Issue 11.03 - March 2003

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Surviving 7G

Humans want to go to Mars. Too bad the journey turns our bodies into mush. NASA's solution: strap down a few civilians and spin them around really fast.

By Josh McHugh

"Medical team ready?"

"Medical ready."

Kai Wiechmann The author gets set for a tolerance run at NASA Ames Research Center.

I'm strapped into a modified fighter jet seat, my head encased in a blue helmet bolted to the top of the chair. The chair is inside a windowless box at one end of a 58-foot platform at the human centrifuge facility in Building N-221A of the NASA Ames Research Center in Moffett Field, California. At the other end, there's a 6- by 71/2-foot chamber - about the size of a minivan - where I'll be spending the next 22 hours. But first, a tolerance run in the chair to see how much gravitational force I can bear. A 300-horsepower engine causes the entire apparatus - the chamber on one end, the chair on the other - to spin on an axis inside a 62-foot-wide circular bunker.

"Operator ready?"

"Operator ready."

The voices of a team of NASA technicians and doctors are piped in through a speaker in the chamber's ceiling. Electrodes on my chest, neck, and left wrist feed my vital signs into wires laced through the skintight singlet I'm wearing under a canvas harness. The wires converge in a white umbilical cord a little thicker than a standard coaxial cable, which relays the data into a rack of 1970s-era computers behind the chair.

"Data acquisition ready?"

"Data ready."

A Doppler sensor, taped to a freshly shaved patch of skin above my right temple, measures the velocity of blood flow to my brain. Each time my heart squeezes blood past the sensor, a control-room speaker emits a noisy slurp, like someone abruptly finishing off a milk shake through a straw.

"Subject ready?"

"I'm good."

About an arm's length from my eyes is a metal halo known as a light bar. Two rows of red dots on either side of my head march inward, starting from just beyond my peripheral vision and meeting directly in front of me. I've been told to focus on the center for the duration of the run. In my right hand I'm holding a bike handlebar grip with a button on top and a hinged switch like a hand brake. To reset the lights, I click the button on top of the grip as soon as I see them. If I fail to do this quickly enough, the centrifuge operator will know that the g forces have radically narrowed my field of vision and will stop the run. If I want to terminate the run, I release the hand brake, which will set off an alarm.

"Light bar ready?"

"Light bar ready."

"For the record: 20-g centrifuge study HR1-213. Principal investigator: Cohen; medical monitor: Pelligra; test subject: McHugh. Tolerance run. Begin run in five, four, three, two, one."

With me in the chair, the box shudders into motion. Its plywood walls, spray-painted black and studded with leftover bolts and brackets from experiments past, creak as the centrifuge picks up speed.

"Extensive research has been conducted using human subjects exposed to increased g-forces, although not for the duration of exposure to which you will be subjected." - Human Research Consent Form, NASA Feasibility Study HR1-213

Kai Wiechmann The 20-g centrifuge at rest.

NASA has chosen four civilian test subjects to help tackle a problem that's been holding back the space program: In the zero gravity of outer space, the human body slowly turns to mush. We have evolved in an environment about 4,000 miles from the center of Earth with a steady pull of 9.8 meters per second squared, a pull defined as 1 g. The cells that make up our bodies expect that pull and build up their walls with support structures, called cytoskeletons, accordingly. In space, the pull doesn't exist, and so the cells' cytoskeletons collapse. Muscles atrophy and bones decalcify. The heart shrinks.

This is a large part of why we're nowhere near deploying a manned Mars mission. After traveling in zero gravity for 18 months, the first human to step down onto the Red Planet would probably snap an anklebone and collapse into a small pile of goo. NASA has nearly completed the prototype of a spacecraft that would cut travel time to three months each way, but even in that reduced timeframe, zero gravity would have a debilitating effect on the body. NASA astronaut Jerry Linenger remembers how the absence of gravity caused extreme back pain for some passengers on the Russian space station Mir. In his book, Off the Planet, which recounts five months on Mir, Linenger says he experienced a 13 percent bone loss in his hips and lower spine. Two years later, he still hadn't recovered fully. Translation: Human physiology remains the primary stumbling block to a prolonged space journey. "On a long-duration trip to Mars, there's going to be significant bone loss," Linenger said on NPR's Fresh Air. "That could be a show-stopper."

Long-term exposure to microgravity makes humans weak, so hypergravity should have the opposite effect, right? In a 2001 study, 10 Australian fighter pilots routinely exposed to 2 to 6 gs while flying experienced an average 11 percent increase in the density of their spinal vertebrae over a 12-month period. NASA figures that astronauts could use a solar-powered, onboard centrifuge to stave off muscle and bone deterioration in space. Thanks to the hypergravity chamber, they'd be completely healthy upon arrival. To find out if this might work, I and my fellow test subjects - all of whom needed to be 5-foot-9 or shorter, because of the chamber's cramped quarters - will participate in seven daylong hypergravity sessions. Malcolm Cohen, a ruddy psychologist with thick, busy hands and a booming voice, is supervising the experiment. Each session will increase in intensity, ending with a 22-hour whirl at 2 gs. Before and after each spin, NASA will measure our adaptation to hypergravity with "tolerance runs" in the fighter chair. Compared with the marathon chamber spins, the tolerance runs - accelerating 1 g every 15 seconds - are manic, full-on sprints.

In hypergravity research, passing out and blacking out are not the same thing. Passing out is known as G-LOC, for gravity-induced loss of consciousness. Blackout, preceded by grayout, is the point at which g force keeps blood from getting into the eyeballs. Ralph Pelligra, the experiment's white-goateed chief medical monitor, will be watching out for the exact timing of such effects. If the hypergravity training sessions have the desired effect, the subjects will black out (or gray out) at ever-higher g levels as the experiment progresses. At no point will we be subjected to more than 7 gs.

Contributing editor Josh McHugh (josh@buzzkiller.net) wrote about Google in Wired 11.01.

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