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tanford
has a practical bias," says Clark Cohen. "That's one of the joys of the place.
You're strongly challenged to keep your feet planted firmly on the ground."
As a Stanford graduate student, Cohen began helping to test Einstein's Theory of General Relativity. Now he leads a company that's landing jumbo jets and guiding tractors on straighter plow lines for greater crop yields. Talk about bringing space-age technology down to earth!
With the end of the Cold War, Cohen thinks the opportunities for converting aeronautics and astronautics technologies into practical commercial tools have never been better. His own niche of Global Positioning Systems (GPS) is the poster child for the opportunity argument. Originally a secretive, military satellite-linked system for locating troops and aircraft, GPS has created booming markets for civilian gadgets such as pocket hiking aids, automobile navigation systems, and surveying tools.
Professor
Bradford Parkinson, one of the acknowledged fathers of GPS, was a major
reason Cohen came to Stanford. "It was a chance to study under an extraordinarily
respected person with amazing credentials," says Cohen. "Brad had previously
put together the GPS program and now managed the Gravity Probe B relativity
project, a project that is audacious right down to its core objectives and
approaches. That project reflects exactly what Brad is — audacious." It didn't take Cohen long to contribute to the Stanford relativity experiment. His early graduate work produced an innovative system for using trapped magnetic flux to measure changes in the spin of the gyroscopes — the perfect spheres at the very heart of the audacity. Cohen's other contribution involved GPS. The satellite had been studded with antennas so that signals were never shadowed out. Cohen saw an opportunity: If he could measure the positions of separate antennas with centimeter-level accuracy, he could then figure out exactly where the satellite was pointed.
"I thought the carrier phase of GPS seemed like its most underutilized capability," says Cohen, who quickly perceived several non-satellite applications, such as measuring attitude in rolling jet fighters and landing 737s in the fog. "I certainly didn't see why it couldn't be done," states Cohen.
Cohen's mentor had heard such eagerness before. "I've been associated with GPS for 30 years," recalls Professor Parkinson, "and I told Clark it was a very hard problem. A lot of people had tried it by averaging signals, which slowed the update rate, defeating the whole purpose of dynamic information. Clark told me 'Yeah, I understand that, but I think I can get around it.'"
One problem with coaxing extremely precise positioning information from GPS signals is cycle ambiguity. Although you can precisely measure the 19-centimeter-long wavelength, you might be several cycles off, leading to errors greater than six feet — an ambiguity that is significant to a jet pilot reaching for the deck of an aircraft carrier.
Cohen's solution involved placing transmitters on the landing surface. Signals from these fixed "integrity beacons" allowed an aircraft to abolish cycle ambiguities and compute a reliable fix on its centimeter-level dynamic position. In dramatic style, Cohen led a team of graduate students who demonstrated the system with over one hundred successful automatic landings of a commercial Boeing 737. Adoption of the GPS alternative as a low-cost worldwide standard could provide a safe way to reduce weather-related, air travel delays.
To commercialize such high-performance positioning applications, Cohen founded IntegriNautics Corporation in 1994. In addition to working on various civilian and military aircraft contracts, IntegriNautics has now partnered with Alliant Techsystems on tactical, unmanned, aerial vehicles; with NASA on air and space projects; and with various corporations on ground-based products such as automated tractors.
For Clark Cohen, the road from superconducting space gyroscopes to razor-straight plow lines through corn fields has become increasingly less mysterious with age. He is fond of quoting John Muir's line about how if you pull hard enough on anything in nature you eventually get the whole universe.
"That's the way it's been with Stanford," he says. "The connections are everywhere."
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