What is Space Debris?
Space debris is a broad term used to refer to any man-made object that no longer serves any useful purpose and has been left in orbit. Objects such as decommissioned satellites, defunct spacecraft, used rocket boosters, and fragments from collisions make up a lot of the debris in our orbit. It should also be noted that debris could be anything as small as a screw, paint chip, or even residual fuel.
How much Debris is there?
The one thing to know about space debris is that it is extremely difficult to actively track. Given the scale of our orbit and how fast debris travels, it can be complicated to know exactly how much is up there. According to the ESA, we are actively tracking approximately 36,240 debris objects in orbit (as of Aug. 2024). While this is the case, there is projected to be over 40,500 pieces of debris greater than 10cm in size, over 1,100,000 between 1-10cm, and over 130,000,000 between 1mm-1cm in size. With that in mind, it indicates that actual figures of debris in orbit are much higher than what we can currently track with currently available technology.
What is the composition of Space Debris?
Space debris comes in many different shapes and sizes depending on the object it initially originated from and if it is the result of a debris-producing event or not. Over the years of sending various rockets, satellites, and other infrastructure into orbit, we have left a lot of debris behind as small as a speck of paint and as large as an upper-stage rocket body. Not to mention, there is an increasing population of “unidentified debris” cluttering our orbit as it is either too small or unknown in origin to understand what it is.
Listed below are some debris categories including a graph on how they compare in numbers up in orbit since 1957:
- Rocket Stage Boosters, Rocket Fragments, General Rocket Debris
- Payload & Mission-Related Objects
- Residual Fuel
- Small Debris (i.e. paint chips, screws, etc.)
- Unidentified Debris
How fast does debris travel?
The speed of debris varies, but in LEO it can reach speeds up to 17,500mph (~28,163kph). For reference, the average speed of a bullet is roughly 1,700mph (~2,736kph) and the fastest speed ever recorded in a plane was the X-15 at 4,520mph (~7,275kph). That means space debris travels nearly 10x faster than the speed of a bullet and nearly 4x faster than the speed of the fastest plane in recorded history. Even a small piece of debris such as a screw can cause serious damage at those speeds.
What debris is the most dangerous?
Technically, all debris can be considered dangerous, especially when considering the speeds it can travel. No matter if the debris is as small as a screw or as large as an upper-stage rocket body, it can do some level of damage to whatever it hits. To make it easier to explain, here is a table showcasing what different-sized debris can do to another object in orbit.
Size | Potential Risk to Satellites | Impact on Satellites |
>10cm | Debris is trackable Debris is too large for effective shielding | Catastrophic damage if not complete destruction |
1-10cm | Larger debris in this range is trackable Debris is still too large for effective shielding in most cases | Moderate to severe damage if not complete destruction |
<1cm | Debris is not trackable Effective shielding exists for this range of debris | Minor damage |
As you can see, the larger the debris, the harder it is to protect against it. In good news, we can actively track most debris around 10cm or above with current tracking technology. While this is the case, though, our orbit is still a large environment, and accidents can still happen with debris of this size. This is what makes them the most dangerous objects in our orbit. Defunct satellites, upper-stage rocket bodies, and other large debris objects can also still collide with each other. Whether through collisions, breakups, or explosions, these debris objects create the biggest risk to our orbital regime as they have the largest potential of generating thousands if not millions of new pieces of debris.
It should be emphasized again, though, that all debris still poses a threat due to its sheer speed. Smaller debris can still puncture spacesuits, inflict damage to windows on spacecraft or space stations, and even damage external systems to infrastructure. Because most debris can’t be tracked, we are playing a dangerous game as we continue to increase space activities in orbit with new satellites, more rocket launches, new space stations, etc.
Here are some examples of what even small debris can do at high speeds:
Where is all of the debris located?
Space debris is mostly located across Earth’s three main orbital zones LEO, MEO, & GEO. In terms of where the most debris is located, though, over 60___% can be found in LEO which ranges between the start of orbit to 2000 km in altitude. Consequently, most of our satellites, infrastructure, and overall human space activity also take place in LEO. This leads to somewhat of a catch-22 situation as LEO provides endless benefits for humanity in orbit, yet it is also the location of the highest probability of issues due to the ever-growing debris field there.
https://www.spacex.com/
Does debris ever re-enter our atmosphere?
The short answer is yes, debris can/does eventually re-enter our atmosphere – but it varies based on a few different factors. The biggest factor to talk about is what altitude the debris is at. The higher the altitude, the longer it will take for the debris to naturally decay into our atmosphere as there is less drag from it the higher you go. Here is a chart from SpaceX that can help give an idea of decay times based on altitude. For reference, the highest point of LEO is around 2000 km in altitude, which isn’t even shown on this chart. As we can see, where the average Starlink satellite is located between 500-600 km in orbit, it will only take about 5 or so years to naturally decay, which is generally the length of service for a Starlink satellite. Around the 700 km mark, we start to see an exponential increase in decay times to where we see those times hit around 100 years at the 800 km altitude.
For added reference, a generation tends to be between 20-30 years, meaning at the 800 km altitude, debris and satellites will take an average of 3-5 generations to decay naturally into the atmosphere. Anything higher than that, we are talking hundreds, if not eventually, over a thousand years. So, yes, while debris and satellites can re-enter our atmosphere, it isn’t as simple as one might think. And, this is also why we are starting to see reusability, active debris removal (ADR), and in-orbit servicing, assembly, and manufacturing (ISAM) opportunities grow as they all serve as possible options for mitigating future debris growth and cleaning up our orbit.
Have there been any collisions?
Unfortunately, collisions are an inevitability based on probability alone – and they have happened many times throughout our history in orbit. Some collisions have been minor, while others have been headlined for the catastrophic damage they caused. Every collision is what we call a ‘debris-producing event’ and each event, no matter how minor or severe it seems, can contribute a significant amount to the debris population in our orbit. It should even be noted that some collisions happen and we won’t even know they happened or don’t know the cause of how it happened. This has led to the growing need for improved Space Situational Awareness (SSA) and Space Traffic Management (STM) technologies and policies.
There are a few notable examples of debris-producing events in orbit. In terms of space debris generation, some of the worst have been from Anti-Satellite Tests (ASATs), specifically, China’s destruction of the Fengyun-1C in 2007, which generated 3,037 trackable pieces of debris as of 2010 and in 2018, 2,392 objects related to the event were still detected. The collision of the Cosmos 2251 and Iridium 33 in 2009 was another landmark event in the history of space debris – as it was the first-ever hypervelocity collision of an intact spacecraft. Furthermore, this event created nearly 2,000 pieces of trackable debris, most of which are still in orbit and will be for decades. Finally, these events – and numerous others like them – took place in low earth orbit (LEO), and the debris they generated has primarily stayed there, clogging the most used and useful area of space and increasing the chances of future collisions.
Looking ahead, as things stand, we are already seeing close calls with debris and other satellites grow exponentially. As more satellites and infrastructure are sent up into orbit, the chances of collisions continue to increase if we are not careful. We will inevitably see more collisions happen in the future – some will be minor, while others will cloud our orbit with thousands to millions of pieces of debris. As our SSA and STM technologies continue to improve, we can hopefully mitigate catastrophic collisions at a minimum.
Why is debris a problem & why should we care?
We are launching more objects into orbit this decade than we have in the previous 60 years combined. Our orbit is a rapidly changing and dynamic environment and as we continue adding new satellites and other infrastructure there, operating risks continue to rise. This means the probability of collisions will continue to skyrocket as we continue to send more things up. We are currently actively tracking over 30,000 objects in orbit, but that pales in comparison to the potential millions that we can’t track due to being too small. Combining the current projections of debris in orbit, with new debris formation, tens of thousands of new satellites, and new space stations or other infrastructure, our orbital environment will continue to reach a possible point of critical mass to where we overload our orbit without any care.
Reaching a point of critical mass could potentially trigger a theoretical event called the Kessler Syndrome, which would cause the debris in orbit to produce a cascade of collisions that becomes self-sustaining. This event could also deem LEO useless for generations to come, making operating risks so bad that it would fail any cost-benefit analysis and push any space activity to an early grave.
This is what leads us to why we need to care about space debris and why we need to do something about it before it’s too late. First off, all of the current and active infrastructure we have in orbit such as satellites, space stations, etc. plays a critical role in different aspects of our society. For example, a lot of satellites have an impact on our daily lives as they support activities such as GPS, banking & finance, weather tracking, communications, and much more. We are also seeing the rise of mega-constellations today which have modernized the opportunity for low-latency space-based internet. On top of that, satellites allow us to get a holistic view of global threats we face today such as climate change, deforestation, pollution, and much more through earth observation. Without these satellites, our lives will fundamentally change and push society back decades’ worth of progress.
With all of the above in mind, it should also be said that our activity in space has allowed humanity to innovate in ways we could never have imagined just a few decades ago. The Space Race during the Cold War opened our eyes to what space could offer humanity for pushing the boundaries of innovation in rocket technology, but the modern world can take it even further. In the past, our time in space has given us access to many things such as navigation, laptops, meteorology, insulin pumps, streamlined banking/finance, and so much more. We have also massively improved our understanding of the universe we live in through the use of the Hubble Telescope, James Webb Telescope, and many more.
When looking into the future, we have barely scratched the surface of what could be possible. In our orbit alone, we could see the rise of In-orbit Servicing, Manufacturing, and Assembly (ISAM), which could help break the boundaries into a new era of production and manufacturing. Microgravity has proven to have unique properties that could open up avenues for many different industries including biotech, pharma, electronics, and much more.
Not only do you know why space debris is a problem now, but you also know why we have to care. We are just getting started with what is possible for humanity in space. If we allow space debris to take over our orbit and even stop us from accessing it, we could lose a lot. Space has nearly limitless benefits for humanity, even with how scary it might seem out there. The time for change is now, and it all starts with creating a safer and more sustainable environment in our orbit.
