A Celestial Landfill
For decades, every rocket launch and satellite deployment has left something behind. Today, the space around our planet is cluttered with defunct satellites, spent rocket stages, and millions of smaller fragments from collisions and explosions. More than
22,000 of these objects are large enough to be tracked, but an estimated 128 million are smaller than a centimetre. Travelling at speeds of up to 28,000 kilometres per hour, even a tiny paint fleck can inflict catastrophic damage on a functioning satellite or the International Space Station. This growing cloud of debris poses a significant threat to our communication networks, weather forecasting, and future space missions. Experts warn of a potential 'Kessler Syndrome', a chain reaction where collisions create more debris, leading to more collisions, potentially rendering low-Earth orbit unusable.
The High-Tech Harpoon
One of the most direct methods for capturing large, uncooperative pieces of junk is the space harpoon. The concept is straightforward but technologically complex: a chaser satellite identifies a target, such as a dead satellite, and fires a tethered harpoon into it. Once embedded, the chaser can then tug the debris, either pulling it into a lower orbit where it will burn up in the atmosphere or moving it to a designated 'graveyard orbit'. The European Space Agency (ESA) has been a key proponent of this technology. The RemoveDEBRIS mission, which launched in 2018, successfully demonstrated a harpoon test in orbit, firing a projectile at 20 metres per second into a target panel extended from the satellite itself. Lasers often play a crucial role in these missions, not as a weapon, but as a highly accurate ranging and targeting system to ensure the harpoon hits its mark.
A Magnetic Attraction
While harpoons are designed for legacy debris, another innovation looks to the future: magnetic capture. Companies like the Japan-based Astroscale are pioneering this technology. Their ELSA-d mission successfully demonstrated a magnetic docking system in 2021. This method involves a 'servicer' spacecraft rendezvousing with a piece of debris. The system works best with future satellites that are designed with a compatible magnetic docking plate. Once close, the servicer can attach magnetically to the defunct satellite, allowing it to be safely controlled and de-orbited. Astroscale's vision includes a reusable architecture where a 'servicer' vehicle captures multiple pieces of debris and hands them off to a separate 'shepherd' craft that guides them to a fiery atmospheric reentry, making the process more cost-effective. This approach is part of a broader push for 'design for removal' (D4R), ensuring new satellites can be easily cleaned up.
Robotic Claws and Giant Nets
Harpoons and magnets are not the only tools in the orbital cleanup kit. Swiss startup ClearSpace, under a contract with ESA, is developing the ClearSpace-1 mission, slated to launch around 2028. This mission will use a four-armed 'space claw' to grab a piece of retired ESA hardware and drag it down to burn up in the atmosphere. This approach is like sending a tow truck into orbit. Other concepts include casting giant nets to capture multiple smaller fragments or even a single large object. The UK Space Agency has awarded funding to both Astroscale and ClearSpace to remove defunct British satellites, with Astroscale developing a robotic arm for its COSMIC mission. These varied approaches show that there is no single solution, but rather a growing toolbox for tackling different types of debris.
