High Dive

Together, the two plan to demonstrate a record-breaking 120,000-foot jump by 2009, and the truly unprecedented 60-mile space dive within two years-an audacious timetable. If all goes well, they´ll reach even higher. "Our ultimate goal," Tumlinson says, "is to have individual human beings return from orbit alive." That´s a drop from 150 miles-or more-involving increased heat and near-deadly Gs, essentially turning their divers into human meteorites.

Even that´s survivable, says NASA Jet Propulsion Laboratory engineer Robert Manning, who designs reentry systems for unmanned craft. Given the right protection-including thermal protection, oxygen, an aerodynamic heat shield and a control system-Manning says, a human being could, theoretically, fall to Earth from any height and survive. The question is whether Tumlinson and Clark can turn theory into fact, and whether anybody would be crazy enough to give their thrill ride a try.

Team Up

They´re an odd couple. Tumlinson is a space-obsessed entrepreneur with a colorful rsum. With his biker jacket and distinctly anti-corporate demeanor, he´s made a career of clever agitprop, bashing NASA in the press and in congressional hearings for being too timid. "My cause is to open space to the human species," he says. "I believe it´s our time in history to make this happen." Tumlinson loves grand rhetorical gestures, and he has the salesman´s gift of projecting a firm belief in what he´s selling. His great hope, he says, is that 60-mile death-defying plunges will grab headlines and "make space sexy to a much younger demographic."

Although his enthusiasm is infectious, Tumlinson knows that his reputation–he describes himself as "the bad boy of rock 'n' roll in the space field"–doesn't always help his cause. So when he met Clark in late 2006, he recognized a perfect counterpart: a man with a sterling CV who would help ground the effort in the legitimate realm of astronaut safety.

Clark is classic military-man–quiet and more clean-cut than Tumlinson–with an impressive resume. He's a board-certified neurologist and a 26-year Navy veteran who completed parachute training with the Special Forces. He developed an expertise in extreme-environment medicine that suited him well as a flight surgeon at NASA, where he went when his wife Laurel, also a physician in the Navy, joined the astronaut corps as a mission specialist. At the end of her first trip to space, in early 2003, the shuttle broke apart on reentry. Clark is reticent about his loss, but his work since then says plenty.

Hoping to help avert future spaceflight fatalities, the widower has studied just about every high-altitude mishap in history, from balloons and skydives to jets, rockets and return capsules. He's an encyclopedia of "all the ways you can die in space and on the way down from it," he says. To a stranger, his aspect might seem flat. But after a few minutes of discussing the science of falling, it becomes clear that it is the dignified reserve of a man whose wife died a national hero, combined with a trace of continuing shell shock. "It's just so weird that my life took this turn," he says.