NASA is
hoping for a Monday liftoff for the Dawn spacecraft, a probe bound to visit the
two largest asteroids in the solar system.
Dawn is now
set to ride a United Launch Alliance Delta 2 rocket into space July 9 at 3:56
p.m. EDT (1956 GMT) after
new issues scrapped plans
for a Sunday liftoff.
Mechanical
difficulties with a telemetry relay aircraft, combined with the unavailability of
a tracking ship and an unfavorable weather forecast for rocket fueling, delayed
plans for a Sunday launch, NASA officials said. Weather forecasts for Monday improve
to a 60 percent chance of favorable liftoff conditions, they added.
Dawn's
planned Monday launch will kick off an eight-year trip to Vesta
and Ceres, the two largest space rocks in the Asteroid Belt that rings the
Sun between the planets Mars and Jupiter. The $449 million mission will mark
NASA's first to orbit two different planetary bodies, and will study space
rocks that formed about 4.6 billion years ago while the solar system was still
young.
"What's
exciting to me is that this is comparative planetology at its best," said David
Lindstrom, NASA's Dawn program scientist, during a Friday briefing. "We
truly are going back in time; back to the dawn of the solar system."
Powered by
an ion drive, Dawn is due to enter orbit around Vesta in October 2011 and use
three onboard instruments to study the space rock's surface before heading off
towards a February
2015 orbital rendezvous with Ceres.
Vesta is a
dense body scarred by an ancient impact that, researchers believe, sent a
myriad of small meteorites falling to Earth. Ceres, with its spherical shape and a diameter about 600
miles (almost 1,000 kilometers) wide, is so large it is considered
to be a dwarf planet and may sport a subterranean cache of ice or water,
mission scientists added.
Examining
the differences between dense, bright Vesta and the dimmer, less-dense Ceres
may yield new answers for researchers studying the formation of planets, NASA
officials said.
Dawn's ability
to shift from one target to another hinges on its three xenon ion-driven thrusters,
which allow the probe to maneuver with less propellant than that required for chemical-based
rockets.
"We
couldn't do this mission without the ion drive," said Mark Sykes, a Dawn
mission co-investigator from the Planetary Science Institute at the University
of Arizona. "It's an extremely flexible way of moving around the solar
system."
NASA now
has until July 19, a window eight days longer than first announced, to launch
Dawn before standing down to allow preparations for the planned Aug. 3 liftoff
of Phoenix, the space agency's next Mars
lander mission.
"We're
kind of just threading the needle with these two launches," Kurt
Lindstrom, NASA's Dawn program executive, told SPACE.com.
The next
opportunity to launch the mission arises this fall. By the end of October the
distance between Vesta and Ceres - which are currently relatively close to one
another - will begin increasing, mission managers said, adding that the two
space rocks will near each other again in 15 years.
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