\n<\/p>\n
While that collective experience is enough to have taught us how the body responds when gravity\u2019s pull is substantially reduced, the magnetosphere still shields the I.S.S., and only the 24 astronauts who flew in the Apollo program have gone beyond it. (The moon orbits an average of more than 238,000 miles away.) Though these two dozen astronauts spent little more than a week at a time without its protection, they have died of cardiovascular disease at a rate four to five times as high as that of their counterparts who stayed in low Earth orbit or never entered orbit at all, which suggests that exposure to cosmic radiation might have damaged their arteries, veins and capillaries.<\/p>\n
We can\u2019t send people to Mars, or to live on the moon, until we can be reasonably confident that they\u2019ll survive getting and residing there. But the space-based medical science needed to make that possible has been hindered by small sample sizes that aren\u2019t representative of the general population. (All of the Apollo astronauts were white men born between 1928 and 1936.) Space tourism, though, promises to offer opportunities to study the effects of radiation and low gravity on a much broader demographic than \u201creally well-selected superpeople,\u201d as Dorit Donoviel, the director of the Translational Research Institute for Space Health (TRISH) at the Baylor College of Medicine, describes those who have historically qualified to leave the planet. \u201cOld, young, pre-existing health conditions \u2014 we are starting to gather a knowledge base that in the future will be essential even for NASA,\u201d Donoviel told me, \u201cbecause we have to learn about the edge cases to really understand what is going on in our bodies to adapt to a hostile environment. You don\u2019t learn as much from people who are healthy. It\u2019s when people get sick that you understand how people get sick and how to prevent it.\u201d<\/p>\n
Epidemiologists face the same predicament on Earth: Before they can figure out how to protect the population, they must wait for harm to come to enough people to expose the causes. As less-rigorous medical screening allows more tourists to reach space, the chances increase significantly that someone will get hurt or have a health emergency there. Aerospace medicine is one of three specialties certified by the American Board of Preventive Medicine, because surgeons for a given flight tend to be stuck on the ground; they have to optimize the health of their patients and ward off potential disasters before<\/em> departure. The problem is, they can\u2019t know what those disasters will be until they occur. Which means that, as with every expedition into the unknown, at some point some intrepid or desperate souls are just going to have to blast off and see what happens.<\/p>\n Scientists once<\/strong> predicted that we couldn\u2019t live in the absence of Earth\u2019s gravity. Without this still-barely-understood force pulling us downward, how would we swallow? Wouldn\u2019t our tongues loll back into our throats? Wouldn\u2019t we choke on our own saliva? And if we survived those perils, wouldn\u2019t escalating pressure in our skulls kill us after a week or so? But when Yuri Gagarin returned from his single, 108-minute orbit around our world in 1961, humanity\u2019s first trip beyond the mesosphere, he proved that our internal musculature could maintain our vital functions in conditions of weightlessness. He ate and drank up there without difficulty. Technically, he hadn\u2019t escaped Earth\u2019s influence; to orbit is to free-fall toward the ground without ever hitting it, and he was in a condition known as microgravity. This felt, he reported, \u201clike hanging horizontally on belts, as if in a suspended state,\u201d a circumstance passingly familiar to anyone who has been on a roller coaster or jumped off a diving board. Gagarin said he got used to it. \u201cThere were no bad sensations,\u201d he added. <\/p>\n Either Gagarin was fibbing, or he had a strong stomach. Initially, many space travelers puke, or at least feel motion-sick \u2014 space-adaptation syndrome, or S.A.S., is what such nausea, headache and vomiting are called outside our atmosphere. \u201cIt\u2019s the same as sitting in the back of the car in childhood, reading something with your head down,\u201d says Jan Stepanek, director of the aerospace-medicine program at the Mayo Clinic in Scottsdale, Ariz. \u201cIt\u2019s a mismatch of what the eyes are seeing and what the inner ear is telling you.\u201d Only in this case, that mismatched perception is a result of the organs and hairs of the vestibular system floating free without their usual gravitational signals. You acclimate eventually. In fact, researchers only learned about the prevalence of S.A.S. symptoms in the 1970s, when they heard Skylab astronauts talking about it with one another over a hot mic. Astronauts, it turns out, are not ideal subjects for medical study, because they are notoriously stoic and unforthcoming about any symptom that might ground them.<\/p>\n<\/div>\n