The new mission, Deep Impact, aims to crash a 500 kilogram (1,100 pound) copper spacecraft into Comet Tempel 1 in 2005, creating a crater as big as a football field and as deep as a seven-story building.
The earlier mission, Champollion or Deep Space 4, was to map the icy surface of the comet, land a small spacecraft there in 2005 and collect samples for on-site analysis and a later return to Earth.
NASA attached $240 million price tags to both missions and Deep Impact, like Champollion, will be managed by NASA's Jet Propulsion Laboratory.
So what's the deal?
Jay Bergstralh, NASA's program scientist for the division that includes Deep Impact, said Friday that the newer mission is unique in that it will sample the comet's core. He said the decision to can Champollion was "not in any way predicated on the selection of Deep Impact."
"We think that the pristine matter in comet nuclei is the stuff that the solar system is made of," he said. "These are fossils. If we can get through this processed crust and look at the pristine matter beneath it we think we'd have a better idea of the chemicals that were in the nebula, the cloud of gas and dust that the solar system formed from."
"Champollion got the ax because of problems with funding. It had grown beyond it's original scope. The phasing of costs over time was one reason Champollion got the ax. Champollion was supposed to be principally a technology demonstration program and it had grown outside that envelope," Bergstralh said. "Deep Impact is a qualitatively different kind of mission. It doesn't do the same kinds of things Champollion was intended to do."
The earlier mission was headed up by NASA's Brian Muirhead, leader of the Mars Pathfinder mission. The new mission will be led by Michael A'Hearn at the University of Maryland in College Park. That move follows a NASA cost-cutting trend to put more aspects of missions in the hands of university researchers and contractors.
The day after NASA scrapped Champollion, the European Space Agency grabbed media attention by unveiling a model of the Rosetta spacecraft, set for a 2012 rendezvous and landing on the comet Wirtanen. That feat would have made them the first agency to land on a comet given the cancellation of Champollion.
NASA's Deep Impact will precede the European landing -- although it's clear that a controlled crash is not the same as a landing.
Bergstralh said NASA planned months ago to announce the Deep Impact mission in July. As for whether the European Space Agency timed its unveiling to upstage NASA following the death of Champollion, Bergstralh wouldn't venture to say.
Deep Impact, which shares its name with a 1998 movie about a comet crash on Earth (this is definitely a coincidence as the name was selected before the movie was announced), is set for a January 2004 launch (Champollion was set for a 2003 launch). The plan is to put a camera and infrared spectrometer aboard Deep Impact to collect data on the icy spray from the crash, which is set to occur July 4, 2005.
The impact date hearkens to the Pathfinder landing of July 4, 1997.