While we usually think of space as empty, as time passes it is less and less so. Every month new satellites are launched into orbit. Even more crucially, old satellites and rocket upper stages are often left there, sometimes even breaking up and exploding. This creates space debris: tiny fragments orbiting our planet.
Given the high velocities, they move at, a collision with them poses significant risks to active spacecraft. As such, the European Space Agency is developing solutions and is set to launch a demonstration debris removal mission in 2026: Clearspace-1.
Space debris is a broad term that can be used to describe a variety of objects. In general, refers to man-made objects in space that no longer serve any useful purpose. Usually, the term is used in the context of Earth Orbit, since this is where the issue is most significant.
When a satellite reaches the end of its life it should be disposed of. When orbiting close to the Earth, the satellite is usually deorbited and made to burn up in the atmosphere over the Pacific ocean. However, in geostationary orbit this maneuver would take too much fuel, so the satellite is moved up to what is called a graveyard orbit.
No useful satellites operate there, so it is used to store defunct ones. When these operations do not happen, either because the satellite abruptly ceased to function or because disposal was not planned, the spacecraft becomes a piece of debris. The same thing happens to spent rocket stages, which too should be safely deorbited.
While not ideal, these big pieces of debris are still relatively easy to deal with. Owing to their large dimensions, they are easy to track. As such, active spacecraft can plan maneuvers to avoid any risk of collision.
Bigger trouble arises when smaller pieces of debris form. This can happen due to the breakup or explosion of bigger debris. Causes can range from propellant leaks to component failure. These small fragments are very hard or impossible to track, meaning collisions with them are often impossible to avoid.
Another source of small fragments is collisions between large pieces of debris, or between a large piece of debris and an active spacecraft. One example of this is the 2009 collision between the Iridium 33 communication satellite and Kosmos 2251, a defunct Soviet military satellite. Space debris has also been created as a consequence of the testing of anti-satellite weapons. These weapons can destroy a satellite simply by crashing into it at extremely high speed. In the past, these tests have been carried out by the US, China, Russia, and India.
The potential damage caused by space debris varies widely in severity. Large solar arrays suffer from degrading power output due to debris strikes. Some spacecraft have been made unusable by space debris impacts in the past, like the Russian BLITS laser ranging satellite in 2013.
Even crewed missions have been affected in the past, luckily never causing mission-critical damage. Some mitigation measures exist, such as using a layered shield that breaks up the debris and then absorbs the energy of the smaller fragments over a large area. This concept is known as the Whipple shield, and it’s used on ISS modules for this very purpose.
Tackling the problem
Limiting the amount of space debris is a necessity. The first strategy to employ is to properly dispose of satellites and upper stages at the end of their lifetime.
However, we can’t realistically expect this strategy to be employed on 100% of objects in space. Moreover, many pieces of debris are already in space for which this isn’t an option. As such, we need to develop some form of direct space debris removal technology.
Many ideas for this have emerged in the past. Some, for example, aim at deorbiting debris using lasers, based either on the ground or in space. These would impart a force either via photon pressure or by ablating the surface of the debris. The latter method would produce small amounts of plasma from the material which, while expanding, would exert a force on the debris. Another option being looked into is using a spacecraft to grab a large piece of debris and deorbiting it. This is what ESA is aiming to demonstrate in 2026.
Clearspace-1 is a mission conceived by ESA’s Clean Space initiative, which is aimed at tackling the problem of space debris.
The contract to develop and build the spacecraft has been assigned to Swiss startup Clearspace SA, hence the name of the mission. The company was founded in 2018 by veteran researchers on the topic of space debris. The spacecraft is currently under development in close partnership with the space agency.
The spacecraft is equipped with the systems needed to rendezvous with a piece of debris and deorbit it. These are a propulsion system to change orbit, attitude control thrusters to fine-tune the approach to the target, and four robotic arms to get hold of it. These four claws are the most distinctive feature of the spacecraft.
Clearspace-1 is expected to launch around 2026. It will initially be put into a 500 km orbit, where it will perform extensive system checks. It will then proceed to rendezvous with its target, which orbits at an altitude between 660 and 800 km.
The debris chosen for the mission is a Vespa payload adapter left behind by the second flight of the VEGA rocket, in 2013. The mission launched two Earth observation satellites, stacked using an adapter that completely enclosed the bottom one. The top part of the adapter, conical in shape, is the target of Clearspace-1.
The Vespa adapter has a mass of around 100 kg, is rigid, and has a geometry that makes it relatively easy for the robotic arms to grab it. This makes it ideal for a first demonstration of space debris cleanup capabilities.
After getting hold of the debris, Clearspace-1 will use its engine to deorbit the two objects. Both of them will then burn up in the atmosphere, thus completing safe disposal.
Space debris cleanup is a developing field. Launching just one demonstration mission will not solve the problem, but it will certainly be a small step in the right direction.
The same company has already been contracted by the United Kingdom Space Agency to perform another debris removal mission, and many other entities are working on such capabilities. Given the increasing commitments, we can look forward to making Low Earth Orbit a better place.