A NASA mission being readied for launch and designed to explore two large asteroids in the solar system has been officially cancelled.
"We made the decision yesterday to cancel Dawn," said Andrew Dantzler, director of NASA's solar system division in Washington, D.C.
Dantzler told SPACE.com that NASA is looking at distributing Dawn hardware to other missions currently being considered or in the future. "Some of the subsystems should be good for other spacecraft," he said.
The Dawn spacecraft was to utilize an ion engine system, making use of xenon gas. A slow-but-steady acceleration is created via an ionized propellant stream. Ion propulsion relies on interactions of external and internal magnetic fields with electric currents driven through the stream, thereby imparting thrust to a spacecraft on which is it mounted.
Making use of its ion engine, Dawn was to reach 4 Vesta in 2011 and 1 Ceres in 2015. These objects are the two most massive asteroids known, yet are very different from each other. Scientists had hoped by studying the asteroids they would glean clues about the formation of the solar system.
As a NASA Discovery-class mission, Dawn was selected in December 2001--one of NASA's corps of spacecraft that are developed on a fast-paced schedule and at modest cost compared to so-called "flagship" missions.
Dawn was managed by the Jet Propulsion Laboratory (JPL) in Pasadena, California with Orbital Sciences Corporation of Dulles, Virginia developing the spacecraft.
The mission had been on NASA's books for liftoff in mid-June 2006, but late last year was placed in "stand down" mode. Technical issues and cost-growth in the project led to the decision, with an independent team assigned the duty 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."
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