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(meteorobs) The Leonid Sample Return Mission


The Leonid Sample Return Mission
NASA scientists will try to capture and return a Leonid meteoroid
http://science.nasadot gov/newhome/headlines/ast16nov98_3.htm

November 16, 1998: High above the clouds on November 17th a NASA weather
balloon will lie in wait for the Leonid meteors. The goal: to capture a
meteoroid and return it to Earth intact. "The chances of success are small,
probably less than 10%", says Dr. David Noever, the project leader at NASA's
Marshall Space Flight Center, "but of course the payoff is rather huge." One
of the goals of the experiment is to see if the "Stuff of Life" -- organic
compounds and other molecules -- are present in the debris of comet
Tempel-Tuttle, the source of the Leonid meteoroids.

Amino acids and other organic molecules necessary for life as we know it on
Earth are thought to be common in meteorites and comets. While life probably
doesn't thrive inside comets, the compounds they carry might have
contributed to the genesis of life on Earth billions of years ago.
Scientists would like to know whether the comet, which passed Earth just
last January, contains organic compounds, and if organic molecules are
created when a Leonid meteor burns up in Earth's atmosphere.

To answer these questions researchers from the Marshall Space Flight Center
hope to capture a piece of the comet Tempel-Tuttle. Tuesday's meteor storm
is like "room service for science", says Dr. David Noever, a member of the
Astrobiology Institute. "Instead of us going to the comet, it's coming to
us."

Scientists will use a particle collector made of aerogel carried aloft on a
helium-filled weather balloon. Weather permitting, the balloon is scheduled
for launch from the Marshall Space Flight Center at 2 am Central Standard
Time on November 17th . The payload will include a meteoroid collection
device, and a CCD video camera. The balloon will spend up to 4 hours aloft
and reach a maximum altitude of 100,000 ft.

High above the clouds and far away from city lights the view could be
spectacular. Live video from the flight will be available to the public at
Leonids Live! (http://www.leonidslive.com) in RealVideo format beginning
approximately 0800 UT November 17th (0200 CST). Video and images from the
NASA's East Asia plane flights will also be posted at that web site.

Aerogel is the lightest known solid, and is considered the best substance
available for capturing fragile particles from a comet 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.

The sample collector on tomorrow's balloon mission will consist of
twenty-four 1" diameter circular wells of aerogel films clustered in a 6"x4"
payload. The aerogel has a mean density around 0.08 g/cc and is
semitransparent. The total weight is less than a few ounces (mainly
container and structural supports, not aerogel), so it should have a
negligible effect on the flight of the balloon.

According to Dr. David Noever, "The drawback I see is that we are forced to
catch everything from ground to 100,000 feet, mainly because we do not have
time to fashion a remote control door that opens or closes to expose the
capture media. This experiment should be considered an engineering test, and
we'll make improvements prior to the 1999 Leonid shower."

Prelude to Stardust

The Leonids Return Mission is an interesting prelude to another NASA mission
with possible connections to Astrobiology: the Stardust Mission. Stardust is
a spacecraft, scheduled for launch in early 1999, designed to collect and
return to Earth particles flying off the nucleus of Comet Wild-2 in January
2004. It will also bring back samples of interstellar dust including the
recently discovered dust streaming into the solar system from other stars.
The spacecraft will count the comet particles striking the spacecraft, and
produce real-time analyses of the composition of the material coming off the
comet. Like the Leonids balloon flight, Stardust will use an aerogel-based
collector to capture bits of the comet.

"The transparency of aerogel is critical to the success of Stardust; tracing
particle tracks by eye or microscope requires a reasonably clear material",
explained David Noever. Aerogel made on earth is not perfectly transparent
because of irregularities in the pores which permeate the substance (aerogel
is 99% empty space). There is some evidence that aerogels manufactured in
low gravity are much clearer, and an experiment was just conducted on space
shuttle mission STS-95 to test the idea.

"Space-manufactured aerogels could significantly improve our ability to
capture comet particles," commented David Noever. "Using centrifuges we can
make aerogel with a density gradient: low density on one side for low damage
particle capture, backed by a denser section to insure nothing escapes out
the other side. This kind of thin-to-dense aerogel is unique in this dust
capture business and may be unique to the way we make aerogel in space. It's
an open question at the moment."

When Stardust swings by Earth in January 2006, the aerogel samples encased
in a reentry capsule will be jettisoned and parachute to a pre-selected site
in the Utah desert.
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