June 2002


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Written by
Jessica Mesman

Illustrations and
courtesy of NASA

NASA’s Deep Space 1 mission may shed light on everything from the origins of the universe to engine design for deep space travel. The mission’s successes and failures reflect directly upon its project scientist, Robert Nelson, who earned a PhD at Pitt in 1977. His studies here in the geology and planetary sciences department helped lead him to his role with NASA.

Lost in

In a control room at NASA’s Jet Propulsion Laboratory[*], where one wrong command might kill a mission, waste millions of tax dollars, and embarrass dozens of researchers, Robert Nelson paces the floor, wishing he could smoke. A small space probe is hurtling into the wake of a comet. Once there, the probe will take pictures and chemical samples that might help identify the comet’s composition and lead to some startling revelations. It’ll be up to Nelson, and the team of scientists he directs, to interpret those pictures and test results. But the mission isn’t going as planned.

Deep Space 1 is flying blind. NASA launched the little aluminum barrel in 1998 to test a dozen new technologies, including software that enables the craft to make navigation decisions without the help of ground control and, more spectacularly, utilize an ion propulsion engine. By pushing ionized atoms of xenon instead of traditional rocket fuel, the engine can deliver 10 times as much thrust per pound of gas as liquid or solid fuel engines, enabling longer deep space travel with larger payloads—maybe even astronaut missions to the outer solar system. All this Star Trek stuff tested so beautifully that Nelson, the Deep Space 1[*] project scientist, and his team recommended in the summer of 2001 that the probe’s mission be extended to rendezvous with the comet Borrelly. NASA agreed with the recommendation.

By summer’s end, things aren’t going so well. The probe’s standard navigation devices have failed. Deep Space 1 is adrift in a kind of free fall, waiting in safe mode for a command from home. As Nelson paces near the 30 or so computer monitors that serve as his window into mission control, project engineers use new software to try to reboot the aging probe. The goal is to get the probe back on track, and into the wake of the comet. Technically, Deep Space 1 completed its original mission successfully. Just knowing the new equipment works will make guidance decisions easier in future missions. But Nelson knows that most people expect a NASA mission to reach a target and do something. If Deep Space 1 fails to return hard data—like new images of something in outer space––it will be like showing up to the prom in a tuxedo without a date, he says.

With no navigation device, little remaining fuel, and many of its experimental instruments pulling double-duty, the chances that the probe will even find Borrelly are slim; chances it will return data and usable images are considerably less. Just one sliver of debris could knock out the probe’s camera. Worse, Deep Space 1 is not designed to withstand Borrelly’s menacing jets of ice. While a chancy comet encounter might cast a pall on the probe’s earlier success, if Deep Space 1 succeeds, it could bring NASA that much closer to tapping the secrets of the cosmos. The stakes are high, which is why Nelson paces and frets and longs for the pipe he gave up 20 years ago.

Originally a US Army rocket experiment station, the JPL campus was taken over by NASA in 1958, just after the Soviet Union launched Sputnik and began the space race. Nelson remembers the time well; it’s when he decided that he wanted to devote his life to space exploration. At the time, Nelson was a 10-year-old Boy Scout growing up in Pittsburgh’s hardscrabble Hill District neighborhood. He had dreamed of playing right field like Roberto Clemente. Baseball seemed like a more realistic goal. NASA was as distant and exotic as outer space.

Nelson demonstrated early on that he could stand up for his beliefs. He didn’t understand why he could eat in certain restaurants when his friends couldn’t, or why, in some places, they had to drink from separate water fountains. As a young graduate student, he joined nine others at the lunch counter of a roadside diner in Baltimore and insisted the owners serve his African-American friends first. The police led them away at gunpoint.

Standing up for what you think is right, even if it means taking risks, is a quality that has served Nelson well over the years. Geology and Planetary Sciences Professor Emeritus Bruce Hapke, who took Nelson on as a Pitt graduate student in planetary sciences, says, “As a scientist, you have to be willing to stick your neck out. You’ll never be one of the innovators if you’re not willing to take risks.”

When Hapke took Nelson under his wing in the mid-1970s, few people could have imagined today’s satellite-mounted telescopes and high-resolution scanners that have revolutionized space study. Nelson says he owes his career to Hapke’s decision to take a chance on a poor kid from an uneducated family.

Nelson’s mentor has impressive credentials. Hapke, who retired last year as professor emeritus after teaching 34 years at the University, wrote Theory of Reflectance and Emittance Spectroscopy. The 469-page book has become a bible for many researchers, Nelson says. In the early 1980s, Hapke developed what became known as the Hapke Model. The model is a mathematical formula that describes how light, radio waves, and other kinds of radiation interact with a planet’s surface.

The formula is used to determine the particle size, porosity, and other characteristics of planet surface. The model is also used to process many of NASA’s interplanetary pictures that turn up in newspapers and magazines. Last year, the American Astronomical Society recognized Hapke with its most prestigious award, the Gerard P. Kuiper Prize in Planetary Science. And in Hapke’s honor, Pitt will host an international symposium in September dealing with remote sensing in space research.

Hapke and Nelson share a passion for remote sensing––think of it as long-distance learning. In remote sensing, the information carried in reflected sunlight is used to study many aspects of the surfaces of other worlds, such as the surface’s composition, its geologic events (including volcanoes, craters, and wind erosion), and its textures (such as whether a white appearance is fluffy drifts of snow or a frosty layer of ice crystals).

The debut of photography in the 19th century also marked the beginning of remote sensing. Not long after, pictures of Paris were snapped from cameras mounted in balloons. Next, kite-mounted cameras were used worldwide. But modern remote sensing is a lot more than pictures of faraway places. It takes sonar, radar, lasers and other high-tech tools to do everything from looking for signs of water on Mars to measuring the hole in the Earth’s ozone layer. Two years ago, the Landsat 7 Gateway satellite recorded the formation of four lakes in one part of the Sahara Desert, the first lakes in that region in 6,000 years.

Remote sensing is a key component in Pitt’s geology and planetary science program. No more than a dozen students are accepted into the program here annually, Hapke says. Its graduates have few problems finding jobs teaching at universities or working in labs. Nelson, who regularly visits Pitt and continues to collaborate with Hapke on research papers, hires summer interns from Pitt to work at JPL. A Pitt graduate is currently doing post-doctorate work there. And at Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland, Deborah Domingue, who graduated from Pitt in 1990, is working as the deputy project scientist on Messenger, NASA’s spacecraft that will study the rocky surface of Mercury. Launch of the $256 million craft is scheduled for March 2004.

Nelson’s career got an early boost from a NASA-funded graduate student project while he was still at Pitt. With Hapke’s help, Nelson built a steel and aluminum contraption, the size of a small broom closet, which uses reflected light to measure the texture of materials. Measurements of things such as rocks, glass, and soil are then compared with data collected by satellites. In this way, scientists can understand planetary surfaces and the processes that create them.

The thinking behind the device, called a goniometer, is as sound today as it was when Nelson made the device 25 years ago. Students can still use it. Hapke notes it’s among only four goniometers worldwide dedicated to planetary science research.

On New Year’s Eve in 1977, Nelson, on winter break from Pitt, worked alone on his dissertation in a University of Texas observatory, deep in the Davis Mountains. Happy to have telescope time, he didn’t miss singing Auld Lang Syne. He observed the satellites of Jupiter, carefully measuring their spectral properties in which the spectral measurements look at the color or wavelength behavior of light and can be used to understand the composition of planet surfaces. He analyzed these measurements and used the resulting data to form hypotheses about what was happening on the surface of Jupiter’s third largest satellite.

When he returned to Pitt, he had some excellent spectral measurements of Jupiter’s satellites. Hapke says they’re some of the best to date. Nelson was also reasonably sure he’d made an important discovery. He and Hapke scratched their heads over the spectrum of the satellite Io—his analysis indicated the presence of sulfur. Not the powdery, yellow stuff you find in a child’s chemistry set, but a richer, redder version created by melting and then quickly cooling the substance, usually a result of volcanic activity. At the time, there wasn’t evidence of volcanic activity in the outer solar system. No one imagined they had hot interiors required for volcanic activity. Peer reviewers warned Nelson that publishing his findings would make both him and his mentor look foolish. But Hapke encouraged him to move forward anyway.

Nelson thought, “Hell, the evidence points to volcanism. Let’s just say it.”

Nelson’s Io observations were published in a 1978 issue of the scientific journal, Icarus. A few months later, the Voyager spacecraft flew past Jupiter and took images of volcanoes popping off the satellite Io, spewing dark red sulfur.

The Voyager scientists wanted to claim the discovery of Io’s volcanoes for themselves, but Carl Sagan, then editor of Icarus and a member of the Voyager team, pointed to young Nelson’s observations as “remarkably prescient.”

“It was a major thrill,” Nelson says, still sounding amazed.

Today, as the project scientist for Deep Space 1, Nelson coordinates the research of 15 scientists, plus all of their assistants. During the harrowing days before they attempt the comet encounter, he rides the six miles from his home to JPL on his ten-speed bicycle, wearing a helmet and a backpack with flashing red lights. Biking is his way to burn extra energy—when he gets to work, he does a lot of waiting, quietly pacing, letting his engineers work undisturbed.

Deep Space 1 continues to float aimlessly, awaiting commands that it’s unable to receive. Project engineers are frantically trying to find a way to issue commands in a way that Deep Space 1 will understand. Finally, the space probe’s camera is pressed into duty as a backup navigation device—which is something like sightseeing while someone else holds the binoculars.

It seems to work.

Nelson paces some more, less out of anxiety than excitement. He awaits the raw data the probe might beam to Earth. Although Nelson and his team of scientists have been intimately involved with the project from the start, the real work is just ahead. It will be up to them to interpret the data relayed by the probe. Nearly 200 million miles away, Borrelly streaks toward the sun, a dark storm of rock, dust and ice swirling chunks of crusty charcoal debris in its wake. Deep Space 1 gives chase.

“The fantastically rich science data from Borrelly will be the basis for much of the scientific work on comets for years to come.”

—Jessica Mesman is a freelance writer and is enrolled in Pitt’s MFA writing program. Kris B. Mamula, senior editor of this magazine, contributed to this story.


Walking with his father, a boy gazes at the night sky. Not all of the lights above are stars, his father explains. Some are planets.

Do people live on them? the youngster asks. The father shrugs.

Soon after that walk with his father in the 1930s, Bruce Hapke emptied his bank and sent the coins to a pulp sci-fi magazine for a telescope kit, complete with cardboard tubes. His interest wasn’t a boyhood whim. Hapke retired last year as professor emeritus after teaching 34 years at Pitt in the geology and planetary sciences department.

One of his many achievements stemmed from the NASA moon missions. That enabled him to analyze the moon’s soil and rocks, in part to solve a mystery. Scientists recognized that the moon should shine twice as bright as it does; they hoped the samples would show why it is dull. After testing, noted scientists reached the same conclusion: meteorites slam into the moon, creating a dark glass that causes the moon to appear darker.

Hapke wasn’t convinced. He mimicked their testing and his glass was light. He hypothesized that space weathering caused the muted moon surface. Space weathering occurs when solar wind (gas that evaporates from the sun), which travels at a rate of 3,000 miles per second, crashes into the moon and vaporizes the iron from the soil. The surface becomes darker when the vaporized iron coats the soil after resettling.

Nobody believed Hapke. For almost 30 years. He moved on to other projects. However, in the early 90s, photos of the asteroid Ida from the spacecraft Galileo showed indisputable evidence of darkening similar to what occurs on the surface of the moon. Yet, it wasn’t caused by glass because the speed with which meteorites hit the surface of an asteroid is too low for melting to occur.

Then last year, a scientist at the Johnson Space Center examined lunar rocks under a powerful microscope. He discovered an iron coating on them. Scientists believe Hapke now.

Meghan Holohan

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