pieces of debris. As per a NASA report, despite the breakup occurring 15 years ago, the collision was high enough that the orbits for most of the debris have hardly decayed; the greatest number of debris is in the 850 km altitude bin.

India ASAT Debris

(Orbital debris (red) created by Indian ASAT (red), with the orbit of the International Space Station (white) as a comparison. Credits: The Diplomat)

On March 27, 2019, India became the fourth nation in history to conduct ASAT ‘Mission Shakti’ to destroy its Microsat-R satellite in low Earth orbit. India’s ASAT initially created 400 trackable fragments, however, the last piece of debris decayed in the orbit on June 14, 2022.

From Space Age To Space Debris

On October 4, 1957, the first artificial satellite to orbit Earth, called Sputnik 1, escaped the gravitational pull of Earth at a speed of 18,000 miles per second (8 km/s) and marked the beginning of the Space Age. The human race has reaped countless benefits since then. For example, satellite communications have revolutionized the way we communicate with each other, and satellite navigation systems have made it easier than ever to travel around the world. 

The Space Age has been the reason that today we can send probes to explore the Moon, Mars, and other planets, not to mention SpaceX’s Starlink constellation of satellites in low Earth orbit (LEO) to provide internet access.

However, since the launch of Sputnik 1, we have launched thousands of satellites into space, and that has created a problem: space debris. 

space debris from start of space age

And, given the fact that humans benefit enormously from the space industry, the number of satellites orbiting the Earth is only going to increase exponentially, warned the researchers from the University of Plymouth, The University of Texas at Austin, the Jet Propulsion Laboratory, Spaceport Cornwall, and the Zoological Society of London in their study ‘Protect Earth’s Orbit: Avoid high seas mistakes’.

satellites increase quote

NASA, in its study ‘Cost and Benefit Analysis of Orbital Debris Remediation’ shares, “The number of tracked and untracked debris in LEO is projected to grow. The number of debris grows even if no new satellites are launched into space, yet launch traffic is likely to increase in the coming decade compared to recent history.” 

The report further adds, “The proposed satellite constellations, sometimes called ‘mega-constellations’, may each contain thousands to tens of thousands of satellites. They represent a substantial increase in the number of operational satellites in space and therefore an increase in the number of pieces of debris that can result from satellite failures or poor post-mission disposal procedures.

emerging mega constellation satellites

The increasing number of satellites would add more to the problem of space debris. Dr. Kimberley Miner, a scientist at the NASA Jet Propulsion Laboratory, adds, “Minimizing the pollution of the lower Earth orbit will allow continued space exploration, satellite continuity, and the growth of life-changing space technology.”

Who tracks the orbital debris?

As per ISRO’s Space Situational Assessment 2021 report, radar and optical telescopes are the main ground-based facilities for tracking space objects, including space debris. ISRO’s Space Debris Tracking and Orbital Prediction Centre (SDTOPC) tracks and catalogues space debris in Earth orbit using ground-based radar and optical telescopes.

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ISRO’s Spacecraft Collision Avoidance Subsystem (SCAS) detects and avoids collisions between ISRO spacecraft and space debris by using the data from the SDTOPC. It then uses thrusters to maneuver ISRO spacecraft to avoid collisions.

Globally, the United States Department of Defense monitors the debris with the Space Surveillance Network (SSN). The ESA’s Space Debris Office continuously tracks and monitors the debris situation and publishes an annual report every year on the current state of the debris environment. The NASA Orbital Debris Program Office (ODPO) is responsible for leading NASA’s efforts to understand, mitigate, and remove space debris. The Space Situational Awareness (SSA) Programme of the UK Space Agency and the Canadian Space Agency (CSA) Space Debris Office also work to track space debris.

How much space debris is there?

As per the latest data from ESA’s Space Environment Report 2022, more than 30,000 pieces of space debris, the size of a softball, are regularly tracked with reasonable accuracy by SSN, which include objects larger than about 5-10 cm in low-Earth orbit (LEO) and 30 cm to 1 m at geostationary (GEO) altitudes. 

ESA’s Space Environment Report 2022 Space Debris Population

Much of the orbital debris is in the low-Earth orbit (LEO), which is relatively closer to Earth’s surface at an altitude of less than 1000 km but as low as 16 km above Earth. The proximity of LEO to Earth makes it one of the most commonly used orbits for satellite imaging, as it allows us to take images with higher resolution. 

Some debris has also been detected in the geostationary orbit, also referred to as the geosynchronous equatorial orbit (GEO), which is approximately 36,000 km from the Earth’s equator. It is used for parking satellites at a stationary position for purposes such as telecommunication, remote sensing, broadcasting, etc. 

LEO GEO orbitsImage: ESA

Space Debris: In Numbers

As per the ESA models, the population of debris objects larger than 1 cm in size is approximately 1 million. There is more to what meets the eye. As per NASA, there is even smaller micrometer-sized debris (0.000039 of an inch in diameter, equivalent to 0.001 mm). 

size of space debrisHow fast does space debris travel in low Earth orbit?

Satellites and objects in LEO are estimated to be travelling between 17,500 and 18,000 miles per hour (7 and 8 km/s). It is at this speed that the force of gravity on Earth keeps the satellites from flying off the tangent and travelling around the planet. 

However, when two objects move towards an anticipated collision, their relative velocity can be more than 31,000 miles per hour (as high as 14 km/s). As per NASA, the average impact speed of space debris with another object in LEO can be approximately 6 miles per second (10 km/s), ten times faster than a rifle bullet.

What are the hazards of space debris?

Even a ping-pong ball size space debris object can do severe damage to satellites, robotic missions, human spaceflight, and spacecraft, resulting in the loss of a mission or even a life. If a piece of space debris were to strike a spacecraft, it could release harmful chemicals or radiation into the cabin. 

Let us break down the impact of collision from different-sized space debris objects. An impact from objects that are approximately or greater than 10 cm in diameter can be equivalent to a TNT blowing up. An impact from debris objects between 1 cm and 10 cm can be equivalent to being hit by a truck on a highway, which is enough to destroy a satellite or rocket body. Further, an impact from debris objects greater than 1 mm to 1 cm can cause craters or cracks in walls and windows. 

In May 2021, a small piece of debris punched a 5mm wide hole in the Canadian robotic arm ‘Canadarm2’ attached to the ISS, according to a statement by the Canadian Space Agency. Luckily, the arm continues to carry out the mission.

Canadarm2 Space Debris Hit

Image: Canada Space Agency

The ISS is the most heavily shielded spacecraft sent into space ever. However, the ISS, which houses astronauts, had to perform three maneuvres in 2022 to dodge collisions with orbital debris. 

Several instances of space debris hitting the ESA-built Cupola Observation Module on the ISS have been reported. In May 2016, one of the fused-silica and borosilicate-glass windows got impacted by space debris, possibly a fleck of paint or a small metal fragment. 

ESA astronaut Tim Peake took this photo from inside the cupola to show the 7-mm diameter chip on the window.  (Image below: ESA)

ISS cupola paint fleck space debris hit

Space debris also increases the risk of Kessler Syndrome

Kessler Syndrome theory was first proposed in 1978 by NASA scientist Donald J. Kessler in the study titled ‘Collision Frequency of Artificial Satellites: The Creation of a Debris Belt’, which described a scenario in which the density of objects in LEO due to congestion in space is high enough that collisions between objects would generate a chain reaction of collisions leading to the growth of a belt of debris around the Earth.

kessler syndromeImage: NASA

How long does orbital debris remain in Earth’s orbit?

Space debris objects can continue to circle Earth for a thousand years, decades, or even indefinitely. As shown in the figure below, ESA shares that abandoned satellites can take thousands of years to be pulled by the planet’s atmospheric drag, depending on their orbital altitude. Had the Romans launched a satellite to 1200 km about 2000 years ago, it would only have re-entered Earth now.


Image: ESA

NASA also explains that as the altitude of the orbits goes higher, the longer the orbital debris will typically remain in Earth’s orbit. Debris left in orbits below 600 km (370 miles), normally falls back to Earth within several years. At altitudes of 800 km (500 miles), the time for orbital decay is often measured in decades. Above 1,000 km (620 miles), orbital debris will normally continue circling Earth for a century or more.

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Does space debris fall on Earth?

According to the National Oceanic and Atmospheric Administration (NOAA), an average of 200 to 400 pieces of tracked space debris fall into Earth’s atmosphere every year.

A study from Canada’s University of British Columbia published in Nature.com found that there was a 10% chance of one or more people being killed by space debris in the next decade. Though, there have been numerous instances of debris falling from space on Earth.

Here is an excerpt from the study that explains the fall of space debris on Earth (in a controlled and uncontrolled way):

space debris falling on earth

Space Debris Falling On Earth: Global Events

space debris south wales

Image: Dr Brad Tucker

In July 2022, a chunk of space debris landed in a large area of fields in New South Wales, Australia (Image above). The debris was confirmed to come from a SpaceX capsule after inspection by astrophysicist Dr. Brad Tucker and the Australian Space Agency (ASA). 

In November 2021, a Long March 5B rocket, launched by China to deliver a module for its space station, re-entered the Earth’s atmosphere. Ultimately, the debris fell into the Indian Ocean near the Maldives, with no reported injuries or significant damage.

So what are we doing about it?

passivation space debris

ESA in its article on ‘Mitigating space debris generation’ states that the prevention of in-orbit explosions or collisions is the most effective short-term course to reducing the growth of space debris. 

Additionally, the most effective long-term means to stabilise space debris include strong compliance with post-mission disposal guidelines. ESA highlights that passivation is an important part of the end-of-life disposal procedures which involves de-orbiting or deactivating spacecraft at the end of their mission.

The mitigation of space debris is a complex and challenging issue. Some of the numerous efforts to mitigate space debris by space-faring nations include: 

  • Launching spacecraft to physically capture space debris, 
  • Using the natural forces of gravity and solar radiation to deorbit space debris, 
  • Using ground-based radar and tracking systems to identify potential collisions between spacecraft and space debris, 
  • Decommissioning satellites post-mission life to comply with the United Nations (UN) and the Inter-Agency Space Debris Coordination Committee’s (IADC) recommended space debris mitigation guidelines, 
  • Developing international standards for the design of spacecraft that will minimize the amount of space debris they create. This includes standards for the materials used in spacecraft construction, the types of propulsion systems used, and the procedures for disposing of spacecraft at the end of their mission.

Global Efforts

The Federal Communications Commission (FCC) required all satellites launched into GEO to be pushed into a higher, ‘graveyard’ orbit at the end of their life span. In 2018, the FCC issued a rule requiring that all new satellites launched into GEO be equipped with a propulsion system that can be used to deorbit the satellite at the end of its life. The FCC also requires that satellite operators submit a plan for deorbiting their satellites.

graveyard orbit

Inter-Agency Space Debris Coordination Committee (IADC): The IADC is an international forum for cooperation on space debris mitigation. In 2002, the IADC published the Space Debris Mitigation Guidelines. One of the measures in the debris mitigation guidelines is the 25-year rule, which states that a payload or rocket body operating in the LEO Protected region, with either a permanent or periodic presence, shall limit its post-mission presence in the LEO Protected region to a maximum of 25 years from the end of the mission. There are a few exceptions to the 25-year rule. For example, objects that are used for scientific research may be allowed to remain in orbit for extended periods of time.

In 2020, the European Space Agency (ESA) finalized a contract with ClearSpace SA, a Swiss start-up company, to launch the ClearSpace-1 mission in 2025. The ClearSpace-1 mission will be the first to capture and dispose of a piece of orbiting space junk. The ClearSpace-1 mission is also a major step forward for the ESA’s Clean Space initiative. The ClearSpace-1 spacecraft will use a robotic arm to capture debris. ESA’s RemoveDEBRIS mission will use technologies including a net, harpoon, drag sail, laser broom, and a vision-based navigation system to capture debris.


This agency is making efforts to clean up space debris via @esa pic.twitter.com/RbeGxZ5MJv

— Interesting Engineering (@IntEngineering)
June 8, 2019

Future Outlook

Space debris is a growing threat to the sustainability of space activities. The urgency and criticality of space debris mitigation cannot be overstated. It is not merely a matter of scientific concern but a vital necessity for the future of space exploration and the burgeoning space economy.

McKinsey & Company in its report titled ‘The role of space in driving sustainability, security, and development on Earth (May 2022)’ cited that the space economy will eventually exceed $1 trillion by 2030. As we strive toward a projected $1 trillion space economy by 2030, the impact of space debris on such a thriving industry would be detrimental. To safeguard the future of the space economy, a multifaceted approach is essential.

The $1 trillion space economy projected for 2030 should prioritize space debris mitigation as a foundational pillar. Investments in research, development, and implementation of advanced technologies to detect, track, and remove space debris are imperative. Additionally, international policies and regulations must be established to ensure responsible space operations and prevent further debris generation.

The successful management of space debris will require a combination of measures. These include satellite design improvements, advanced tracking and surveillance capabilities, international collaboration, and incentives for debris removal. 

By prioritizing space debris mitigation, the space economy can ensure the long-term sustainability of space operations, safeguarding investments and fostering continued exploration and utilization of outer space.

Categories: Trends
Source: HIS Education

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