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December 13, 2002

Should a comet fear the turtle?
University professor wants to send an angry Testudo crashing into a comet
By Jeremy Hsieh

(Special to The Diamondback)

Michael A'Hearn
University astronomy professor Michael A'Hearn is the principal investigator for the Deep Impact project. AUSTIN CHOW -THE DIAMONDBACK

The last thing the comet Tempel I will encounter before a spacecraft crashes into it on July 4, 2005, may be an angry Testudo, if university project members have anything to say about it.

Deep Impact, a university professor's six-year project to study a comet by crashing a multi-million dollar spacecraft into it, is passing another milestone as testing of three key components for the pair of spacecraft in the mission winds down.

The collision between the impactor spacecraft and the comet will create a crater and spew the contents of the comet's interior outward. A second flyby spacecraft will observe the comet bits and transmit data back to Earth for analysis.

While the vast majority of the project's parameters has been preset, there is at least one point of contention. Project members would like the copper plate on the impactor, the first part to strike the comet, to bear a message or logo. "Fear the Turtle," "This one's for the dinosaurs," the team members' signatures and the Testudo logo have all been considered, said Carey Lisse, instrument scientist for Deep Impact and a university research associate.

Ball Aerospace and Technologies Corp. in Colorado, the company building the two spacecraft and their components, is completing construction of three custom-made telescopes, said Dennis Wellnitz, a representative of the university's science team to BATC and a university research associate. High- and medium-resolution instruments will allow the flyby to record the impact from a distance of at least 300 miles and still provide sharply focused images. The impactor targeting system, the third telescope, will be mounted on the impactor and will record images of the comet as it approaches and feed data to its propulsion system for trajectory adjustments.

Construction is a back-and-forth procedure between testing and tweaking the instruments. BATC is encountering "typical problems," Lisse said. However, he said no space project will ever be problem-free.

Problems are being discovered and dealt with through testing at BATC. Wellnitz said the instruments are undergoing vibration, thermal cycling and thermal vacuum tests. The tests subject the instruments to conditions similar to those they would be exposed to at launch, during atmospheric flight and in deep space. However, time has been allotted to deal with these problems, and they do not jeopardize the mission.

"Everything is on schedule, within days of the optimal schedule," Wellnitz said. "We are staying, so far, under the cost cap."

The next step after each instrument is individually tested is checking everything together. This stage should not be trivialized, Lisse said, because interference from one instrument to another may occur. All three instruments are expected to be ready for integration with the spacecraft by the end of February.

If everything continues as planned, the spacecraft will be reviewed a final time by NASA in September and shipped to the Kennedy Space Center in Cape Canaveral, Fla., no later than Oct. 15, 2003.

The project will cost NASA $279 million and has united NASA, BATC, the Jet Propulsion Laboratory at the California Institute of Technology and hundreds of scientists around the world - including several from the university - in an effort to trace the origins of the solar system.

"The reason for wanting to understand a comet is that the comets, in their interior, should preserve a record of the ices that condensed at the beginning of the solar system and therefore, they tell us what their temperature and density conditions were when all the planets formed," said Michael A'Hearn, Deep Impact's principal investigator and university astronomy professor. "The outer layers have been altered by the comet going around the sun, so we're trying to get down deep enough to find out how different the interior is."

There is a fixed launch window from Jan. 2 to Jan. 21, 2004, during which a rocket must deliver the impactor and flyby into space as an integrated unit, though Wellnitz said they are still aiming for a Jan. 2 launch date.

On July 3, 2005, the impactor and flyby will separate. The impactor's battery will power it independently for the next 24 hours until the comet overtakes it, and much of the impactor will be vaporized on impact.

More information about Deep Impact is available on the Web at

(This article was reproduced with permission from the author. The original can be found at:

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