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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-
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“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].
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Technics
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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.
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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.
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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