SDG Month feature
As Earth’s orbits grow increasingly crowded with satellites and space debris, York University researcher Zheng Hong (George) Zhu is developing technologies to keep space safe and sustainable.
In addition to the more than 11,500 operational satellites orbiting Earth, according to the Satellite Industry Association, tens of thousands of pieces of space junk – including retired satellites, discarded rocket components and metal fragments – now occupy Earth’s orbital environment.
Managing orbital debris has become central to the long‑term sustainability of space activity, as NASA prepares new crewed missions to the moon, cargo vehicles continue servicing the International Space Station and companies such as SpaceX’s Starlink deploy thousands of satellites.
“In the past, we thought of Earth’s orbit as having infinite space, but it doesn’t,” says Zhu, professor in the Department of Mechanical Engineering at York’s Lassonde School of Engineering and Tier 1 York Research Chair in Space Technology. “If you don’t clean up, eventually it becomes very risky.”
As waste accumulates, the risk of collisions with satellites and spacecraft rises. This can eventually lead to the so-called Kessler Syndrome, where collisions trigger a chain reaction that produces more and more fragments which, in turn, cause additional collisions.
Even small objects travel at extreme speeds: a fragment no larger than a bolt can disable a satellite that supports services people rely on every day, from global communications and weather monitoring to navigation and emergency response.
Without effective strategies to reduce and remove debris, humanity’s ability to safely operate in space may be compromised.
Zhu has spent more than a decade developing solutions to that challenge.
His interest in space debris mitigation goes back to 2010, when he says few researchers were focused on the issue. Two high‑profile events sharpened his attention: China’s 2007 antisatellite missile test – which destroyed one of its own aging weather satellites and scattered thousands of fragments – and the 2009 accidental collision between an operational U.S. communications satellite and a defunct Russian satellite, the first known crash between two intact satellites in orbit.
“It was a wake‑up call that caught my attention,” says Zhu.
He began exploring how a technology he was studying, called electrodynamic tethers – long, thin conductive wires that interact with Earth’s magnetic field – could help address the problem. Originally investigated as a way to generate electricity in orbit, Zhu realized the technology could also act as a brake, slowing satellites and objects so they safely re‑enter Earth’s atmosphere.
This helps address a major contributor to space clutter. Most satellites are not designed to return to Earth at the end of their missions. Once they run out of fuel or stop working, they can drift in orbit for years or decades before gravity and atmospheric drag eventually bring them down. By slowing these satellites with an electrodynamic tether, Zhu’s system accelerates their orbital decay, helping them re‑enter the atmosphere far sooner than they would naturally.
Since 2010, he has been pursuing this technology as a way for satellites and spacecraft to be pre‑emptively equipped with disposal systems, allowing them to safely remove themselves at the end of their missions without adding new refuse or relying on costly clean up efforts. This approach could make sustainable orbital management the default, rather than the exception.
One of his projects, called DESCENT, put this concept into practice as Canada’s first on‑orbit test of space debris removal technology. Launched from the International Space Station, the Canadian Space Agency–funded mission consists of two CubeSat satellites connected by a 100‑metre electrodynamic tether, which will deploy in orbit to demonstrate how the system can actively lower a satellite’s orbit.
Complementing this work is Zhu’s research in autonomous space robotics, which he pursues alongside his efforts in keeping space clean. His lab develops systems capable of tracking, approaching and manipulating free‑floating and tumbling objects, using advanced perception, robotic dexterity, AI‑enabled decision‑making and control strategies to rendezvous with and grasp challenging targets. While these systems are developed primarily for on‑orbit servicing – such as repairing, refuelling or upgrading satellites without human spacewalks – Zhu believes they also have important applications for active debris removal, where autonomous robots can identify and capture defunct or tumbling objects in orbit.
Building on the autonomous robotic work, Zhu is exploring advanced swarm‑based approaches. He swarms of small satellites that autonomously coordinate to locate and interact with the waste. “My concept is very cheap, small satellites that can be mass‑produced, launched into space and then work as a swarm,” he says. “It’s decentralized control – more like ants. When one satellite finds a target, it shares the information so others can approach without collision among themselves and coordinate to dock onto or push the debris.”
Each satellite is designed to nudge or influence space litter using tethers or contact‑based mechanisms, rather than complex robotic arms, and the swarm is intended to deorbit along with the debris after interaction.
Currently, as part of his Tier 1 York Research Chair in Space Robotics and AI (2024-29) and as director of the NSERC CREATE Program in Smart Autonomous Robotic Technology for Space Exploration (SMARTART), Zhu is actively publishing and presenting on these concepts while nurturing the next generation of engineers and researchers who could bring them to fruition. Through SMARTART, students gain industry‑oriented training in AI, autonomous robotics, computer vision and systems engineering, equipping them with the skills needed to tackle challenges like coordinated spacecraft swarms and active debris removal.
Seeing his students embrace these ideas and contribute to the field, Zhu notes the growing global engagement with space debris issues.
As someone who once felt he was among the few raising concerns about space debris in 2010, Zhu is encouraged by the reception and interest his work now receives, as well as the efforts he sees worldwide from researchers and organizations.
“My reward is seeing more people following my path to do this,” he says. “I’m glad to see more people paying attention and recognizing the importance of this issue.”