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A new plasma thruster aimed at contactless space-debris removal produced about 25 millinewtons of force on a target in a laboratory test, using 5 kilowatts of radio-frequency power. The result improves on an earlier version of the concept, but it is not an orbital cleanup mission: no real debris object has been removed, and the force available at practical operating distances remains an important question.
What the researchers demonstrated
A team led by Kazunori Takahashi at Tohoku University reported the result in Scientific Reports on August 20, 2025. The device is more precisely described as a cusp-type bidirectional radio-frequency (RF) plasma thruster with magnetic nozzles, rather than a conventional gridded ion engine. In the experiment, it delivered a maximum target force of about 25 mN at 5 kW of RF input power. The target was a laboratory structure, not an uncontrolled satellite or rocket stage in orbit. The study reports the experiment and its limitations.
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The advance is a stronger laboratory demonstration of a promising idea—not proof that space junk can now be cleared. The work builds on a 2018 proof of concept in which researchers demonstrated bidirectional plasma ejection and force transfer to a target plate while keeping the thruster’s net force near zero. The earlier configuration produced roughly 8 mN; the 2025 cusp-field version reached about 25 mN. The earlier study describes the foundational concept.
Why push debris with plasma?
Active debris removal means deliberately changing the orbit of an existing, nonfunctional object—usually a large, hazardous object such as a defunct satellite or spent rocket stage. It is different from:
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- Collision avoidance: an operating satellite maneuvers itself away from a predicted close approach.
- Post-mission disposal: a spacecraft uses its own systems to leave a congested orbit at the end of service.
- Debris tracking: operators monitor objects and predict their paths without changing them.
Many capture concepts require a servicing spacecraft to grapple, tether, net, or otherwise attach to a target. That can be difficult if the object is tumbling, damaged, or has no safe attachment point. A plasma thruster could, in principle, transfer momentum without mechanical contact. It would still need to approach and track the target; “contactless” does not mean that the spacecraft can act from far away.
How the bidirectional thruster works
- A propellant gas is fed into the thruster.
- Radio-frequency energy ionizes the gas, producing plasma.
- Magnetic fields guide and accelerate plasma through two open ends of the device.
- One plume is aimed at the debris. When it reaches the surface, it transfers momentum and exerts a small force.
- A second plume exits in the opposite direction to counter the reaction force on the servicing spacecraft.
That last step addresses a basic problem: firing a beam at debris also pushes the spacecraft in the opposite direction. Without compensation, the servicing craft would tend to drift away from the target. The opposing plume is intended to keep the thruster’s net force near zero while momentum is transferred to the debris. Tohoku University has also explained this reaction-force challenge in its overview of the concept.
The plasma is not a gravity-like “tractor beam.” It must physically reach and interact with the object. The proposed operation would gradually change the target’s momentum so its orbital energy falls. That lowers its orbit; atmospheric drag might eventually bring it down, but the change would not make the object disappear immediately.
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What the cusp magnetic field changes
The 2025 design introduces a cusp magnetic-field configuration, forming converging-diverging magnetic-nozzle structures at both exits. The researchers say this arrangement helps limit plasma losses to the device walls and improves the force delivered to the target while maintaining near-zero net thrust on the thruster itself. The measured result—about 25 mN—was roughly three times the approximately 8 mN reported for the earlier configuration.
The paper discusses argon as a usable propellant and as a potentially less costly or more readily available alternative to xenon. That is a potential supply advantage, not evidence that a complete spacecraft mission using the system would be inexpensive.
How much is 25 millinewtons?
It is a small force: roughly the weight-force of a few grams at Earth’s surface. In orbit, the important effect is the gradual accumulation of momentum, not lifting an object against gravity. Whether the force could meaningfully change an object’s orbit depends on its mass, the duration and alignment of the beam, the required velocity change, and how efficiently the plasma transfers momentum to its surface.
So 25 mN is not enough information to calculate a deorbit time. The laboratory result does not establish how long the system would take to lower a real satellite or rocket stage, or whether the measured force could be sustained at a useful distance.
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- Distance and plume behavior: Plasma expands as it travels and may detach from the magnetic nozzle. The force delivered to a target is expected to depend on separation, so a result obtained against a nearby laboratory target cannot simply be assumed at an operational stand-off distance.
- Power and heat: The reported maximum required 5 kW of RF power. A spacecraft would also need power-generation and conditioning equipment, thermal management, propulsion, navigation, communications, and attitude control. The experiment does not establish a complete spacecraft power budget or show that 5 kW is the total mission requirement.
- Target motion and surface: A tumbling object, irregular shape, or different material and surface finish could change how effectively the beam transfers momentum. Accurate tracking and sustained alignment would be essential.
- Near-zero thrust control: The opposing plumes must remain balanced well enough for the servicing spacecraft to maintain safe relative motion near the target.
- Testing scale: The researchers say further work on plasma expansion and detachment, and validation in a larger space-simulation chamber, are needed. The 2025 report does not describe an orbital demonstration.
- Mission and authorization: Rendezvous, collision avoidance, target identification, and safe operations are still required. Changing another party’s object orbit would also require appropriate authorization and coordination; “contactless” does not remove those obligations.
Even if the thrust works as intended, deorbiting is a controlled orbital maneuver, not an instant cleanup. A poorly planned change could put an object into another congested orbit rather than promptly removing it. Any mission would need to account for the target’s mass and orbit, the desired trajectory, and how long the object remains trackable.
How it compares with other removal approaches
No single method fits every object. Robotic capture can physically secure a target but requires a successful rendezvous and grapple; nets and tethers also involve contact and bring risks of snagging or entanglement. An ion-beam shepherd is another contactless concept that uses an ion beam to impart momentum, but it has its own beam-control and reaction-force challenges. Laser-ablation concepts aim to alter a target with energy from a distance and raise different questions about coupling, pointing, and safety. Electrodynamic tethers and controlled end-of-life disposal apply to particular spacecraft and mission designs, rather than serving as universal ways to remove existing debris.
The bidirectional RF plasma thruster’s potential distinction is its paired beams: one acts on the target while the other is intended to balance the force on the servicing craft. Its laboratory result does not establish that it is more mature or effective than these alternatives. The demonstrated device is not a retail product, and the cited research does not report an operational cleanup service based on it.
What the 25 mN result means
The study advances a contactless debris-removal concept by showing that a cusp-type magnetic nozzle can increase target force in a laboratory while keeping the thruster’s net force close to zero. Whether that can become a practical mission depends on distance, power, beam control, target behavior, spacecraft operations, and further testing. For now, it is a research result—not a deployed solution to orbital debris.
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