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NASA Getting Ready to Smash Comet -- Deep Impact Spacecraft to Blast Crater, Analyze Ice, Dust on July 4 Mission

Posted on: Tuesday, 4 January 2005, 12:00 CST

CAPE CANAVERAL, Fla. - The big, grown-up boys on the NASA team can hardly wait. Next Fourth of July, they get to bust up a comet, Hollywood-style.

"Blow things up? I'm there. Yeah, I don't have any issue with that," says Richard Grammier, manager of the project for Jet Propulsion Laboratory. (And, oh yeah, he used to work with explosives in the military.)

The spacecraft is called Deep Impact just like the 1998 movie about a comet headed straight for Earth. NASA's goal is to blast a crater into Comet Tempel 1 and analyze the ice, dust and other primordial stuff hurled out of the pit.

Mission planners say the energy produced will be like 4.5 tons of TNT going off - producing a fireworks display for the world's observatories.

Scientists know little about comets and even less about their nuclei, or cores. They believe that penetrating the interior for observations by space and ground telescopes is the next best thing to actually landing, scooping up samples and delivering them to Earth.

"A sample return would be the ultimate, but this is one exciting mission because for the first time we're actually reaching out and we're going to create our own crater," says Donald Yeomans, a senior research scientist at JPL in California - and an adviser on the movie.

"We'll understand how the comet is put together, its density, its porosity, whether it has a surface crust and underlying ices, whether it's layered ice, whether it's a wimpy comet or whether it's a rock-hard ice ball. All of these things will become apparent after we smack it."

Astronomers are counting on Deep Impact to live up to its Hollywood name on July 4, six months after its mid-January launch.

This is one spacecraft NASA wants to smash and trash.

"It would be like it's standing in the middle of the road and this huge semi coming down at it at 23,000 mph, you know, just bam!" Grammier says.

If all goes well, Deep Impact will be the first spacecraft to touch the surface of a comet. NASA's Stardust spacecraft - on its way back to Earth with dust from Comet Wild 2 - flew through the coma, or dusty gas cloud.

Deep Impact will have traveled 268 million miles from the time it is launched aboard an unmanned rocket until it intersects with Comet Tempel 1 just beyond the orbit of Mars, at a point more than 80 million miles from Earth.

Liftoff is targeted for Jan. 12, two weeks late because of software and rocket problems. NASA has until Jan. 28 to launch Deep Impact. After that, Tempel 1 will be beyond rocket reach and scientists will have to pick another comet and swallow a lengthy delay.

That's what happened to the European Space Agency's Rosetta spacecraft, which will attempt a controlled landing on a comet, but not until 2014.

Deep Impact, by contrast, will provide "instant gratification," says Grammier. The entire $330 million mission should be wrapped up a month after impact.

Comet Tempel 1 is a typical comet - all the better for scientific analysis - yet has a large nucleus and weak coma, all the easier for the impactor to survive the dusty obstacle course and to nail the nucleus.

Grammier says the latest calculations put the chance of the impactor missing its target at less than 1 percent. The automatic navigation software has already been tested in space; this will be a fancier version of what successfully flew on NASA's Deep Space 1, a testbed spacecraft launched in 1998, and Stardust, the earlier comet spacecraft.

"We all feel pretty comfortable with that (the odds), but as we've all said before, we're doing something we haven't done before," Grammier says.

No matter what, fans of the 1998 disaster film can rest easy.

NASA guarantees that no matter how powerful the punch or how big the crater, Deep Impact will barely alter the comet's orbital path around the sun and will not - repeat, not - put the comet or any part of it on a collision course with Earth.

Yeomans calculates that to move Tempel 1 or a piece of it into an Earth-intersecting orbit, the impactor would have to be 6,000 times more massive than what will shoot out of the mothership on July 3. The very next day, the 820-pound impactor will strike at the heart of the comet, creating one awesome Fourth of July display.

Source: Commercial Appeal, The

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