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14 July 2020

A WALL•E to Clean Up Space Debris

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Since the 1957 launch of the first satellite, the famous Sputnik I, which ushered in the space age, another 9,600 devices have ascended into Earth’s orbit, but only a small portion of them, some 2,300, are still in operation. This strange population of abandoned satellites, wandering through space, shares occupancy with the remains of the rocket boosters that lifted them into their orbits and the millions of fragments into which they break down when they collide or explode. This agglomeration has been given the indisputably appropriate name of space junk. In numerical terms, 95% of all man-made objects spinning around the Earth are garbage

The risks to our communication systems and the future of space flight posed by this useless space debris are nevertheless enormous. “Imagine how dangerous sailing the high seas would be if all the ships even lost in history were still drifting on top of the water. That is the current situation in orbit, and it cannot be allowed to continue,” said Jan Wörner, director-general of the European Space Agency (ESA), after the agency’s last ministerial summit in Seville last November. At the summit, the member states commissioned the first space mission, ClearSpace-1, to remove one of these inert pieces of debris. 

The hunter and the prey 

The goal of ClearSpace-1 is to remove from orbit the VESPA (Vega Secondary Payload Adapter) upper stage, which after a flight from the ESA’s Vega launcher in 2013 became stranded in orbit more than 600 kilometres above the Earth’s surface. With a mass of 100 kg, the VESPA is around the size of a small satellite and has a sturdy and relatively simple construction. It is the prey. 

The hunter is a sophisticated Swiss-made microsatellite. Looking somewhat like a washing machine to which an elaborate quartet of robotic arms has been added, it has been tasked with finding and catching the VESPA, defined by engineers as an “uncooperative” object, i.e. one that was designed with no intention of being recovered once in orbit. The VESPA has no GPS or any sensor on board to facilitate an approach or capture, so in a sense ClearSpace-1 will be going in blind.

In general, space debris measuring more than ten centimetres in diameter, as is the case with VESPA, is tracked from the ground using radar technologies and in some cases telescopes. With these observations, engineers calculate the orbits they occupy and link them to specific satellites or collisions to catalogue them in a database, but this location is approximate. It will be in space where they obtain more precise coordinates. 

If the hunt is successful, ClearSpace-1 will meet up with the VESPA somewhere in its orbit. Its robotic arms will grasp the debris and leave it firmly secured. Then the hunter and the prey, locked in an embrace, will face their irrevocable end together, falling into the Earth’s atmosphere where they will burn up before ever touching the ground.

The mission is part of a new ESA project called ADRIOS (Active Debris Removal/ In-Orbit Servicing) to develop guidance, navigation and control technologies and rendezvous methods to de-orbit dead or damaged satellites, such as the VESPA. It will be carried out by a commercial consortium led by the ClearSpace company, made up of space debris researchers based at the Swiss Federal Institute of Technology in Lausanne. The launch is scheduled for 2025.

The Kessler effect

“NASA and ESA studies show that the only way to stabilise the orbital environment is to actively remove larger debris items. Even if all space launches were halted tomorrow, projections show that the overall orbital debris population will continue to grow,” explains Luisa Innocenti, who leads ESA’s Clean Space initiative. “We need to develop technologies to avoid creating new debris and removing the debris already up there. This new mission, implemented by an ESA project team, will allow us to demonstrate these technologies, achieving a world first in the process.”

Innocenti refers to the Kessler effect, named after NASA space debris expert Don Kessler. He observed that, once past a certain critical mass and even if not one more satellite is put into space, the total amount of space junk will continue to increase; collisions of orbiting debris produce more debris which in turn leads to more collisions, and so on in an endless chain reaction.

In view of the latest data, the task seems more urgent than ever; more than 50 countries are involved in low-Earth orbit —ranging from 200 to 2,000 km above the planet’s surface— and models estimate that space junk will triple in quantity by 2030. In addition, in the coming years the number of satellites may increase by up to an order of magnitude with the launching into orbit of multiple mega-constellations, both national and private, such as the one planned by SpaceX and its Starlink network, composed of honeycombs of hundreds or even thousands of satellites working collaboratively in telecommunications, surveillance and monitoring services. Space is becoming a busy neighbourhood indeed.

Eugenia Angulo



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