Tractor beams trap and move objects using laser light. If you've seen one in action you were probably watching Star Trek or a science fiction movie.
However, laser-based trapping of particles isn't fanciful or beyond technological know-how says Paul Stysley, one of three NASA scientists who recently won funding to study methods for corralling particles and transporting them via laser light to a robotic rover or orbiting spacecraft for analysis.
"The original thought was that we could use tractor beams for cleaning up orbital debris," Stysley said. "But to pull something that huge would be almost impossible -- at least now. That's when it bubbled up that perhaps we could use the same approach for sample collection."
Current sample-collection techniques work but are expensive and have a limited range and sample rate. Tractor beams, reason the scientists, could grab desired molecules from the upper atmosphere on an orbiting spacecraft or trap them from the ground or lower atmosphere from a lander.
"They could continuously and remotely capture particles over a longer period of time, which would enhance science goals and reduce mission risk," Stysley said.
The scientists have identified three different approaches for transporting particles, as well as single molecules, viruses, ribonucleic acid, and fully functioning cells, using the power of light. They'll pursue the technique which they determine is most technologically feasible:
- The optical vortex or "optical tweezers" method -- This method involves two counter-propagating beams of light that form a ring-like geometry which confines particles to the dark core of the overlapping beams. By alternately strengthening or weakening the intensity of one of the light beams -- in effect heating the air around the trapped particle -- researchers at Australian National University have shown in laboratory testing that they can move the particle along the ring's center. This technique, however, requires the presence of an atmosphere.
- Optical solenoid beams -- These light beams' intensity peaks spiral around the axis of propagation. Testing has shown that the approach can trap and exert a force that drives particles in the opposite direction of the light-beam source. In other words, the particulate matter is pulled back along the entire beam of light. Unlike the optical vortex method, this technique relies solely on electromagnetic effects and could operate in a space vacuum, making it ideal for studying the composition of materials on one of the airless planetary moons, for example.
- Bessel beams -- This technique exists only on paper and has never been demonstrated in the laboratory. Normal laser beams when shined against a wall appear as a small point, but with Bessel beams, rings of light surround the central dot. In other words, when seen straight on, the Bessel beam looks like the ripples surrounding a pebble dropped in a pond. According to theory, the laser beam could induce electric and magnetic fields in the path of an object. The spray of light scattered forward by these fields could pull the object backward, against the movement of the beam itself.
"We want to make sure we thoroughly understand these methods. We have hope that one of these will work for our purposes," said team member Barry Coyle at NASA's Goddard Space Flight Center. "Once we select a technique, we will be in position to then formulate a possible system" and compete for additional [NASA Innovative Advanced Concepts] NIAC funding to advance the technology to the next level of development."
"We're at the starting gate on this," Coyle added. "This is a new application that no one has claimed yet."