Image: Stardust and Earth
The Stardust spacecraft, shown in this artist's conception as it zoomed toward Earth for a flyby, has been given another assignment: revisiting Comet Tempel 1, which was the focus of Deep Impact's primary mission.
updated 7/3/2007 8:45:28 PM ET 2007-07-04T00:45:28

NASA on Tuesday gave new assignments to two robotic space travelers that have already completed the missions for which they were designed: the comet-watching Deep Impact spacecraft, and the comet-sampling Stardust probe.

The Deep Impact spacecraft, which flew by Comet Tempel 1 after sending an impactor in its path in 2005, is due to fly past yet another comet in 2008 and observe stars known to have planets circling them.

Stardust, meanwhile, will be sent to pay its own visit to Comet Tempel 1 in 2011. The Stardust spacecraft dropped off a sample capsule containing comet dust and interstellar samples as it flew past Earth last year, and has essentially been in an interplanetary holding pattern ever since.

"These mission extensions are as exciting as it gets," Alan Stern, associate administrator for science at NASA Headquarters, said in a written announcement on the missions. "They will allow us to revisit a comet for the first time, add another to the list of comets explored and make a search for small planets around stars with known large planets. And by using existing spacecraft in flight, we can accomplish all of this for only about 15 percent of the cost of starting a new mission from scratch."

The new assignments come after months of deliberation over what to do with the two spacecraft, which came away from their comet encounters with their observing instruments and navigation systems intact.

"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," Stern said.

The costs for the past missions were $212 million for Stardust, and $333 million for Deep Impact. The extensions were approved under NASA's Discovery program for missions of opportunity, which carries a cost cap of $35 million per mission. Stern told via e-mail that the combined cost for the two new missions comes to $55 million.

Along with the new assignments come new names: EPOXI for the Deep Impact probe, and NExT for the Stardust probe. Here are further details about each of the missions, as described by NASA:

EPOXI: Two assignments in one
The EPOXI mission melds two science investigations: the Deep Impact Extended Investigation, or DIXI; and the Extrasolar Planet Observation and Characterization, or EPOCh.

DIXI will involve a flyby of Comet Boethin, which has never been explored. Boethin is a small, short-period comet, or one that returns frequently to the inner solar system from beyond Jupiter's orbit. This investigation will allow the recovery of some of the science lost with the 2002 failure of the CONTOUR mission, which was designed to make comparative studies of multiple comets. DIXI will be targeted to fly by Comet Boethin on Dec. 5, 2008.

Image: Deep Impact
An artist's conception shows the Deep Impact "Flyby" spacecraft in the foreground, shooting a copper-sheated impactor at Comet Tempel 1 in 2005. The "Flyby" mothership will go on to study planets circling distant stars as well as Comet Boethin.
The EPOCh investigation also will use the Deep Impact spacecraft to observe several nearby bright stars, watching as the giant planets already known to be orbiting the stars pass in front of and then behind them. The collected data will be used to characterize the giant planets and to determine whether they possess rings, moons, or Earth-sized planetary companions.

EPOCh's sensitivity will exceed both current ground and space-based observatory capabilities. EPOCh also will observe Earth in mid-infrared wavelengths, providing comparative data for future efforts to study the atmospheres of extrasolar planets. This search for extrasolar planets will be made this year, en route to Comet Boethin.

Michael A'Hearn of the University of Maryland, College Park, is EPOXI's principal investigator and the leader of the DIXI science team. L. Drake Deming of NASA's Goddard Space Flight Center is EPOXI's deputy principal investigator and leads the EPOCh investigation.

"EPOXI is a wonderful opportunity to add to our growing body of knowledge of exoplanets," said John Mather, chief scientist for NASA's Science Mission Directorate. "Watching planets go behind or in front of their parent stars can tell us about their atmospheric chemistry."

NExT: Revisiting Comet Tempel 1
The other newly selected Discovery mission of opportunity is called NExT, or New Exploration of Tempel 1. The mission will reuse NASA's Stardust spacecraft to revisit Comet Tempel 1. This investigation will provide the first look at the changes to a comet nucleus produced after its close approach to the sun. It will mark the first time a comet has ever been revisited.

NExT also will extend the mapping of Tempel 1, making it the most mapped comet nucleus to date. This mapping will help address the major questions of comet nucleus "geology" raised by images of areas where it appears material might have flowed like a liquid or powder. The images were returned by Deep Impact from its encounter with the comet on July 4, 2005. NExT is scheduled to fly by Tempel 1 on Feb. 14, 2011.

Joseph Veverka of Cornell University is NExT's principal investigator.

Stardust launched in Feb. 7, 1999. It traveled over 2 billion miles to fly within 150 miles of the Comet Wild 2 in January 2004 to bring back samples that may provide new insights into the composition of comets and how they vary from one another. The container with the comet samples returned to Earth in January 2006 while the rest of the spacecraft remained in space.

This report is based on information released by NASA and supplemented by's Alan Boyle.

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