Risks of Cluttering the Skies with Too Many Satellites

Space Debris and its Impact on Space Exploration

A lot has changed since the launch of Sputnik in 1957, and space exploration is now an industry in which participants from all over the world have a vested interest. Whether the area for discussion is low Earth orbit (LEO) or beyond to new planets and moons, space is now a place where many missions are routinely being conducted. One problem, however, is that alongside the increase of space travel is the increase of space debris—i.e., the junk that is jettisoned or left behind or old technology that is simply just “hanging out” in space no longer serving any meaningful function. Space debris consists of defunct satellites, spent rocket stages, fragments from collisions, and other remnants of human endeavors in space. Space debris represents a serious problem because it can affect future space operations and explorations and even clog up the skies making it harder for researchers to probe the reaches of the universe with their telescopes. In short, space junk is turning the skies into a kind of highway full of litter that no one is bothering to collect and remove, and soon the highway will be impassible. This paper examines the problem of space debris, its sources, the risks it presents, and what measures can be taken to reduce its impact.

Nature and Sources of Space Debris

Space debris can be categorized based on where it comes from and its size. It can range from large objects, such as inactive satellites and spent rocket stages, to smaller fragments that have been created by collisions and explosions. According to the European Space Agency (ESA), there are approximately 34,000 debris objects larger than 10 cm, 900,000 objects between 1 and 10 cm, and an estimated 128 million objects smaller than 1 cm orbiting Earth (ESA, 2023).

The main sources of space debris include satellites that have reached the end of their operational lives but remain in orbit; upper stages of rockets that have completed their mission and remain in space; collisions between space objects that create numerous fragments, and more.

For example, the ESA’s Envisat is an Earth observation satellite that launched in 2002 but that stopped operations in 2012. Envisat weighs over eight tons and is 26 meters long—and it is one of the largest defunct satellites in earth’s orbit, at an altitude of approximately 785 km. The fact that it is there represents a collision risk to other space objects (ESA, 2023). There has been some discussion about its removal (capturing and deorbiting it), but doing so would require substantial heft (Estable et al., 2020).

Rocket stages that have completed their missions also contribute to space debris. One example is the core stage of the Long March 5B rocket, launched by China in May 2020. Weighing around 20 tons (100 feet long and 16 feet wide), this rocket stage re-entered Earth's atmosphere in an uncontrolled manner, which raised international concern due to the potential risk of debris falling in populated areas like New York City (Leman, 2020). Fortunately, most of the debris fell into the Atlantic Ocean. Nonetheless, incidents like these show the risks and challenges that large, uncontrolled rocket stages remaining in orbit represent for people below.

Collisions between space objects represent another critical source of debris. In February 2009, the defunct Russian satellite Kosmos 2251 collided with the operational Iridium 33 satellite over Siberia. This collision occurred at a relative speed of 42,120 km/h and generated thousands of debris fragments (NASA, 2009). This event highlighted the catastrophic potential of space debris collisions, significantly increasing the debris population in low Earth orbit (LEO) and raising concerns about the long-term sustainability of space activities.

Explosions of satellites and rocket stages, often due to residual fuel or batteries, also contribute to the space debris problem. In 2015, the NOAA-16 weather satellite that had been decommissioned since 2014 broke up due to explosion. Debris fragments from explosions like this represent another form of risk and concern, and show the need for better design and end-of-life disposal measures to prevent more space debris from filling up the sky. Likewise, anti-satellite (ASAT) tests have increased the amount of space debris. In January 2007, China conducted an ASAT test that destroyed its Fengyun-1C weather satellite with a missile, generating over 3,000 trackable pieces of debris (David, 2021). Deliberate actions like this are why the long-term problem of space debris needs to be taken seriously.

These real-world examples represent the real-world reasons, space debris matters. The increasing population of space debris not only poses a major challenge to the sustainability of space exploration and satellite operations but also a risk to the safety of people down below on earth. Space debris challenges will not be solved, however, without further technological innovations and international collaboration.

Risks Posed by Space Debris

Because space debris travels at high velocities, even small fragments can cause significant damage to operational satellites, the International Space Station (ISS), and other spacecraft. The high velocity of debris means that collisions can knock satellites completely off-line and create more debris (a chain reaction known as the Kessler Syndrome) (Wall, 2022). Moreover, damage to operational satellites can disrupt communication and Earth observation services. Space debris also represents a future risk for future space exploration missions. The increased debris in LEO alone complicates the planning and execution of future missions, as mission planners must account for potential collision risks and design spacecraft with more protection measures.

Mitigation Measures

One attempt to reduce risk is to make satellite and rocket design improvements that can help minimize the creation of new debris. For example, passivation techniques to reduce fuel could prevent explosions. End-of-life disposal mechanisms like controlled re-entry into Earth's atmosphere or moving to a graveyard orbit or propulsion systems that can be used to move them out of harm’s way, could reduce the number of defunct satellites in LEO (Wall, 2022).

Active debris removal technologies are being discussed to remove existing large debris from orbit, and these ideas include such things as robotic arms, nets, harpoons, and lasers—all of which have been proposed to capture and deorbit debris. One notable project is the ESA's ClearSpace-1 mission, scheduled for launch in 2026, which has the goal of showing the feasibility of capturing and removing a defunct satellite (ESA, 2024).

Effective space traffic management systems could also help with avoiding collisions by providing accurate tracking and prediction of debris movements. Surveillance and tracking systems are needed for this to work, and it depends on international collaboration as well. The global nature of space exploration depends on this collaboration as well. The United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) and the Inter-Agency Space Debris Coordination Committee (IADC) are helpful in promoting guidelines, such as the Space Debris Mitigation Guidelines of COPUOS, for responsible use of space.

Future Outlook

The deployment of large satellite constellations, such as SpaceX's Starlink and OneWeb, represent both challenges and opportunities for space debris management. These constellations increase the number of satellites in LEO, but they also incorporate design features like autonomous collision avoidance systems and end-of-life disposal plans. This shows that recommended best practices and collaboration among operators are being implemented to help address the space debris issue.

On-orbit servicing technologies like satellite refueling, repair, propulsion, and relocation, can extend the operational lives of satellites and reduce the number of defunct satellites that end up in orbit. Companies like Northrop Grumman's Space Logistics and Astroscale are developing capabilities to offer these services, so as to improve the sustainability of space operations (Rudico et al., 2024). Likewise, advancements in debris mitigation technologies like improved shielding materials and more efficient propulsion systems for maneuvering, as well as new active debris removal concepts can all be of important use. All of this can also be supported by strengthening international policies and regulations to promote responsible behavior in space activities by making it so that going forward companies must meet best practice thresholds and standards. There will need to be the establishment of binding agreements and the enforcement of existing guidelines to secure compliance and enforce accountability among space-going nations and private entities.