In 1957, the Space Age officially began with the launch of humanity's first artificial satellite - known as Sputnik 1. Constructed and orbited by the Soviet Union, this satellite was a simple technology demonstrator designed to emit radio pulses.
However, the impact its deployment had was much more far-reaching than that. Not only was this a pivotal moment in the history of human spaceflight, and a big scare for the West, it was also the first of thousands of satellites to be launched from Earth.
Today, roughly sixty years later, some 8,950 satellites have been launched by more than 40 nations into orbit. Based on the most recent estimates, about 5,000 of these satellites remain in orbit, though most have reached the end of their lifespan.
Only around 1,950 of these satellites remain operational while the rest have become space debris. These now-defunct satellites are joined by thousands of bits of debris, which are collectively referred to as "space junk".
What is space junk?
Space junk is a general term that refers to every bit of non-functioning hardware and bits of debris that is currently floating around in Earth's orbit. It includes inoperative satellites, but also the spent first and second stages of rockets, and also fragments of spacecraft, satellites, and other missions.
This creates something of a problem for space exploration. Basically, any operational mission in orbit - ranging from working satellites and space stations to space telescopes and spacecraft - is at risk of colliding with this debris.
And with many missions to Low Earth Orbit (LEO) and beyond planned for the coming years, there are concerns that the problem of space debris will only get worse and become a serious hazard to any mission we send to space.
This raises some questions. For starters, how big of a problem is it? Also, much worse is it expected to get? And finally, how do we deal with it?
According to the most recent numbers released by the Space Debris Office at the European Space Operations Center (ESOC), about 5450 launches have taken place since Sputnik 1 was launched into space - excluding failed launches.
On top of all that, it is estimated that more than 500 break-ups, explosions, or collisions haven taken place in the past sixty years. Over time, this has led to the current situation in Low Earth Orbit (LEO), which is littered with space debris.
These objects pose a significant threat to operational satellites, spacecraft, and space stations. At present, roughly 22,300 of these objects are regularly tracked and cataloged by the U.S. Department of Defense's Space Surveillance Network (SSN).
However, these are just the objects that are large enough to be tracked by ground-based radar. All told, there are an estimated 34,000 objects in orbit that measure about 10 cm (4 in) in diameter, another 900,000 objects that measure between 1 cm (0.39 in) and 10 cm, and a whopping 128 million objects that measure between 1 mm and 1 cm.
While these last objects might sound underwhelming, even the tiniest objects can pose a severe collision hazard. This is due to the velocity of objects in orbit, which can get as high as 7 or 8 km per second (4.3 to 5 mps), which works out to about 12875 km/h (8,000 mph).
At these speeds, even small flecks of matter can cause serious damage to satellites, spacecraft or space stations. However, the biggest danger in having so much debris in orbit is the way it can become increasingly worse over time all on its own. This is what is known as the...
Also known as the Kessler Effect or collisional cascading, this phenomenon was originally proposed by the NASA scientist Donald J. Kessler in 1978. In this scenario, the density of objects in Low Earth Orbit (LEO) becomes high enough that collisions between objects would cause a cascade effect.
As objects collide, they produce smaller objects that collide with others, and so on in this fashion. With every collision, more space debris is generated and the likelihood of further collisions increases at an exponential rate.
The danger in this scenario is that self-perpetuating debris fields in orbit will impede space exploration. With even tiny collisions having the potential to cause catastrophic damage, launching payloads and crews to space will simply be too hazardous and expensive.
While several mitigation strategies are being developed to remove (or deorbit) space junk, tracking and monitoring the pieces that pose the greatest collision risk remains the most effective way of protecting missions in orbit.
Hence why space agencies and other organizations make it a point to track objects in orbit and issue warnings about possible collisions in advance. This way, operational missions can adjust their orbit to get out of an object's path.
Monitoring all the junk
Today, there are multiple entities that are dedicated to keeping track of the most hazardous debris in orbit. In the U.S. and Russia, ground-based radar and optical measurements are performed by space surveillance systems.
This allows for real-time tracking of objects larger than 5–10 cm(2 to 3.9 inches) at altitudes of 2,000 km (1,200 mi) or less - or Low Earth Orbit (LEO) - and objects larger than 0.3 - 1.0 m (1 to 3.3 ft) at an altitude of 36,000 km (22,370 mi) above the equator - Geostationary Orbit (GSO).
In 1982, NASA organized the first dedicated conference on space debris, which was followed by the European Space Agency (ESA) holding the first workshop on the reentry of space debris in 1982.
These were motivated by Skylab's reentry in 1979, which resulted in debris falling to Earth. There was also the breakup of the Soviet spy satellite Kosmos-1402 in 1982, which nearly resulted in radioactive debris falling to Earth.
In 1993, growing concerns about space debris led to the formation of the Inter-Agency Space Debris Coordination Committee (IADC), which included representatives from NASA, the European Space Agency (ESA), the Japan Aerospace Exploration Agency (JAXA) and the Russian Space Agency (Roscomos).
The IADC was created as a forum for the multi-lateral exchange of technical knowledge and to allow members to coordinate on matters pertaining to space debris. Today, it is regarded as the leading international body in the field of space debris monitoring and mitigation.
Since 1993, several more agencies have joined, including additional European national space agencies, the China National Space Agency (CNSA), the Canadian Space Agency (CSA), the Korea Aerospace Research Institute (KARI), the India Space Research Organization (ISRO), and the State Space Agency of Ukraine (NSAU).
Every year, representatives of UN member states and various organizations meet with COPUOS' Scientific and Technical Subcommittee to exchange information on their space debris research activities.
In 1995, NASA issued the first comprehensive set of orbital debris mitigation guidelines. Two years, later the U.S. government used these guidelines to develop the Orbital Debris Mitigation Standard Practices.
In 2002, the IADC published the IADC Space Debris Mitigation Guidelines and presented them to the UNCOPUOS Scientific & Technical Subcommittee, which has since served as a baseline for national legislation and standards, and as a starting point for technical standards.
In 2007, the UN General Assembly endorsed the Space Debris Mitigations Guidelines, which calls for member states to voluntarily adopt standards and measures to address the debris that results from their space missions.
Since 1962, UNOOSA has also maintained the United Nations Register of Objects Launched into Outer Space, a database that allows which member states bear international responsibility and liability for space objects.
In 1976, the UN enacted the Convention on Registration of Objects Launched into Outer Space. All those member states and international organizations that agree to abide by the Convention are required to provide information in the UN Register and establish their own national registries as well.
The future of space junk
Today, multiple national space agencies are sending satellites, payloads, and even crewed missions to orbit. Whereas space exploration was once the province of just two superpowers (the U.S. and the Soviet Union/Russia), China, India, and the European Union are now actively participating.
At the same time, there has been an explosion in the aerospace industry (aka. NewSpace), with more and more companies providing commercial launch services and things like satellite-based broadband internet. The current situation in orbit is only likely to get worse.
This growth is due in part to the fact that the costs associated with launching payloads into space have dropped considerably in the past decades. Between reusable first stage rockets (like the Falcon 9 and Falcon Heavy), single-stage-to-orbit rockets, tailored and rideshare launch vehicles.
Because of this, private corporations, research institutes, and other organizations are sending more satellites into space and offering more in the way of satellite-based services. A good example is the burgeoning satellite-internet market.
Beginning in 2015, Elon Musk (founder of SpaceX) announced a new venture called Starlink. The purpose of this new company is to create a constellation of satellites in orbit that would provide broadband internet access to the entire world.
In May of 2019, the first batch of 60 satellites was sent to a very low orbit above Earth - to altitudes of 328 km to 580 km (200 to 360 mi). This decision was motivated in part to minimize the risk posed by “space junk”, but also because it will allow SpaceX to send more satellites to space (and provide internet services) sooner.
Already, SpaceX has received FCC approval for a constellation of 12,000 satellites. However, the company recently issued filings with the International Telecommunication Union (ITU) for an additional 30,000 satellites.
The request consisted of 20 filings in total, each one for an additional 1,500 satellites. This plan alone, if fully realized, would increase the number of satellites in orbit by a factor of five.
However, SpaceX is not alone in looking to break into the satellite internet market. For example, Amazon founder Jeff Bezos also wants to deploy a constellation of internet satellites in what is known as Project Kuiper.
According to the application filed by Amazon with the FCC, they hope to send 3,236 broadband satellites into orbit in the coming years. And then there's OneWeb, a global internet company that also plans to launch more than 1000 satellites to provide services to the entire world.
Mark Zuckerberg (founder of Facebook) has also announced intentions to create an internet constellation in recent years. Airlines like Delta and American also hope to create their own internet constellations to provide in-flight internet.
Another contributing factor is the development of small satellites known alternately as CubeSats or nanosatellites. These are a special class of satellites, responsible for conducting research, scientific investigations, technology demonstrations, or commercial services.
A single satellite typically measures just 100 cm² (15 inches²), which allows them to be stacked to form larger scientific packages - to a maximum of 24 units, arranged in configurations measuring 40 cm (15.75 in) by 30 cm (12 in).
In short, these nanosatellites are allowing more entities (like research institutes and universities) to send satellites to space. In other words, it's not only federally-funded space agencies that can afford to conduct satellite-based research anymore.
While this represents a major opportunity for scientific research, it also means that thousands of additional satellites will be sent into orbit in the coming years and decades. This too has the potential to make a bad problem worse.
All told, UNOOSA estimates that spacecraft are being sent to orbit at a rate of 70 to 90 launches a year. At the same time, an increasing number of these launches are deploying 30 or more small satellites to orbit at a time.
Given the rate at which collisions and breakups occur - which works out to an average of four to five a year - the amount of debris in space is projected to increase dramatically in the next few years.
Given the situation, there are those who have advocated for a "No New Launches" policy. However, a 2005 study conducted by the NASA Orbital Debris Program Office (ODPO) found that even if no future launches occurred, collisions between existing objects would still increase the debris population at a rate faster than atmospheric drag would remove objects.
This scenario highlights the need for an active debris removal (ADR) program. This would need to consist of mitigation strategies being adopted at the earliest phases of mission planning, and remediation strategies that call for the deorbiting of debris.
Strategies for reducing space junk
Several strategies have been proposed to mitigate and remediate the problem of space debris. These include curtailing the creation of new debris, designing satellites to withstand impacts, adopting procedures to reduce the risk of collisions and breakups.
One method that is sometimes used is known as upper-stage passivation, where delta boosters release residual propellant to reduce the risk of explosions caused by collisions. This practice is not yet implemented across the board.
Another method is to deploy satellites to orbits where they will enter Earth's atmosphere and burn up sooner. Both OneWeb and SpaceX adopted this policy in 2017 when issuing filings with the FCC for the creation of the satellite constellations.
Based on the filings, both companies intend to place their broadband internet satellites in a very low Earth orbit, which will cause them to reenter Earth's atmosphere one year after they become inoperative.
There's also a policy known as "one-up, one-down", where space agencies and companies that send rockets to space would also be responsible for rendezvousing with objects in orbit and forcibly deorbiting them.
Another method of debris mitigation involves the mission architecture itself. For example, second-stage boosters can be launched to ensure that they reach an elliptical geocentric orbit that will allow for rapid orbital decay.
However, there is currently no international treaty where signatories are required to adopt these measures. The guidelines published by COPOU.S. in 2007 are voluntary and the rules that govern launches and responsibility for orbiting missions are a matter of national law.
In addition, governments could incentivize the cleanup of space debris by imposing penalties on commercial polluters. Essentially, companies like SpaceX, Blue Origin, Arianespace and others would have to pay a fine if any debris resulted from their missions.
Clean-up in Earth orbit!
There are also numerous technologies that have been proposed to remove or destroy space debris. Unfortunately, most of these are still in the research and development phase, while others remain theoretical.
A popular concept is to send remotely-controlled (or autonomous) spacecraft to orbit that would be able to rendezvous with debris and force it to deorbit and burn up in our atmosphere. To date, multiple concepts have been explored by NASA, the ESA, and other space agencies.
Recently, NASA partnered with Vestigo Aerospace to conduct a six-month study to assess the feasibility of attacking drag sails to space debris. Once attached, these sails would increase atmospheric drag, forcing the object to reenter Earth's atmosphere sooner than expected.
There is also the Horizon 2020 Future and Emergent Technology (FET) program spearheaded by the European Commission, which has fostered ideas for dealing with space debris. As part of this program, a team of scientists from the Universidad Carlos III de Madrid (UC3M) developed a tether system that would allow satellites to deorbit themselves.
This is known as the Electrodynamic Tether technology for Passive Consumable-less deorbit Kit (E.T.PACK) system. It consists of a strip of aluminum tape coated with a special material that causes the tether to become attracted to Earth’s magnetic field, thus lowering its altitude until it burns up in Earth’s atmosphere once it's no longer functioning.
In Europe, the Surrey Satellite Technology Ltd, the Surrey Space Center, and Airbus Defense and Space came together to create the RemoveDebris spacecraft. This small satellite relies on a harpoon, a tether, and a drag sail to capture and forcibly deorbit space debris.
More ambitious concepts include the use of magnetic space tugs, an idea proposed by the ESA based on a study from the Institut Supérieur de l’Aéronautique et de l’Espace in France. This space tug would generate magnetic fields to both attract or repel satellites and force them into decaying orbits.
There's also the ambitious plan to launch satellites that would destroy or push orbiting debris into the atmosphere using directed-energy (lasers). In recent years, China has joined agencies like NASA in conducting feasibility studies on this idea.
Sails, nets, harpoons, lasers, and an international regulatory framework. It seems like these are the most widely-explored means for combatting what is sure to become a very serious problem in the coming years.
With the exception of administrative or legislative solutions, the methods for cleaning up Earth's orbit are still quite theoretical and will be very expensive to realize.
But given humanity's expanding presence in space, and all the plans to commercialize LEO in the near future, the cost of inaction is sure to be much higher!
- UNOOSA - Space Debris
- CSA - What is a Cubesat?
- NASA - What is Orbital Debris?
- USCUSA - UCS Satellite Database
- ESA - Space Debris by the Numbers
- NASA - ARES Orbital Debris Program Office
- NASA - Space Debris and Human Spacecraft
- NASA Orbital Debris Program Office (ODPO) - FAQ
- USSTRATCOM - Space Control And Space Surveillance
- UNOOSA - United Nations Register of Objects Launched into Outer Space
- UNOOSA - Space Debris Mitigation Guidelines of the Committee on the Peaceful Uses of Outer Space