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Featured in science fiction staples such as “Star Wars” and “Star Trek,” tractor beams are a force field-like device used to capture and move large objects at great distances. But this fictional technology may soon find its way into the real world.
A NASA team, according to a recent statement, received funding to develop tractor beams, which in this case are described as laser light beams that can move or trap objects.
Unlike in the movies, however, these tractor beams will not be able to reel in massive spaceships like the “Millenium Falcon,” but will instead focus on much smaller objects—dust particles floating through space, molecules, or even cells.
A practical application for the beams would be to place them on rovers, probes, or orbiting spacecraft, allowing for the easy collection of small objects. The rovers could then sample different layers of a planet’s atmosphere or sample a piece of an asteroid careening through space.
A team of scientists recently devised several different approaches in using the light beams to transport small particles including viruses, single molecules, ribonucleic acid, and entire cells.
“The original thought was that we could use tractor beams for cleaning up orbital debris,” said Paul Stysley, a researcher working on the NASA tractor beam project. “But to pull something that huge would be almost impossible—at least now,” adding that a technology that would move smaller objects would be much more practical.
In the past, NASA has used aerogel, an extremely low-density solid substance, to drill and capture samples from comets, as well as from the surface of Mars. But researchers don’t favor this technique, due to its high-cost and limited range of operation. Scientists are now looking at a tractor beam trapping method that would have a longer range and work over a longer period of time.
NASA wants to test a method dubbed “optical tweezers” that uses two alternately strengthening and weakening counter-propagating beams of light. By changing the intensity of the two beams, the air around a desired particle is heated, causing it to move. But the technique suffers from a major drawback— without air or atmosphere it will not work in space.
Another method, according to Michael Schirber in a recent Physics journal article, is focusing several beams so light mainly scatters “where the object’s shadow would normally be.”
A strategy to manipulate small objects, he writes, “is to stimulate a small object with light in such a way that it re-radiates the light mostly in the forward direction.”
“The object—in order to compensate the change in the light’s momentum—will be continuously drawn back towards the light source,” Schirber notes. The method would involve a random cluster of small spheres and beams with differing phase and polarization.
The most experimental method, which has never been tested and only exists in theory, involves the use of a Bessel beam, which differs from a normal laser beam in that it has rings of light surrounding the central ray. When directed on a wall, the beam looks like ripples encircling a stone dropped in water.
“According to theory, the laser beam could induce electric and magnetic fields in the path of an object,” NASA said. “The spray of light scattered forward by these fields could pull the object backward, against the movement of the beam itself.”