Princeton University - Council of Science & Technology

POPE PRIZE

With a low whine, a rocket pitches from the thin atmosphere onto iron-red soil and rock. It has arrived on Mars. Bitter winds raise dusty clouds obscuring the rocket, which has opened to reveal a large box. As the sun looms starkly on the cold horizon, the box, like a giant egg, hatches slowly. Flaps unfolding, metallic wings unfurling, a strange winged machine emerges, sunlight glinting in shards off its thin back. With a mechanical whirring, this first airplane on Mars hovers off into the air of the Red Planet, skimming over dry and ancient canyons. It is December 12, 2003, one hundred years to the day from a similar event on more similar terrain - the Wright Brothers' first powered flight at Kitty Hawk.

Many miles and many years away from this scenario of the future, in his office at the engineering building of Princeton University, professor Edgar Choueiri is pointing to his nose. Currently, it is slightly red from the exertion of dealing on the phone with Choueiri's secretary, his wife on line two, and an interviewer. It is also, Choueiri says, adeptly maneuvering the first two conversations to an end, and with finger still indicating his nose, farther than John Glenn's latest outerspace destination.

Choueiri is extemporaneously creating a scale model of the universe, wherein his small, squarish face is the earth rimmed by curly brown hair, and John Glenn's recent triumphal orbit is somewhere in the vicinity of the professor's oval framed glasses, not quite making it to the tip of the professorial nose. On this scale, the moon is one hundred and fifty feet off in the linoleum-tiled corridor where students with backpacks walk between their classes. On this scale, Glenn's flight suddenly seems insignificant.

How can we humans expand space exploration when we do not push ourselves," says Choueiri, excitedly waving towards the corridor, where a few students continue to pass by, Unaware of their sudden translation to interstellar space. "It's as if someone told Christopher Columbus that he had to practice touching his toes for thirty years before crossing the Atlantic." Choueiri's idea of an Atlantic-size challenge lies across a cold, silent expanse of two hundred and fifty million miles in space - his target is our planetary neighbor, Mars. This professor of mechanical and aerospace engineering has proposed to commemorate the centennial of man's first powered, controlled flight at Kitty Hawk with the maiden voyage of ,in airplane on the fourth rock from the sun.

In the reduced scale model system, where John Glenn orbits a nose and moonlight is lost in institutional fluorescent wattage, Mars is five miles removed. Across the engineering building, past the library and cobblestone plaza, beyond even the trees of the nearby Princeton battlefield, naked in winter, it is indeed a faraway vision.

So far away, in fact, that when Choueiri first circulated the idea quietly amongst departmental colleagues in early 1997, the proposal stayed out of sight and out of mind, languishing for nearly two years. It was not the first suggestion of a remotely controlled Martian plane flight in the scientific community, although no one else had linked it to the First Flight centennial anniversary, Previous ideas in circulation from Malin Space Science Systems, the Naval Research Laboratory, and NASA's Ames Research Center were ruled out by NASA as too complicated, and liable to go wrong. Numerous spacecraft missions aimed at Mars were already planned for launch within the next decade, including the Orbiter and Lander portions of the Mars Surveyor Project, designed to gather information on Martian climate. It was hard for yet another Mars proposal to attract interest.

Today, it is difficult to conjure up Choueiri's original proposal. Its author frowns at his enormous computer, which is refusing to print a copy of that article. In between mouse clicks, he explains the difficulties inherent to Martian exploration. A little flock of chesthigh brass lamps shine their curious, muted light on the comer of one wall, on the edge of the desk, on the professor's polished shoe.

The Red Planet, which is half as big as its neighbor Earth, but farther from the sun, has two moons and no living inhabitants. Harsh conditions on Mars include extreme temperatures, which run from eighty below zero to the balmy sixties and howling winds that relentlessly kick up storms of iron-rich dust. Any probes, which will be exposed to these rough elements, must withstand large temperature changes, and scouring, gravelly winds, all while minimizing weight, which is at a premium when designing compact projectiles.

Why choose Mars at all for an airplane flight then? It is the nearest planet with an atmosphere. Airplanes rely on the pressure of molecular collisions on the surface of their wings to produce the lift necessary for flight. Traditionally, the upper surface of a wing is more curved than the lower surface. This curved upper surface constricts the flow of air more than the flatter lower surface, causing the air above the wing to speed up more than the air below. The faster the air speeds up, the lower its pressure becomes, as the air molecules are travelling faster, and colliding with the wing less frequently. So the faster moving air above the wing has less pressure than the slower moving air below. This pressure differential pushes the wing up, lifting the airplane. On Mars, though, gravity is a force two and a half times less that on Earth, providing a slight compensation. Objects with mass, such as a plane, weigh less on Mars, requiring less lift to become airborne.

However, the Martian atmosphere is predominantly carbon dioxide. In recognition of the lack of "air" as Earthlings know it, Choueiri named his proposed project the Aresplane, taking the Greek name of the bellicose god of War known to the Romans as Mars. The forbidding personality of the god seems to aptly characterize the challenges of flying a plane on the planet named in his honor.

Because it lacks heavier elements, such as nitrogen, which are commonplace in Earth's air, the Martian atmosphere is one hundred times less dense. On Mars, an airplane's wing would feel one hundred times fewer impacts from gas molecules, resulting in one hundred times less of a lift than on Earth. Thus, a successful Martian airplane design taxes the ingenuity of aerospace engineers by requiring a re-working of the classic airfoil wing shape to yield greater lift What would the plane look like? Choueiri speculates that such a design would include larger wings of light, lithe materials. "It must resemble the Wright Brothers' biplane, though," he adds, pointing out that the Mars plane must evoke its scientific predecessor. "After all, we could easily fly a hot air balloon on Mars, but," he grins, "where is excitement in that?"

Excitement, the real co-pilot of the Aresplane. Like Kitty Hawk, the Aresplane would fly on currents of human progress. But the Mars plane endeavor will differ significantly from Kitty Hawk in one crucial aspect. There will be no human pilot on this plane, no two brothers on site, one holding his breath while the other launches into history. It is too risky a project, especially as humans can not breathe the poisonous Martian atmosphere of carbon dioxide.

Since there can be no pilot, another necessary component of the Aresplane will be an advanced autonomous guidance system. Mars is separated from Earth by an enormous distance varying, from thirty-five to two hundred and fifty million miles, depending on the planetary positions in their respective orbits. Radio signals between the Aresplane and controllers on Earth would take between eight and fifteen minutes to traverse space one way. For a flight which is limited by fuel reserves to a few hours, a reaction time on the order of twenty minutes is too long, and too slow. Directing the flight from Mars would be like operating a remotely controlled car with an incapacitating delay time.

Given all these complications, even the Wright Brothers might have given up.

They had only the sand dunes and disbelieving natives of North Carolina with to contend. But to Edgar Choueiri, only such a problem is on the "order of magnitude needed to make a respectable tip of the hat to the Wright Brothers." He bristles at the idea of a lesser tribute to the pair, whose first solo flight is often attributed to lucky tinkering. "They were true engineers," he defends, rattling off their accomplishments in using wind tunnels and unwieldy equations. And he should know, he's an engineer himself with a specialty in the field of spacecraft propulsion, He seeks to develop alternative light fuel sources that will someday enable manned rocket travel to Mars.

Born in Lebanon, Choueiri graduated from the University of Syracuse in 1983 with a master's degree in aerospace science. During the low point of the aerospace field in the early nineties, when industry was shrinking and NASA was restructuring, forcing out older scientists, Choueiri continued his schooling at Princeton, earning a Ph.D. in plasma science in 1991.

Since those lean years, the aerospace field has experienced a rejuvenation that is due to a shift in emphasis from the Cold War space race to telecommunications. Third world and developing countries are demanding telecommunications systems which do not rely on infrastructure that is susceptible to breaking down. Constellational satellites, one such system, are being employed more frequently, and their development has created a need for spacecraft engineers like Choueiri and his students.

After earning his doctorate, Choueiri's research interests settled in electric and advanced propulsion for spacecraft. His vitae reads like an entry in an aerospace textbook, citing contributions to the understanding of many topics in the fields of plasma dynamics, plasma propulsion and astronautics. His titles include Chief Scientist at Princeton's Electric Propulsion and Plasma Dynamics Lab, assistant professor in the Mechanical Engineering Department and Associate Faculty at the Astrophysical Sciences Department.

For all these personal distinctions, Choueiri's prime motivation in proposing the Aresplane was out of a love for aerospace science. "This will be a symbolic and poetic gesture," said Choueiri, of the commemorative flight, I think exploring the frontiers of space is one of the most worthwhile pursuits of mankind." He does add the qualifier, however, that the importance of Martian exploration is hardly a universal consensus. His wife, for instance, doesn't always agree, especially when the subject of human space exploration causes late rights at work.

Edgar Choueiri's good fortune in the field of propulsion apparently extend beyond that of most rocket scientists, for, after lying dormant at Princeton for a few years, his proposal was rapidly ejected into the upper stratosphere of NASA administration, where it went into an orbit of contemplation and a universe of possibilities materialized. It has yet to descend. A member of the Princeton faculty, possessing a copy of the 1, 997 proposal, perceived its potential and forwarded it to a friend. That friend was Dan Goldin, head administrator of NASA.

Goldin realized that the linking of the Wright Brothers centennial with the Aresplane flight provided an impetus for the Martian flight project which would generate both enthusiasm and a timeframe in which to complete it. It would also be the ultimate exclamation to a century of aeronautical engineering, which has seen the human race from hilltops to beyond the sound barrier. Suddenly, it seemed there were many benefits from an Aresplane flight. NASA adopted the idea with enthusiasm. Goldin scheduled a press conference to broadcast news of the )-o.iect, calling Choueiri to thank him for the centennial commemoration idea.

"It was nice of him to call," said Choueiri a month afterward, when NASA had assumed control of the project, petitioning Congress for budget approval and preparing to search for a team of scientists. Choueiri won't be leading that team, though. His specialty is propulsion. "My proposal [linking the Aresplane flight to the Wright Brothers' Centennial] provided an impetus, a timeframe."

A three-hour flight could cover one thousand miles on the Red Planet, which is roughly half the size of Earth. The Aresplane would combine the wide-ranging flying coverage of an orbiting spacecraft along with the higher resolution of reconnaissance features previously possible only in surface rovers. By covering roughly one thousand miles in three hours, the plane could avoid the disadvantages associated with previous Martian exploration methods.

Orbiting spacecraft can't make out features smaller than about six feet square, and surface rovers are unable to maneuver over rough landscape or large distances. The explorations of the Sojourner rover, though right on the Martian surface, covered only the length of a football field. Equipped with instruments such as cameras, laser altimeters and magnetometers, the Aresplane would fly within a half a mile of the surface, and possess the ability to survey the landscape at a resolution of just a few inches square. Radio signals could be sent back to Earth and broadcast so that the public, along with NASA, would enjoy the view, albeit minutes delayed.

One potential application of Mars exploration involves the search for candidate locations to sample Martian soil and rocks below the soil surface. Instruments like a magnetometer can sense the gravitational and magnetic fields, which together can reveal patterns of subsurface rocks. In combination, a thermal infrared imaging spectrometer can be used to probe the structure and composition of rock. An instrument that measures electric fields may be able to detect the presence of liquid water - the prime prerequisite for life - within five miles of the soil surface, because water changes the electrical conductivity of rock.

A key target of investigation is the Valles Marineris, an enormous canyon that runs along Mars. It is of interest to both geologists, who study the planet's formation, and to biologists, who seek signs of life in places where there are geological indications of the past presence of water and layered sediments. No one knows how Valles Marineris was formed. There is some evidence that the canyon was formed by a type of faulting in which the ground pulls apart and a block of rock sinks, forming the canyon bottom.

But the canyon walls are striped with layers of rock, suggesting parallels with similar formations on Earth which result from deposition through the action of flowing water or lava erupting from a volcano. Valuable information is exposed on the rock faces of the canyon, which are effectual cross sections of Mars and include rocks that could be billions of years old. Valles Marineris could yield clues about the overall history of Mars. For instance, if it turns out to have been carved by water, this indicates a large amount of water was once on Mars, and may still exist buried beneath the surface.

Evidence of running water in past epochs of Mars history has potential implications for understanding the origins of both Earth and Mars. Water can not exist in the liquid state on the surface of Mars, due to low atmospheric pressure and cold temperatures. If water is shown to have run across Martian terrain in the past, then early Mars may have had a warmer, thick, and more gentle atmosphere, much like that of Earth's pre-oxygen epoch. Scientists must then answer for the reason behind the change of atmospheric conditions on Mars, if such a phenomenon has implications for environmental changes on Earth, and whether life may have arisen oil Mars during its early, Earth-like years.

As the Aresplane skims over Mars, data will be continuously beamed back in the form of radio waves, speeding back to eager scientists on Earth within eight minutes. The plane itself, however, must be abandoned on Mars when the flight is through, because it would be too costly to retrieve. Given the extreme temperatures and unforgiving winds of the planet, the Aresplane will probably not last long. I hope the Wright Brothers will forgive us for creating rubbish in their name," said Choueiri with a grin. At fifty million dollars, this eventual "rubbish" would be one of NASA's less expensive endeavors. NASA received the Congressional go-ahead on its budget proposal in early March, and opened the plane design to competition between development groups on April 1.

Princeton is assembling a team of engineers. Choueiri is one of them.

The computer finally agrees to print the document, and Choueiri disappears at a brisk trot down the hall, past Mars, to the printer to fetch it. One of the little lamps has its brass head cocked at the fourth in a series of post card-sized framed prints adorning the office. They are the professor's theoretical work, rendered in illustration: elliptical lines swing past grids and cells, growing as unknown functions. They are his best thoughts, embodied, given a pine and supporting walls. Perhaps, some day, in 2003, a drawing of an airplane will 'here too.