ty to look into the problems.
Assessment team findings
Last year it was becoming clear that there were issues with Dawn, Dantzler explained. "The path for resolving all the technical issues and the certainty on the cost number were not clear," he said.
The independent assessment team for Dawn was pulled together to dig in and take at look at mission issues "and what it would take to get Dawn to be ready."
That team reported to NASA in January that there were 29 individual major issues that needed to be dealt with before Dawn was ready to go, Dantzler said. Also, there was an increased cost growth of 20 percent over Dawn's confirmation cost cap of $373 million, he added, as well as a 14-month or more delay in launch.
"Over the past month or so we've been deliberating over those findings," Dantzler said, leading to yesterday's decision. Canceling Dawn was "the fiscally responsible thing to do," he said, "...and at some point you just have to draw the line."
NASA reached a point where it was not clear how long and how much money it would take to get Dawn off the ground, Dantzler said. The space agency is looking at a close-out cost--handling such things as hardware storage and close-out paperwork--of somewhere between $9 million to $12 million, he said.
"This is clearly a tough decision. We don't take it lightly at all. But, ultimately, I believe it's the right one for the good of the Discovery program," Dantzler said.
Among the technical problems encountered, "there were still serious concerns" about the readiness of the ion engine propulsion system for Dawn, Dantzler said.
When word came last year of the stand down, Dawn's principal investigator, Christopher Russell of the University of California, Los Angeles (UCLA) told SPACE.com that the mission could tolerate a later launch date - without any science impact. He remained hopeful that NASA would allow the mission to proceed to launch.
"I am having a difficult time processing and accepting the cancellation," said Lucy McFadden of the Department of Astronomy at the University of Maryland in College Park, Maryland and a Dawn team member.
"With the success of the Discovery Program's Deep Impact and Stardust missions, and the recent and exciting scientific results from the Hubble Space Telescope on Ceres...we were poised to emerge into the asteroid frontier with the Dawn spacecraft," McFadden told SPACE.com.
McFadden said that scientists can better understand asteroids as true protoplanets, "if we could only send the spacecraft there." Furthermore, there are equally intriguing clues to the intricacy of Vesta, a very different asteroid that was also on Dawn's trajectory, she explained.
"There are hundreds of people in this country and in Europe who have worked on the [Dawn] project for four years and had committed another decade to it...and now we are dropped," McFadden said. "What can I say? It makes me cry."
- NASA Asteroid Mission Won't Launch This Year
- NASA Dawn Asteroid Mission Told To 'Stand Down'