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Planetary News: Dawn (2006)A New Day for DawnBy Amir Alexander27 March 2006 In a heartening reversal of a decision taken earlier this month, NASA has restarted work on Dawn -- a mission to two of the largest minor planets in the asteroid belt, Ceres and Vesta. On March 2, citing technical problems and cost overruns, NASA's Science Mission Directorate canceled the Dawn mission. Four days later, the Jet Propulsion Laboratory (JPL), which is charged with overseeing the mission's development, appealed the decision to the Office of the Administrator. A panel headed by NASA Associate Administrator Rex D. Geveden reviewed the appeal, considering both the criticisms included in the original report and the responses provided by JPL. On March 23 they met and decided: Dawn will move forward. "We congratulate the DAWN team and are delighted that NASA has reversed the earlier cancellation" said Louis Friedman, Executive Director of The Planetary Society. "They deserve commendation for changing their decision. The exploration of the two largest asteroids, or should we call them planets, is an important and exciting step in exploration." Bruce Betts, The Planetary Society's Director of Projects, also welcomed NASA's decision: "Reinstatement of the Dawn mission is an exciting and welcome development for planetary exploration, particularly in light of the proposed hits to other areas of planetary exploration in the administration's proposed FY07 budget" he said. "Dawn will take us to two objects that are unlike any we have yet explored." Dawn is the first mission ever designed to enter orbit around two celestial objects in succession. Projected to launch in July or August 2007, Dawn will rendezvous with the minor planet Vesta in the asteroid belt between Mars and Jupiter on July 30, 2010. For the next 9 months, Dawn will remain in orbit around Vesta, scanning it closely with a camera and two spectrometers. Then, on July 3, 2011, Dawn will fire its engines and set off towards Ceres, the largest object in the asteroid belt. After a journey of 3 years, Dawn will arrive at its destination on August 20, 2014, where it will remain, orbiting and gathering data for 9 months. If all goes well, the Dawn mission may then be extended, and the spacecraft may move on to scan additional objects in the asteroid belt.
By visiting Vesta and Ceres in succession, Dawn will provide scientists with a comparative view of two worlds very similar in some respects, but strikingly different in others. Both Ceres and Vesta, scientists believe, formed about 10 million years after the initial formation of the solar system 4.6 billion years ago. But whereas Ceres, the larger of the two, remained a largely undifferentiated mass, Vesta developed into a layered and volcanically active world. By studying the two worlds with the very same instruments, scientists hope to gain insights into the history and evolution of both objects, and by extension learn more about the development of the solar system as a whole. To accomplish this double rendezvous, Dawn is equipped with an ion engine, an innovative technology first tested by NASA on the Deep Space 1 probe. An ion engine operates by shooting charged atoms (ions) of xenon gas from the spacecraft at speeds of 110,000 kilometers per hour (68,000 miles per hour), thereby accelerating the craft slowly but surely. And while the technology is necessary for Dawn to accomplish its goals, it also proved to be one of the mission's main vulnerabilities. Among other reasons for its recommendation to cancel the project, the Science Missions Directorate cited the difficulties encountered in developing a reliable ion engine and a record of test failures. In its appeal of the cancellation decision, JPL successfully argued that the main technical difficulties have either been resolved, or are well on their way to being resolved. JPL also committed to keeping a lid on the mission's costs, which had risen to $446 million from the original estimate of $373 million. The review panel concurred: "We revisited a number of technical and financial challenges and the work being done to address them" said Geveden. "Our review determined the project team has made substantial progress on many of the mission's technical issues, and, in the end, we have confidence the mission will succeed." |
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