The space agency earlier this month scrapped the Dawn mission to orbit the asteroids Ceres and Vesta. The move came nearly a half year after it was put on hold due to cost overruns and technical problems.
But NASA decided to review the cancellation 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 issues 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," Mr Geveden said during a telephone briefing today.
Dawn was supposed to launch in June on a nine-year voyage, but NASA ordered a stand down last autumn amid budget concerns and problems with the spacecraft's xenon fuel tanks, which ruptured during testing last year.
The about-face decision means that Dawn is now scheduled to launch in July 2007. The mission was cost-capped at US$373 million (A$530 million), but NASA will pony up an extra US$73 million to launch the spacecraft instead of spending US$14 million to terminate it.
Powered by a xenon ion engine, Dawn would be the first spacecraft to circle Ceres and Vesta, which reside in the main asteroid belt between Mars and Jupiter.
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.
The delayed launch would not affect the spacecraft's arrival time, Geveden said. Dawn was scheduled to reach Vesta, 354 million kilometres from Earth, in 2011 and then fly to Ceres, about 415 million kilometres from Earth, in 2015.