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Mission control


Deep Impact's Michael A'Hearn

Comet stalker Michael A'Hearn. Photo by Matt Mendelsohn

Comet stalker Michael A'Hearn. Photo by Matt Mendelsohn

By Tom Nugent

On the southern flank of California's San Gabriel Mountains, the 165-acre campus of the Jet Propulsion Laboratory (JPL), with its giant satellite dishes and low-slung buildings, looks like an outpost on some desert planet. Staffed by 5,500 employees and operated as a division of the California Institute of Technology, the JPL is the nerve center for all robotic space exploration conducted by NASA, the National Aeronautics and Space Administration.

On the mild Sunday afternoon of July 3, 2005, a swarm of engineers, technicians, and more than 50 international print and electronic journalists (BBC, Yomiuri Shimbun, the Discovery Channel) cleared a security checkpoint and entered the JPL's sprawling headquarters complex, most headed for the von Karman Auditorium. As they crossed the lobby into the auditorium, they passed, mounted on the walls, a half-dozen video screens on which were displayed a dramatic image.

The photo, taken through a NASA telescope, was of a massive, pickle-shaped rock, the comet Tempel 1. Often described by NASA officials as "a dirty snowball half the size of Manhattan," Tempel 1 was at that moment traveling in a solar orbit at a speed faster than 66,880 miles an hour.

In the next dozen hours, technicians at the space complex would attempt to hit the rock with an 820-pound, copper-plated vehicle about the size of a washing machine. The Impactor, which carried a telescopic camera and the radio gear to transmit photos, had been ferried to its present location, roughly 83 million miles from Earth, by a Delta II rocket–launched NASA mother ship, often referred to by NASA engineers as Flyby.

The day before, Flyby (roughly the size of a mid-range SUV) had accomplished its mission of releasing Impactor into a trajectory aimed at crashing the tiny spacecraft head-on into the comet. Then the solar-powered mother ship had briefly fired its small thrusters, allowing it to slide safely off crash course and into a harmless, moving "parking space." From its vantage point (some 5,300 miles distant at impact) Flyby would snap thousands of optical and infrared photos.

If everything went according to plan, the NASA project, christened Deep Impact, would mark the first time that humans had touched a comet in space. The collision would take place around two o'clock the following morning, which meant that it would occur on the Fourth of July.

AT THE rear of the von Karman Auditorium, the metal doors swung open and a large, white-bearded man, Michael A'Hearn '61, hurried through the milling throng of engineers, technicians, scientists, and reporters who had gathered there to follow the events. The name tag he wore read Deep Impact Principal Investigator, signaling that he was essentially the chairman and CEO of this $330 million enterprise and the coordinator of all scientific aspects of the project. His name tag didn't note that A'Hearn (pronounced "ah-HEARN") is also a faculty member of nearly 40 years' standing in the University of Maryland's astronomy department, where his title is Distinguished University Professor.

At 64, the broad-shouldered and jut-jawed astronomer in some ways still resembles the youthful athlete who played tight end for the Boston College High School Eagles. Round-faced and balding on top, he moves like a good-natured bear. His eyes, a deep blue, are more restless.

Tempel 1. Photo by NASA/JPL-Caltech/UMD

Tempel 1. Photo by NASA/JPL-Caltech/UMD

"To be honest, I'm pretty frantic right now," the astronomer told a reporter. "There's too much to do, that's all." A'Hearn would be spending the night ahead perched on a swivel chair at the back of the mission control room, located in the same building. He'd be with members of his Deep Impact Science Team, a dozen or so specialists in areas such as reflectance spectroscopy, cratering, image analysis, and cometary grains. The assignment: to "try and figure out what we're seeing" in the messages transmitted to their computer consoles from NASA's Deep Space Network of radio antennas and from telescopes on Earth.

Among the key questions that might be answered by data collected that night and into the next day:

What is the molecular structure of the dust and gas contained in Tempel 1, and what can that tell us about the birth of the solar system?

How much ice is trapped inside the comet? Is there enough to support the theory (strongly advocated by A'Hearn in journal articles and media interviews) that a large share of the water contained in the Earth's oceans arrived here via a barrage of comets (as many as one a year) during the first billion years or so of the Earth's existence? Is there any evidence of organic material aboard the comet—or of the complex carbon compounds that are the precursors of life?

Does Tempel 1 consist primarily of hard-packed, rock-like material? Or is it a kind of cosmic snow cone, a cluster of ice crystals and dust particles held together by gravity as it loops eternally along its 5.5-year circuit of the sun? (Answering that one might someday help the human race fend off an apocalyptic collision with an approaching comet.)

The content of comets holds enormous interest for astronomers: It is thought that most comets were formed at the beginning of the solar system, more than 4.5 billion years ago, and that they were forged out of the same "primordial soup" (vast clouds of interstellar dust and gases) that coalesced to form the sun, the Earth, and the other planets. Astronomers believe comets have remained virtually unchanged since, that they are, in essence, "fossil" indicators of Earth's rudimentary past.

On July 3, NASA's engineers put the odds that Impactor would land where it was supposed to at better than 99 to 1. And how much control would A'Hearn have over the flight as the rendezvous loomed? "Believe me, I'd love to be sitting here with a joystick in my hand," he said. "But from 27 hours out, just about everything that happens at the physical level is autonomous. To do the job right, we have to think through every possible eventuality in advance, and then figure out how to respond to it. And if you're going to think of moves to make in advance, you might as well go ahead and program them into the computer."

He looked at his wristwatch. "This is the toughest part—the waiting."

IMPACTOR'S JOURNEY started six months before, on January 12, with liftoff from Cape Canaveral, Florida. But the effort to crash a sensor into a comet began at least 10 years earlier than that, when A'Hearn and several other astronomers at the University of Maryland and elsewhere began assembling a proposal to strike a different target, the dead comet Phaethon. NASA denied funding. "The science panel was not convinced that Phaethon was a comet and they did not believe we could hit it," recalls Alan Delamere, an engineer then with the Colorado-based Ball Aerospace & Technologies, which ultimately designed and constructed Deep Impact's spacecrafts. In 1998, A'Hearn substituted Tempel 1 as the target, the engineers incorporated a "fine guidance" auto navigation system into plans for the Impactor, and the project received preliminary NASA approval.

The next hurdle for A'Hearn's team was preparation of a second, more detailed version of the proposal—300 pages in all. "It was a huge job," he says, "and we . . . barely made the deadline. The final version had to be hand-carried on an airplane by one of our team members to the NASA brass in Houston." A'Hearn recounts learning that Deep Impact had gotten the green light, in 1999. "I was on vacation in London," he says today, "and I got a message from Washington that they wanted me to call NASA. I remember making the phone call from a phone booth in Russell Square—but I don't remember what happened for a minute or two after I hung up, because I was too excited to focus.

"The euphoria lasted for a day or two, and then the grind really began." What followed were several years of planning and preparation, led by a dozen astronomers, aeronautical engineers, navigators, software designers, and other specialists—about half of them from U.S. universities and the remainder from NASA.

The biggest engineering challenge, according to Alan Delamere, was to create "a very stable flyby spacecraft." The project would have "800 seconds or so to gather high-fidelity images and data," during some of which Flyby might be passing through a dangerous field of comet debris.

Twelve hours after the $330 million project achieved its goal, A'Hearn takes questions from the press. Photo by Gene Blevins/Corbis

Twelve hours after the $330 million project achieved its goal, A'Hearn takes questions from the press. Photo by Gene Blevins/Corbis

The toughest task of the 10-year project, in A'Hearn's view, was "coordinating all aspects of the mission during the last few months before the launch . . . making sure that all the parts fit." As Flyby and Impactor raced toward their early-morning rendezvous with Tempel 1, many on the Deep Impact staff, increased now to 250, had been working 12 hours a day for the past two months.

The engineering challenge of Deep Impact has been described as equivalent to hitting a speeding bullet with a second bullet, while a third bullet streaks past both of them, taking pictures. In fact, all three projectiles would be traveling at least 20 times faster than the average bullet. The collision was expected to produce a crater in the comet about the size of Yankee Stadium. Three U.S. orbiting space telescopes (including the Hubble), the European Space Agency's Rosetta spacecraft, and astronomers at 50 earthbound observatories in nearly 20 countries were ready to monitor it.

In addition to taking thousands of optical photos, Flyby would be employing its infrared sensors for a spectral analysis of the comet's makeup. Fourteen minutes after the collision, the little mother ship would pass the comet at its closest distance—310 miles—protected by dust shields, its cameras shut down. A half hour later, as it traveled away, it would swivel its cameras backward and begin collecting and transmitting data again, until the image of the comet became too small. Provided that Flyby wasn't "sandblasted into oblivion" by the dust and other materials from the explosion, says A'Hearn, the mother ship would continue on and might eventually be rerouted to study other interesting objects in the solar system, including, perhaps, a recently discovered comet, Boethin, located 3.5 years distant from the site of Deep Impact. As for Tempel 1, the effect of the collision on the comet's course would be "undetectable—the astronomical equivalent of a mosquito running into a 767 airliner," according to NASA.

The mission control room at JPL is a large, square enclosure containing two parallel rows of desks, each topped by a computer console and several telephones. About 15 JPL communications and engineering technicians usually sit here, along with their managers, during key segments of unmanned NASA space missions. As the engineers ran through their immense checklist of pre-impact procedures on the final night of the Deep Impact project, from time to time the video monitors around the auditorium and elsewhere in the complex would light up with printed announcements from the flight managers. These bulletins were then repeated in authoritative baritones on overhead loudspeakers throughout the facility:

Impactor trajectory is right on the money, copy.

Telecomm, 20 seconds to start of imaging sequences on Flyby.

Mike A'Hearn got into astronomy because he wanted to do "applied science rather than theoretical science" (after majoring in physics as an undergraduate at Boston College). In a matter of hours he and his colleagues would be collecting results from an astronomy experiment of unearthly proportions.

WHEN NOT at the JPL, A'Hearn works out of an office in the University of Maryland's Computer and Space Sciences Building—a neo-Georgian redbrick structure that serves as headquarters for the science component of Deep Impact. Waist-high stacks of paper cover nearly every surface in the room. Computer printouts of cometary light-emission spectroscopic analyses, coffee-stained copies of Icarus: The International Journal of Solar System Studies—"it's a real mess, all right," says A'Hearn. "Most of the time, I can put my hand on whatever information I need to keep the project running, but finding the right document quickly can be a real struggle at times."

On a summer morning, he wears a pair of navy-blue walking shorts, a sports shirt with a pattern of wave-cresting sailboats, and clunky brown sandals. The six-foot-two, 250-pound astronomer has pedaled to campus on a battered Schwinn bicycle.

His passion for space "really got started," A'Hearn says, during a 1960 summer school course he took at Harvard with famed cosmologist Owen Gingrich, between his junior and senior years at BC, to which he commuted from his home in Braintree, Massachusetts. He earned his Ph.D. in astronomy from the University of Wisconsin in 1966 by arguing in his dissertation that the clouds of Venus could not possibly be water vapor. (He was proved right in the late 1970s, when NASA's Pioneer spacecraft probed the Venusian clouds and found mostly sulfuric acid droplets.)

From Wisconsin, A'Hearn went on to the University of Maryland, where he has since taught and published widely on subjects including interstellar dust, comet nuclei, cometary gas, and the planet Pluto. The Deep Impact project, he says, "simply grew out of my continuing interest in the origins of the solar system."

Prior to the Deep Impact project, NASA had dispatched several spacecraft to snap photos and collect data on comets. The International Comet Explorer (a joint venture with the Europeans) traveled through the comet Giacobini-Zinner's tail in 1985 and the following year joined what NASA officials have called an "international armada of robotic spacecraft" deployed to observe the near approach of Halley's comet. Improved images and data on gas and surface composition were transmitted by NASA's Deep Space 1 flyby of the comet 19P/Borrelly in 1998. And at this writing the spacecraft Stardust is making its way back to Earth bearing particles collected from the cloud around the comet 81P/Wild 2; it is expected to make a soft desert landing in Utah in January 2006.

"What excited me most about the [Deep Impact] project," says A'Hearn, "was the chance to actually dig into a comet and get a close-up look at its guts. All of us who've worked on Deep Impact over the past 10 years feel an intense excitement about getting our hands dirty as space scientists, rather than simply making astronomical observations or restricting ourselves to theoretical concerns."

Seven years and one month after the project was approved, impact photos arrive at mission control. Photo by Gene Blevins/Pool/Corbis

Seven years and one month after the project was approved, impact photos arrive at mission control. Photo by Gene Blevins/Pool/Corbis

A'Hearn is quick to point out that the original idea of taking a direct shot at a comet was hardly his own. NASA had been turning down similar project proposals since at least the 1980s. And the science fiction writer Arthur C. Clarke depicted just such an experiment in his novelization of the 1968 screenplay of 2001: A Space Odyssey. Clarke e-mailed A'Hearn in 1999: "I'm glad someone is finally doing it."

According to colleagues, the laid-back and usually soft-spoken A'Hearn was the perfect choice to manage the enterprise. "Mike really doesn't seem to have an ego," says veteran NASA space-exploration manager and physicist Frank B. McDonald. "He's also got a brilliant, creative mind."

Adds astronomer Lucy McFadden, a member of the Deep Impact team and a teaching colleague of A'Hearn's: "It was important to have a manager who could stand up to the pressures involved. . . . Our nerves did get frayed at times. But Mike never became impatient or unreasonably demanding of others. He has a real knack for lightening your load by coming up with a funny joke at just the right time."

Ask A'Hearn how he coped with the pressure of Deep Impact, and he'll start talking about his 28-foot sloop, the Ceol na Farriga (Song of the Sea, in Irish), and about lengthy voyages along the Atlantic seaboard. One of his three sons is an oceanographer. Another is an engineer, and the third, an economist. A'Hearn's wife, Maxine, recently retired as an adjunct professor of anatomy and neurophysiology at several Washington, D.C.–area universities.

1:52 a.m. EDT on the Fourth of July, 2005:

Mission Control, we have confirmation. We have confirmation. Stand by for image downlink from Flyby, copy.

SITTING BESIDE Project Manager Rick Grammier, the JPL executive in charge of Deep Impact's minute-by-minute operations at Mission Control, A'Hearn released a deep breath. NASA's three Earth-orbiting telescopes were reporting a brilliant flash of white light deep in the constellation Virgo—the unmistakable evidence that Impactor had slammed into the heart of the comet.

Five agonizing minutes of waiting followed, then the video screens in the control room suddenly began to light up. And there it was—the fat dill-pickle image of the comet, complete with its dimpled craters and fuzzy tail (a trailing 50,000-mile-long cloud of gases and water vapor). The bottom left corner of the rock was glowing furiously, marking the spot where Impactor, traveling at a relative speed of 23,000 miles an hour, had blasted through the comet's surface and heated its crumbly, powdery skin by several thousand degrees Kelvin. After hurtling 172 days and 268 million miles, Impactor had collided with Tempel 1 within roughly 55 yards of the projected bull's-eye. The onboard camera reportedly had snapped detailed pictures until just before Impactor vaporized.

When the glowing image of the comet appeared on the video screens, the JPL control room erupted in pandemonium. There were shouts—"We did it! We did it!"—and there was long and vigorous applause. While some of the crew waved fists triumphantly, others saluted the moment with coffee cups raised high. There was plenty of backslapping and more than a few hugs, and two or three elated technicians actually jumped up and down a few times.

For several moments, A'Hearn stood blinking at the back of the control room, grinning broadly from time to time. A few minutes later, voice shaking, he announced to the press gathered in the auditorium: "The images show that there was a spectacular impact, and there's so much data here, it's difficult to know where to begin. The final image was taken from a distance of only 18.6 miles from the comet's surface, and from that distance we can resolve features on the surface that are less than four meters [roughly 13 feet] across.

"When I signed up for this mission, I wanted to get a close-up look at a comet, but this is ridiculous!" he exulted.

SEVEN WEEKS later, A'Hearn sat in his University of Maryland office and ticked off the key findings to have emerged so far from Deep Impact. Among them:

To a depth of at least 30 feet, the surface of the comet is "essentially a very fine snowbank that also contains some dust." As recorded by Flyby's cameras and sensors, the explosion at impact released millions of droplets of water. Significance: These findings lend support to A'Hearn's theory that the Earth's oceans were deposited by comets over eons.

As expected, the material in the comet consists almost entirely of "very simple molecules," mostly oxygen, hydrogen, nitrogen, and carbon compounds. Significance: Tempel 1 most likely was formed 4.5 billion years ago from the primordial soup that provided the matter for the sun and planets in our solar system, and the guts of the comet haven't changed significantly since then. In addition, the presence of carbon molecules—the building blocks of life—indicates that living organisms might exist elsewhere in the universe, although these rudimentary particles don't provide any evidence that such organisms are actually out there, says A'Hearn.

The porous texture at the comet's surface provides evidence for the theory that most comets are more like snow cones than like ice cubes. Significance: This finding could help Earth's scientists and engineers figure out how to deflect a large comet from a collision with the planet.

With his colleagues, A'Hearn continues to study the gases, silicates, and various carbon compounds that were identified by the spectroscopic instruments aboard Flyby. "I feel very privileged to have been part of this enterprise," he says. "At the tender age of 64, I figure I've still got some years of hard work left in me—and Deep Impact has given me enough detailed information to carry me all the way to the end of my career."


Tom Nugent is a freelance writer based in Detroit.


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