Low Earth orbit is getting uncomfortably full of junk, a mix of satellites that have ceased operating and pieces that have fallen off past missions. A possible solution, a “hunter-killer” satellite that will blast junk with plasma, has been demonstrated in the lab.
The US Department of Defense is currently tracking 20,000 bits of space junk, and satellites sometimes have to take evasive action to avoid being hit. The great fear is collisions can shatter satellites into many pieces, creating an avalanche. Finding a way to remove most of what is up there is becoming urgent.
A Japanese-Australian collaboration proposes creating a fleet of satellites, that will fire plasma beams at space debris to make items fall from their orbits. The challenge, they note in Scientific Reports, is that ejecting plasma in space pushes the plasma source in the opposite direction, taking it away from the object it is trying to deorbit before it can finish the job.
The authors' answer is to send out another jet of plasma in the opposite direction, maintaining balance in the force on the satellite. Professor Roderick Boswell of the Australian National University told IFLScience achieving this is “testing thermodynamics at the limit of its applicability.”
With this in mind, Boswell and co-authors designed a magnetic nozzle plasma thruster with two exits. Although yet to test it in space, the authors describe attaching the thruster to a pendulum, demonstrating its capacity to apply force to other objects through the plasma, while canceling out the forces on itself.
Boswell told IFLScience the satellite would operate on solar power, and probably use xenon gas as a propellant. “It would take a lot of xenon to stop a large item outright, but you don't need to do that,” he said. “All you need is to slow the junk down, which moves it into a lower orbit.” Once an orbit is low enough to encounter significant friction from the Earth's atmosphere, it will start to decay further until the object burns up.
The plasma-satellite idea is probably only suitable for reasonably large objects, such as dead satellites, Boswell added, as smaller pieces of junk would not justify the complex maneuvering required for close approach.
Many alternatives to tackle space junk have been proposed. “For most of them it is not clear it the idea will work at all, let alone if it will be the most effective solution,” Boswell said. “Lasers would be fun”, but lacking mass will have trouble applying “sufficient wallop to change [the target's] velocity."
Catching satellite's in nets, as was demonstrated recently looks spectacular, but is a single-use system, and still leaves the problem of how to bring the target down.