Extreme Medicine (19 page)

Above the surface of the ocean, helicopter platforms open up avenues of exploration and rescue unthinkable in earlier centuries and with an immediacy unparalleled in any other age. Borne at high speed out over the tropical seas of the Pacific or the icy waters of the North Sea, we rely upon that remarkable engineering to extend and protect us. It takes mere minutes to segue from the warmth and security of an airport terminal to flight above an environment entirely inhospitable to human life. All that lies between us and miles of open water is an aluminum can suspended beneath an absurd engine that throws air at the ground in an effort to defy gravity.

With helicopters and cylinders of air, we have projected ourselves over and beneath the ocean, extending our capabilities in rescue and exploration. But those innovations provide only the barest protection from environmental extremes. Mishaps are promptly punished and rarely forgiven. Augmented by technology and engineering, we simultaneously become more capable and more vulnerable.

W
hen I decided after my astrophysics degree to turn around and head back through the revolving doors of my university to study medicine, my parents cried. Like many immigrant parents, they'd always dreamed of their son becoming a doctor.

My bank manager was close to tears for different reasons. I was running out of cash. I spent weekends filing slides in a photographic agency, worked shifts as a doorman at the student union, and even had a laughably short and shockingly bad stint as a DJ. None of it quite paid the bills.

But I had a plan: NASA. NASA was a multibillion-dollar agency in the business of launching human beings into space. If they were doing that, then they must need doctors, so they must have pots of cash to fund people like me.

NASA, of course, had billions of dollars, but they were all spent—and then some. They had no grant money, and, even if they had, my British passport wasn't going to help me get to it. As a federal agency of the United States, NASA is forbidden, under executive order of the president, from employing non-Americans. Most of the replies to my inquiries made that point none too subtly.

I gave up on the idea of getting a grant and decided instead to send dozens of letters asking to spend some time as an intern with a NASA research lab. I'd have to do it for free—but at least I'd get up close to the place that had fascinated me throughout my childhood.

Here, too, I was met with a barricade of polite refusals. Then came the age of the dial-up modem, and I started blizzarding out e-mails. I was lucky. It was a time before people had figured out spam filters. Somewhere, somehow, one of those letters, faxes, or e-mails got me an application form—and unbelievably, that application form won me a place in an aerospace-medicine course at Johnson Space Center in Houston.

—

I
F YOU RISE UP THROUGH THE
atmosphere from sea level, the going gets tough long before you get anywhere near space. Anything above 5,000 feet counts as “high altitude” as far as physiologists are concerned. Even at this modest height, the medical problems caused by altitude can begin to develop.

Once you get to around 29,000 feet, just five and a half miles above the ground, you reach the highest point on the surface of the planet: the summit of Mount Everest. This appears to be very nearly the high-altitude limit for unsupported human life. A couple of hundred feet higher and the mountain would be unscalable without supplemental oxygen.

Mountaineers arriving at the summit of Everest do so only barely alive, having altered their physiology over weeks, adapting to the challenges presented by the rarefied atmosphere. Here, with or without oxygen, every step becomes a task of Herculean scale. Summiteers describe the excruciatingly slow plod along the last ridge that stands between them and their goal, each stride punctuated by great gasping bursts of hyperventilation as they struggle to repay the oxygen debt incurred. Even after weeks of adaptation, their bodies are only just capable of this feat. An unadapted individual, who hadn't endured the weeks of acclimatization, would be incapacitated in seconds by exposure to the same altitude.

A typical commercial jet airliner cruises at around 36,000 feet—a few thousand feet higher than the summit of Everest—but the passengers and crew within are breathing normal, low-altitude air. It is only pressurization of the cabin that leaves them able to enjoy in-flight movies and moan about the lack of legroom, rather than loll around unconscious in their seats as a prelude to death from oxygen starvation.

Reduction of pressure causes us problems at high altitude. With fewer molecules of oxygen in every breath, the pressure exerted by the oxygen in our lungs falls and so too does the rate at which it passes across the membranes of the alveoli and into our bloodstream. This leaves our red blood cells, and therefore our tissues, starved of oxygen. You can compensate for that in one of two ways: either by pressurizing your environment—as commercial airlines do—or by increasing the amount of oxygen in the air that you breathe.

Commercial airlines rely upon pressure to keep their passengers properly oxygenated. In preflight safety videos, flight attendants calmly show off the yellow oxygen mask that would pop out of the ceiling and dangle above your seat if cabin pressurization fails. Part of their briefing urges you to behave selfishly, asking that you put your own oxygen mask on before attending to anyone else. But there's a good reason for this rule. At 36,000 feet, in the absence of supplementary oxygen, a sudden loss of cabin pressure will incapacitate you in less than thirty seconds—roughly the time it would take you to fight a recalcitrant toddler—by which time both of you would be left helpless.

Things only get worse as you ascend. Pilots of unpressurized aircraft have to compensate for the reduction in atmospheric pressure as they climb higher by increasing the concentration of oxygen that they breathe. The lives of World War II bomber crews, flying at altitudes of up to 40,000 feet, depended as much on the oxygen supplied to their face masks as they did on avoiding flak batteries and enemy fighters.

The higher you go, the greater the concentration of oxygen you require in the gases that you breathe. But above 40,000 feet, even pure oxygen isn't enough to keep you alive. At this altitude, the pressure falls to less than a fifth that at sea level. Here the oxygen doesn't exert enough pressure to drive itself across the membranes of your alveoli and load the molecules of hemoglobin in your bloodstream.

To support human life at these higher altitudes, oxygen must be breathed under pressure. These more advanced oxygen systems comprise masks that form an airtight seal around the face and then force oxygen into your lungs at a huge rate of flow. Wearing one feels like sticking your head out of the window of a car thundering down the highway and trying to breathe against the rush of air. The effect is to inflate your lungs like a balloon, raising the pressure within them above the ambient pressure of the air outside, facilitating the loading of hemoglobin with oxygen, and thereby ensuring your survival. And even this only works up to a point.

Above 63,000 feet, you encounter the Armstrong line, an atmospheric limit above which the poor oxygenation of your bloodstream is no longer the only factor threatening your life. (Although the Armstrong limit refers to a spaceflight boundary, it takes its name from aviation physiologist Harry George Armstrong, as opposed to he of the “one small step.”)

The Armstrong limit is essentially the altitude at which you begin to boil. Let me explain. Pressure cookers work because the boiling point of water, and all other liquids, rises as ambient pressure rises. Your carrots cook more quickly in a sealed cooker because the pressurized water inside is able to reach a temperature higher than 100°C. (212°F.) before it boils. The reverse is also true: The boiling point of liquids reduces as the pressure falls.

At the summit of Everest, water would boil at a little over 70°C. (158°F.). At around 63,000 feet, the boiling point of water falls further, to 37°C. (98.6°F.), the same as the human body's normal core temperature. At this, the Armstrong limit, water contained in the tissues of the body spontaneously begins to boil. Bubbles of vapor evolve and expand, swelling soft tissues, causing the body to balloon. It's interesting that—contrary to sci-fi lore—the blood in your arteries doesn't boil. The muscular walls of those vessels behave like a crude pressure cooker, preventing the water in the arterial bloodstream from reaching its boiling point.

But in the veins, the story is different. Here the blood flows at much lower pressures, and bubbles of water vapor can and do form. With longer exposure to high vacuums, these bubbles grow and cause airlock, bringing the circulation to a halt and eventually causing cardiac arrest. To avoid this fate, people venturing above the Armstrong line must swap their oxygen masks for pressure suits, surrounding themselves entirely with an artificial sphere of survival. So astronauts wear helmets and bulky sealed outfits, insulated against the ravages of space, taking a little bubble of Earth's atmosphere with them.

The Armstrong limit defines the height above which simple augmentation of physiology is no longer enough. Beyond this, human life depends entirely upon artificial life support for survival. That layer around Earth, just twelve miles high, represents the narrowest of slivers. If Earth were the size of a soccer ball, then the zone in which life exists unsupported would be thinner than a sheet of paper wrapped around its surface.

—

S
PACE BEGINS AT AN INDEFINITE POINT.
For physiologists it is the Armstrong limit that marks its threshold, but to aircraft engineers it starts at the von Kármán line, 100 kilometers (328,000 feet, or 62 miles) above sea level. Here the atmosphere is so thin that ordinary aircraft can no longer push against it to steer or generate lift. To the physicist, true space starts many thousands of miles away, where the statistical probability of collision between two gas molecules becomes insignificant. But for astronauts it's not about altitudes or pressures. For them the frontier of space and all of its attendant risk begins on the launch pad, from the moment the rocket engines light.

I arrived in Florida at the beginning of July 2011, a few days before the big launch.
Atlantis
stood ready on the pad, waiting to carry its crew of four astronauts into orbit. She was the last of her kind; her sisters
Challenger
and
Columbia
had been lost to tragic accidents.
Discovery
and
Endeavour
had already been withdrawn from service and now lay stripped down in hangars, being made ready for transport, preparing to take their place as historical exhibits in other cities. This mission was to be the last of the space shuttle program. After three decades and 135 flights, NASA had called a halt to the project.

On the morning of launch, the air outside was humid. Tropical storm fronts had blown ashore one after another in the past couple of days, throwing lightning at the ground and drenching the soil. The weather around Cape Canaveral was always unpredictable in the summer: Blue skies could turn to thundercloud gray in minutes, carrying sudden torrents of rain with them.

For the past twenty-four hours, I'd been glued to meteorological Web sites, trying to make sense of isobars and radar pictures, watching fronts evolve out at sea and migrate inland. I wouldn't usually care, but today at 11:21
A.M.,
there had to be nearly cloudless skies above Kennedy Space Center for ten minutes. Whatever happened before or after that didn't much matter.

Within those ten minutes lay the launch window for
Atlantis.
They marked the fleeting period when Earth would rotate Pad 39A into just the right position, so that when
Atlantis
's engines were lit, the thrust would carry the spacecraft—and her crew of four—into orbit, to arrive at precisely the right place and time to allow her to rendezvous with the International Space Station (ISS).

The space station itself was traveling around Earth at 17,000 miles per hour. That huge velocity gave it enough energy to remain in stable orbit, allowing it to resist the forces that would otherwise bring it crashing back to our planet.

To catch up with that platform,
Atlantis
had to become a missile, acquiring enough energy to accelerate to the same speed. She would get a little kick from the Earth, borrowing some of the energy of its rotation. Like everything else on the surface of the planet, the launch site wasn't stationary. It was rotating with the Earth at a little over 900 miles per hour from west to east.

The rockets could make use of that, like a long jumper starting the run-up on a supersonic conveyor belt. While that sounds like a good start, most of the acceleration that would drive
Atlantis
to more than 17,000 miles per hour had to be achieved through the brute force of rocket engines.

The environment of space is uniquely hostile, but when it comes to orbital spaceflight, the dominant threat to human life comes from the vehicles and their launchers and the way they behave. Two hundred fifty miles, roughly the distance from the surface of Earth to the altitude of the space station, doesn't sound like a long way. But rocket science isn't about distance; it's about defeating the force of gravity and the energy released in accomplishing that feat.

Atlantis
was already standing exposed on the launch pad, towering over two hundred feet above sea level. Its fat, orange external tank had been filled overnight with hundreds of thousands of liters of liquid oxygen and hydrogen. Those cryogenically stored fuels, sealed in the insulated tank strapped to
Atlantis
's belly, were gently boiling off.

At the pad, the stack was creaking and groaning, straining with the competing thermal stresses of the freezing fuel and muggy warmth of the Florida air. Elsewhere hoses hissed and vapors poured forth. At launch that liquid fuel would feed the shuttle's three main engines, which sat in a cluster at
Atlantis
's rear.

Flanking the tank and the orbiter were the two solid rocket boosters (SRBs). Nearly four meters across and about as long as an Olympic swimming pool, those cylinders were filled with five hundred metric tons of ammonium perchlorate blended with aluminum: an explosive combination studded with oxygen atoms, whose energy was just waiting to be released. That material was combined with a binding agent, leaving it in solid state with the consistency of putty. When lit, it would burn at temperatures comparable to those of the surface of the sun and massively augment thrust in the first two minutes after ignition.

Atlantis
had stood waiting on the pad for several weeks, undergoing meticulous final preparations. The orbiters returned from space nearly dead: gliding without power, bodies scorched, fuel and energy spent, engines thrashed to the limits of their endurance. For the hundreds of engineers responsible for turning them around again and returning them to flight, it was an act akin to resurrection.