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Stardust: Close encounter of a cometary kind
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Stardust
encountered Comet Wild 2 on January 2, entrapping bits of
cometary dust in its tennis racket-like collector. At about
800 pounds, the relatively low-cost unmanned craft is solar
powered and flies close to Earth to get gravitational boosts
during its journey.
PHOTO COURTESY OF NASA/JPL-CALTECH |
Their unique exploration project just achieved its historic climax:
an encounter with Comet Wild 2 to retrieve cosmic dust from beyond
earth’s orbit and snap the best ever photos of a comet’s
surface. Although indications are that everything went without
a hitch on January 2, when the dramatic flyby occurred, project
engineer Peter Tsou (B.S.’65, M.S.’66 EECS) and principal
investigator Donald Brownlee (B.S.’65 EECS) won’t
really know until 2006—when the spacecraft returns safely
to earth—whether the mission was an unqualified success.
“This has been my dream for the last 20 years, so I guess
I’m pretty persistent,” says Tsou, who also serves
as deputy principal investigator on the project, known as Stardust.
It is the first NASA mission dedicated to exploring a comet and
the first U.S. mission designed to robotically obtain samples
from deep space and return them to Earth. It is also NASA’s
first sample return mission since the manned Apollo mission of
1971-72.
“Getting a sample from a comet is probably the best chance
we have of discovering what the solar system was like four-and-a-half
billion years ago,” Tsou says. “Comets develop far
from the sun and are in the deep freeze for so many years that
they have preserved a point in time when the solar system was
forming.”
Comets are bodies of dust and ice that accumulated at the edge
of the solar system, near Pluto. When they travel close to the
sun, the solar heat causes the ices to sublime and the solar wind
pushes the sublimed gases and dust to form a comet’s characteristic
tail, creating the spectacular shows Earthlings are so fond of.
Unlike the planets—which have been altered by weathering,
plate tectonics, and other factors—comets remain relatively
unchanged, preserving the most pristine state of the material
from which they originally formed.
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Peter
Tsou (right) specially designed the capture medium, a continuous
gradient density silica aerogel that is 99.8 percent air and
so lightweight it almost floats. Particles captured in the
aerogel (left) will leave a carrot-shaped trail and be embedded
at the tip. The flyby is expected to yield about one-thousandth
of an ounce of cometary dust for study.
PHOTOS COURTESY OF NASA/JPL-CALTECH |
Launched February 7, 1999, Stardust met Comet Wild 2 (pronounced
Vilt 2 after its Swiss discoverer) on January 2, 2004,
an estimated 242 million miles from Earth. The craft flew through
the coma—the cloud of dust and gas coming off the nucleus—picking
up tiny particles of cometary dust using a special capture medium
called aerogel. Meanwhile, a camera on board snapped 72 photographs
as the craft passed within 142 miles of the comet’s pockmarked
surface.
Although Tsou and Brownlee graduated from Berkeley Engineering
the same year, somehow they didn’t cross paths until they
teamed up on the Stardust project. Following his Berkeley degree,
Tsou got his Ph.D. at UCLA and has been a behind-the-scenes researcher
at Jet Propulsion Laboratories (JPL) for 29 years. Brownlee’s
path, which led to a Ph.D. in astronomy from the University of
Washington and worldwide renown as a cosmic dust expert, started
when the senior EECS major took an astronomy class on a lark.
He ended the semester by launching a high-altitude balloon-borne
cosmic dust collector from the Greek Theater.
“My engineering background has been a plus because most
astronomers don’t know a lot about engineering issues,”
says Brownlee. “A project like Stardust is primarily engineering:
nuts and bolts, electronics, project management, the whole ball
of wax.”
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Donald
Brownlee (left), now a world-famous astronomer, launched his
career in cosmic dust collection with his senior astronomy
project in 1964 (right). It was a collector flown below two
weather balloons to collect cosmic dust at 100,000 feet, launched
from the Greek Theater.
PHOTOS COURTESY OF NASA/JPL-CALTECH AND DONALD BROWNLEE |
The biggest challenge, Tsou and Brownlee agree, is working with
the hypervelocity speed of objects in space. The capture occurred
at 13,650 mph, about six times the speed of a high-powered rifle
bullet. The spacecraft had to be equipped with protective bumpers
and shields to protect it. Data beamed back after the flyby indicate
that the ship encountered an abundance of the comet dust it went
seeking. Stardust’s tennis racket–shaped collector
was expected to trap about 500 tiny particles (>15 mm), which
should yield enough material to keep many analysts occupied for
the next decade.
In returning to earth, scheduled for January 15, 2006, at Utah
Test and Training Range, the spacecraft must withstand loads up
to 100 times the force of gravity. By that time, Stardust will
have spent seven years in space and covered 3 billion miles at
an average speed of 48,000 mph.
The Stardust concept was born, Tsou says, when the Halley Intercept
Mission he was working on in 1981 was scrapped as too expensive
in an era of double-digit inflation. More than a decade later,
Stardust was made possible by NASA’s Discovery Program,
which maintains low project costs by keeping scientific objectives
highly focused, development timelines relatively short, and by
recruiting experts from industry, business, and academics to collaborate
on implementing the project for under $200 million.
For more details about the mission and images from the flyby,
see the Stardust Web site at http://stardust.jpl.nasa.gov.
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