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Technics Brief notes about the world of science and technology at Southwest Research Institute Low-profile direction finding antenna set for ground vehicles The ability to identify and locate enemy forces from a single moving vehicle is a challenging yet potentially life-saving capability for today’s warfighters. Southwest Research Institute engineers designed the AVM-375 low-profile antenna set to overcome the challenges of identifying and locating the source of communications signals from a vehiclemounted direction finding system on the move. As part of a Transportable Direction Finding (TDF) equipment series, this antenna set consists of four specially designed antennas distributed around the body of the vehicle to reduce the visible signature of the array. “Most DF antennas are mounted on an extended mast to avoid signal perturbations associated with rooftop clutter; however, this creates a more obvious target for enemy threats and limits vehicle mobility,” said Patrick Siemsen, a principal engineer in SwRI’s Signal Exploitation and Geolocation Division. “The AVM-375 improves mission stealth and vehicle mobility while providing geolocation of enemy forces from a single moving platform. Multiple platforms can be networked to provide enhanced DF and geolocation.” The antenna set provides real-time, 360-degree direction finding across two frequency bands, covering 120 MHz to 3 GHz. Many famous comets originally formed in other solar systems Many of the most well-known comets, including Halley, Hale-Bopp and, most recently, McNaught, may have been born in orbit around other stars, according to a new theory by an international team of astronomers led by a scientist from Southwest Research Institute (SwRI) in Boulder, Colo. Dr. Hal Levison (SwRI), Dr. Martin Duncan (Queen’s University, Kingston, Canada), Dr. Ramon Brasser (Observatoire de la Côte d’Azur, France) and Dr. David Kaufmann (SwRI) used computer simulations to show that the Sun may have captured small icy bodies from its sibling stars while it was in its birth star cluster, thereby creating a reservoir for observed comets. While the Sun currently has no companion stars, it is believed to have formed in a cluster containing hundreds of closely packed stars that were embed- D017574 “The direction finding data from the system are highly accurate,” Siemsen said. “The DF error is typically less than five degrees across the VHF and UHF frequency bands.” SwRI’s mobile DF processor and a unique algorithm assemble and process data from the distributed arrays. “Our state-of-the-art processor is compact, weighing about 10 pounds and consuming less than 30 watts of power,” Siemsen said. “The brick-sized package offers wideband functionality, rapid frequency scanning operations and DF of simultaneous signals. Multiple operator displays and interfaces can be run from a single processor.” Contact Siemsen at (210) 522-2995 or [email protected]. ded in a dense cloud of gas. During this time, each star formed a large number of small icy bodies (comets) in a disk from which planets formed. Most of these comets were gravitationally slung out of these prenatal planetary systems by the newly forming giant planets, becoming tiny, freefloating members of the cluster. The Sun’s cluster came to a violent end, however, when its gas was blown out by the hottest young stars. These new models show that the Sun then gravitationally captured a large cloud of comets as the cluster dispersed. “When it was young, the Sun shared a lot of spit with its siblings, and we can see that stuff today,” said lead author Levison. “The process of capture is surprisingly efficient and leads to the exciting possibility that the cloud contains a potpourri that samples material from a large number of stellar siblings of the Sun,” said co-author Duncan. Evidence for the team’s scenario comes from the roughly spherical cloud Technology Today • Summer 2010 of comets, known as the Oort cloud, that surrounds the Sun, extending halfway to the nearest star. It has been commonly assumed this cloud formed from the Sun’s proto-planetary disk. However, because detailed models show that comets from the solar system produce a much more anemic cloud than observed, another source is required. The article, “Capture of the Sun’s Oort Cloud from Stars in its Birth Cluster,” by Levison, Duncan, Brasser and Kaufmann, was published in the June 10 issue of Science Express. Funding for this research was provided by NASA’s Astrobiology Institute, Outer Planets Research and Origins of Solar Systems programs, the Natural Science and Engineering Research Council of Canada, and Germany’s Helmholtz Alliance. Contact Levison at (303) 546-9670 or [email protected]. 15 Technics D017559 Source of zodiac glow identified The eerie glow that straddles the nighttime zodiac in the eastern sky is no longer a mystery. First explained by Joshua Childrey in 1661 as sunlight scattered in our direction by dust particles in the solar system, the source of that dust was long debated. In a paper to appear in the April 20 issue of The Astrophysical Journal, David Nesvorny and Peter Jenniskens put the stake in asteroids. More than 85 percent of the dust, they conclude, originated from Jupiter Family comets, not asteroids. “This is the first fully dynamical model of the zodiacal cloud,” says planetary scientist Nesvorny of Southwest Research Institute in Boulder, Colo. “We find that the dust of asteroids is not stirred up enough over its lifetime to make the zodiacal dust cloud as thick as observed. Only the dust of short-period comets is scattered enough by Jupiter to do so.” This result confirms what meteor astronomer Jenniskens of the SETI Institute in Mountain View, Calif., had long suspected. An expert on meteor showers, he had noticed that most consist of dust moving in orbits similar to those of Jupiter Family comets, but without having active dust-oozing comets associated with them. Instead, Jenniskens discovered a dormant comet in the Quadrantid meteor shower in 2003 and has since identified a number of other such parent bodies. While most are inactive in their present orbit around the Sun, all have in common that they broke apart violently at some point in time in the past few thousand years, creating dust streams that now have migrated into Earth’s path. Nesvorny and Jenniskens, with the help of Harold Levison and William Bottke of Southwest Research Institute, David Vokrouhlicky of the Institute of Astron- omy at Charles University in Prague, and Matthieu Gounelle of the Natural History Museum in Paris, demonstrated that these comet disruptions can account for the observed thickness of the dust layer in the zodiacal cloud. This work was funded by the NASA Planetary Geology and Geophysics Program and the NASA Planetary Astronomy programs. Contact Nesvorny at (303) 546-9670 or [email protected]. SwRI researchers design and build gas bearing test rig Researchers at Southwest Research Institute (SwRI) have designed and built a 60,000 rpm gas bearing test rig to test the rotordynamic stability of gas bearings. The use of gas bearings has increased over the past several decades to include microturbines, air cycle machines and hermetically sealed compressors and turbines. Gas bearings have many advantages over traditional oil-lubricated or rollingelement bearings. Gas bearings typically have a longer life span, can accommodate high shaft speeds and can operate over a wide range of temperatures. And because there are no lubricants, there is no process contamination. Good rotordynamic stability is important for bearings to function properly. Gas bearings are challenging to design and require a fully coupled, thermo-elastic, hydrodynamic analysis to test their stability. However, few methods exist to verify bearing stability. “To assist industry in the design of gas bearing systems, we have designed a test rig that overcomes the many challenges of measuring rotordynamic coefficients,” said Dr. J. Jeffrey Moore, a program manager in SwRI’s Mechanical Engineering Division. 16 The bearing undergoing evaluation is supported by a cantilever bearing housing that prevents pitching of the bearing and allows the bearing to transmit forces to load cells mounted in the horizontal and vertical planes. D016686-3493 Two accelerometers mounted on the bearing housing measure the inertial forces of the bearing in the horizontal and vertical planes, and proximity probes measure the relative displacement. A patent on the concept is being pursued. Contact J. Jeffrey Moore at (210) 522-5812 or [email protected], or visit.www.rotordynamics.swri.org. Technology Today • Summer 2010