An artist's interpretation of NASA's Dawn spacecraft in flight.
This story was updated at 4:45 p.m. EST.
NASA?s once-canceled Dawn mission to visit a pair of asteroids has been reinstated following a mission review, space agency officials said Monday.
NASA initially canceled the Dawn mission, which calls for an ion-powered spacecraft to visit two large asteroids, earlier this month only to reverse that decision, which drew ire and opposition from planetary scientists at this month?s 37th Lunar and Planetary Science Conference (LPSC).
After an in-depth study of the cost overruns and technical challenges plaguing Dawn?s development, NASA officials concluded that the mission should proceed towards a summer 2007 launch target.
?When you?re doing deep planetary missions?.there are always pretty tall challenges,? NASA associate administrator Rex Geveden told reporters in a Monday 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 earlier this month.
?This mission goes up and down, but I?m happy,? Dawn team member Lucy McFadden, of the Department of Astronomy at the University of Maryland in College Park, Maryland, told SPACE.com. ?I want to get to work and get this thing off the ground.?
Dawn?s new light
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, NASA?s deputy associate administrator for science mission directorate, during the teleconference. ?The things we?re doing here are tough, they?re not easy.?
?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 Dawn?s 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 had already been spent, the agency said.
An additional $14 million would have been required to cancel the mission completely, NASA said.
Off again, on again
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.?
But a review process instituted by NASA chief Michael Griffin to evaluate the cancellation of NASA space missions proved successful for Dawn?s supporters.
?The science mission 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, D.C. headquarters, during an interview last week.
NASA officials said Monday that the process is likely not one that will occur often, adding 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,? NASA associate administrator Rex 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.?
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