A NASA
probe blasted into space early Thursday, kicking off an unprecedented mission to
explore the two largest asteroids in the solar system.
Riding atop
a Delta 2 rocket, NASA's
Dawn spacecraft launched toward the asteroids Vesta and Ceres at 7:34 a.m.
EDT (1134 GMT) from Cape Canaveral Air Force Station in Cape Canaveral, Fla.
"In my
view, we're going to be visiting some of the last unexplored worlds in the
solar system," said Marc Rayman, Dawn director of system engineering at NASA's
Jet Propulsion Laboratory (JPL) in Pasadena, Calif.
Dawn's
eight-year mission will carry the 2,685-pound (1,212-kilogram) probe across
three billion miles (4.9 billion kilometers) on NASA's first sortie deep into
the asteroid belt, a ring of space rocks that circles the Sun between the
orbits of Mars and Jupiter.
By visiting
the bright, rocky asteroid Vesta and the large, icy Ceres, researchers hope
Dawn will shed new light on the formation of planets and solar system's early
evolution.
Aside from
a wayward ship, which delayed today's launch by 14 minutes when it encroached
into the Atlantis Ocean splashdown zone for segments of Dawn's rocket, the
liftoff went as planned, NASA launch director Omar Baez said.
Long
journey ahead
Dawn is
expected to rendezvous and orbit the 330-mile (530-kilometer) wide Vesta
between August 2011 and May 2012, then move on to Texas-sized Ceres by February
2015. With its spherical shape and 585-mile (942-kilometer) diameter, Ceres is
so large it is also considered a dwarf planet.
"It will be
the first mission to journey to, and orbit around, two celestial bodies, and
the first to visit a dwarf planet," said Dawn program manager Jim Adams, at
NASA's Washington, D.C. headquarters, of the asteroid-bound flight.
Dawn
carries an optical camera, gamma ray and neutron detector and a mapping
spectrometer to
study Vesta and Ceres. Some of those tools will get a trial run during a
planned Mars flyby in 2009, researchers said.
To power
those instruments, the spacecraft is also equipped with the most powerful solar
arrays ever launched into deep space.
With a
wingspan of nearly 65 feet (almost 20 meters), or about the distance from the
pitcher's mound to home plate on a baseball field, the arrays will generate
more than 10 kilowatts near Earth, though that output will decrease as the
spacecraft moves further from the Sun.
NASA
officials set Dawn's mission cost at $357.5 million excluding the cost of its
Delta 2 rocket, according to a September update. In a July briefing, Dawn
researchers said the asteroid-bound flight could cost a total of $449 million
and incur an extra $25 million in overhead due to launch delays.
Attempts to
launch the mission in July were thwarted first by poor weather and rocket
glitches, then by difficulties arranging ship and aircraft tracking equipment
in time for liftoff. NASA also canceled the mission outright in March 2006,
only to reinstate the expedition a few weeks later.
"It has
been quite an emotional rollercoaster," Chris Russell, Dawn's principal
investigator at the University of California, Los Angeles, said of the mission.
"And part of the emotional rollercoaster is the gratitude that we have for all
of the people that defended Dawn in those times."
An
asteroid trek on ion power
Built by Virginia-based
Orbital Sciences, the Dawn spacecraft has been touted as the Prius of space
probes because of the uncanny fuel efficiency of its three-engine ion drive.
Dawn
carries 937 pounds (425 kilograms) of Xenon gas, to which it gives an electric
charge to create ions that are then catapulted out of its engines at nearly
90,000 miles per hour (144,840 kph). Over time, the ion push builds up, and
allows Dawn to change its flight path to first rendezvous, then orbit, multiple
targets like Vesta and Ceres without requiring massive amounts of conventional
rocket fuel.
"The first
time I ever heard of ion propulsion was in a 'Star Trek' episode," said Rayman,
adding that such engines are also touted to propel the TIE fighters – or Twin
Ion Engine - of "Star
Wars" fame. "Dawn does the TIE fighter one better because it has three ion
engines."
While it
will take Dawn four days to go from zero to 60 miles per hour (96 kph), the
probe will gradually pick up speed as it fires its ion drive nonstop for the
next six years, NASA has said, adding that the mission is the agency's first
operational science expedition powered by ion propulsion.
"That would
make it the longest powered flight in space history," said Keyur Patel, NASA's
Dawn project manager at JPL, just before liftoff.
Each of the
three ion engines weighs about 20 pounds (nine kilograms) and is about the size
of a basketball.
"From
such a little engine you can get this blue beam of rocket exhaust that shoots
out at 89,000 miles per hour," Patel said before launch day. "It is a
remarkable system."
NASA
will hold a post-launch briefing on Dawn's asteroid-bound mission at 1:00 p.m.
EDT (1700 GMT) on NASA TV.
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