Deep Impact's echoes still reverberate
Boulder-built craft's comet mission hit bull's-eye a year ago
Daily Camera, July 2, 2006
A Boulder-built spacecraft celebrated humanity's first contact with a comet one year ago Monday. At 11:52 p.m. on July 3, 2005, an explosion burst from the frozen belly of comet Tempel 1, triggered when a copper-laden, barrel-sized module of the Deep Impact spacecraft struck at a relative speed of 23,000 mph.
The $330 million Deep Impact was a short-term triumph, and with a Hollywood ending that distinguished it from so many space missions that simply fade away with failing instruments and dying batteries. But Ball Aerospace & Technologies Corp., which built the spacecraft, and the rest of the scientific community considered Deep Impact a long-term investment.
One year later, it appears to be paying off. Deep Impact has led to a host of new business opportunities for Ball Aerospace. And the flood of data from the mission, much of it still being studied, is changing scientists' basic assumptions about comets.
Deep Impact made for a challenging introduction to deep space. Tempel 1 was darker than charcoal and of unknown shape and size, flashing around the solar system at 66,000 mph. At impact, it was 83 million miles from Earth, nearly as far as the sun. Ball Aerospace engineers likened it to hitting a charcoal briquette with a BB from a distance of six miles - at night.
Charles Elachi, director of NASA's Jet Propulsion Laboratory, called Deep Impact "one of the most daring and risky space missions that we have ever undertaken" as the spacecraft approached its target. Elachi's laboratory, a partner on the mission with the University of Maryland, has sent spacecraft to eight planets.
David Taylor, CEO of 3,000-employee Ball Aerospace, said his company works hundreds of projects at a given time. But in an interview last week, he called Deep Impact "a major program and a major mission for us."
Ball Aerospace had been building satellites for low-Earth orbit - a few hundred miles above the planet - since 1959. But the company had never been the lead contractor on a deep -space mission. To join that club, it had to prove it could operate light-minutes from Earth.
"Did we take a risk? Well, sure," Taylor said. "Had it not worked, it would have been a problem for us."
Taylor said the mission's success has opened doors both in the civil and the defense markets, the latter because of the mission's high profile and extreme difficulty. He said Ball Aerospace is now a "qualified deep -space teammate" with the Jet Propulsion Laboratory and is collaborating with that organization in proposing four NASA Mars Scout missions.
Such missions, with a maximum cost of $325 million, would send various probes to the Red Planet. In addition, Ball is working with the Jet Propulsion Laboratory and the University of Maryland on a mission called Deep -Rosetta, or DeepR.
DeepR would send a Deep Impact clone to the comet Churyumov-Gerasimenko, the target of the European Space Agency's Rosetta comet-lander mission. With Rosetta and DeepR's flyby module looking on, DeepR's impactor module would smash into the comet on July 29, 2015. NASA will decide on DeepR this fall.
Another proposed mission, called the Deep Impact Extended Mission, or DIXI, would use Deep Impact's surviving flyby module to inspect comet Boethin in December 2008.
Others are taking cues from Deep Impact's example using the "impact approach" to scientific discovery.
Phil Christensen, a professor at Arizona State University, has proposed a Mars Scout mission that involves a copper-laden impactor smashing into the surface of Mars. It would expose possible buried ice and other materials for viewing by a surviving spacecraft.
"We had been thinking about ways to get beneath the surface of Mars, including an impactor," Christensen said in an e-mail. "The success of Deep Impact certainly convinced us that this was an idea that would work, and that would be an approach that NASA would find viable and would be willing to support."
Tempel 1 was the fourth comet humanity had ever observed up close, with Halley, Wild 2 and Borrelly rounding out the group. Scientists are interested in comets because they were probably key players in the formation of the solar system. In particular, many scientists think comets delivered water and carbon-based molecules critical to life to Earth, a hot, dry place after its formation 4.6 billion years ago.
Scientists are still wading through data and imagery Deep Impact gathered before impact as well as observations from several dozen space- and ground-based telescopes after the fireworks.
Early findings indicated that Tempel 1 was more of a "snowy dirtball" than the "dirty snowball" first postulated by Harvard astronomer Fred Whipple in 1950. Telescopes spotted as much as 10 times more dust than ice. Contrary to expectations that a hard shell would cover the comet, Tempel 1's consistency is more like Steamboat Springs powder, scientists found.
Using a massive vertical gun at the NASA Ames Research Center in Silicon Valley, Brown University professor Peter Schultz has conducted ballistic experiments to recreate Deep Impact's pyrotechnics. "Super-fluffy snow" seems to behave most similarly, Schultz said.
But he cautions that Deep Impact hit only one spot on Tempel 1.
"You wouldn't go out and characterize the United States by digging in a sandbox in Galveston," Schultz said. "There are mountains in Colorado."
Schultz said the science team is still trying to discern the crater, which was obscured by a wash of dust. He said they believe the pit to be of unknown depth and between 150 and 250 meters in diameter.
If they fail, NASA's Stardust spacecraft may succeed. Scientists have proposed sending the orbiting mother ship of Stardust, which successfully returned cometary dust particles to Earth in January, to Tempel 1 when the comet returns in 4½ years. That mission would be called Scar Quest.
Deep Impact scientist Michael Belton is leading work that could "change our models on the formation of comets," as University of Maryland professor Lucy McFadden put it.
The prevailing theory has comets forming grain by grain. Belton and others, using images of depressions and ridges taken on approach to the comet, now believe they formed splat by splat.
"We've convinced ourselves of these fundamental layers - formed in low-velocity collisions - that came together and went 'splat,'" McFadden said. They call the layers "talps." That's "splat" spelled backwards.
The recipe of cometary ingredients scientists promised before impact is pending. Using an instrument on the Spitzer Space Telescope that Ball Aerospace built, a team led by Carey Lisse, of the Johns Hopkins University's Applied Physics Laboratory, found clays, carbonates, silicates, water and sulfides among the material ejected by the collision with the 800-pound impactor.
Clays and carbonates were big surprises. They require liquid water to form, suggesting that either comets themselves or a good deal of cometary material formed close to the sun. McFadden said the full list of compounds Spitzer spotted is pending publication in the journal Science.
"It gives us clues to the complexity of the formation of comets," McFadden said.
A few hours before last year's encounter, Thomas Bank said: "Tomorrow, my career starts to get a whole lot more boring."
Bank, Ball Aerospace's lead engineer on the five-year Deep Impact mission, now works on proposals for future NASA missions.
"My career has not gotten a whole lot more boring, but it's been a whole lot less stressful this past year," he said last week.
Deep Impact isn't completely behind him. Bank said Ball engineers last radioed the flyby module in February, just before it disappeared behind the sun until August.
If the DeepR mission happens, Bank stands a good chance of being involved, he said.
He said he sees some of the 300 colleagues who worked on Deep Impact every day.
"There's a camaraderie that those of us who endured Deep Impact share. You know them a little better than the rest of the people you work with," Bank said. "It's a very nice feeling."
© 2008 Todd Neff