Europe plans space claw to capture orbiting junk | Science
A representation of the ClearSpace 1 mission holding a discarded payload adapter with its four-armed claw.
ClearSpace SA / European Space Agency
By Daniel CleryDec. 1, 2020, 2:00 p.m.
The European Space Agency (ESA) today signed a contract to launch a mission in 2025 that will be the first to collect and dispose of a piece of orbiting space debris. The ClearSpace-1 mission, built by Swiss startup ClearSpace, will track down a piece of debris the size of a washing machine, hold it in place with a four-armed claw, and put it into a lower orbit where the duo will enter atmosphere and burn.
Darren McKnight, space debris expert at technology company Centauri, welcomes ESA as one of the few agencies to take action. However, he is concerned about the slow progress in removing debris in orbit, which he believes will increasingly threaten functioning satellites and astronauts. “If we don’t start soon, we’re going to be in big trouble,” he says. “We have to take small steps quickly.”
The space around the earth is becoming increasingly crowded as satellites have traditionally been left in orbit at the end of their useful life. In higher orbits, they can stay there for hundreds if not thousands of years. Discarded rocket stages are another major source of space debris if they do not enter the atmosphere after use.
The 5,500 launches in the 60 years of the space age left 23,000 objects in orbit larger than a grapefruit. There are many millions of smaller objects that cannot be tracked. At the speeds moving in near-earth orbit, even a collision with a stray bolt can be catastrophic. However, large objects are the most worrying as they can collide and create cascades of smaller collisions. It happened in 2009 when a working Iridium communications satellite collided with a dead Russian military satellite, creating thousands of new, trackable, and many smaller pieces of debris. Two years later, the International Space Station had to move to avoid debris from the crash. In 2012 some passed within 120 meters.
ClearSpace starts with something simple. In 2013, one of ESA’s Vega rockets launched a payload of two satellites. The 112-kilogram payload adapter with which ESA’s PROBA-V earth observation satellite is attached to the launch vehicle has been in orbit between 664 and 800 kilometers since then. It is now in the ClearSpace crosshairs. “It’s a simple structure, like a small satellite,” says Muriel Richard-Noca, ClearSpace’s chief engineer.
The challenge is to develop an imaging system that can quickly and autonomously characterize the object before the claw detects it, says Luisa Innocenti, head of ESA’s clean space office. “You don’t know how it moves, and the only way to know is by looking up,” she says. Innocenti says she and her colleagues also argued over the capture technique: grabbing with a claw requires a tight approach, while catching in a net can be done from a safe distance – but needs to work the first time. According to Richard-Noca, ClearSpace chose the Claw because you can make multiple attempts. “You can rehearse the entire process. It gives us the flexibility we need for this first mission, ”she says.
Other missions test similar ideas with self-made rubble. An EU-funded mission called RemoveDEBRIS, designed by the University of Surrey, flew in 2018 and tested a harpoon and net of small targets it used. The test of a tug to accelerate the descent into the atmosphere could not be used, so the reentry is slower. In March 2021, the Japanese company Astroscale plans to start a privately funded mission called ELSA-d. During the mission, a service vehicle releases a target vehicle with a ferromagnetic docking plate and detects it with magnets. It’s an option if future satellite designers adopt the idea, but not for old junk.
ClearSpace has bigger plans. “We will continue to move towards bigger and more ambitious goals,” said Luc Piguet, CEO of ClearSpace, as well as missions where multiple cost-cutting goals may be available.
That will be necessary, says Hugh Lewis, who models space debris at the University of Southampton. He points out that ClearSpace-1 will spend 100 million euros (86 million euros from ESA) to clean up just over 100 kilograms of space debris. At that price, Envisat – a defunct ESA 8,000-kilogram bus-sized satellite with Earth observation – would be prohibitively expensive, although Lewis says it is “the riskiest object in orbit”.
At the International Astronautical Congress in October, McKnight presented an analysis of the 50 most affected debris in low-earth orbit. He asked eleven teams around the world to create their top 50 list based on criteria such as mass, expected orbit life, and proximity to working satellites. Then he put together a composite list. The first 20 items on the list are Soviet and Russian missile stages that were launched between 1985 and 2007 and are in overcrowded deployment lanes. Each is heavier than an elephant and the size of a school bus. These giant objects are more of a threat than the growing fleets of relatively small Internet communications satellites launched by SpaceX with plans and capabilities to deorbit. “Clusters of dead things are more dangerous than constellations of living things,” he says.
However, experts say that political will is lacking even though technology is beginning to develop. According to McKnight, the space agencies policy is “study, wait and hope” while we want to “monitor, characterize and act.” Almost all of the debris on McKnight’s top 50 list was dumped there by state space agencies. “It’s a superwicked problem,” says Lewis. “The people who are trying to solve the problem are also who are causing it.”