How Spacesuits Keep Astronauts Alive

When astronauts step outside a spacecraft, the only thing between them and the vacuum of space is a suit they can wear.

It has to supply air, hold pressure, heat and cool the body,

block harsh sunlight and shrug off tiny particles moving faster than bullets,

all while letting a person bend their fingers enough to turn a bolt.

That is why engineers often describe a spacesuit as a spacecraft built for one.

Here is how it works, layer by layer, and what earlier suits taught the people who design them.

What Space Would Do to an Unprotected Body

Space is not just cold and empty. For a human body, it presents several threats at once:

• No air pressure: Without pressure, a person would lose consciousness within about 15 seconds as oxygen leaves the blood, and body fluids would begin to form vapor, causing tissues to swell. Despite movie myths, the body would not explode.
• Extreme temperatures: In orbit, surfaces in direct sunlight can reach about 120 degrees Celsius (250 degrees Fahrenheit), while those in shadow can drop to about minus 157 degrees Celsius (minus 250 degrees Fahrenheit).
• Radiation and ultraviolet light: Without the atmosphere as a filter, sunlight carries intense ultraviolet rays, and charged particles pass through freely.
• Micrometeoroids and debris: Grains of dust and flecks of old spacecraft travel at several kilometers per second, fast enough to puncture thin materials.

Two Kinds of Suits

Astronauts actually use two very different types of suits.

Launch and entry suits are worn inside the spacecraft during the riskiest phases of flight.

They are relatively light and are designed to keep the crew alive if the cabin suddenly loses pressure.

Those suits exist because of hard lessons.

In 1971, the three cosmonauts of Soyuz 11 died when their capsule depressurized during the return to Earth, and they were not wearing pressure suits.

From then on, Soviet and later Russian crews wore pressure suits for launch and landing.

After the Challenger accident in 1986, NASA shuttle crews also began wearing orange pressure suits during launch and reentry.

Spacewalking suits are a much bigger engineering challenge.

NASA's suit for work outside the station, known as the Extravehicular Mobility Unit, first flew in 1983.

Russia developed its own family of spacewalking suits called Orlan,

which a cosmonaut enters through a hatch in the back instead of pulling on separate upper and lower halves.

The Layers That Keep You Alive

A spacewalking suit is built from many layers, each with a specific job.

From the inside out, the main ones are:

1. Cooling garment: A stretchy, long-underwear-like layer laced with about 90 meters (300 feet) of thin plastic tubing. Chilled water circulates through the tubes to carry away body heat, because the hard work of a spacewalk generates plenty of it.
2. Pressure bladder: An airtight, rubber-coated layer that holds the oxygen around the body.
3. Restraint layer: A tough fabric shell that keeps the bladder from ballooning into a rigid, unbendable shape.
4. Thermal and micrometeoroid protection: Several sheets of thin, reflective insulation that keep heat in or out, topped by a rugged outer fabric woven from materials used in bulletproof vests and firefighter gear.

The upper body of the NASA suit is a hard fiberglass shell, which provides mounting points for the arms, helmet and backpack.

Arms, legs and gloves come in different sizes and are assembled to fit each astronaut.

The Backpack: A Life Support System

The bulky backpack on a spacewalking suit is a miniature life support system.

It supplies breathing oxygen from pressurized tanks and removes the carbon dioxide the astronaut exhales, which would otherwise build up to dangerous levels.

A fan keeps the gas flowing through the helmet and suit.

Cooling happens in a clever way.

The backpack exposes water to the vacuum of space through a device called a sublimator.

The water freezes, then turns directly from ice into vapor, carrying heat away with it.

The backpack also contains a battery, a two-way radio and a backup oxygen supply for emergencies.

A suit like this can support a spacewalk lasting roughly eight hours, with reserves on top.

Controls for the system are mounted on the astronaut's chest, where they are hard to see from inside the helmet.

The labels are printed in reverse, so astronauts read them with a small mirror strapped to the wrist.

Helmet, Visor and Gloves

The helmet is a clear plastic bubble that gives a wide field of view.

Over it fits a visor assembly with a thin coating of real gold,

which reflects much of the sun's infrared heat and blocks harmful light while still letting the astronaut see.

Lights and cameras mounted on the helmet let mission control follow the work.

Inside, a small drink bag with a straw provides water, and a soft foam block lets the astronaut rub their nose or clear their ears.

Gloves may be the hardest part of the whole suit.

A pressurized glove resists every bend of the fingers, so gripping tools for hours is exhausting, like squeezing a tennis ball over and over.

Gloves are fitted to each astronaut's hands and include heaters in the fingertips for work in cold shadows.

Even so, sore hands and damaged fingernails have been common complaints after long spacewalks.

Getting Ready for a Spacewalk

A spacewalking suit is pressurized far below normal cabin air, at roughly 30 percent of sea-level pressure in NASA's suit, and filled with pure oxygen.

The low pressure makes the suit flexible enough to work in. Otherwise, it would stiffen like an overinflated balloon.

That pressure drop creates a risk.

Nitrogen dissolved in the blood can form bubbles when pressure falls quickly, causing decompression sickness, the same condition scuba divers call the bends.

To prevent it, astronauts breathe pure oxygen for a period before going outside,

sometimes combined with exercise or with lowering the airlock pressure overnight, to flush nitrogen from their bodies.

Once outside, safety comes from redundancy. Astronauts stay clipped to the station with tethers,

and NASA spacewalkers have carried a small emergency jetpack that uses bursts of nitrogen gas to fly back if a tether ever fails.

Lessons From the Suits of the Past

Every generation of suits has been shaped by surprises.

During the first spacewalk in 1965, Alexei Leonov's suit ballooned so much in the vacuum that he could not fit back into his airlock.

He had to let some air out of his suit, a dangerous move, to squeeze back inside.

The Apollo moonwalkers discovered how troublesome lunar dust could be.

The fine, sharp grains clung to everything, scratched visors and wore at fabric and seals,

and astronauts said it smelled like spent gunpowder once they brought it back inside the lander.

In 2013, water from the cooling system leaked into the helmet of astronaut Luca Parmitano during a station spacewalk, covering his eyes and nose.

He made it safely back inside, and afterward engineers added absorbent pads and a breathing tube to the helmet to guard against a repeat.

A Spacecraft Built for One

A spacesuit packs pressure, air, cooling, insulation, communications and protection from radiation and dust into something a person can wear and move in.

Each layer answers a specific danger, and each generation of suits builds on lessons learned the hard way.

The next time you see an image of a spacewalker floating above Earth,

remember that the white suit is doing the work of a whole spacecraft.