NASA evaluating "tractor beam" technologies
By Darren Quick
November 6, 2011
NASA is looking to turn another staple of science fiction to practical use by studying ways to make "tractor beams" a reality. While none of the technologies under the microscope will be able to transport anything the size of a modified YT-1300 Corellian freighter - at least in the short term - the researchers will examine if it is possible to trap and move planetary or atmospheric particles using laser light so they can be delivered to a robotic rover or orbiting spacecraft for analysis.
NASA says current extraterrestrial sample collection techniques, such as the aerogel used by the Stardust space probe to gather samples as it flew through the coma of comet Wild 2 or the drilling and scooping of samples by NASA's next Mars rover, have proven successful but are limited by high costs and limited range and sample rate.
"An optical-trapping system, on the other hand, could grab desired molecules from the upper atmosphere on an orbiting spacecraft or trap them from the ground or lower atmosphere from a lander," says Principal Investigator Paul Stysley. "In other words, they could continuously and remotely capture particles over a longer period of time, which would enhance science goals and reduce mission risk."
Approaches being studied
The first approach the team will study is dubbed the optical vortex or "optical tweezers" method. This involves the use of two counter-propagating beams of light that create a ring-like geometry that confines particles to the dark core of the overlapping beams. By heating the air around the trapped particle by alternately strengthening or weakening the intensity of one of the light beams, the particle can be made to move along the ring's center. Although this technique has been demonstrated in the laboratory, it requires the presence of an atmosphere to work.
Unlike the optical vortex method, the second technique under examination relies solely on electromagnetic effects, giving it the advantage of being able to operate in a space vacuum. Testing has shown that using optical solenoid beams, whose intensity peaks spiral around the axis of propagation, it is possible to exert a force that traps and drives particles in the opposite direction of the source of the light beam. The researchers say this method would be ideal for studying the composition of materials on an airless planetary moon, for example.
The third and final approach being considered exists only on paper and has never been demonstrated in a laboratory. It involves the use of a Bessel beam - which does not diffract or spread out as it propagates, unlike normal laser beams that spread out after being focused down to a small point. When seen straight on, Bessel beams appear with rings of light surrounding a central dot, much like ripples surrounding a pebble dropped in a pond. Although creating a true Bessel beam would require an infinite amount of energy, reasonably good approximations can be made that exhibit little or no diffraction over a limited distance. Theoretically, a Bessel beam could induce electric and magnetic fields in the path of an object and the spray of light scattered forward by these fields could pull the object backward, against the movement of the beam itself.
The team consisting of Stysley, Barry Coyle and Demetrios Poulios from NASA's Goddard Space Flight Center in Greenbelt, Maryland, will study the state of the technology to determine which of these three techniques would be best suited to sample collection after being awarded US$100,000 in Phase-1 funding from the NASA Office of the Chief Technologist (OCT). The funding is through the OCT's recently re-established NASA Innovative Advanced Concepts (NIAC) program that is designed to spur the development of "revolutionary" space technologies.
"We want to make sure we thoroughly understand these methods. We have hope that one of these will work for our purposes," said Coyle. "Once we select a technique, we will be in position to then formulate a possible system" and compete for additional NIAC funding to advance the technology to the next level of development.
The video below shows how a hypothetical future mission might eventually employ "tractor beam" technology.
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