The ultimate crash test protects future astronauts from hard landings.
By Mary Roach
Crash simulation is a world composed largely of metal and men. The simulator at Ohio’s Transportation Research Centre resides in a clanging, hangar-sized room with few places to sit, and none of them upholstered. The room holds little beyond the crash sled, on a track down the middle, and a few engineers in safety goggles, forever walking back and forth with coffee mugs. Other than the reds and oranges of warning lights and hazard signs, colour is hard to find.
The cadaver seems almost a homey touch. Subject F wears blue Fruit of the Loom underpants and no shirt, as though he were lounging around in his own apartment. He looks deeply relaxed. As dead men do. Are. He slumps slightly, and his hands rest on his thighs. Were F alive, he would not be so relaxed. In a few hours, a piston as fat as a redwood will shoot a slug of pressurised air at the seat in which he’ll be strapped. Both the force of the impact and the position of the seat can be adjusted to create whatever crash scenario a researcher requires. Today it’s Nasa’s new Orion capsule, dropping from space onto the sea. F gets to play astronaut.
In a space capsule, every landing is something of a crash landing. Unlike a plane or the space shuttle that Orion and its booster rocket were designed to replace, a capsule has no wings or landing gear. It doesn’t fly back from space; it falls. (If US President Obama’s termination of the Constellation programme comes to pass, Orion’s entire purpose may be falling back to Earth, as an escape pod for the International Space Station.) The 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 re-enters the Earth’s atmosphere, its broad, flat bottom ploughs into the thickening air; the drag slows it down to the point where parachutes can open without tearing. The capsule drifts down to the sea, and if all goes well, the touchdown will feel like a mild fenderbender – 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 impact.
To be sure Orion’s crew are unhurt no matter what sort of wild card the seas present, crash-test dummies and, lately, cadavers have been taking rides in an Orion seat mockup here at the research centre. Crash-test dummies can provide only limited information; their rigid bodies are best suited to measuring head-on or side impacts, which is why car manufacturers find them so useful. To find out how a landing impacts soft tissue or bone, researchers need to use actual bodies donated to science. The simulations are a collaboration involving the centre, Nasa and Ohio State University’s Injury Biomechanics Research Laboratory.
Dead people make Nasa uncomfortable. They don’t use the word cadaver in their documents and publications, preferring instead the new euphemism postmortem human subject. Corpses in spaceships take them to places they’d rather not visit: Challenger, Columbia, the Apollo 1 fire. But the students appear at ease. Earlier this morning, two of them stood beside F, talking and laughing as they untangled the long, fine wires that trail from strain gauges mounted on F’s bones. Rather than seeming gruesome, the scene had a comfortable feel, like a family stringing lights on a Christmas tree. To them, the cadaver seemed to inhabit an in-between category of existence: less than a person, but more than a piece of tissue. F was still a “he”, but not someone you need to worry about hurting.
Now F sits on a tall metal chair beside the piston track. Ohio State 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 the strain gauges, these instruments will measure the forces of the impact. Kang’s 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.
A useful model for the kind of impact Nasa must plan for – multi-axis and unpredictable – is the race-car crash. In April 2009, Nascar’s Carl Edwards, travelling at around 300 km/h, smacked another car, launching his own high into the air, where it spun like a flipped coin before slamming down into a wall. Whereupon Edwards casually got out and jogged away from the wreckage. How is this possible? To quote from Stapp Car Crash Journal, “a very supportive and tight-fitting cockpit seating package”. Note the word choice: package. Safeguarding a human for a multi-axis crash is not all that different from packing a vase for shipping. Since you don’t know which side the UPS guy is going to drop it on, you need to stabilise it all around. Racecar drivers are strapped tightly into custom- fitted seats with a lap belt, two shoulder belts and a crotch strap. 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.
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, 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 working. But 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 Nasa crew survivability expert Dustin Gohmert. “It was like putting a turtle on its back.”
Worried that Nascar-style shoulder bolsters might dangerously extend the time it takes an astronaut to get out of the Orion capsule, Gohmert and his colleagues ran some simulations with head bolsters only. For these they used crash-test dummies – or “mannequins”, as Gohmert calls them, causing me to picture them taking their hits in department store outfits. It was a bad business. Gohmert described the slow-motion video footage to me. “The head stayed stationary and the body kept moving. We were actually concerned about the mannequin being okay.” As a compromise scenario, the shoulder bolsters are still there but have been scaled down.
A further complication for the astronaut: he’s got vacuum cleaner parts attached to his suit – hoses, nozzles, couplings, switches. To be sure the hard parts of a suit don’t injure the soft parts of an astronaut in a rough landing, F will be wearing a suit simulator: a set of rings duct-taped in place around his neck, shoulders and thighs. The rings are facsimiles of the mobility bearings, or joints, of a spacesuit. (Tomorrow’s cadaver, presently thawing, will be wearing a vest with “umbilicals” – life-support hoses and couplings – mounted on it.) One specific concern today is whether, on a sideways touchdown, a mobility bearing might collide with the seat’s shoulder bolster and be driven into the astronaut’s arm with enough force to break a bone.
The present challenge is to get F into the seat on the sled. Think of wrestling a comatose drunk into a taxicab. Two students have F’s hips, and another has his hands beneath F’s back. F is lying with his bent legs raised, like a man whose dinner chair has tipped over. John Bolte, who runs Ohio State’s Injury Biomechanics Research Laboratory and is overseeing today's tests, cues the push. "One, two, three!" The piston is off to F's right; he'll be impacted along his lateral axis . the most dangerous kind of hit.
When an unsecured head whips from side to side, the brain gets slammed back and forth against the sides of the skull. The brain is a smushable thing; it alternately compresses and stretches out as this happens. In a lateral impact, the stretching pulls on the long neurons, called axons, that connect the brain's two lobes. The axons swell, and if they swell too much, you may go into a coma and die.
A similar thing happens to the heart. A heart, when it's full of blood, can weigh a good 300 grams. In a side impact, there's more room for it to whip back and forth on the aorta. If the aorta stretches far enough and the heart is heavy with blood, the two may part ways. "Aortal severation", as Gohmert puts it.
F is finally ready. We've moved upstairs to watch the action from the control room. A bank of lights comes on with a dramatic phumph. The actual impact itself is anticlimactic. Because it is air that's doing the impacting, sled tests are unexpectedly quiet, crashes without a crash. And they are fast, too fast for the eye to register much of anything. The video is shot at ultrafast speed so that it can be played back in extremely slow motion.
We all lean in to see the screen. F's arm bends up underneath the shoulder bolster, the space where the rib bolster had been removed. The arm appears to have an auxiliary joint, bending where arms shouldn't. "That can't be good," someone says.
F endured a peak impact of 12 to 15 g's . right on the cusp of injury. The extent of an accident victim's injuries will depend not only on how many g's of force there were, but also on how long it takes the vehicle to come to rest. If a car stops short the instant it hits a wall, say, the driver may endure a split-second peak load of 100 g's. If the car has a collapsing bonnet (a common safety feature these days), the energy of those same 100 g's is released more gradually, reducing the peak force to maybe 10 g's . highly survivable.
The students slide F on to a stretcher and load him into a van. At the Ohio State medical centre he'll be scanned and X-rayed. The images, and an autopsy later, will reveal any injuries caused by the force of the impact and, in turn, contribute to the body of knowledge that will prevent future astronauts from ending up in F's seat. The whole procedure will unfold exactly as it would with a live patient, right down to a 45-minute wait and a problem with the billing.
Click here to check out Nascar’s Carl Edwards’s “flying” car at Talladega Superspeedway back in April 2009.
©2010 by Mary Roach, All Rights Reserved. Excerpted from Packing for Mars: The Curious Science of Life in Space, by Mary Roach, to be published on November 1, 2010, by Oneworld Publications.