Researchers at Tohoku University in Japan have developed a new type of plasma propulsion engine designed to remove space debris from Earth's orbit without physical contact. The system uses a unique bidirectional plasma stream to push orbital junk towards the atmosphere, offering a safer alternative to current cleanup methods.
This innovation addresses the critical issue of kickback force, a problem that has hindered previous plasma-based deorbiting concepts. By firing two plasma streams in opposite directions, the engine can maintain a stable position while acting on a target, a significant step forward in orbital maintenance technology.
Key Takeaways
- A new engine developed at Tohoku University uses dual plasma streams to deorbit space junk contact-free.
- The bidirectional design cancels out kickback force, allowing the removal satellite to remain stable.
- A specialized magnetic field was shown to triple the engine's deceleration force in lab tests.
- The system operates on argon, a more abundant and cost-effective propellant than traditional options.
The Growing Threat of Orbital Debris
Low Earth Orbit (LEO) is becoming increasingly crowded. Decades of space activity have left behind a trail of defunct satellites, spent rocket stages, and fragments from past collisions. According to official trackers, there are over 14,000 large pieces of debris currently orbiting our planet, with countless smaller, untracked objects.
These objects travel at extremely high velocities, often exceeding the speed of a bullet. A collision with even a small piece of debris can cause catastrophic damage to active satellites, which are essential for communication, navigation, and scientific research. The International Space Station also faces a constant threat from this orbital clutter.
Preventing the Kessler Syndrome
The accumulation of debris raises concerns about a theoretical scenario known as the Kessler syndrome. This is a chain reaction where a single collision creates a cloud of new debris, which in turn increases the probability of further collisions. If triggered, this cascading effect could render large portions of Earth's orbit unusable for generations.
Associate Professor Kazunori Takahashi, the lead researcher on the project, highlighted the danger. "Owing to their uncontrolled motion and velocity exceeding that of bullets, space debris orbiting around Earth poses a serious threat by a significant increase in the potential risk of collisions with satellites that support sustainable human activity in space," he stated.
A New Approach to Debris Removal
Current methods for removing space debris often rely on direct physical contact. These techniques involve using robotic arms, nets, or tethers to capture and drag junk out of orbit. However, these methods carry significant risks, as many pieces of debris are tumbling uncontrollably, making a safe capture difficult and potentially dangerous for the removal spacecraft.
The concept of using a plasma thruster to push debris is not new. The idea is to direct a stream of plasma at an object, creating a force that slows it down. This deceleration would cause its orbit to decay, eventually leading it to burn up safely in Earth's atmosphere. The primary obstacle has been the thruster's own recoil.
When a conventional plasma engine fires at a target, it generates an equal and opposite force that pushes the removal satellite away. This kickback makes it difficult to maintain the correct distance and alignment needed to effectively deorbit the debris.
How the Bidirectional Thruster Works
The team at Tohoku University has engineered a solution to the recoil problem with their "bidirectional plasma ejection type electrodeless plasma thruster." The core innovation is its ability to eject two streams of plasma at the same time from a single unit.
Solving the Recoil Problem
The engine directs one plasma stream at the target piece of debris to apply the necessary deceleration force. Simultaneously, it fires a second, identical plasma stream in the exact opposite direction. This second stream perfectly cancels out the kickback force from the first, allowing the removal satellite to hold its position relative to the target.
"This propulsion engine applies deceleration force to the target object by ejecting plasma, while avoiding excessive thrust on itself by ejecting another plasma plume in the opposite direction," Takahashi explained in a press release.
Enhancing Performance with Magnetics
To further improve the system's effectiveness, the researchers incorporated a specially shaped magnetic field known as a "cusp" magnetic field. This field helps to contain and focus the plasma, significantly increasing the force it exerts on the target debris.
Tripled Performance in Tests
During tests conducted in a vacuum chamber to simulate space conditions, the team confirmed the bidirectional system successfully balanced its own thrust. Furthermore, the addition of the cusp magnetic field tripled the deceleration force compared to results from previous, similar experiments.
Future Implications and Sustainability
The successful demonstration of this technology marks a significant step toward a viable and safer method for cleaning up Earth's orbit. The findings were published on August 20, 2025, in the journal Scientific Reports.
An additional advantage of the new thruster is its fuel source. The system is designed to run on argon, an inert gas that is far more abundant and less expensive than xenon, the propellant commonly used in traditional ion engines. This could make future debris removal missions more cost-effective and sustainable.
With this technology, cleanup satellites could systematically target and remove large, high-risk pieces of debris, significantly reducing the probability of collisions and helping to preserve the orbital environment for future space activities.
"This achievement represents a significant technological advancement toward developing a propulsion system capable of efficiently and safely removing space debris," Takahashi concluded. The development offers a promising tool in the ongoing effort to ensure the long-term sustainability of space exploration and operations.
