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Telescopes and space missions

Telescopes and space missions

Electromagnets could help clean up space junk

29 Nov 2021 Isabelle Dumé
Jacob Abbott
Jake J Abbott developed a new way to manipulate orbiting space debris using spinning magnets. (Courtesy: Dan Hixson/University of Utah College of Engineering)

Researchers at the University of Utah in the US have used a set of electromagnets to move non-magnetic objects remotely – a technique they say could come in useful for cleaning up debris in space, where objects in low-Earth orbit are becoming an increasingly serious hazard.

In May 2021, NASA reported that the US Department of Defense was tracking more than 27,000 pieces of space debris in Earth orbit. This number does not include objects that are too small to track, and the number of trackable objects increased significantly in mid-November after a Russian anti-satellite missile test turned a defunct Soviet-era satellite into a debris cloud. Because these objects tumble and travel at speeds of up to 17,500 mph, they could cause serious damage to satellites or spacecraft if they collide with them. Such collisions also create fresh debris, potentially leading to a chain reaction known as Kessler syndrome.

Non-contact technique

Because most of these objects are made from non-magnetic aluminium, removal mechanisms that rely on magnets are generally not effective at “grabbing” them. The new non-contact technique developed by Jake Abbott and colleagues, however, can be used to manipulate any electrically conductive object. It works using magnetic induction, in which a fast-changing (rotating) magnetic field induces an electrical current that forms circular loops known as eddy currents in the conductor. These loops in turn produce their own, secondary magnetic field, thereby turning the conductive object into an electromagnet that exerts magnetic forces on the source of the original magnetic field.

If this field is produced by a moving or rotating magnet, the induced force opposes the original motion and slows the magnet’s motion. This “drag” effect is already exploited as a braking system for some trains as well as in industrial motors and magnetic propulsion systems for roller-coasters, among other applications. Indeed, scientists have been making use of magnetic induction since the 1800s to wirelessly transmit energy between conductors across short distances for applications in electrical transformers, wireless smartphone charging and, of course, in induction pots and pans.

Abbott and colleagues tested their approach by grabbing and moving a copper sphere floating in a tub of water, mimicking the low-friction environment of space. They showed that their magnet was able not only to move the sphere around a square, but also to rotate it.

Capturing space debris

The researchers say the technique could be used to slow the tumbling motion of space debris in a safe way, and then to tow it to a lower orbit for disposal. The technique might also be used to stop a damaged satellite from spinning so that it could be repaired – something that isn’t possible at present, they add. And since it is non-contact, it could allow engineers to manipulate particularly fragile objects, too.

The Utah team says it is now planning to manipulate objects for which the researchers do not have a model in advance. “For this work, we will have to learn the model as we manipulate it, observing how the object moves due to its rotating magnetic fields,” Abbott tells Physics World.

The present work is detailed in Nature.

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