NASA studying ways to make 'tractor beams' a reality

ScienceDaily (Nov. 3, 2011) — Tractor beams -- the ability to trap and move objects using laser light -- are the stuff of science fiction, but a team of NASA scientists has won funding to study the concept for remotely capturing planetary or atmospheric particles and delivering them to a robotic rover or orbiting spacecraft for analysis.

The NASA Office of the Chief Technologist (OCT) has awarded Principal Investigator Paul Stysley and team members Demetrios Poulios and Barry Coyle at NASA's Goddard Space Flight Center in Greenbelt, Md., $100,000 to study three experimental methods for corralling particles and transporting them via laser light to an instrument -- akin to a vacuum using suction to collect and transport dirt to a canister or bag. Once delivered, an instrument would then characterize their composition.

"Though a mainstay in science fiction, and Star Trek in particular, laser-based trapping isn't fanciful or beyond current technological know-how," Stysley said. The team has identified three different approaches for transporting particles, as well as single molecules, viruses, ribonucleic acid, and fully functioning cells, using the power of light.

"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."

With the Phase-1 funding from OCT's recently reestablished NASA Innovative Advanced Concepts (NIAC) program designed to spur the development of "revolutionary" space technologies, the team will study the state of the technology to determine which of the three techniques would apply best to sample collection. OCT received hundreds of proposals, ultimately selecting only 30 for initial funding.

Replace Current Sample-Collection Methods

Currently, NASA uses a variety of techniques to collect extraterrestrial samples. With Stardust, a space probe launched in 1999, the Agency used aerogel to gather samples as it flew through the coma of comet Wild 2. A capsule returned the samples in 2006. NASA's next rover to Mars, Curiosity, will drill and scoop samples from the Martian surface and then carry out detailed analyses of the materials with one of the rover's many onboard instruments, including the Goddard-built Sample Analysis at Mars instrument suite.

"These techniques have proven to be largely successful, but they are limited by high costs and limited range and sample rate," Stysley said. "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. 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."

Team to Study Three Approaches

One experimental approach the team plans to study -- the optical vortex or "optical tweezers" method -- involves the use of two counter-propagating beams of light. The resulting ring-like geometry 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 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.

Another technique employs optical solenoid beams -- those whose 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.

The third technique exists only on paper and has never been demonstrated in the laboratory, Poulios said. It involves the use of a Bessel beam. Normal laser beams when shined against a wall appear as a small point. With Bessel beams, however, 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," Coyle said. "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. "We're at the starting gate on this," Coyle added. "This is a new application that no one has claimed yet."

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NASA studying ways to make 'tractor beams' a reality

ScienceDaily (Nov. 3, 2011) — Tractor beams -- the ability to trap and move objects using laser light -- are the stuff of science fiction, but a team of NASA scientists has won funding to study the concept for remotely capturing planetary or atmospheric particles and delivering them to a robotic rover or orbiting spacecraft for analysis.

The NASA Office of the Chief Technologist (OCT) has awarded Principal Investigator Paul Stysley and team members Demetrios Poulios and Barry Coyle at NASA's Goddard Space Flight Center in Greenbelt, Md., $100,000 to study three experimental methods for corralling particles and transporting them via laser light to an instrument -- akin to a vacuum using suction to collect and transport dirt to a canister or bag. Once delivered, an instrument would then characterize their composition.

"Though a mainstay in science fiction, and Star Trek in particular, laser-based trapping isn't fanciful or beyond current technological know-how," Stysley said. The team has identified three different approaches for transporting particles, as well as single molecules, viruses, ribonucleic acid, and fully functioning cells, using the power of light.

"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."

With the Phase-1 funding from OCT's recently reestablished NASA Innovative Advanced Concepts (NIAC) program designed to spur the development of "revolutionary" space technologies, the team will study the state of the technology to determine which of the three techniques would apply best to sample collection. OCT received hundreds of proposals, ultimately selecting only 30 for initial funding.

Replace Current Sample-Collection Methods

Currently, NASA uses a variety of techniques to collect extraterrestrial samples. With Stardust, a space probe launched in 1999, the Agency used aerogel to gather samples as it flew through the coma of comet Wild 2. A capsule returned the samples in 2006. NASA's next rover to Mars, Curiosity, will drill and scoop samples from the Martian surface and then carry out detailed analyses of the materials with one of the rover's many onboard instruments, including the Goddard-built Sample Analysis at Mars instrument suite.

"These techniques have proven to be largely successful, but they are limited by high costs and limited range and sample rate," Stysley said. "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. 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."

Team to Study Three Approaches

One experimental approach the team plans to study -- the optical vortex or "optical tweezers" method -- involves the use of two counter-propagating beams of light. The resulting ring-like geometry 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 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.

Another technique employs optical solenoid beams -- those whose 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.

The third technique exists only on paper and has never been demonstrated in the laboratory, Poulios said. It involves the use of a Bessel beam. Normal laser beams when shined against a wall appear as a small point. With Bessel beams, however, 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," Coyle said. "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. "We're at the starting gate on this," Coyle added. "This is a new application that no one has claimed yet."

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Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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Crab pulsar beams most energetic gamma rays ever detected from a pulsar

ScienceDaily (Oct. 7, 2011) — Astrophysicists have detected pulsed gamma-ray emission from the Crab pulsar at energies far beyond what current theoretical models of pulsars can explain.

With energies exceeding 100 billion electron-volts (100 GeV), the surprising gamma-ray pulses were detected by the VERITAS telescope array at the Whipple Observatory in Arizona and reported by an international team of scientists in a paper in the October 7 issue of Science. Corresponding author Nepomuk Otte, a postdoctoral researcher at the University of California, Santa Cruz, said that some researchers had told him he was crazy to even look for pulsar emission in this energy realm.

"It turns out that being persistent and stubborn helps," Otte said. "These results put new constraints on the mechanism for how the gamma-ray emission is generated."

Otte, Andrew McCann of McGill University in Montreal, and Martin Schroedter of the Smithsonian Astrophysical Observatory performed most of the analytic work for the study, which involved nearly 100 scientists in the VERITAS collaboration. VERITAS spokesperson Rene Ong, professor of physics and astronomy at UCLA, credited Otte as the leading advocate for using the powerful gamma-ray observatory to study the Crab pulsar.

"To me it's a real triumph of the experimental approach, not going along with the flow and making assumptions, but just observing to see what there is. And lo and behold, we see something different than what everybody expected," Ong said.

The Crab pulsar is a rapidly spinning neutron star, the collapsed core of a massive star that exploded in a spectacular supernova in the year 1054, leaving behind the brilliant Crab Nebula, with the pulsar at its heart. It is one of the most intensively studied objects in the sky. Rotating about 30 times a second, the pulsar has an intense, co-rotating magnetic field from which it emits beams of radiation. The beams sweep around like a lighthouse beacon because they are not aligned with the star's rotation axis. So although the beams are steady, they are detected on Earth as rapid pulses of radiation.

Scientists have long agreed on a general picture of what causes pulsar emission. Electromagnetic forces created by the star's rapidly rotating magnetic field accelerate charged particles to near the speed of light, producing radiation over a broad spectrum. But the details remain a mystery.

"After many years of observations and results from the Crab, we thought we had an understanding of how it worked, and the models predicted an exponential decay of the emission spectrum above around 10 GeV. So it came as a real surprise when we found pulsed gamma-ray emission at energies above 100 GeV," said coauthor David Williams, adjunct professor of physics at UC Santa Cruz and a member of the VERITAS collaboration.

Prior to these new results, a phenomenon known as curvature radiation was the leading explanation for the Crab's pulsed gamma-ray emission. Curvature radiation is produced when a high-energy charged particle moves along a curved magnetic field. But according to Otte, this mechanism cannot account for gamma rays with energies above 100 GeV.

"The conventional wisdom was that the dominant mechanism is curvature radiation. But the VERITAS results have shown that there must be a different mechanism at work," Otte said. "Curvature radiation can explain the lower-energy emission, but we really don't know what causes the very high-energy emission."

One possible scenario may be a process known as inverse Compton scattering, which involves energy transfer from charged particles to photons. "That seems to be a more likely scenario now, but we still don't know the details of how this works," Otte said. It is also not clear whether one mechanism dominates at all gamma-ray energies, or if curvature radiation dominates at lower energies and something like inverse Compton scattering dominates at higher energies.

According to Ong, researchers will need to characterize the very high-energy gamma-ray emission in much greater detail in order to gain more insight into the mechanisms behind it. "We need to take more measurements and get the exact shape of the spectrum at these very high energies," he said.

The VERITAS observations open up a new avenue for testing Einstein's theory of special relativity, which says that the speed of light is a universal constant. One of the predictions of a quantum theory of gravity, which emerges from efforts to reconcile quantum mechanics and general relativity, is that the speed of light actually may have a small dependence on the energy of the photon. This would be a violation of "Lorentz invariance," which is at the core of special relativity, but it might be detectable in the VERITAS data, Otte said. Photons with a range of energies are emitted by the pulsar at the same time. If photons with different energies travel at different speeds, the effect would manifest itself as a slight shift in the position of the pulses at different energies.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California - Santa Cruz. The original article was written by Tim Stephens.

Journal Reference:

The VERITAS Collaboration et al. Detection of Pulsed Gamma Rays Above 100 GeV from the Crab Pulsar. Science, October 7, 2011 DOI: 10.1126/science.1208192

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