Lightning Prompts 24-Hour Launch Delay for Asteroid Probe

NASA's Dawn probe will spend at least one more day on Earth before launching toward two large asteroids after a lightning threat prevented fueling of its Delta 2 rocket on Sunday.

Lightning within five miles (eight kilometers) of Dawn's Pad 17B launch site at Florida's Cape Canaveral Air Force Station kept pad crews from loading propellant into the second stage of the asteroid probe's Delta 2 booster, NASA spokesperson George Diller said.

"The second stage is fully fueled now," Diller told SPACE.com, adding that pad crews caught up on their lost work Monday.

Originally scheduled to launch early Wednesday, Dawn is now set to lift off Thursday at 7:20 a.m. EDT (1120 GMT) on an eight-year mission to the asteroids Vesta and Ceres.

The mission's liftoff has been delayed since July due to a series of glitches ranging from poor weather and rocket booster glitches to difficulties securing a launch tracking aircraft and ship. Mission managers said in July that the delays could add $25 million to Dawn's $449 million mission cost.

Powered by a novel ion propulsion system, NASA's Dawn probe is expected to rendezvous with Vesta in 2011, and then head off for a February 2015 arrival at Ceres.

Both Vesta and Ceres sit in the belt of space rocks that circle the Sun in the gap between the orbits of Mars and Jupiter. While Vesta is bright and dense, Ceres is large enough to be considered a dwarf planet. Researchers hope that by studying the two massive space rocks, they will shed new light on the origin of the solar system and its planets.

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