Mary Roach - Packing for Mars

In a space capsule, every landing is something of a crash landing. Unlike a plane or the Space Shuttle, a capsule has no wings or landing gear. It doesn’t fly back from space; it falls. The Orion space capsule has thrusters that can correct its course or slow it down enough to drop it from orbit, but not the kind that can be fired to soften a landing. As a capsule reenters the Earth’s atmosphere, its broad bottom plows into the thickening air; the drag slows it down to the point where a series of parachutes can open without tearing. The capsule drifts down to the sea, and if all goes well, the touchdown will feel like a mild fender-bender—2 to 3 G’s, 7 at most.

Touching down on water rather than earth makes for a gentler landing. The trade-off is that oceans are unpredictable. What if a cresting wave slams into the capsule as it’s coming down? Now the occupants need restraints that protect them not only against the forces of being dropped straight down, but also against a sideways or upside-down landing impact.

To be sure Orion’s occupants are unhurt no matter what wild card the seas present, crash test dummies and, lately, cadavers have been taking rides in an Orion seat mock-up here at the Transportation Research Center. The landing simulations are a collaboration involving the Center, NASA, and Ohio State University’s Injury Biomechanics Research Laboratory.

F sits on a tall metal chair beside the piston track. Graduate student Yun-Seok Kang stands at his back, using an Allen wrench to mount a wristwatch-sized block of instrumentation on an exposed vertebra. Along with strain gauges glued to various bones on the front of the body, these instruments will measure the forces of the impact. Scans later this evening and an autopsy will reveal any injuries caused by that force. Kang was up late with yesterday’s cadaver and in early this morning, but he’s alert and cheerful. He has one of those happy, high-achieving personalities that self-help programs promise but rarely manage to create. He wears rectangular glasses and long bangs that march around to the sides of his head. His gloved fingers are glossy with fat. The fat—because it’s slippery and because there’s a fair amount of it—makes Kang’s task difficult. He has been working on this mount for more than half an hour. The dead are infinitely patient.

F will be taking a hit on his lateral axis. Picture a foosball figurine—the little wooden soccer player with the skewer run sideways through his rib cage. That skewer is the body’s lateral axis. Say the foosball man goes for a drive, and another car T-bones his car at an intersection. His body and organs, if he had any, would be accelerated to the left or right along that skewer. In a head-on crash or a rear-ender, they’d be accelerated along the transverse axis: from front to back, or vice versa. The third axis that researchers consider is the longitudinal—along the spine. Here the foosball player is operating a helicopter. It stalls and drops straight down to the ground. Foosball man’s heart stretches down on its aorta like a bungee jumper. Should have stuck to sports.

Because astronauts are reclining on their backs during touchdown, a space capsule hitting the ocean in calm conditions creates a force on the transverse axis—front to back—by far the body’s most durable. (Lying on their backs, fully supported and restrained, they can tolerate three to four times as much G force—a tenth of a second of up to 45 G’s—as they could seated or standing, wherein the more vulnerable longitudinal axis takes the strain.) [31] Thus the best way to survive in a falling elevator is to lie down on your back. Sitting is bad but better than standing, because buttocks are nature’s safety foam. Muscle and fat are compressible; they help absorb the G forces of the impact. As for jumping up in the air just before the elevator hits bottom, it only delays the inevitable. Plus, then you may be squatting when you hit. In a 1960 Civil Aeromedical Research Institute study, squatting on a drop platform caused “severe knee pain” at relatively low G forces. “Apparently the flexor muscles…acted as a fulcrum to pry open the knee joint,” the researchers noted with interest and no apparent remorse.

Crashes often involve forces along not just one axis, but two or three of them. (Though simulations study just one at a time.) Add high seas to the capsule touchdown equation, and now you have to consider forces along multiple axes. A useful model for the kind of impact NASA must plan for—multiaxis and unpredictable—is the race-car crash. The week I visited Ohio, NASCAR’s Carl Edwards, traveling at close to 200 miles per hour, slammed another car, launching his own high into the air, where it spun like a flipped quarter before slamming down into the wall. Whereupon Edwards casually got out and jogged away from the wreckage. How is this possible? To quote a recent Stapp Car Crash Journal paper, “a very supportive and tight-fitting cockpit seating package.” Note the word choice: package . Safeguarding a human for a multiaxis crash is not all that different from packing a vase for shipping. Since you don’t know which side the UPS guy’s going to drop it on, you need to stabilize it all around. Race-car drivers are strapped tightly into custom-fitted seats with a lap belt, two shoulder belts and a crotch strap to keep them from sliding down under the lap belt. A HANS (Head and Neck Support) device keeps the head from snapping forward, and vertical bolsters along the sides of the seat keep the head and spine from whipping left or right.

Dustin Gohmert, a NASA crew survivability expert, has spent a lot of time talking to the people who design restraint systems for race cars. He and two colleagues have traveled from the Johnson Space Center to oversee the simulations this week. Gohmert has agreed to answer some questions while Kang and three other students finish instrumenting F. Gohmert has blue eyes and black hair and a lively Texas wit that he mostly sets aside while speaking into a tape recorder. He sits straight-backed and motionless while answering my questions, as though merely talking about upper torso restraints is holding him still in his chair.

Early on, NASA had dismissed race-car seats as models for Orion. For one thing, race-car drivers are sitting up, not reclining. Bad idea for astronauts who’ve been in space for a while. Lying down is not only safer (provided you don’t have to steer); it keeps astronauts from fainting. Veins in the leg muscles normally constrict when we stand, to help keep blood from pooling in our feet. After weeks without gravity, this feature stops bothering to work. Compounding the problem is the fact that the body’s blood volume sensors are in the upper half of the body. Where, without gravity, more of the body’s blood tends to pool; the sensors misinterpret this as a surplus of blood, and word goes out to cut back on production. Astronauts in space make do with 10 to 15 percent less blood than they have on Earth. The combination of low blood volume and lazy veins makes astronauts lightheaded when they return to gravity after a long stay in space. It’s called orthostatic hypotension, and it can be embarrassing. Astronauts have been known to faint during postmission press conferences.

There is a problem with lying on your back in a spacesuit in a very safe seat: “We threw a racing seat on its back, put a guy in it, and said, ‘Can you get out?’” recalls Gohmert. “It was like putting a turtle on its back.” Some months back, I watched a horizontal egress (getting out of the capsule) test of a suit prototype at Johnson Space Center. The verb “to turtle,” as in “I’m kind of turtling out,” was in fact used.

Getting out fast is mainly a concern when something goes wrong: The capsule is sinking, say, or it’s on fire. The last time things went wrong aboard a space capsule, it was the Soyuz capsule, returning to Earth with members of the ISS Expedition 16 and 17 crews, in September 2008. (NASA has been paying the Russian Federal Space Agency to fly ISS crews home when no space shuttle is available.) The Soyuz module entered the atmosphere out of position—as it had with Boris Volynov aboard in 1969. This interfered with the aerodynamic lift that normally helps flatten its course and gentle its reentry and landing. Reentry subjected the crew to a full minute of 8 G’s—rather than the customary peak of 4 G’s—and a landing bump of 10 G’s. The capsule landed far afield of its targeted landing site, in an empty field on the Kazakh Steppe, where sparks from the impact started a grass fire.