A team of researchers from Tohoku University in Japan and the Australian National University has come up with a plasma beam shooting satellite that could push space debris out of orbit. Mounted on a satellite, the two-way facing beam is produced by a bespoke ion thruster that uses its discharge to decelerate debris so it can burn up in the Earth's atmosphere.

There are over 7,000 pieces of man-made debris orbiting the Earth – most of its consisting of derelict satellites, spent boosters and general rubbish – all the way down to paint flecks. With each one having the potential of causing a devastating collision, the job of cleaning up the orbital lanes around the Earth is a major concern. However, the field is still very much in its infancy, with engineers developing space sails, harpoons, nets and other devices to snare and deorbit debris.

Called the ion beam shepherd, the new device being investigated by a team of researchers led by Kazunori Takahashi of Tohoku University in Japan Tohoku University would see an unmanned hunter satellite match orbits with a piece of debris, then use the exhaust from its ion thruster to slow down the target until it burns up on re-entry into the atmosphere. In principle, this is as simple as cleaning dust off of a keyboard with a can of compressed air, but in practice, things are bit more complicated.

Schematic of a magnetic nozzle rf plasma thruster (helicon plasma thruster Tohoku University

Takahashi's team has calculated that it's feasible to build a thruster with sufficient power to decelerate debris, but then there's Newton's pesky law stating that for every action there is and equal and opposite reaction. So the problem is the thruster will push both the debris and the hunter satellite.

To prevent this, two thrusters could be mounted on the hunter with one pointing in the opposite direction, but this would mean duplicating a bewildering number of systems, making the satellite much more complex and heavy. On top of that, balancing the output of the two thrusters so the hunter remains at a constant distance from the debris target would be very tricky.

Instead, the team a new bi-directional thruster that acts a bit like a recoilless rifle, which is a gun barrel open at both ends. Instead of being stopped by the conventional breech plate, the expanding gases from the propellant charge blow out the back while the projectile flies out the front. The slug of gas acts as its own breech plate and the bi-directional discharge balances the forces, so there's little or no recoil.

A concept for space debris removal by bi-directional momentum ejection from a satellite Tohoku University

The same thing happens with the ion beam shepherd. The thruster is open at both ends and as the ion beam is accelerated out the front, an identical beam goes out the back, keeping the hunter satellite in one place. By proper adjustment, the satellite can maintain a constant distance from the target as it switches between acceleration, deceleration, and debris removal modes.

"The helicon plasma thruster is an electrode-less system, which allows it to undertake long operations performed at a high-power level," says research team leader Kazunori Takahashi. "This discovery is considerably different to existing solutions and will make a substantial contribution to future sustainable human activity in space."

The ion beam shepherd has been tested under controlled laboratory conditions, but there is no word as to if or when it will be developed for practical testing.

The results were published in Scientific Reports.

Source: Tohoku University