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 Nov. 1, 1999: Last year when
Science@NASA flew a weather balloon to the stratosphere for a
high altitude view of the Leonids, over one million people watched
the live webcast or saw the replay the next day at LeonidsLive.com.
While the video camera on the balloon captured images of blazing
fireballs, an aerogel collecting device may have captured bits
of comet Tempel-Tuttle -- the parent of the Leonid meteoroid
stream. Researchers are still poring over the
data.
Right: A short video segment showing
a Leonid fireball as seen from the stratosphere in 1998. It was
recorded by a digital video camera carried aloft by a 3m weather
balloon.
This year, with experts predicting an even bigger Leonid display,
the meteor balloonists are planning another flight. Liftoff is
scheduled for 0630 UT (0130 EST) on Thursday, November 18 from
the Marshall Space Flight Center. The balloon will carry a sensitive
low-light CCD video camera to monitor the shower from an altitude
of about 32 km (105,000 ft), far above any obscuring clouds or
bad weather. Web surfers can watch and listen to live transmissions
from the balloon at LeonidsLive.com between 0130 and 0430 EST,
on November 18th. Replays will be available after the flight.
"We're going to be carrying a more sensitive camera
than we did in 1998," said Ed Myszka, an engineer and radio
amateur who built the balloon payload, "so the images could
be even better than before. The payload this time around will
be similar to what we flew during the August
Perseid shower. One of the problems we encountered during
that flight was the balloon spinning. The camera was sweeping
across the sky pretty quickly, which made it hard to see faint
meteors. This time I've added ball bearing swivels to the lines
between the balloon and the payload package. That'll reduce spin
and make it easier to pick up meteors and fireballs
during the webcast."
An important addition to this year's payload is an INSPIRE
VLF radio receiver, which is sensitive to radio emissions
below 10 kHz. The very low frequency (VLF) radio band is filled
with exotic-sounding signals called spherics, tweeks and whistlers.
All three are impulsive bursts caused by distant lighting. "Spherics,"
which are caused by lightning strokes within a couple of thousand
kilometers of the receiver, sound like twigs snapping or bacon
sizzling on a grill. Tweeks and whistlers are caused by more
distant lightning, and sound like brief descending musical tones.
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Dennis Gallagher, a plasma physicist at the Marshall Space Flight
Center, thinks that the VLF receiver might also pick up natural
radio emissions from the Leonid meteors.
"Meteoroids produce an ionized trail as they plummet through
the atmosphere," explained Gallagher. "There's a low
density wake right behind the meteoroid. Because electrons are
more mobile than protons, they move in to fill the void faster.
That could set up plasma oscillations and trigger radio emissions."
Above: This time-frequency plot
(or dynamic spectrum) shows two whistlers, one at 9 minutes and
one at 12 minutes. They are caused by VLF radio emissions from
lightning strokes that travel long distances along magnetic field
lines. Other types of VLF radio emissions include tweeks, chorus,
and spherics. To learn more about the physics of these emissions,
click
here. To hear what they sound like, click
here.
The VLF receiver was donated to the Marshall Space Flight Center
for this and possible future flights by the Goddard
INSPIRE program. It's been christened the "Marina receiver"
after the newborn daughter of Flavio Gori, an Italian scientist
who first suggested flying the receiver.
Gallagher and his colleagues also plan to operate a Marina VLF
receiver at the launch site to provide a ground reference for
comparison with data collected from the stratosphere. During
the flight signals from the receiver will be converted to audio
sounds and transmitted along with images from the CCD video camera.
Web viewers at LeonidsLive.com will be treated to an unusual
combination of meteoritic sights and sounds.
The question of radio emissions from meteors is an intriquing
one, says Gallagher, and you don't need to send your receiver
to the stratosphere to listen in. Anyone with a VLF receiver
can monitor the Leonids on November 18 and Gallagher hopes that
INSPIRE participants across the USA will join in the effort.
The best way to collect data is to record the output of the receiver
on a two-track audio recorder. Record the VLF signal on one track
and a WWV time signal on the other. This way VLF pulses can be
correlated with the times of bright meteors seen from your observing
site. It's also a good idea to conduct at least one observing
session a few days before or a few days after the Leonids for
comparison. Details about the upcoming meteor shower may be found
at http://www.LeonidsLive.com.
Catch a falling star....
The video images and VLF sounds will be exciting, but the
most important part of the payload may be something else entirely.
The balloon will also carry aloft a special device designed to
capture actual Leonid meteoroids and return them to Earth.
 Meteoroids are typically smaller than a
grain of sand and much less dense. Although they are insubstantial,
they can create very bright "shooting stars" because
they travel at high speeds -- over 160,000 mph (72km/sec) for
the Leonids. How do you catch a fluffy, microscopic, 160,000
mph fast ball? Very carefully!
Right: This photo shows the payload
from the 1998 Leonids meteor balloon after it was recovered
from a briar patch in Chatsworth, Georgia on November 18,
1998.
The meteoroid capture device on the upcoming flight uses xerogel
(a close relative of aerogel)
and a variety of low density acrylic materials to capture flying
particles.
"It works like flypaper," explains NASA astronomer
Dr. John Horack. "We expose these materials to the air up
in the stratosphere while the meteor shower is underway. When
tiny particles strike the exposed xerogel, they stick. Then they
return to Earth along with the rest of the payload."
Aerogel
is the lightest known solid, and is considered the best substance
available for capturing fragile particles like comet dust without
damaging them. When a high-velocity dust particle hits the aerogel,
it buries itself in the material, creating a carrot-shaped track
up to 200 times its own length. Since aerogel is translucent
scientists can use these tracks to find the tiny particles. The
track is largest at the point of entry, and the particle can
be collected intact at the point of the cone.
 Left: This photo from a laboratory
experiment shows the cone-shaped track made by a tiny high-velocity
particle in aerogel. The captured particle is located just beyond
the narrow end of the cone. Photo credit NASA/JPL.
Experimenters agree that the chances of catching a Leonid meteoroid
are slim, but that it's worth a try. Costing less than $4,000,
the balloon mission could snag a tiny piece of comet Tempel-Tuttle
(the parent of the Leonid meteoroid stream) and enable scientists
to study material formed in the outer solar system.
The balloon is scheduled to lift off from the The Atmospheric
Research Facility (ARF) on the Marshall Space Flight Center (MSFC)
Campus in Huntsville, AL at 0130 EST on Thursday, November 18.
It will climb to a maximum altitude of approx. 105,000 ft in
200 minutes, followed by a 20-minute descent. Video and audio
from the payload will be downlinked as an amateur TV signal at
426.25 MHz transmit frequency (Cable Ready TV Channel 58). The
transmission should be detectable for several hundred miles around
the launch site for readers who would like to directly monitor
the flight. |
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