Just weeks after NASA killed a spacecraft mission to two of the solar system's largest asteroids, the space agency reversed course and gave the green light for a 2007 launch.

NASA had axed the Dawn project earlier this month, citing cost overruns and technical issues. But it decided to take a second look after the Jet Propulsion Laboratory, which managed the mission, made an appeal.

NASA Associate Administrator Rex Geveden, who chaired the review panel, said the Dawn team has made significant progress in addressing the technical problems and was confident the mission would succeed.

"There are always pretty tall challenges, and it looks like Dawn is prepared to take those on and beat them," Geveden said Monday.

Dawn was supposed to lift off in June on a nine-year voyage to the asteroids Ceres and Vesta, which reside in the main asteroid belt between Mars and Jupiter. But NASA ordered a stand down last fall amid budget concerns and problems with the spacecraft's xenon fuel tanks, which ruptured during testing.

The about-face means that Dawn is now scheduled to launch in July 2007. The mission's cost was originally capped at $373 million, but NASA decided to pony up an extra $73 million to launch Dawn instead of spending $14 million to terminate it.

"I'm terribly excited. We're all jumping up and down," said Lucy McFadden, a Dawn team member from the University of Maryland. "I'm pleased that NASA hasn't given up on science altogether."

Powered by a xenon ion engine, Dawn would be the first spacecraft to circle Ceres and Vesta. It will spend several months orbiting each asteroid, photographing the surface and studying the interior composition, density and magnetism.

Ceres and Vesta are believed to have formed in different parts of the solar system about 4.5 billion years ago. Studying them could provide clues to how the sun and planets formed.

Dawn's cancellation came at a precarious time at NASA, which had been forced to cut or delay several science projects to help pay for the development of new manned vehicles to return to the moon next decade.

Jet Propulsion Laboratory director Charles Elachi appealed the cancellation, saying the technical problems were either fixed or would be corrected in time for a liftoff next year.

"With the agency's go-ahead, we can proceed with this intriguing mission that will explore two asteroids from deep in the heart of the asteroid belt," Elachi said in a statement.