Wear the right stuff: spacesuit science. (Cover Story).
* 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."
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.
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").
While most nitrogen you inhale is expelled during exhale, some gets dissolved in the blood and tissues. The bends happen when rapid decompression causes nitrogen in the body to bubble, which hinders oxygen supply. (It's also why scuba divers must resurface slowly.) The bends cause nausea and vomiting. Tissue swelling causes joint and abdominal pain, and in extreme cases death.
FREEZE AND FRY
"Space itself has no temperature to speak of because there are no molecules," says West. But objects in space can reach extreme temperatures. Why? Sunlight travels through space and transfers radiant heat (heat from invisible electromagnetic waves). The temperature of an object--including an astronaut--zooming by the sun can soar well over 121 [degrees] C (250 [degrees] F), and when blocked from sunlight, may plunge below -129 [degrees] C (-200 [degrees] F). The human body can't handle a much higher or lower core temperature than 37 [degrees] C (98.6 [degrees] F).
To maintain normal body temperature, astronauts wear a Liquid Cooling and Ventilation Garment (LCVG) underneath the EMU gasbag. An LCVG is made of 91 m (300 ft) of water-filled plastic tubing, all held together by a Spandex bodysuit. The life-support backpack circulates water and regulates the LCVG's temperature.
And for insulation, inside the spacesuit a liner divides the gas-bag from the thermal micrometeoroid garment--made with five layers of aluminized Mylar (silver party-balloon material). A vacuum sits between each layer. With a gap devoid of gas molecules between layers, heat can't transfer by conduction (direct contact between hot and cold matter), or convection (mixing of different-temperature gas molecules). And the silver coating helps bounce radiant heat off. "Just as a thermos keeps the hot stuff hot and the cold stuff cold," says West, "this is like a series of thermos bottles, one inside another."
The ISS orbits Earth at around 17,000 mph. And traveling along its path are micrometeoroids (particles including rocks and human space trash like paint chips, nuts, and bolts). While the velocity (speed) of debris varies, with some zipping by at 8,000 meters per second, "getting pelted is a concern for spacewalkers," says West.
For a shield, the EMU's shell is made from Orthofabric, woven from sturdy material like Nomex (found in firefighter suits) and Kevlar (found in bulletproof vests). The multiple layers of an EMU also help protect from debris impact. As a bombarding particle penetrates each layer, it loses more energy and slows down. "This makes it less likely to break through to the gasbag," says West.
To keep EMUs in tiptop shape to withstand space beatings, they're returned to Earth for repair after 25 wears,
"Wearing a spacesuit is confining," says West. "You have to endure long hours, too. Not good if you're claustrophobic or need to scratch your nose." And what about the bathroom? "Adult diapers, the ones from stores," says West. "But we sew in extra layers of padding." Like the multiple layers of a spacesuit, "it's for heavy-duty protection."
After a successful mission in 1971, the Russian spacecraft Soyuz II was homebound when a pressure-equalization valve sprang open while reentering Earth's ionosphere (30 to 250 miles above ground). The valve was intended to slowly open near ground to gently equalize cabin and outside air pressure.
Instead, all cabin air was sucked out in 30 seconds. Tissue damage and suffocation killed three cosmonauts--none were wearing spacesuits.
Today, shuttle astronauts wear bright orange, helmeted-gloved-and-booted Advanced Crew Escape Suits (ACES) while lifting-off or de-orbiting space. On Earth you feel gravitational force (force that pulls things to Earth) at 1g (1 x body weight). But while accelerating to and from space, astronauts feel as much as 3gs. The increased gravitational force pulls blood from the brain to the lower body. And decreased oxygen supply to the brain causes dizziness, which can lead to blacking out. Inflatable bladders in the ACES counteract pooling blood by applying pressure on the lower body to maintain blood circulation.
The specialized spacesuits also include oxygen supply, and connect to survival gear like a parachute and life raft. "Just in case they have to bail out during landing," says Phil West.
SPACE WEAR GOES--AND GROWS--UP
Suiting up for space has come a long way. Here, some breakthroughs that came with each frontier.
Daredevil aviator Wiley Post strives to break high-speed and altitude records. Post developed some of the earliest pressurized suits to protect the body at low pressure.
In 1948, a monkey named Albert rode a U.S. rocket high into the atmosphere. But the first Earthling in space was Laika--the puppy orbited Earth on the Russian satellite Sputnik 2.
On April 12, 27-year-old Yuri Gagarin became the first human in space. During reentry, Gagarin parachuted from Vostok I at four miles above ground and landed in a field.
On May 5, Alan Shepard became the first American in space. The silvery coating on the pressure suits below reflected heat to keep the body cool.
In March, Russian Aleksei Leonov spacewalked for 12 minutes attached to a tether. Unbalanced pressure ballooned his spacesuit--he had to deflate to reenter the spacecraft. American Ed White spacewalked in June.
On July 20, Neil Armstrong and Buzz Aldrin became the first humans on the moon. Portable life-support systems gave astronauts freedom to explore the lunar surface.
The first space shuttle mission took place 20 years after Gagarin's historic space flight. Today, shuttles routinely transport astronauts to and from the ISS.
Humans Reach Mars? What will astronauts wear?
ANATOMY OF A SPACESUIT
A spacewalking suit contains multiple layers of fabric. Here are some of them:
Liquid Cooling and Ventilation Garment helps maintain body temperature.
Pressure garment "gasbag" keeps blood from boiling.
Restraint layer gives gasbag shape and size.
The outer layer protects astronauts from the impact of high-speed space debris.
Thermal Micrometeoroid Garment works like a thermos to protect astronauts from the sun's rays.
Spuds in Space
Micrometeoroids (tiny debris) travel at high speed. An encounter with one could spell disaster for an astronaut. How does velocity affect impact: Do this exercise and find out. Learn what makes good protective gear.
potato * plastic straw * plastic coffee stirrer * material to make "spacesuit" for a potato (e.g., tissue, note paper, paper towel, foil, plastic wrap, wax paper) * rubber bands * scotch tape * paper * pencil * goggles * work gloves
CAUTION: Wear work gloves and goggles before proceeding.
1. Hold potato steady in one hand and straw in other hand.
2. Slowly pierce the potato once with straw.
3. How deep did the straw penetrate? Observe and record.
4. Quickly pierce the potato once with straw.
5. How deeply did the straw penetrate? Observe and record.
6. Repeat Steps 1 to 5 with a coffee stirrer.
7. Study your observations to design a lightweight and flexible protective outfit for your "potato-naut."
8. Wrap potato in spacesuit gear. (Try different materials and combinations of materials).
9. Repeat Steps 1 to 6.
Which suit provided the best protection against impact? Which suit provided the least? Why? How does mass affect impact? How does velocity affect impact?
Did You Know?
* Many clothes you wear are partly the result of spacesuit-design technology: running shoes, shock-absorbing helmets, sweat-wicking sportswear, sports bras, ski goggles, thermal gloves and boots, and ski boots, to name a few items.
* An 8-year-old boy with nevoid basal cell carcinoma--a rare form of skin cancer that may cause deadly lesions from the slightest exposure to sunlight--can finally play outdoors thanks to a spacesuit. The suit, similar to those worn by Apollo astronauts, protects him from more than 99.9 percent of the sun's harmful ultraviolet (UV) rays.
Directions: Match word(s) in the left column with the correct phrase in the right column. -- 1. vaporize a. space void of pressure -- 2. decompression b. heat transfer through the mix of molecules at different temperatures -- 3. conduction heat c. turn to gas -- 4. vacuum d. force exerted by gas molecules pulled to Earth by gravity -- 5. convection heat e. heat transfer by direct contact between hot and cold matter -- 6. radiant heat f. heat from invisible electromagnetic waves -- 7. atmospheric pressure g. decrease in pressure
English: Watch a space-exploration movie like The Right Stuff or Apollo 13. Then write a stow from the first-person point of view on preparing for a space mission.
National Science Education Standards
Grades 5-8: motions and forces * transfer of energy * properties and changes of properties in matter * structure and function in living systems * regulation and behavior * Earth in the solar system
Grades 9-12: structure and properties of matter * chemical reaction * motions and forces * interaction of energy and matter * conservation of energy and increase in disorder
Suited Spacewalking Teacher's guide may be downloaded from spacelink.nasa.gov/Instructional.Materials/NASA. Educational.Products/Suited.For.Spacewalking
Outer Space, Volume 10, "Astronauts and Cosmonauts," by Alyson Evans, Grolier, 1998
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|Article Type:||Cover Story|
|Date:||Oct 15, 2001|
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