In the Hollywood thriller "Gravity," screenwriters concocted a frightening space scenario. Two NASA astronauts on a spacewalk, portrayed by Sandra Bullock and George Clooney, find themselves stranded in the emptiness of space, after their spacecraft is wrecked by debris from a satellite destroyed by a missile.
While that particular dilemma was fictional, it resonated powerfully with movie audiences, because those of us who grew up watching the triumphs and tragedies of the Space Age know that being an astronaut is dangerous work. We've heard about the deaths of the three Apollo astronauts during a launching pad test exercise in 1967, the six who lost their lives when the space shuttle Challenger disintegrated 73 seconds after liftoff in 1986, and the seven who were killed when the Columbia shuttle broke up during re-entry in 2003 [source: Airsafe.com].
But while leaving Earth and returning to it are both risky business, the time that astronauts spend in the airless, cold and highly irradiated void of space is fraught with ever-present lethal peril, too. Space is so dangerous, in fact, that it's amazing that only three humans—a trio of Soviet cosmonauts on a 1971 mission—have actually perished there. Here are 10 of the ways in which the cosmos is unforgiving of our inherent frailties.
If an astronaut became untethered during a spacewalk, as the characters did in "Gravity," his or her spacesuit—the extravehicular mobility unit, or EMU, in NASA lingo—would still provide oxygen and remove carbon dioxide for as long as eight-and-a-half hours [source: NASA]. But if the suit failed, or an astronaut was somehow subjected to the airless, pressure-less void of space without such protection, he or she would lose consciousness within 15 seconds [source: NASA].
Death would quickly ensue, as a grisly textbook example illustrates. In 1971, three Soviet cosmonauts were about 104 miles (167 kilometers) above Earth when a valve in their life-support system ruptured, making them the only humans ever exposed directly to the vacuum of space. When their capsule, which was being guided by an automatic re-entry system, landed, recovery teams were shocked to find them dead in their seats, with dark-blue blotches on their faces and blood seeping from their noses and ears [source: Dhar].
If an astronaut is exposed to a space vacuum without protection, other nasty stuff would happen, too. Without atmospheric pressure to balance things out, the unfortunate space traveler's final breath would expand in his or her lungs, tearing the delicate gas-exchange tissues that line them. At the same time, water in the person's soft tissues would vaporize, causing the body to swell up grossly, though the skin would provide enough resistance to keep him or her from bursting like an overinflated balloon. Bubbles would form in the veins, blocking blood flow, and the astronaut's bowels, bladder and stomach would expel their contents. (This was what happened to dogs exposed to near vacuum as part of a study. If the time they spent was less than 90 seconds, most of the effects went away once the air was repressurized; more than that and they usually died) [source: Gosline].
If that's not bad enough, a condition called ebullism can set in, in which the boiling point of bodily fluids would decrease below the body's normal temperature, causing the astronaut's saliva to boil on his or her tongue [source: NASA].
The sun emits energy over a wide range of wavelengths, including ultraviolet radiation that we can't see or feel. UV radiation isn't a completely bad thing, because short exposures to it generate vitamin D in our bodies, but if we're out in the sunlight too much, it can cause sunburn and ailments such as cataracts, suppression of the immune system, skin cancer and premature aging of the skin. And that stuff still happens, even though we've got the planet's atmospheric ozone layer to filter out most of the UV that the sun gives off, before it reaches us [source: EPA].
If an astronaut's bare skin was exposed to unfiltered sunlight in space, though, he or she quickly would develop a very bad case of sunburn. That won't happen as long as the astronaut is wearing a spacesuit, though, because the only transparent part is the helmet visor, whose plastic is coated with several layers of filtering to provide protection against such radiation [source: NASA].
Even if you don't get space sunburn from UV, the space environment would bombard astronauts with plenty of other types of harmful radiation, and they wouldn't have Earth's atmosphere and magnetic field to filter out most of the nasty particles. (Just to duplicate the protection that we normally get from the atmosphere, a spaceship would have to have metal walls that were 3 feet, or 1 meter, in thickness [source: Tate].)
A robotic probe sent on a flight to Mars revealed that astronauts making the same 253-day trip would be exposed to the equivalent of a whole-body CT scan every five or six days [source: Tate]. Scientists say that unless we figure out some better way to shield astronauts in interplanetary space, they would be at risk of dying along the way from radiation sickness. And even if they didn't, they would almost certainly succumb to cancer at some point [source: Halvorson].
Just like in the movie "Gravity," space junk actually is a real-life threat in space. In March 2012, six astronauts on the International Space Station had to take refuge in the station's lifeboat-like space capsules, after they got an urgent warning that a leftover piece of an old Russian telecommunications satellite was headed their way. Fortunately, the hunk of debris — one of 2,000 pieces that were created when the satellite smashed into a U.S. satellite in 2009—whizzed by the ISS without collision, missing by 6.8 miles (11 kilometers) [source: Malik].
It gets worse: NASA is tracking some 500,000 pieces of debris that are hurtling around Earth at speeds of 17,500 mph (28,164 kph), but there are probably a lot of smaller pieces that it can't detect. It doesn't take a big piece to demolish a spacecraft or knock out an astronaut on a spacewalk. Some space shuttle windows were replaced because of damage from what turned out to be paint flecks floating in space – or hurtling might be more like it [source: NASA].
Compared to airlessness, huge radiation doses and other hazards, a little dust would seem to be no big deal. NASA already knows from the Apollo program that astronauts suffer from the lunar equivalent of hay fever from dust inhalation [source: Armagh Planetarium].
Explorers who someday visit Mars will have to worry about the superfine dust containing fine-grained silicate materials, which carry static electricity and stick to everything. If astronauts breathe it in, it can react with water in their lungs to create damaging chemicals and cause effects similar to black-lung disease in coal miners. While visitors to Mars will be wearing spacesuits when they're out on the surface, the sticky dust is going to be tough to keep out of their suits and consequently, their habitats [source: Jaggard].
Astronauts get sick more easily in space — 15 of the 29 Apollo astronauts, for example, contracted bacterial or viral infections either on their mission or shortly after returning [source: Young]. That's because space has a bad effect on their immune systems. In particular, microgravity seems to interfere with the activation of T-cells, a type of white blood cell that helps to protect the human body against infections.
On Earth, when a person is exposed to a virus or harmful bacteria, a signaling system known as the PKA pathway turns on 99 different genes, which tell the T-cells to attack the threat. But in a 2005 study, researchers at the University of California-San Francisco found that simulated microgravity can shut off 91 of those genes. The effect was so severe that the researchers compared it to a person having an HIV infection. The problem could worsen on long interplanetary spaceflights, because microgravity and radiation would combine to exacerbate the damage [source: Young].
Your skeleton may seem hard and stiff, but your bones actually are living tissue, in which cells called osteoclasts break down old, worn bone material and release calcium into your bloodstream, while other cells, called osteoblasts, lay down new minerals along the bone surfaces.
On Earth, these two processes work together in a healthy young person, so that bone is replaced at the same rate that it's broken down. As a person gets older, the balance sometimes gets out of kilter, and the bones weaken in a condition called osteoporosis. Unfortunately, an extended stay in the microgravity environment of space has an effect similar to aging, scientists say.
Studies of Russian cosmonauts who spent several months in space, for example, found that they lost as much as 20 percent of their bone mass. The effects of microgravity can leave bones so weak that they can't support astronauts' bodies when they return to Earth, putting them at risk of suffering fractures from stress. Researchers currently are trying to figure out whether tinkering with astronauts' diet, exercise and hormonal levels while in space could stave off some of the damage [sources: NASA, BBC ]. If that's not bad enough, the microgravity environment also causes changes in the spinal disks that give astronauts really bad backaches
[source: Sayson et al.].
Probably due to swelling of the optic nerve and changes in eye structure caused by the space environment, about 60 percent of International Space Station astronauts and 29 percent of space shuttle astronauts have reported a decline in vision clarity. After a few weeks aboard the ISS in 2007, for example, Canadian astronaut Bob Thirsk reported that his close-up vision had changed to the point that he had to ask for help in focusing cameras [source: NASA].
In some cases, the effects could cause permanent damage to the eyes, researchers worry. While space might not be able to make astronauts blind, it could reduce their vision enough to put them at risk of suffering a fatal accident. NASA medical researchers are looking for a solution, but in the meantime, they've developed special adjustable-focus glasses for astronauts to wear in space [source: NASA].
The space environment is pretty psychologically stressful for astronauts. They may have difficulty adjusting to microgravity, suffer fatigue and struggle with sleeplessness from disruption of their circadian rhythm. There's also the intense, high-pressure workload, and the aggravations that inevitably result when a bunch of people are confined in a small space for days or weeks at a time.
NASA tries to select astronauts who'll be able to function well mentally in the stressful environment of space, and the agency carefully monitors astronauts' behavior while they're there for signs of trouble. While nobody's had a major psychological crisis on a flight so far, astronauts have suffered from mood and anxiety disturbances, and the data suggests that the longer a mission lasts, the greater the risk to astronauts' mental health. When astronauts start making multiyear trips to Mars or even more distant destinations, this could be a big worry [source: Slack et al.].
The International Astronomical Union has named two craters after the Apollo 8 astronauts. HowStuffWorks takes a look.
Author's Note: 10 Ways Space Is Trying to Kill You
When I watched the television broadcast of Neil Armstrong setting foot on the moon in 1969, I have to admit that I was so caught up in the excitement of the moment, and had so much faith in the space program's technology, that it never occurred to me how much of a risk that he was taking. It didn't sink in until years later, when I learned that if Armstrong and Buzz Aldrin had been stranded on the moon, then-President Richard Nixon had a contingency plan in place. The telecommunications link would have been shut down, so that the public would be spared the trauma of watching the astronauts die, and instead Nixon would have given a speech in which he praised them for their bravery. Fortunately for all of us, he didn't have to give that speech.
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