By Leonard David Senior Space Writer Space.Com
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An artist's rendering of Stardust with its Dust Collector
deployed, using Aerogel to capture interstellar grains.
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WASHINGTON --
Space probes using Earth to slingshot their way outward into the
solar system appear to have received an extra boost by a mysterious
force - perhaps an unknown component of gravity.
Scientists
hope to confirm the unusual effect as the Stardust spacecraft
whips by Earth this coming January.
Analysis by
radio scientists of the post-Earth flyby trajectories of three
spacecraft have shown each craft to have picked up an unexpected
increase in speed: The Galileo spacecraft in December 1990; the
Near Earth Asteroid Rendezvous (NEAR) probe in January 1998; and
the Saturn-bound Cassini spacecraft in August 1999.
The Galileo
spacecraft slipped by Earth a second time in December 1992. But
the vehicle dipped too close to Earth making the measurement of
any "flyby effect" unusable.
Doin’
the Doppler shift
"This
problem has been with us for about 10 years, and we haven’t
found a solution," said John Anderson, a senior research
scientist and member of the Stardust science team at the Jet Propulsion
Laboratory (JPL) in Pasadena, California.
"We’re
looking forward to the Stardust flyby. That would be our fourth
measurement of this anomalous effect," Anderson told SPACE.com.
Using JPL’s
Deep Space Network of radio telescopes, the velocity of Stardust
is measured by analyzing its Doppler shift. In this case, a change
in frequency or wavelength of sound due to the relative motion
between the emitting source, Stardust’s radio transmitter,
and ground receiving equipment.
Stardust is
expected to show a bump up in velocity as it flies by, Anderson
said. "We can’t find any source or any mechanism that
would do that," he said.
"Cassini,
NEAR, Galileo...they all show it. If it follows the pattern that
we’ve seen in the other three, it should be clearly measurable,"
Anderson said. "That’s why we’re so anxious to
get the Stardust data," he said.
X-band
rated
The Stardust
spacecraft will zoom past Earth on January 15, 2001, at the end
of its first elongated orbit of the Sun, said Donald Brownlee,
Stardust’s principal investigator of the University of Washington,
Seattle.
Launched in
February 1999, Stardust is on a long-and-winding road to comet
Wild-2. In 2004 the probe will snag cometary material, then return
the samples to Earth in 2006.
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