NASA's
beleaguered Dawn asteroid probe will have to wait at least one more day to
launch after lightning prevented workers from fueling the spacecraft's rocket
Thursday.
Initially
targeted for a Saturday
afternoon liftoff, Dawn is now set to launch from Florida's Cape Canaveral
Air Force Station on Sunday, July 8 at 4:04 p.m. EDT (2004 GMT). Current
forecasts predict a 60 percent chance that poor weather will prevent the
weekend space shot.
A lightning
advisory prevented launch pad workers from fueling the second stage of Dawn's
Delta 2 booster, NASA spokesperson D.C. Agle told SPACE.com from the
agency's Kennedy Space Center spaceport in Cape Canaveral. The United Launch
Alliance rocket's payload fairing was also too warm to begin loading the Delta
2 with the super-chilled oxidizer for its propellant, NASA officials said,
adding that fueling operations should resume by Friday.
The delay
is the latest in a series of difficulties for NASA while preparing Dawn for its
$449 million mission to study the asteroids
Vesta and Ceres.
In recent
weeks, the mission managers have repaired last-minute damage to the
spacecraft's solar arrays, weathered the late delivery of rocket parts that
delayed Dawn's planned June 20 liftoff, and wrestled with a malfunctioning
crane while assembling the probe's Delta 2 booster. Mission managers also needed
more time to study the impact of higher than expected loads on parts of the
Delta 2's solid rocket motors and substitute a launch tracking ship with an
aircraft.
The Dawn
spacecraft, too, has traveled a rocky road to the launch pad. NASA initially canceled
the asteroid-bound mission in March 2006 due to cost overruns and technical
challenges with the probe's xenon-powered ion engine. But the space agency reinstated the
mission a few weeks later after an in-depth study into those hurdles.
Researchers
hope the 2,684-pound (1,217-kilogram) Dawn spacecraft will answer questions on
the formation of Vesta, which sports signs of lava flows on its surface, and potentially
water ice-harboring Ceres. The probe is due to swing by Vesta in October
2011 and then rendezvous with Ceres in February 2015.
NASA's
window to launch Dawn closes on July 11, when the space agency will shift over
to prelaunch preparations for the Mars
Phoenix lander and the shuttle Endeavour. Phoenix is slated to launch on
Aug. 3 and be followed by Endeavour's STS-118 mission to the International
Space Station on Aug. 7.
If Dawn
misses its July launch window, it would be delayed until later this fall and
cost an extra $25 million due to the need to replace the spacecraft's Delta 2
rocket's second stage, mission managers have said.
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