Technical and managerial problems, as opposed to NASA’s broader budget picture, led the agency to suspend work on the Dawn asteroid-orbiter mission pending a top-to-bottom review of the project, according to a senior NASA official.

Colleen Hartman, NASA deputy associate administrator for science, said the agency expects to complete the review in February and then decide whether and how to proceed with Dawn, a Discovery-class mission that until recently was being readied for a June 2006 launch. Dawn is designed to orbit the solar system’s two largest known asteroids over a nine-year period.

According to NASA, Dawn is running about 11 percent over its $373 million budget as program officials wrestle with a number of technical problems mostly related to development of the spacecraft’s ion propulsion system.

NASA successfully demonstrated ion propulsion in 1998 on its Deep Space 1 mission. But Dawn would be NASA’s first purely scientific mission to rely exclusively on the highly efficient propulsion technology.

Deep Space 1’s xenon-ion propulsion system powered the experimental spacecraft for more than three years until NASA finally ended the mission in December 2001. It was during that same month that NASA announced its selection of the Dawn proposal for funding under the Discovery program of cost-capped science missions.

Dawn, like Deep Space 1, is being managed by the Jet Propulsion Laboratory, Pasadena, Calif.

Hartman said the ion propulsion system is the primary source of Dawn’s technical problems. She said the Dawn team has run into trouble with the engine’s power processing unit and is experiencing qualification problems with its xenon propellant tank. It is not clear that the team knows how to solve the problems, she said .

At the same time, Hartman said, NASA has concerns about the overall management of the project that it wants to review in depth before going forward. NASA has told the Dawn team to “stand down” for three months while separate technical and managerial reviews are conducted.

“When you have these kinds of problems, a stand-down is the most sensible way to go to make sure nothing is done that will do any further harm,” Hartman said. “This is just a time to take a look at the systems engineering of Dawn overall to make sure we are confident about the path to closure on all of these things.”

Hartman said the stand-down, while unusual for a mission as close to launch as Dawn, should not be construed as an indication that NASA intends to cancel the mission.

“I have no a priori conclusions,” she said. “We have every managerial option we can use at our disposal.”

She also said the order was not meant to send a message that NASA is taking a harder line on cost growth.

“I don’t think it’s a change in terms of a harder line or not a harder line,” she said. “We are very serious about cost containment in these missions. Good systems engineering and good program management are always the things that help us close our programs.”

Dawn’s principal investigator, Christopher Russell of the University of California at Los Angeles, said he is confident that NASA will decide to go forward with the mission at the conclusion of the reviews.

Russell also said Dawn can tolerate a launch delay without jeopardizing the science objectives of the mission. The launch window the Dawn team has been shooting for, he said in a recent interview, is over a year long.

Meanwhile, NASA plans to select its next Discovery mission candidates in the year ahead. An announcement of opportunity is due to be released in the coming months.

NASA is raising the cost cap on the next round of Discovery missions to $425 million. Hartman said the $75 million increase, the program’s first in three years, was overdue.

“Our cost of doing business has increased, particularly for launch vehicles,” she said.

Brian Berger is editor in chief of and the SpaceNews magazine. He joined in 1998, spending his first decade with the publication covering NASA. His reporting on the 2003 Space Shuttle Columbia accident was...