Spacecraft get new missions

The Baltimore Sun

Available: Deep Impact and Stardust. Older model spacecraft, already in orbit. Only a few billion miles on them. Big science! Huge markdown!

Well, NASA liked the pitch.

The space agency has decided to reactivate the two semi-retired comet-hunters and reassign them to two more comet flybys. Deep Impact will also turn its instruments on some gigantic planets circling nearby stars, and back toward Earth to see what a living planet looks like from a distance.

The two mission extensions announced this week will cost no more than $55 million, according to NASA officials. That compares with up to $900 million with two new spacecraft.

"These new mission assignments for veteran spacecraft represent not only creative thinking and planning, but are also a prime example of getting more from the budget we have," said Alan Stern, associate administrator for science.

University of Maryland astronomer Michael A'Hearn, principal investigator for the combined missions, agreed. Recycling deep space missions is "a tremendously cost-effective approach to doing science," he said. But it does have added risks.

"You don't get to design newer and better instruments to do the job," he said. And "with an old mission, there is some chance of parts wearing out. But you're saving a huge amount of money."

Deep Impact was launched in January 2005. On July 4, 2005, it lobbed an 820-pound copper projectile onto the icy nucleus of Comet Tempel 1. The impact blasted a crater that allowed scientists to study the comet's interior structure. Data in hand, scientists steered the spacecraft back toward Earth and placed it in hibernation while they lobbied for an extended mission.

Among their discoveries on Tempel 1: unexpected bursts of gas erupting from the nucleus as it rotated into the sunlight.

"The question is, are these various discoveries typical or is there something really unusual about Tempel 1?" A'Hearn said. For answers, scientists needed to send the same instruments to another comet.

In its new assignment, called DIXI (for Deep Impact Extended Investigation), the spacecraft will be reawakened and sent off to a smaller comet called Boethin, which returns from beyond Jupiter to the inner solar system every 11 years.

The Boethin flyby is scheduled for Dec. 5, 2008. While en route later this year, the spacecraft will turn its instruments toward several nearby bright stars to learn more about the planets believed to circle them.

Deep Impact will also observe Earth from afar, gathering data on its atmosphere for comparison with observations of planets circling distant stars.

Stardust was launched in 1999. In 2004 it flew within 150 miles of Comet Wild 2 and captured samples of comet dust. In January 2006, the dust was parachuted safely to Earth in a capsule.

The spacecraft itself flew on. Now it will be redirected to intercept Comet Tempel 1 in 2011, repeating many of Deep Impact's observations there.

That will allow scientists to see any changes that have occurred since the comet's last close approach to the sun. The new mission is being led by Cornell University astronomer Joseph Veverka.

frank.roylance@baltsun.com

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