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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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