In science fiction movies, the spaceships of the good guys are often caught in the invisible tractor beam. But what was once just science fiction could soon become a reality. Scientists are developing a real tractor beam, called an electrostatic tug. This beam, however, wouldn’t suck helpless spaceships, but rather push space junk safely out of Earth‘s orbit.
More and more satellites in orbit
With the boom of the commercial space industry, the stakes are significantly high. It is predicted that the number of satellites in Earth’s orbit will increase exponentially. When this myriad of satellites eventually wears out, it will turn the space around Earth into a massive junkyard of debris. This could potentially crash into functioning spacecraft, plummet to Earth, pollute the atmosphere with metals, and obscure the view of the cosmos. Furthermore, if left unchecked, the problem of space junk could hinder the thriving space exploration sector.
The electrostatic tug could potentially alleviate this problem by safely moving debris away from Earth’s orbit, where it would drift harmlessly for eternity. Although the tug wouldn’t completely solve the issue of space junk, the concept presents numerous advantages.
A prototype could cost millions, and a full-scale operational version even more. But if the financial hurdles can be overcome, the tractor beam could be operational within a decade. “The science is practically there, but the funding isn’t” declared project researcher Kaylee Champion, a doctoral student in the Department of Aerospace Engineering Sciences at the University of Colorado.
How the tractor beam works
Tractor beams depicted in Star Trek suck spaceships through artificial gravity or an ambiguous energy field. Such technology is likely unattainable. But the concept inspired Hanspeter Schaub, a professor of aerospace engineering, to conceptualize a more realistic version.
Schaub first had the idea after the first major satellite collision in 2009. In that case, an active communications satellite, Iridium 33, collided with a defunct Russian military spacecraft, Kosmos 2251. Schaub wanted to avoid such an event from happening again. So, he realized it was possible to move spacecraft using the attraction between positively and negatively charged objects.
The electrostatic tug would use a spacecraft (servicer) equipped with an electron gun. This would shoot negatively charged electrons onto a dead target satellite. The electrons would give the target a negative charge, leaving the servicer with a positive charge. The electrostatic attraction between the two would keep them locked together despite being separated by 20 to 30 meters of empty space. Once the servicer and the target are connected, the servicer would be able to pull the target out of orbit without touching it. Ideally, the defunct satellite would be dragged into a more distant graveyard orbit from Earth.
Advantages and limitations of the technology
With our current technology, the electrostatic attraction between the two spacecraft would be very weak. This would entail very slow maneuvers to get as close as possible to the vehicle to be towed. It could take more than a month to completely move a single satellite out of orbit. If the satellites were moved one at a time, a single electrostatic tug would not be able to keep up with the satellites that cease functioning.
“This is very different from the tractor beams in the movies, which are inevitable and quickly drag their prey. This is the main difference between science fiction and reality” said project researcher Julian Hammerl. But the electrostatic tug has an undeniable advantage over other methods. It operates without any direct contact.
“There are these large spaceships, the size of a school bus, that rotate very quickly” Hammerl said. “If you shoot a harpoon, use a large net, or try to dock with them, physical contact can damage the spacecraft. So, you’re just exacerbating the problem”.
Researchers are currently working on a series of experiments in their Electrostatic Charge and Plasma Interactions with Spacecraft laboratory (ECLIPS). Once the team is ready, the last and most challenging hurdle will be securing funding for the first mission.
Most of the mission’s cost would come from the construction and launch of the servicer. Researchers ideally want to launch two satellites for initial tests, a servicer, and a target. This would allow for greater control over the tests, but it would also double the costs. If they somehow manage the funding, a prototype of the tractor beam could be operational in about 10 years.
Although tractor beams may seem like an unrealizable dream, experts are optimistic about the technology. “Their technology is still in its early stages” said John Crassidis, an aerospace scientist. “But I’m quite confident it will work.”