NASA revives mission to explore 2 large asteroids


LOS ANGELES -- The Jet Propulsion Laboratory's Dawn mission to the asteroids Ceres and Vesta, canceled this month, was given a reprieve yesterday when NASA officials said they would reinstate the project despite cost overruns and technical problems.

The cost overruns are not unprecedented given the complexity of the mission, and the technical hurdles are well on the way to being overcome, Rex Geveden, associate administrator of the National Aeronautics and Space Administration, said in a teleconference.

"I am thankful for this support and excited to be moving ahead," said JPL director Charles Elachi.

Dawn is the first space probe designed to orbit two solar system bodies and the first scientific mission to use a new ion propulsion system, which was tested on the Deep Space 1 probe.

That motor, which requires a relatively small amount of propellant, will allow the craft to spiral into a low orbit around Vesta, accelerate away from the asteroid, then spiral into a similar orbit at Ceres.

Engineers testing the motor and its fuel tank found abnormalities in both, necessitating a delay in the launch, which had been scheduled for this summer, then leading to cancellation of the mission.

Later testing indicated that the problem had more to do with temperatures during the testing than with the components of the motor.

The delays associated with the problems have led to a 20 percent cost overrun, raising the cost of the mission from an initial estimate of $373 million to $446 million.

The craft is scheduled for launch in the summer of 2007. Because of celestial mechanics, the delay in the launch will not change the date of the craft's scheduled arrival at Vesta in 2011 and Ceres in 2015.

The asteroids are between Mars and Jupiter.

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