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.
Asteroid frontier
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."
advertisement
