NASA’s decision to reinstate the Dawn mission to visit a pair of asteroids was applauded on both sides of the Atlantic.

The mission, a project involving the Jet Propulsion Laboratory, the University of California at Los Angeles, NASA, and the German and Italian space agencies, was cance led in March as a result of technical problems and cost overruns. But NASA officials announced March 27 they were reversing course and reinstating Dawn based on the findings of a recent review of the progress that has been made to get the program back on track.

The Dawn mission to use an ion-powered spacecraft to visit two large asteroids was popular with many planetary scientists. NASA decided to review the cancellation after that decision was harshly criticized by researchers who attended the 37th Lunar and Planetary Science Conference (LPSC) in Houston March 13-17.

Germany’s space agency, DLR, applauded NASA’s decision to continue funding the asteroid-exploration satellite, which has German and Italian instruments.

The decision to reinstate Dawn will provide “new opportunities for European planetary research,” DLR Chairman Sigmar Wittig said in a March 28 statement. “Dawn is the first American mission to have two European experiments at its heart.”

Dawn will carry a DLR-provided camera, based on a similar instrument now flying on the European Space Agency’s Mars Express satellite. Dawn also will carry a mapping spectrometer provided by the Italian Space Agency (ASI), and built by the Institute for Space Astrophysics in Rome.

After an in-depth study of the cost overruns and technical challenges plaguing Dawn’s development, NASA concluded the mission should proceed towards a summer 2007 launch target.

“When you’re doing deep planetary missions … there are always pretty tall challenges,” NASA A ssociate A dministrator Rex Geveden told reporters during a March 27 teleconference. “And it looks like Dawn is ready to take those on and beat them.”

The decision buoyed Dawn mission scientists, who had mourned the project’s cancellation.

“This mission goes up and down, but I’m happy,” said Dawn team member Lucy McFadden of the department of astronomy at the University of Maryland, College Park . “I want to get to work and get this thing off the ground.”

NASA first approved the Dawn mission in 2001 as part of its low-cost Discovery mission program.

The spacecraft’s novel ion-propulsion system draws on technology demonstrated by NASA’s Deep Space 1 probe, though Dawn would mark the agency’s first science mission to employ such an engine. Europe’s Smart-1 probe currently circling the Moon also uses ion propulsion.

“This is, in fact, quite an ambitious mission,” said Colleen Hartman, deputy associate administrator for NASA’s Science Mission Directorate, during the teleconference. “The things we’re doing here are tough, they’re not easy.”

Dawn is destined to rendezvous and orbit both Vesta and Ceres, two of the largest asteroids in the Asteroid Belt. The rendezvous will occur in 2011 and 2015, respectively.

“Getting to Ceres and Vesta will be opening up our eyes to new worlds,” McFadden said, adding that the large asteroids formed quickly in the early solar system and harbor many mysteries for scientists, including their surface composition and features. “We just have the barest hint from maps that we’ve derived from the Hubble Space Telescope on their surface features.”

During its development, the cost of the Dawn mission swelled from an initial $373 million to $446 million due to technical challenges, NASA officials said. That cost overrun — and a 14-month launch delay from its intended summer 2006 target — prompted NASA’s March 2 decision to scrap the mission, which came after $257 million already had been spent, the agency said.

An additional $14 million would have been required to cancel the mission completely, NASA said.

Technical challenges revolving around Dawn’s propulsion system, xenon fuel tank and thermal stresses — among others — contributed to its cancellation, NASA officials said, adding that those concerns have since been addressed by additional data.

“What we had here was a very gut-wrenching decision,” Hartman said. “And we’re very happy to be going forward.”

The review process instituted by NASA Administrator Mike Griffin to evaluate the cancellation of NASA space missions proved successful for Dawn’s supporters.

“The Science M ission Directorate decided to terminate it, and the appeal [was] to see if we continue to fund Dawn or go on with that termination,” said Andrew Dantzler, director of NASA’s solar system division at the agency’s Washington headquarters, during a telephone interview last week.

NASA officials said March 27 that the process is likely not one that will occur often, noting that Dawn has accrued about $5 million in additional costs since the agency ordered mission managers and scientists to stand down last fall when cancellation discussions began in earnest.

“We revisited a number of technical and financial challenges and the work being done to address them,” Geveden said in an earlier statement. “Our review determined the project team has made substantive progress … we have confidence the mission will succeed.”

The funds to save the project likely prevented other programs from moving ahead, Hartman added.

“These are hard choices and sometimes future missions or current missions have to sacrifice,” Geveden added during the teleconference.

Meanwhile, Dawn scientists and engineers have their work cut out for them before they can launch the spacecraft toward its asteroid targets atop a Delta 2 rocket. About half of the spacecraft’s hardware, which includes support components and science experiments, is complete, NASA officials said.

“I want to get to both of them,” McFadden said of Vesta and Ceres. “I can’t believe I have to wait until 2015.”

Staff writer Peter B. de Selding contributed to this article from Paris.