Wear the right stuff: spacesuit science - Cover Story

If you had to install a new front door to your house, you'd probably pull on some jeans and a sweatshirt. In July, astronauts installed a new front door and airlock (pressure-regulated airtight chamber) on the International Space Station (ISS). What would happen if they had done the job in your outfit? "The truth is we don't know for sure," say Phil West, spacesuit engineer at NASA's' Johnson Space Center in Houston, Texas. "We haven't had anyone crazy enough to volunteer for this experiment."

* To find out what could happen if you spacewalked in your jeans, keep reading....

In the 50-year history of human spaceflight, spacesuits have gone through countless changes (see timeline, below). "The first spacesuits and those today are totally different animals," says Amanda Young, preservation expert at the Smithsonian National Air and Space Museum in Washington, D.C. "The earliest space travelers were up in the air for a brief time, and they didn't even step outside."

Space's first human visitor, cosmonaut (Russian astronaut) Yuri Gagarin, orbited once around Earth in 1961 for only 108 minutes. And he merely wore a version of the military's high-altitude aircraft suit. Today's astronauts perform extravehicular activity (EVA), or spacewalks, up to seven hours at a time in virtually a "wearable spacecraft."

UNDER PRESSURE

Without a spacesuit, astronauts would suffer a quick, gruesome death. Why? At sea level you experience atmospheric pressure, or the force exerted by the atmosphere (gas molecules pulled to Earth by gravity's downward force) at approximately 1 atmosphere, or 14.7 pounds per square inch (psi). But you don't feel squished by all this weight because your body exerts an equal internal pressure. This balance lets you exchange a mixture of gases essential for living: you inhale about 79 percent nitrogen and 21 percent oxygen, and exhale about 80 percent nitrogen, 16 percent oxygen, and 4 percent carbon dioxide.

As you scale up in altitude, however, gases thin in the atmosphere. At 5.6 kilometers (3.5 miles) above sea level, the atmosphere is only half as dense, which makes breathing more difficult. And where the ISS orbits--about 402 km (250 mi) above sea level--the atmospheric pressure is zero and void of gas molecules (a vacuum). There's nothing to breathe.

Without an environment pressurized for Earthlings, severe decompression (decrease in atmospheric pressure) would instantly suck air from your lungs and cause gases dissolved in your body to bubble. "Think of your body as a bottle of soda," says Phil West. When you uncap a bottle you get fizz. "That's because the gases dissolved under high pressure inside now want to come out and equalize with the new surrounding."

The principle is called Henry's Law: as the pressure of any gas decreases, less of that gas will dissolve into the solution it's in. And when gas molecules escape a solution, they boil. "People think you need heat to boil liquid," says West. "But lowering air pressure above a liquid can boil it too." Body fluids (the human body is 70 percent water), including blood, can boil in space.

Minus a spacesuit, gases dissolved in a spacewalker's bloodstream would expand and try to escape, causing solids and liquids in the body's tissues to separate. As liquids vaporize (turn to gas), the body inflates; capillaries and eardrums rupture. And without blood functioning normally to transport oxygen, a suitless astronaut would fall unconscious in 15 seconds (the time it takes to cut off all oxygen to the brain), suffer permanent brain damage within four minutes, and then die. When all gases diffuse out of the body, what remains? A crinkled-dried corpse.

PASSING GAS

To avoid turning into a crisp, astronauts wear an Extravehicular Mobility Unit (EMU), or space-walking suit. They wear the nine-layer outer garment in conjunction with essential components like a Primary Life-Support System (PLSS), a backpack with devices to regulate functions like oxygen supply, pressure, and battery power; protective helmet, boots, and gloves; and a communication device.

To envelop the body with pressure, the innermost layer of an EMU is a gas-filled bladder "or what we call a `gasbag,'" says West. "It's like a body-shaped balloon made of nylon (like camping-tent material) coated with urethane, which seals gas in." But if you keep filling a balloon with gas, it'll just get bigger and pop. That's why a Dacron polyester (like extradurable school backpack material) restraint layer follows. "This gives the gasbag shape and size," says West. "And when we adjust sizing to fit each astronaut, that's the layer we primarily change."

An EMU is pressurized at 4.3 psi. This lower-than-sea-level pressure allows astronauts mobility while encased in heavy-duty layers. And to compensate for low pressure, astronauts must breathe 100 percent oxygen to maintain normal body function.

Prior to the trip outdoors, astronauts suited in EMUs sit in an airlock to pre-breathe (breathe pure oxygen). This helps the body adjust to its new environment (times vary and can last up to four hours) and rids it of nitrogen, the biggest culprit of decompression sickness (caisson disease, or "the bends").