From: University of Maryland
Posted: Thursday, February 14, 2002
NASA's Deep Impact project, led by University of Maryland Professor Michael A'Hearn, has passed another milestone on its road toward a January 2004 launch and a July 2005 encounter with a speeding comet.
The Deep Impact project, which will be the first mission to punch a spectacular football field-sized crater seven stories deep into a comet, successfully completed a three-day critical design review last week. After examining details of the mission, three independent review boards concluded that there are no significant flaws in the design and that the project can proceed with building and testing the project's two spacecraft.
"This was a major step for us in ensuring both ourselves and NASA that our designs are solid and reliable," said A'Hearn, who directs the mission as principal investigator. "It is truly exciting to see the first pieces of hardware beginning to arrive at Ball Aerospace and to realize that we are well on our way."
The Deep Impact mission is the eighth mission in NASA's Discovery Program and the third targeted at a comet. The Stardust mission, which is currently en route to comet Wild 2, will bring back a sample of dust from the comet's atmosphere to study in Earth-based laboratories. The CONTOUR mission, which is scheduled to launch in July of this year, will fly past at least two comets of very different histories to understand the evolutionary differences on their surfaces. Deep Impact will intercept comet Tempel 1 in July of 2005. Its flyby spacecraft will release a 770-pound impactor that will excavate a large crater in the comet's nucleus, thus allowing both the flyby spacecraft and Earth-based observers to study the differences between the surface material and the interior of the cometary nucleus and to determine key physical properties of the outer tens of meters of the nucleus.
Comets are essentially giant dirty snowballs orbiting the sun. They are thought to preserve, particularly in their ices, a unique record of conditions in the early solar system when the planets were being formed. Previous passages near the sun by Tempel 1, the target comet for the Deep Impact mission, have led to significant evolutionary changes in the outer layers of the comet's nucleus. However, the nature of this evolution is not understood. Even basic properties, such as mass and density, have never been measured for any cometary nucleus. Deep Impact should allow determination of the density of the surface layers, although no currently planned mission is intended to determine the mass and overall density of any comet until the European Rosetta mission arrives at comet Wirtanen in 2011. Deep Impact will provide the first data probing below the very surface of a cometary nucleus.
Countdown to Deep Impact
The mission launches in January 2004 and orbits the sun for one year, passing again very close to Earth in January 2005. At the Earth flyby, the instruments are tested and calibrated and the spacecraft pair is diverted to comet Tempel 1, arriving in July 2005. On July 3, 2005, the impactor is released from the flyby spacecraft and takes over its own operation, aiming for an impact at 10 kilometers/second on July 4, 2005. Meanwhile, the flyby spacecraft slows down by 100 meters/second and diverts to watch the impact happen and fly past the nucleus at a distance of 500 kilometers (310 miles), 14 minutes after the impact.
The impactor, which is a fully functional spacecraft, will take pictures of the nucleus with ever-increasing resolution as it closes with the comet. These pictures are for scientific purposes and for automatic navigation to ensure an impact. The camera is intended to provide the highest resolution pictures of the cometary surface ever taken, providing unique information about the surface that will give clues to its formation and evolution. The flyby spacecraft has two cameras and an infrared spectrometer to observe the formation process of the crater and the final crater. The measurements are intended to tell scientists about the composition of the interior and the surface and, by observing the crater's formation process, determine the physical properties of the nucleus. The size of the final crater and the length of time it takes to form are key measurements, since these are controlled by the physical properties of the cometary nucleus, properties that are now totally unknown.
The Deep Impact Team
A partnership among the University of Maryland, the Jet Propulsion Laboratory (JPL), and Ball Aerospace & Technologies Corp., is carrying out the Deep Impact mission. The university, through Principal Investigator Michael A'Hearn, is responsible for the entire mission and directly manages the scientific effort, the education and outreach effort, and the development of the instruments on the spacecraft. The science team includes a dozen scientists from the United States and Germany working with several additional supporting scientists. The Jet Propulsion Laboratory, through Project Manager Brian Muirhead, provides the overall project management, provides selected items of hardware and portions of the software, and carries out the in-flight operations. Ball Aerospace & Technologies Corp., under the direction of Deputy Project Manager John Marriott, is building both the two spacecraft and all the instruments.
The Discovery Program
NASA's Discovery Program consists of a series of cost-capped, competitively selected missions proposed by individual scientists and their chosen teams. Using the results of peer reviews by both scientists and engineers, NASA has typically selected one or two new missions every two years. Deep Impact was selected from a proposal submitted in 1998. The total budget for Deep Impact is capped at $279 million in real-year dollars ($240 million in FY99 dollars before adjustment for inflation). This includes all launch costs, communications and operations during flight, delivery of the calibrated data to the scientific community, and education and public outreach activities.
The Critical Design Review is, for all NASA's missions, the point at which NASA gives approval to the detailed design and authorizes the project to complete the building of all the hardware and preparing it for launch. For this mission, the CDR had three separate review boards. The Deep Impact project has its own standing review board of personnel from outside the project, who follow the project closely. JPL's System Management Office appointed a review board to ensure that JPL management is aware of all aspects of the mission. NASA appointed an Independent Assessment Team to provide an independent assessment of mission readiness at this stage of development. All three review boards found that the Deep Impact system design is mature and the project is fully ready to start the spacecraft and science instrument fabrication, assembly, integration and test phases.
The next major review of the system will be in February 2003. Known as the integration and test readiness review, it is conducted prior to shipping the Deep Impact spacecraft to Cape Canaveral for integration into the launch vehicle.
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