NASA restarts once-dead Dawn asteroid mission
BY STEPHEN CLARK
Posted: March 27, 2006
Less than a month after falling victim to budget and technical concerns, the Dawn asteroid explorer was brought back from the grave Monday by a decision to restore funding to the mission and launch the probe by next summer.
NASA announced the reinstatement, a complete reversal of the decision three weeks ago to kill the mission, after an appeal from project officials at the Jet Propulsion Laboratory. The objections prompted yet another review of Dawn, which had undergone a series of investigations since October that assessed the state of the mission after various problems and cost overruns came to light.
The results from that review board eventually led to the cancellation of Dawn on March 2. Findings included an estimated total cost of $446 million, a 20 percent increase over the capped cost of $373 million.
By early March, about $257 million had already been spent in mission development, planning, and construction. An additional $14 million would have been necessary to formally terminate Dawn, while the stand down itself was an expense of approximately $5 million.
"When we looked at the stand down information at that time, we felt in the Science Mission Directorate that there was too much risk still left on the table to go forward," Colleen Hartman, the directorate's deputy associate administrator, told reporters Monday in explaining why Dawn had been cancelled earlier this month. "There is approximately a 20 percent increase (in cost). The information on the table at the time was insufficient for us to feel comfortable going forward. Since that time there was additional information provided."
The most recent review team included only upper level management from NASA headquarters, and they weighed the decision process, the conclusions of the initial assessment team, and the project's rebuttal. They met last Thursday to discuss the matters, and made a final decision over the weekend to reverse the cancellation order.
The group - chaired by Rex Geveden, NASA's associate administrator at agency headquarters - found that the most prominent technical problems no longer stood in the way of Dawn. Testing of composite xenon tanks caused ruptures at lower than expected pressures, but engineers will likely load less xenon propellant than first planned. An issue involving test failures of two power units that provide electricity to the craft's ion propulsion system is also on track to being resolved.
"Those failures are now understood and have to do with transient thermal conditions that are a function of the test configuration," Geveden said. "So we believe, fundamentally, that there is not a flight hardware issue with those units, but rather a test configuration issue. There is a hurdle to clear with that one - those need to go through 500-hour-life testing. That's still out there, but the technical resolution path seems pretty clear."
Another problem centering on thermal and structural concerns during a test has also been addressed, said Geveden. "That had to do with a test configuration situation and that one can be kind of finessed by adding some heaters and managing the thermal environment in the test in a more sophisticated way."
"In all of those cases there's work to do, but the way forward looks pretty clear. I think the risk posture on this mission is not atypical for this kind of mission. When you are doing deep planetary missions and dealing with the environments and the temperature regimes and the complication of integrating a suite of instruments, there are always pretty tall challenges. And it looks like Dawn is prepared to take those on and beat them."
Future costs are also thought be under control with improved management and the technical remedies. Also, President Bush's planned fiscal year 2007 budget features enough margin to carry out the project, including the overruns, but officials couldn't say where funding to cover the extra costs will be coming from.
"Every time something overruns like this it obviously has to come from a pot of money," Hartman said. "The pot of money doesn't change, and somebody is requiring more from it. So as you know there's less for something else. I can't track each dollar and tell you where that dollar came from. We optimized the program and other things got less."
"Cost overruns are pretty typical because the amount of technical uncertainty is normally high, and trying to estimate the cost on the front-end of those missions is very hard to do," said Geveden.
"So you get to this stage of a mission where you are maybe two-thirds of the way through the developmental stage and you have sunk half of the cost. You have to really trade off the remaining cost the mission (and) the scientific value against that remaining cost and judge that against applying that money to new-start missions. That is the kind of difficult trade we had to make. I take cost overruns deadly seriously, as does the Science Mission Directorate, and that's the reason this mission was under review for cancellation and that's the reason why consideration of cancellation was, in my opinion, a very legitimate thing to do."
But Monday's decision doesn't mean Dawn is completely out of danger.
"Reinstatement does not excuse past performance nor guarantee unequivocal future support," Geveden wrote in a letter to Science Mission Directorate associate administrator Mary Cleave and JPL director Charles Elachi. "JPL and the Dawn project are, therefore, required to fully commit appropriate resources and management to the successful completion of this mission."
Dawn principal investigator Chris Russell has long criticized NASA's decision to halt mission preparations and has vigorously defended the mission since its cancellation.
"The stand down spent money but did not progress us meaningfully toward launch," Russell said last week. "Also we now have to rehire folks and retrain to get to launch. So this whole process has wasted money - it defies logic what they did."
Dawn is now expected to be ready for launch between June and August of 2007 aboard a Boeing Delta 2 rocket from Cape Canaveral, Florida. The basic mission plan remains unchanged after the delays of the past few months, and Dawn will reach Mars in early 2009 to receive a crucial gravity assist that will send its path arcing into the asteroid belt.
The spacecraft will reach asteroid Vesta in October 2011, where it will spend over six months orbiting to conduct science observations. After departing Vesta, Dawn will arrive at asteroid Ceres by August 2015 to investigate the solar system's largest minor planet.
"The things we are doing here are tough. They are not easy," Hartman said. "This is a tough business. To have something last this long and reach two destinations and explore them with this resolution and specificity is a very difficult job."
Dawn will carry three primary instruments provided by a team of international scientists. A framing camera built by the German Aerospace Center, DLR, and the Max Planck Institute for Aeronomy will return imagery of the surface of both asteroids. An Italian-built visible and infrared mapping spectrometer will map the two bodies and determine chemical compositions. The Los Alamos National Laboratory in New Mexico is responsible for a gamma ray and neutron detector.
"Because (Vesta and Ceres) basically remained intact since their formation, we're going to be measuring things like their mass, their shape, their volume, their spin rate, and in order to do that we'll be using both imagery, laser altimetry, and gravity measurements onboard," explained Hartman.
Hartman said NASA's Science Mission Directorate never lost sight of the science that will come from Dawn. She described the review process as very "gut-wrenching," and said that NASA is pleased to be going forward with the mission.
"Understanding the major asteroids is a critical part of our exploration program as it is the only way to piece together what happened 4.6 billion years ago (in the early solar system)," Russell said. "Vesta is a rocky planet with an iron core like the Earth. It is one of the building blocks that formed the terrestrial planets. Ceres we now know is an ice planet over a rocky core. The water ice may be liquid inside. Thus it is probably a better place to find life than (Jupiter's moon) Europa. If we could get to Ceres and prove this to the community, then the pressure for a Europa mission would go away and a Ceres lander would be the order of the day."